rexresearch.com 


   
Thalappil PRADEEP, et al.
   
Nano-Silver Water Purification









http://www.newscientist.com/article/mg21829165.400-silver-nanoparticles-provide-clean-water-for-2-a-year.html

Silver nanoparticles provide clean water for $2 a year

SOMETIMES the solution to an enormous problem is tiny. Silver nanoparticles may be the key to supplying clean, affordable drinking water worldwide.

Thalappil Pradeep at the Indian Institute of Technology in Chennai and colleagues have developed a filter based on an aluminium composite, embedded with silver nanoparticles. As water flows through the filter, the nanoparticles are oxidised and release ions, which kill viruses and bacteria, and neutralise toxic chemicals such as lead and arsenic.

Some nanoparticles leach into the water but at concentrations that pose no threat to health. Pradeep describes the process of making the filter as "water positive": 1 litre of water spent on making nanoparticles gives 500 litres of clean water.

In tests, a 50-gram composite filtered 1500 litres of water without needing reactivation, so they estimate that a 120g-filter that costs just $2 would provide safe drinking water for a family of five for one year (PNAS, DOI: 10.1073/pnas.1220222110).

The filters are undergoing field trials in India with the aim of preventing waterborne diseases.



Thalappil Pradeep





http://www.thehindu.com/news/cities/chennai/iitm-develops-lowcost-nano-water-purifier/article4446899.ece

IIT-M develops low-cost nano water purifier

T. Nandakumar

The purifier will be able to provide arsenic-free water at about five paise per litre

Scientists at the Indian Institute of Technology-Madras (IIT-M) are gearing up for the commercial release of an affordable nano technology-based water purifier.

The purifier has been developed to address the problem of arsenic contamination, a threat to drinking water sources and an emerging health hazard in several parts of the country.

The Arsenic Task Force of the government of West Bengal has certified and approved the purifier developed by IIT-M. “The pilot phase is over and we are now preparing to take it to the market,” said T. Pradeep, professor, department of chemistry, who heads the research group working on water purifiers.

The team has incubated a company at IIT-M to commercialise the technology, Dr. Pradeep told The Hindu on the sidelines of the Nano India conference organised by the department of science and technology and the National Institute for Interdisciplinary Science and Technology (NIIST) in Thiruvananthapuram.

The purifier developed by IIT-M uses iron oxyhydroxide, a nanostructured material, to remove arsenic from drinking water. It functions without electricity or piped water supply.

Dr. Pradeep said it could provide arsenic-free water at an approximate cost of five paise per litre. “Over the next few years, we hope it will benefit at least 10 per cent of people living in arsenic-contaminated areas.”

The IIT-M-incubated company will commercialise the technology with partners who can take up distribution.

The research group has also come up with a nano material-based fluoride water purifier. “It will take some more work for field implementation of this purifier. We expect the technology to be ready in six months.”

Dr. Praveer Asthana, director of the nano mission under the Union department of science and technology said the water purifiers developed by IIT-M highlighted the relevance of industry-institution projects in the nano technology sector to deliver affordable, efficient solutions.

Dr. Pradeep said nano materials could play a key role in low-cost solutions to remove water contaminants. “They interact with the contaminant to remove it within a very small contact time. It is also possible to tune the chemistry of any of these materials so they can attack a wide spectrum of contaminants.”

IIT-M has already developed and commercialised a nano silver-based water purifier that breaks down pesticide residue.

The research team is working on an all-inclusive water purifier to address a wide spectrum of contaminants like pesticides, mercury, cadmium, lead, fluoride and arsenic. The group is collaborating with scientists working on other methods of water purification like reverse osmosis, membranes and solar and thermal technologies.



http://www.materials360online.com/newsDetails/39500
6 May 2013

Composite Nanomaterials Purify Drinking Water Affordably

by
Rachel Nuwer

Each year, around 3.6 million people die because of issues related to contaminated water, poor hygiene, and unsanitary conditions. If those households most at risk could gain access to safe drinking water, more than 2 million lives could be saved. Now, one research team has proposed a cheap, safe means of achieving this with an all-inclusive drinking water purifier assembled from several nanocomposites.

“We wanted to show that it is possible to deliver affordable clean water that had all of the contaminants removed,” says Thalappil Pradeep, a materials scientist at the Indian Institute of Technology Madras, and senior author of a paper published in the Proceedings of the National Academy of Sciences describing the new filter. “I’ve been on this dream for quite some time, it’s a very big thing for me.”

Pradeep and his students and colleagues began work on this project several years ago. Contaminated water may contain bacteria, viruses, protozoa, heavy metals, pesticides, or other potential toxins. They knew that silver ions, released from the metal in nanoparticle form, worked as a disinfectant for a number of bacteria and viruses found in contaminated water, while other inorganic toxins, such as lead, iron, and arsenic, can be scavenged from contaminated water with materials containing different chemical properties, particular to each of those elements. Iron oxyhydroxide nanopaprticles scavenge arsenic, for example, while manganese oxide adsorbs lead. “For a diverse array of contaminants, you can use a variety of nanostructured materials to finally get water that is purified,” Pradeep says.

But contaminants found in the water tend to anchor to nanosilver surfaces, blocking the release of silver ions from them. To overcome this problem, the researchers created a unique family of nanocrystalline metal oxyhydroxide-chitosan granular composite materials. This material, which forms a cage-like matrix, strongly bonds to embedded nanoparticles. The nanoparticles remain isolated inside the matrix, which only allows ions to escape at a controlled rate. Those ions then kill microbes found in the water, without releasing nanoparticles.

The materials can all be prepared at room temperature in water, and they gradually settle to form a sand-like material. No electricity is required and all of the elements needed to build the filters are widely available and affordable. For each liter of water needed to make the composite, 500 liters of clean water can be produced. None of the composite materials themselves are toxic. When the material eventually stops releasing silver ions, hot water can get rid of the thin layer of scalants to regain activity in the composite. The purifiers would cost small families about US$2.50 per year.

Pradeep hopes to produce the filters in the remote villages where they are most needed. About 2,000 small community-scale units are being installed in west Bengal, an area plagued by arsenic contamination in its water. Pradeep thinks the filters could be deployed to more than 2 million people over the next two years or so, though other organizations will have to take responsibility for organizing those efforts. The same technology could eventually be used in other developing nations as well so long as tests were carried out to customize the filters to each particular country’s conditions. If all goes well, the new composites could even provide a potential solution for achieving the United Nations millennium development goal of doubling the number of people with sustainable access to safe drinking water by 2015.

“People talk about nanotechnology from the context of advanced computing and high density data storage,” Pradeep says. “Those are important, but at the same time frugal science is also important, and can make a larger impact in the short term.” 



PATENTS

METHODS OF PREPARING METAL QUANTUM CLUSTERS IN MOLECULAR CONFINEMENT
WO2013061109

ORGANIC TEMPLATED NANOMETAL OXYHYDROXIDE
WO2011151725

GOLD AND SILVER QUANTUM CLUSTERS AND METHODS FOR THEIR PREPARATION AND USE
WO2012090034

GOLD SUB-NANOCLUSTERS AND USES THEREOF
US2012052513

SUSTAINED SILVER RELEASE COMPOSITION FOR WATER PURIFICATION
WO2012140520

SINGLE CONTAINER GRAVITY-FED STORAGE WATER PURIFIER
WO2012150506

AXIAL FLOW FILTER BLOCK FOR WATER PURIFICATION
WO2012042388

REDUCED GRAPHENE OXIDE-BASED-COMPOSITES FOR THE PURIFICATION OF WATER
WO2012028964

ORGANIC POLYMER-INORGANIC FINE PARTICLE ANTIMICROBIAL COMPOSITES AND USES THEREOF
WO2011024043

Adsorbent composition, a device and a method for decontaminating water containing pesticides
US2007166224



WO2013061109
METHODS OF PREPARING METAL QUANTUM CLUSTERS IN MOLECULAR CONFINEMENT


Description --

BACKGROUND

[0001] Metal quantum clusters (MQCs) have fascinating size-dependent properties including discrete electronic energy levels and 'molecule-like' optical transitions in their absorption and emission spectra. As such, MQCs can be used for single molecule optics, nanophotonics, bioscience, catalysis, and other similar applications. The practical use of MQCs in such applications will require the large-scale synthesis of monodisperse MQCs.

[0002] Conventional methods for the synthesis of MQCs are based on solution- phase routes. Typically, MQCs of various sizes are made together in a synthetic procedure. In order to get monodispersed MQCs with well-defined molecular formulae, size-separation using elaborate chromatographic techniques is required.

SUMMARY

[0003] This disclosure is not limited to the particular systems, devices and methods described, as these may vary. The terminology used in the description is for the purpose of describing the particular versions or embodiments only, and is not intended to limit the scope.

[0004] Methods of growing metal quantum clusters within a porous gel matrix are described herein. These methods allow for the large-scale synthesis of monodispersed metal quantum clusters using a single-step approach, which may improve the availability and utility of metal quantum clusters. By growing metal quantum clusters within a porous gel matrix, monodisperse uniform nanoparticles may be produced more easily and/or in better yields than in free-solution approaches. It is believed that the growth of the metal quantum clusters is encouraged within but limited by the size of the pores of the gel matrix. Because individual cluster growth is determined by pore size a monodisperse and uniform population is readily made.

[0005] In an embodiment, a method of synthesizing metal quantum clusters includes growing the metal quantum clusters in a porous gel matrix. This embodiment includes formation of a porous gel matrix that encapsulates a metal quantum cluster precursor compound and the introduction of a reducing agent to form the metal quantum clusters.

[0006] In an embodiment, a method of synthesizing metal quantum clusters includes forming a porous gel matrix from the mixture comprising a metal-containing compound, a capping agent, and a gel-forming solution and adding a reducing agent to form the metal quantum clusters.

[0007] In an embodiment, a kit for synthesizing metal quantum clusters includes a metal-containing compound, a capping agent, a gel-forming solution, a reducing agent, and instructions for use.

[0008] In an embodiment, a gel matrix includes a porous gel encapsulating a metal quantum cluster precursor compound.

[0009] In an embodiment, a gel matrix includes a porous gel encapsulating metal quantum clusters of the formula Agi8(glutathione)25.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a flowchart that illustrates an exemplary method for synthesizing metal quantum clusters, in accordance with an embodiment.

DETAILED DESCRIPTION

[0011] Methods of growing metal quantum clusters within a porous gel matrix are described herein. These methods allow for the large-scale synthesis of monodispersed metal quantum clusters using a single-step approach, which may improve the availability and utility of metal quantum clusters.

[0012] In an embodiment, metal quantum clusters are grown within a porous gel matrix. Despite variations in nomenclature concerning small-sized particles based on size regimes, properties, and makeup, the term metal quantum clusters is not intended to be limiting, but instead refer to particular products of the general methods described herein.

[0013] . The average diameter of metal quantum clusters may be less than about 5 [mu][pi][iota], or about 100 nm to about 0.5 ran, or about 10 ran to about 1 nm. Specific examples of average diameters include about 5 [mu][pi][iota], about 400 nm, about 300 nm, about 200 nm, about 100 nm, about 50 nm, about 40 nm, about 30 nm, about 20 nm, about 10 nm, about 1 nm, about 0.5 nm, and ranges between any two of these values. The standard deviation of the diameter of the metal quantum clusters may be less than or equal to about 15% of the average diameter, less than or equal to about 10% of the average diameter, less than or equal to about 5% of the average diameter, or the metal quantum clusters may be monodisperse.

[0014] Materials for making metal quantum clusters are well-known to a person having ordinary skill in the art, and the examples described herein are not intended to be limiting. The metal quantum clusters may comprise Mg, Zn, Fe, Cu, Sn, Ti, Ag, Au, Cd, Se, Si, Pt, S, Ni or combinations thereof. For example, the metal quantum clusters may be of the formula Ag25(glutathione)i8.

[0015] Figure 1 is a flow diagram describing a method for synthesizing metal quantum clusters within a porous gel matrix according to an embodiment. As shown in Figure 1, a metal containing compound and a capping agent may be combined 105 to form a metal quantum cluster precursor compound.

[0016] The metal-containing compound used to make the metal quantum clusters may be a metal thioate, an organometallic compound, a metal oxide, an inorganic salt, a coordination compound, or a combination thereof. In an embodiment, the metal-containing compound used to make the metal quantum clusters may contain Mg, Zn, Fe, Cu, Sn, Ti, Ag, Au, Cd, Se, Si, Pt, S, Ni or a combination thereof. For example, the metal-containing compound used to make the metal quantum clusters may be AgN03. [0017] The surface of the metal quantum clusters may comprise at least one layer of capping agents. The capping agent may be used to control the growth, improve the solubility, provide chemical functionality, or otherwise alter the properties the metal quantum clusters. Materials used as capping agents are well-known to a person having ordinary skill in the art, and the examples described herein are not intended to be limiting. Despite variations in nomenclature regarding surface-functionalization of metals based on chemical makeup and properties, the term capping agent is not intended to be limiting, but instead refers to particular products of the general methods described herein. The capping agent can comprise an aromatic group, a conjugated pi system, a pi bond, a nitrogen atom, an oxygen atom, a sulphur atom, a phosphorus atom, an aromatic thiol or an aliphatic thiol. In an embodiment, the capping agent may be an organosulfur compound. For example, the capping agent may be a thiol. As a specific example, the capping agent may be glutathione thiolate.

[0018] The metal quantum cluster precursor compound is the starting material used in the formation of the metal quantum clusters. The metal quantum cluster precursor compound may be a metal-containing compound, or the metal quantum cluster precursor compound may be formed by mixing a metal-containing compound with a capping agent.

[0019] The metal quantum cluster precursor compound may optionally be sonicated 110. Aggregates may sometimes be present in the metal quantum cluster precursor compound. Any unwanted aggregates may be dispersed by sonicating 110 the metal quantum cluster precursor compound.

[0020] A mixture may be formed 115 by combining a gel-forming solution, a polymerization agent, and a metal quantum cluster precursor compound. The gel-forming solution is a liquid comprising the materials used to form a porous gel matrix. In an embodiment, the gel-forming solution may be a polymer or a polymerizable material. For example, the polymerizable material may be acrylamide, bisacrylamide, piperazine di-acrylamide, diallyltartardiamide, dihydroxyethylene-bis-acrylamide, bis-acrylylcystamine or mixtures thereof. Typical mixtures of the polymerizable material may comprise acrylamide and at least one cross-linker selected from bisacrylamide, piperazine di-acrylamide, diallyltartardiamide, dihydroxyethylene-bis-acrylamide, and bis-acrylylcystamine. In some examples, the polymerizable material may be a mixture of acrylamide and the cross-linker bisacrylamide.

[0021] A gel-forming solution may use a change in temperature, additional reagents, or both a change in temperature and additional reagents to form a porous gel matrix. The additional reagents may be polymerization agents such as catalysts and polymerization initiators and combinations thereof. For example, polymerization agents may be [Nu],[Nu],[Nu]',[Nu]'- tetramethyl-ethane-l,2-diamine (TMED), ammonium persulfate, riboflavin-5'-phosphate, or mixtures thereof.

[0022] The mixture of the gel-forming solution, a polymerization agent, and a metal quantum cluster precursor compound may polymerize and allow formation 120 of the porous gel matrix encapsulating the metal quantum cluster precursor compound. In an embodiment, porous gel matrix matrices are composed of molecular cages which may be used to control mass transfer of reagents and nucleate the preferred metal quantum clusters. Metal quantum clusters grown using this method, may be at least partially encapsulated by the porous gel matrix.

[0023] The materials and methods for making porous gel matrix matrices are well- known to a person having ordinary skill in the art, and the examples described herein are not intended to be limiting. The porous gel matrix may comprise a sol-gel or a polymer. In an embodiment, the porous gel matrix may comprise agarose or cross-linked polyacrylamide. For example, the porous gel matrix may comprise a polyacrylamide cross-linked with bisacrylamide, agarose gel, cellulose gel, or a starch gel. [0024] Methods that vary the pore size of the porous gel matrix may alter the diameter of the metal quantum clusters grown within the porous gel matrix. In some embodiments, increasing the cross-linker concentration in the gel-forming solution may induce a systematic increase in the pore size of the porous gel matrix and may facilitate the growth of larger metal quantum clusters within the matrix. The following table is exemplary only, it is not meant to limit the invention in any way.

[0025] Using the methods described herein, a porous gel matrix made using a gel- forming solution can be made to have desired pore sizes, resulting in a desired quantum cluster of a desired size, wherein the resultant quantum clusters are substantially all the desired quantum cluster and substantially free of polydisperse plasmonic nanoparticles. Preferably the content of the desired metal quantum clusters is greater than about 80%, greater than about 90%, greater than about 95%, greater than about 91%, greater than about 99%, greater than about 99.5%, or greater than about 99.9% of all the metal quantum clusters formed. For example, a porous gel matrix comprising 51% acrylamide monomer and 7.8% bisacrylamide crosslinker yields a matrix comprising metal quantum clusters that are substantially all Ag25(glutathione)i8 metal quantum clusters. Preferably the content of Ag25(glutathione)i8 metal quantum clusters is greater than about 80%), greater than about 90%, greater than about 95%, greater than about 97%, greater than about 99%, greater than about 99.5%, or greater than about 99.9% of all the metal quantum clusters formed.

[0026] Monodispersity of a metal quantum cluster sample may be confirmed by UV-Vis spectroscopy, polyacrylamide gel electrophoresis and electrospray ionisation mass spectrometry. A sample of monodisperse metal quantum clusters may show strong quantum size effects such as multiple molecule-like transitions in the optical absorption spectrum, whereas metal nanoparticles may show a dominant plasmon resonance band. In an embodiment, the UV-Vis spectrum of an aqueous solution of Ag25(glutathione)i 8 metal quantum clusters shows prominent features at about 350, 480, and 650 nm indicating that the clusters obtained were monodispersed. Further confirmation of monodispersity in a metal quantum cluster sample can be had via gel electrophoresis, where elution of a single band may indicate that only one type of cluster is present. In an embodiment, a sample of Ag25(glutathione)i 8 metal quantum clusters produced a single band when subjected to polyacrylamide gel electrophoresis. Finally, a mass spectrum of monodisperse metal quantum clusters may be substantially free of all features not corresponding to the ionized metal quantum cluster and its multiply charged ions that originate from ligand deprotonation. In an embodiment, the electrospray ionization mass spectrum of Ag25(glutathione)j8 taken in negative ion mode showed only the parent peak of [Ag2s(glutathione)i8]<~> at m/z = 1641.1 and peaks from a series of multiply charge ions originating from deprotonation of the 18 glutathione ligands.

[0027] In an embodiment, the porous gel matrix may encapsulate the metal quantum cluster precursor compound. The metal quantum cluster precursor compound may be introduced to the porous gel matrix by adding the metal quantum cluster precursor compound to the gel-forming solution, by adding the metal quantum cluster precursor compound to the porous gel matrix, or by forming the metal quantum cluster precursor compound within the porous gel matrix.

[0028] Referring back to Figure 1 , a reducing agent may be added 125 to the porous gel matrix encapsulating the metal quantum cluster precursor. The reducing agent may be used to form metal quantum clusters within the porous gel matrix through the reduction of the metal quantum cluster precursor compound. Materials used as reducing agents are well- known to a person having ordinary skill in the art, and the examples described herein are not intended to be limiting. The reducing agent may be an inorganic salt. In some embodiments, the reducing agent may be NaBH4, LiAlH4, nascent hydrogen, borane-tetrahydrofuran complex, or sodiumcyanoborohydride.

[0029] The reducing agent may be introduced to the porous gel matrix by adding the reducing agent to the gel-forming solution, by passive permeation of the reducing agent into the porous gel matrix, or by using an applied current to carry the reducing agent through the porous gel matrix.

[0030] In an embodiment, formation of the preferred metal quantum clusters can include lowering the reaction temperature between the reducing agent and the metal quantum cluster precursor compound. For example, the reducing agent and the porous gel matrix encapsulating the metal quantum cluster precursor compound may be cooled below room temperature prior to introducing the reducing agent to the porous gel matrix. In some embodiments, they are cooled to about 20 [deg.]C or below, about 15 [deg.]C or below, about 10 [deg.]C or below, about 5 [deg.]C or below, or to about 0 [deg.]C or to a range between any two of these values. In particular, the reducing agent and the porous gel matrix encapsulating the metal quantum cluster precursor compound may be cooled to about 0 [deg.]C prior to introducing the reducing agent to the porous gel matrix.

[0031] Following formation of the metal quantum clusters, the reaction may be stopped by removing excess reducing agent from the porous gel matrix. Solvent extraction may be used to remove excess reducing agent. The extraction solvent may be an alcohol, such as ethanol or methanol.

[0032] Further use of the metal quantum clusters may include separation or isolation of the metal quantum clusters from the porous gel matrix. Pulverizing the porous gel matrix may improve the isolation of the metal quantum clusters from the porous gel matrix.

[0033] In some embodiments, solvent extraction may be used to extract metal quantum clusters from the porous gel matrix. The extraction solvent may be aqueous. For example, the extraction solvent may be water, water and about 20% methanol, water and about 20% tetahydrofuran, or water and about 20% dimethylformamide. Centrifugation may be used to separate insoluble gel fragments from a solution containing metal quantum clusters. Purification of dissolved metal quantum clusters may be achieved by precipitating the metal quantum clusters. In an embodiment, addition of a solvent may be used to precipitate the metal quantum clusters from an aqueous solution. The precipitation solvent may be an alcohol such as ethanol or methanol, or it may be an organic solvent such as acetone or acetonitrile.

[0034] In other embodiments, the porous gel matrix may be dissolved with a suitable solvent. The metal quantum clusters may dissolve with the porous gel matrix, or may remain insoluble. In embodiments where the metal quantum clusters are not dissolved along with the porous gel matrix, centrifugation may be used to separate the insoluble metal quantum clusters from the solution. In embodiments where the metal quantum clusters are dissolved along with the porous gel matrix, selective precipitation may be used to isolate the metal quantum clusters. [0035] Removal of solvent may be used to acquire a dry powder of metal quantum clusters. Solvent may be removed by applying a vacuum, raising the temperature, decanting, or any combination thereof. For example, solvent may be removed by applying a vacuum at elevated temperature. The isolated yield of metal quantum clusters may be about 30% to about 100%, about 50% to about 80%, about 66%, or about 63%, based on the weight of the metal-containing compound. Specific examples of yield include about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, about 99%, and ranges between any two of these values. In an ideal example, the yield is about 100% or is 100%.

[0036] A phase-transfer reagent may be used to alter the solubility properties of the metal quantum clusters. Water soluble metal quantum clusters may be transferred to an organic solvent by dissolving the metal quantum clusters in an aqueous solvent and adding a phase-transfer reagent dissolved in an organic solvent. The mixture of metal quantum clusters and phase-transfer reagent may be heated, stirred, or heated and stirred. Suitable phase-transfer reagents include but are not limited to quaternary ammonium cations, such as benzyltrimethylammonium chloride or tetraoctylammonium bromide, and phosphonium salts, such as tetraphenylphosphonium chloride. The phase-transfer reagent may be tetraoctylammonium bromide. The organic solvent may be immiscible with water. For example, suitable solvents include organic solvents, such as toluene, dichloromethane, carbontetrachloride, hexane, cyclohexane, pentane, and diethyl ether.

[0037] The aqueous and organic solvents may be separated. Ethanol, for example, may be added to the organic layer to precipitate the phase-transferred metal quantum clusters. The precipitated phase-transferred metal quantum clusters may be washed, isolated, dried, or any combination thereof. The precipitated phase-transferred metal quantum clusters may be redispersible in an organic solvent. The phase-transferred metal quantum clusters may be more stable when compared to the metal quantum clusters in an aqueous solution.

[0038] In an embodiment, a kit for making metal quantum clusters may be provided. The kit may comprise: a metal-containing compound, a capping agent, a gel-forming solution, a reducing agent, and instructions for preparing the metal quantum clusters. In an embodiment, the kit may include four containers, wherein: the metal-containing compound is in the first container, the capping agent is in the second container, the gel-forming solution is in the third container, and the reducing agent is in the fourth container.

[0039] The metal-containing compound provided in the kit may be a metal thiolate, an organometallic compound, a metal oxide, an inorganic salt, a coordination compound, or a combination thereof. In an embodiment, the metal-containing compound provided in the kit may contain Mg, Zn, Fe, Cu, Sn, Ti, Ag, Au, Cd, Se, Si, Pt, S, Ni or a combination thereof. For example, the metal-containing compound provided in the kit may be AgN03.

[0040] The capping agent provided in the kit can comprise an aromatic group, a conjugated pi system, a pi bond, a nitrogen atom, an oxygen atom, a sulphur atom or a phosphorus atom. In an embodiment, the capping agent provided in the kit may be an organosulfur compound. For example, the capping agent provided in the kit may be a thiol. In particular, the capping agent provided in the kit may be glutathione thiolate.

[0041] The gel-forming solution provided in the kit is a liquid comprising the materials used to form a porous gel matrix. In an embodiment, the gel-forming solution provided in the kit may be a polymer or a polymerizable material. For example, the polymerizable material provided in the kit may be acrylamide, bisacrylamide, piperazine di- acrylamide, diallyltartardiamide, dihydroxyethylene-bis-acrylamide, bis-acrylylcystamine or mixtures thereof. In particular, the polymerizable material provided in the kit may be a mixture acrylamide and bisacrylamide. [0042] The gel-forming solution provided in the kit may use a change in temperature, additional reagents, or both a change in temperature and additional reagents to form a porous gel matrix. The additional reagents may be polymerization agents such as catalysts and polymerization initiators and may be included in the kit. In an embodiment two additional containers with the polymerization agents N,N,N',N'-tetramethyl-ethane-l ,2- diamine (TMED) and ammonium persulfate are provided in the kit. As will be appreciated by those skilled in the art, the polymerization agents should be separate from the polymerizable material until polymerization is desired.

[0043] The reducing agent provided in the kit may be an inorganic salt. For example, the reducing agent may be NaBH4.

[0044] The solubility of the metal quantum clusters made using the kit can optionally be changed from organic to aqueous or from aqueous to organic. In an embodiment, the kit will provide an additional container with a phase-transfer agent. The phase-transfer reagent may be tetraoctylammonium bromide.

[0045] Embodiments illustrating the method and materials used may be further understood by reference to the following non-limiting examples.

EXAMPLES

Example 1 : Preparation of metal quantum clusters in a porous gel.

[0046] The metal quantum cluster precursor compound was formed by dissolvingAgN03 (47 mg, 276 mM) and glutathione (GSH) (150 mg, 489 mM) in a 1 mL solution of NaOH (60 mg, 1.5 mM, triply distilled water) at room temperature. The solution was vigorously stirred and sonicated to make a uniform solution of Ag(I)thiolate.

[0047] The gel-forming solution was formed by mixing acrylamide(T)/bisacrylamide(C) (51% T, 7.8%C) and 20 [mu][iota],, of 0.1% ammonium persulfate in a 250 mL beaker. 0.7 mL of the metal quantum cluster precursor solution was added and stirred. With the addition of 10 [mu][iota] N,N,N',N'-tetramethyl-ethane-l,2-diamine (TMED), polymerization leading to the porous gel matrix occurred. The gel was cooled to 0 [deg.]C.

[0048] Formation of the metal quantum clusters was initiated by adding ice cold, aq. NaBH4 (0.5 M, 10 mL) on top of the porous gel matrix encapsulating metal quantum cluster precursor. The color of the gel changed from light yellow to dark brown within half an hour indicating the formation of gel-encapsulated metal quantum clusters.

Example 2: Isolation of metal quantum clusters from a porous gel matrix.

[0049] The porous gel matrix was pulverized, and the metal quantum clusters were extracted into water. This aqueous solution of metal quantum clusters was centrifuged at 15,000 rpm to remove traces of the porous gel matrix. Excess ethanol was added to precipitate the metal quantum clusters. Removal of solvent under reduced pressure led to a dry powder of metal quantum clusters.

Example 3: Phase transfer of metal quantum clusters.

[0050] An aqueous solution of metal quantum clusters (5 mg/mL) was mixed with 5 mM tetraoctylammonium bromide (TOABr) in toluene and stirred vigorously for 2 minutes. Metal quantum clusters underwent immediate and complete phase transfer from the aqueous to the toluene layer. The phase transfer was monitored visually by color changes in the aqueous and toluene layers. The colorless toluene layer turned reddish brown and the aqueous layer, which was originally reddish brown, turned colorless after stirring. Ethanol was added to the toluene layer to precipitate the phase transferred metal quantum clusters. The precipitate was washed two times with ethanol, centrifuged and dried. This powder was redispersible in toluene.

Example 4: Determining product monodispersitv and composition

[0051] The UV-Vis spectrum of an aqueous solution of the product from Example 2 shows prominent features at 330, 478, and 640 nm, and is devoid of a plasmon resonance band. These multiple molecule-like transitions in the optical absorption spectrum are indicative of a sample containing monodisperse metal quantum clusters.

[0052] Polyacrylamide gel electrophoresis gels were made with a 1 mm thick spacer where the total contents of the acrylamide monomers were 28% (bis(acrylamide:acrylamide) = 7:93) and 3% (bis(acrylamide:acrylamide) = 6:94) for the separation and condensation gels, respectively. The eluting buffer consisted of 192 mM glycine and 25 mM tris(hydroxymethylamine). The crude mixture of metal quantum clusters, as a reddish brown powder, obtained in the reaction from example 2 was dissolved in 5% (v/v) glycerol-water solution (1.0 mL) at a concentration of 60 mg/mL. The sample solution (1.0 mL) was loaded onto a 1 mm gel and eluted for 4 h at a constant voltage of 150 V to achieve separation. The metal quantum clusters appeared as a single band in the gel, further indicating that the sample was contained monodisperse metal quantum clusters.

[0053] Electrospray ionization mass spectrometry was performed on the product from example 3 in methylene chloride. The spectrum taken in negative ion mode showed only the parent peak of [Ag25(glutathione)i8]<"">at m/z = 1641.1 and peaks from a series of multiply charge ions originating from deprotonation of the 18 glutathione ligands. The absence of other features and the mass correlation to the desired metal quantum clusters confirms that the synthesized product is Ag25(glutathione)i8 metal quantum clusters.

Example 5 : Preparation of nanoparticles.

[0054] Silver nitrate (AgN03, 47 mg, 276 mM) and glutathione (GSH) (150 mg, 489 mM) will be dissolved in a 1 mL solution of NaOH (60 mg, 1.5 mM, triply distilled water) at room temperature. The solution will be vigorously stirred and sonicated to make a uniform solution of Ag(I)thiolate. Formation of the nanoparticles will be initiated by adding ice cold, aq. NaBH4 (0.5 M, 10 mL) to the solution of Ag(I)thiolate. Polydisperse plasmonic nanoparticles will be isolated by centrifugation, removal of supernatant, dispersion of the resulting pellet in water, and a second centrifugation and removal of supernatant step.

[0055] In the present disclosure, reference is made to the accompanying figure, which form a part hereof. The illustrative embodiments described in the detailed description, figure, and claims are not meant to be limiting. Other embodiments may be used, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figure, may be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein.

[0056] The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the aft. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, reagents, compounds, compositions or biological systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0057] With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

[0058] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g. , bodies of the appended claims) are generally intended as "open" terms (e.g. , the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g. , the bare recitation of "two recitations," without other modifiers, means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g. , " a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or figure, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."

[0059] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

[0060] As will be understood by one skilled in the art, for any and all purposes, such as in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, <'>quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as "up to," "at least," and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member. Thus, for example, a group having 1-3 substituents refers to groups having 1, 2, or 3 substituents. Similarly, a group having 1-5 substituents refers to groups having 1, 2, 3, 4, or 5 substituents, and so forth.



ORGANIC TEMPLATED NANOMETAL OXYHYDROXIDE  
WO2011151725

BACKGROUND

TECHNICAL FIELD

[0001] The present disclosure relates to nanomaterials, and particularly to nanometal oxyhydroxide materials, such as, for example, organic templated nanometal oxyhydroxide materials, together with methods of preparing such materials.

TECHNICAL BACKGROUND

[0002] Amongst all aluminum based compositions, activated alumina is the most popular composition. Activated alumina is typically prepared by complete thermal dehydration of aluminum hydroxide whereas boehmite is typically prepared by partial thermal dehydration of aluminum hydroxide. Activated alumina is an effective industrial desiccant, catalyst support and an effective adsorbent of arsenic and fluoride in water. The United Nations
Environmental Program agency (UNEP) classified activated alumina adsorption among the best available technologies for arsenic removal from water. Aluminum based compounds in general, and alumina in particular, are widely used and are the basis of demonstrated technology for removing arsenic and fluoride from drinking water. The fluoride adsorption capacity of aluminum based compounds, however, is typically very low, for example, on the order of 1 to 10 mg/g. Arsenic adsorption capacity is similarly low. Thus, adsorption technologies and devices which utilize conventional alumina materials are limited by the low arsenic and fluoride uptake capacity and can require frequent regeneration, producing large amounts of solid and liquid waste.

[0003] Typically, granular beads of alumina are used in the applications discussed above. Powder based compositions cannot be directly used due to the inherent poor hydraulic conductivity and the danger of particle leaching. The conventional granular beads are prepared by adding binders along with fine particles of alumina/aluminum hydroxide, and heating the mixture at elevated temperatures in the range of 300 [deg.]C to 600 [deg.]C. Yet another method for obtaining alumina beads is via an oil-drop method wherein a gel obtained by precipitation of an aluminum precursor is allowed to drop into a hot oil bath, forming spherical particles and ageing the particles at higher pressure and temperature. The resulting crystalline spherical alumina particles are obtained after washing, drying and calcining at high temperature. Due to the use of external physical and/or chemical agents, such approaches are lesser environment friendly and uneconomical.

[0004] Metal oxide-chitosan composite materials are one example of organic bio-based materials known for their adsorption capacity to remove, for example, various aquatic pollutants. Ti-Al supported chitosan beads have recently been examined for the removal of fluoride, wherei it was found that chitosan beads dried at 80 [deg.]C swell in water and clog the filter unit. Calcining the beads at elevated temperature (e.g., 450 [deg.]C) can improve the stability of the beads; however, the calcination process reduces the fluoride uptake capacity and can decompose chitosan. These constraints restrict the use of such media for water purification applications.

[0005] Thus, there is a need to address the aforementioned problems and other shortcomings associated with the adsorption materials and water filtration technologies. Specifically, there is a need for bio-friendly materials that having improved fluoride and/or arsenic adsorption capacities. These needs and other needs are satisfied by the compositions and methods of the present disclosure.

SUMMARY

[0006] In accordance with the purpose(s) of the invention, as embodied and broadly described herein, this disclosure, in one aspect, relates to a granular composite material, and specifically to a granular composite of organic templated nanometal oxyhydroxide/hydroxide/oxide, and methods for preparing such materials.

[0007] In one aspect, the present disclosure provides a method for preparing a granular composite of organic templated nanometal-oxyhydroxide/hydroxide/oxide.

[0008] In another aspect, the present disclosure provides a method for preparing a granular composite through an aqueous route comprising a biopolymer and one or more nanometal- oxyhydroxide/hydroxide/oxide particles .

[0009] In another aspect, the methods of the present disclosure can obviate the need for elevated temperatures, pressure or external chemical agents in the preparation of granular composite materials. [0010] In yet another aspect, the present disclosure provides a filtration device comprising the inventive nanometal oxyhydroxide/hydroxide/oxide material.

[0011] Additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or can be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE FIGURES

[0012] The accompanying figures, which are incorporated in and constitute a part of this specification, illustrate several aspects and together with the description serve to explain the principles of the invention.

[0013] FIG. 1 is a schematic representation of chemical reactions involved in the method for preparation of a granular hybrid composite, in accordance with various aspects of the present invention.

[0014] FIG. 2 is a schematic representation of chitosan bound AIOOH particles, in accordance with an embodiment of the present invention, together with micrographs illustrating the pepper corn like shape of the particles.

[0015] FIG. 3a illustrates X-ray diffraction (XRD) patterns of an organic template boehmite nanoarchitecture (OTBN), fluoride adsorbed OTBN and chitosan. FIG. 3b illustrates the XRD patterns of OTBN prepared by various starting materials and OTBN dried by various methods.

[0016] FIG. 4 illustrates FT-IR spectra of organic template boehmite nanoarchitecture (OTBN) and fluoride adsorbed OTBN.

[0017] FIG. 5a illustrates the x-ray photoelectron spectroscopy (XPS) spectra of organic template boehmite nanostructure (OTBN) before and after the adsorption of the fluoride, with FIGS 5b, 5c, and 5d detailing the aluminum, oxygen, and fluorine regions, repsectively. [0018] FIG. 6a illustrates the extent of fluoride adsorption by OTBN as a function of adsorbent dose, and FIG. 6b illustrates the fluoride uptake capacity as a function initial fluoride concentration at an initial fluoride concentration of 10 mg/L and feed water pH of 7 + 0.2.

[0019] FIG. 7a illustrates fluoride uptake capacity of OTBN as a function of time, and FIG. 7b depicts pseudo-second order kinetic plots for the adsorption of fluoride onto OTBN.

[0020] FIG. 8a illustrates adsorption capacity of OTBN as a function of adsorbent dose and FIG. 8b illustrates adsorption capacity of OTBN as function of arsenate concentration at an initial arsenate concentration of 1.1 mg/L and feed water pH of 7 + 0.2.

DESCRIPTION

[0021] The present invention can be understood more readily by reference to the following detailed description of the invention and the Examples included therein.

[0022] Before the present compounds, compositions, articles, systems, devices, and/or methods are disclosed and described, it is to be understood that they are not limited to specific synthetic methods unless otherwise specified, or to particular reagents unless otherwise specified, as such can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, example methods and materials are now described.

DEFINITIONS

[0023] As used in the specification and the appended claims, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a solvent" can include mixtures of two or more solvents.

[0024] Ranges can be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as "about" that particular value in addition to the value itself. For example, if the value "10" is disclosed, then "about 10" is also disclosed. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.

[0025] As used herein, the terms "optional" or "optionally" means that the subsequently described event or circumstance can or can not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.

[0026] As used herein the term "oxyhydroxide/hydroxide/oxide" can refer to an
oxyhydroxide, a hydroxide, an oxide, or any combination thereof. It is not necessary that each of an oxyhydroxide, a hydroxide, and an oxide be present.

[0027] Throughout this specification, unless the context requires otherwise, the word "comprise," or variations such as "comprises" or "comprising," will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0028] Disclosed are the components to be used to prepare the compositions of the invention as well as the compositions themselves to be used within the methods disclosed herein. These and other materials are disclosed herein, and it is understood that when combinations, subsets, interactions, groups, etc. of these materials are disclosed that while specific reference of each various individual and collective combinations and permutation of these compounds can not be explicitly disclosed, each is specifically contemplated and described herein. For example, if a particular compound is disclosed and discussed and a number of modifications that can be made to a number of molecules including the compounds are discussed, specifically contemplated is each and every combination and permutation of the compound and the modifications that are possible unless specifically indicated to the contrary. Thus, if a class of molecules A, B, and C are disclosed as well as a class of molecules D, E, and F and an example of a combination molecule, A-D is disclosed, then even if each is not individually recited each is individually and collectively contemplated meaning combinations, A-E, A-F, B-D, B-E, B-F, C-D, C-E, and C-F are considered disclosed. Likewise, any subset or combination of these is also disclosed. Thus, for example, the sub-group of A-E, B-F, and C- E would be considered disclosed. This concept applies to all aspects of this application including, but not limited to, steps in methods of making and using the compositions of the invention. Thus, if there are a variety of additional steps that can be performed it is understood that each of these additional steps can be performed with any specific
embodiment or combination of embodiments of the methods of the invention.

[0029] It is understood that the compositions disclosed herein have certain functions. Disclosed herein are certain structural requirements for performing the disclosed functions, and it is understood that there are a variety of structures that can perform the same function that are related to the disclosed structures, and that these structures will typically achieve the same result.

[0030] As briefly discussed above, the present disclosure relates generally to a granular composite material. In one aspect, the invention comprises a granular composite of an organic templated nanometal oxyhydroxide/hydroxide/oxide material. In another aspect, such a granular composite can be prepared using a process conducted at least partially in an aqueous medium.

[0031] In another aspect, the present disclosure provides methods for the preparation of a granular composite, such as, for example, an organic templated nanometal oxyhydroxide/hydroxide/oxide. In one aspect, the present disclosure provides methods for preparing a granular composition using an aqueous medium, the method comprising a biopolymer and one or more nanometal oxyhydroxide/hydroxide/oxide particles. In a general aspect, the methods of the present invention comprise contacting a metal or metal precursor with a biopolymer and/or biopolymer solution, and then contacting the resulting mixture with a base.

[0032] In various aspects, a metal and/or metal precursor can comprise a salt of a metal or a solution thereof. In one aspect, the metal from which a metal and/or metal precursor can comprise aluminum, zinc, manganese, iron, titanium, zirconium, lanthanum, cerium, or a combination thereof.. In one aspect, a metal precursor comprises a solution of an aluminum salt comprising aluminum nitrate, aluminum chloride, aluminum sulfate, aluminum isopropoxide, or a combination thereof. In still other aspects, the metal precursor can comprise other metal salts or solutions not specifically recited herein, and the present invention is not intended to be limited to any particular metal precursor. In other aspects, the metal precursor can comprise a mixture of two or more individual metal precursors in any desired ratio, such as, for example, from about 20: 1 to about 1:20, for example, about 20: 1, 10: 1, 5: 1, 3: 1, 2: 1, 1: 1, 1:2, 1:3, 1:5, 1: 10, or 1:20. In one aspect, the metal precursor comprises aluminum nitrate. In another aspect, the metal precursor comprises a mixture of aluminum and iron salts in a ratio of, for example, about 3: 1 (Al:Fe).

[0033] The biopolymer can comprise any suitable biopolymer or mixture of biopolymers. In one aspect, the biopolymer can comprise chitosan, banana silk, cellulose fibers, or a combination thereof. In another aspect, the biopolymer or a portion thereof is a flake biopolymer. In another aspect, functionalized forms of the biopolymer can also be used as biopolymer flakes. In other aspects, chitosan flakes can be used as biopolymer flakes. In one aspect, a biopolymer, such as, for example, a biopolymer flake, can be dissolved in a solution of water and/or a solution of water and a mineral acid, such as, for example, HCl, HNO3 and the like. In such an aspect, the H<+> ions of the mineral acid can at least partially ionize the biopolymer and dissolve it in the water to obtain biopolymer solution. In one aspect, the biopolymer comprises chitosan. In another aspect, the biopolymer comprises a mixture of cellulose and chitosan.

[0034] In one aspect, the metal ions of a metal precursor can interact with a biopolymer through a number of functional groups. The amounts of metal precursor and biopolymer can vary, and any suitable amount for a desired composite can be utilized.

[0035] The base of the present invention can comprise any suitable base for use in preparing the inventive granular composites. In one aspect, a base can comprise sodium hydroxide, ammonia, potassium hydroxide, or a combination thereof. In other aspects, other bases or combination of bases and/or solutions thereof can be used, and the present invention is not intended to be limited to any particular base. In one aspect, upon addition of base to a mixture of metal precursor and biopolymer, metal ions present in the resulting metal- biopolymer complex solution can hydrolyze and precipitate as nanometal oxyhydroxide/hydroxide/oxide particles. In one aspect, functional groups associated with a biopolymer, such as chitosan, can enable the formation of metal-oxyhydroxide/hydroxide/oxide, for example, a combination of oxyhydroxide, hydroxide, and oxide, rather than metal hydroxide.
[0036] In such an aspect, a semi-solid precipitate comprising nanometal- oxyhydroxide/hydroxide/oxide particles aligned on the chitosan biopolymer can be obtained. In one aspect, the size of the resulting nanometal oxyhydroxide/hydroxide/oxide particles can be in the range of from about 1 nm to about 100 nm. In with yet another aspect, the size of the nanometal oxyhydroxide/hydroxide/oxide particles can be in the range of from about 3 nm to about 10 nm.

[0037] In one aspect, the method for preparing the inventive granular composite can be conducted at least partially in an aqueous medium. In another aspect, the method can be conducted in an aqueous medium. In one aspect, the phrase 'an aqueous medium' can refer to a medium comprising water, and optionally other aqueous and/or nonaqueous components. In another aspect, the phrase 'an aqueous medium' can refer to a medium wherein all components are aqueous or at least partially soluble in water. In still other aspects, other items, such as particulate materials, that can form, for example, a suspension, can be present.

[0038] In one aspect, the method can be conducted wherein the temperature of the medium is below about 60 [deg.]C for at least a portion of the process. In another aspect, the method can be conducted wherein the temperature of the medium is below about 60 [deg.]C during the process.

[0039] A metal precursor can be contacted with a biopolymer. In one aspect, the metal precursor or a portion thereof can be in the form of a solution. Upon contacting, the metal precursor and biopolymer can form a metal-biopolymer complex solution. In one aspect, such a complex solution can be subjected to a hydrolysis step wherein the metal precursor or a portion thereof is hydrolyzed by contacted with a base. In one aspect, the base can comprise a solution. In one aspect, the order of contacting can vary. In another aspect, the biopolymer can metal precursor are first contacted, and then the resulting mixture can be contacted with a base or base solution. In other aspects, the degree of mixing can vary, and it is not necessary that the components be thoroughly mixed or that a completely homogeneous mixture be obtained. In another aspect, the components are mixed such that the resulting composition is uniform or substantially uniform. In still another aspect, the components can be vigorously mixed, for example, by stirring, to obtain the desired product.

[0040] After contacting with a base, the resulting product can comprise one or more nanometal oxyhydroxiee/hydroxide/oxide particles. In one aspect, any of the one or more particles can comprise the same or a different chemical composition and/or structure than any other particles.

[0041] In one aspect, a precipitate, such as, for example, a semi-solid precipitate of the one or more nanometal oxyhydroxide/hydroxide/oxide particle-biopolymer composite can be obtained. In such an aspect, the semi-solid precipitate can be subjected to optional filtration and/or drying steps to remove impurities, concentrate the precipitate, and isolate the desired solid nanometal oxyhydroxide/hydroxide/oxide particle-biopolymer composite.

[0042] In another aspect, a solid composite produced from the methods described herein can be ground to obtain a granular composite having a particle size and/or particle size distribution suitable for an intended application.

[0043] In one aspect, the methods of the present invention do not require at least one of elevated temperature, elevated pressure, and/or external chemical agents to prepare a granular composite. In antoher aspect, the methods of the present invention do not require elevated temperature, pressure, or external chemical agents to prepare a granular composite. In such aspects, the inventive methods provide substantial improvements over conventional methods known in the art. As the inventive granular composite includes a biopolymer as a component, the method for preparing the composite can be easy, economical, and environment friendly, especially as compared to conventional methods.

[0044] In various aspects, the present invention provides methods for preparing granular composites of one or more organic templated nanometal-oxyhydroxide/hydroxide/oxide via an aqueous process. In another aspect, the inventive granular composites can have useful adsorption properties and can be used to remove, for example, fluoride and/or arsenic contaminants from water.

[0045] FIG. 1 illustrates an exemplary reaction 100 through which a granular composite of organic templated nanometal-oxyhydroxide/hydroxide/oxide can be obtained. Reaction 100 can be initiated by preparing a biopolymer solution 102 of, for example, a biopolymer flake 101, and then a metal precursor solution 103 can be added to the biopolymer solution 102 to obtain a metal-biopolymer complex solution 105. A base 104 can then be added to the metal-biopolymer complex solution 105 to obtain the composite 106 of biopolymer and nanometal- oxyhydroxide/hydroxide/oxide particles .

[0046] In one aspect, the resulting semi-solid precipitate can be filtered and/or dried to remove impurities, to concentrate the precipitate and to obtain a solid metal oxyhydroxide/hydroxide/oxide particle-biopolymer composite. The particular method of drying, if dried, can vary, and the present invention is note intended to be limited to any particular drying method. In various aspects, exemplary drying methods can comprise freeze drying, surface drying, hot air drying, spray drying, vacuum drying, or a combination thereof. In other aspects, other drying technologies known in the art can be used in addition to or in lieu of any other specifically recited methods.

[0047] In another aspect, the dried solid precipitate can optionally be ground to a desirable size for an intended application, for example, in the range of from about 0.1 mm to about 3 mm. The resulting granular composite can comprise the metal oxyhydroxide/hydroxide/oxide particles and the biopolymer. In another aspect, the resulting granular composite can consist of the metal oxyhydroxide/hydroxide/oxide particles and the biopolymer. Ina specific aspect, a metal oxyhydroxide, such as, for example, aluminum oxyhydroxide, commonly known as boehmite, can be prepared, wherein the granular composite obtained has an organic template boehmite nanoarchitecture (OTBN).

[0048] In another aspect, the reaction 100 can take place at a temperature below about 60 [deg.]C, for example, about 55, 50, 45, 40, 35, 30, or 25 [deg.]C. In another aspect, the reaction 100 can take place at a temperature of about 30 [deg.]C. With the use of bio material and low temperature, the inventive methods described herein can provide easy, economical, and environment friendly methods to prepare composites of organic templated nanometal- oxyhydroxide/hydroxide/oxide .

[0049] FIG. 2 illustrates an exemplary schematic representation of OTBN comprising chitosan bound aluminum oxyhydroxide particles prepared by the methods of the present invention. As shown in the figure, one or more nanoscale aluminum oxyhydroxide particles 202 can be aligned on the surface of chitosan 201. Transmission electron micrographs 203 illustrate the OTBN at various magnifications. As illustrated in the micrographs, the OTBN samples can exhibit nano-whisker morpholigies. Upon close observation, small particles can be attached to the fibrils, where the attached small particles resemble peppercorns. The fibrils can be organic templates and the particles can comprise AIOOH nanoparticles. Also, as illustrated in the figures, the particles can have nanosize dimensions with diameters of, for example, less than about 5 nm.

[0050] Characterization of organic templated boehmite nanoarchitecture (OTBN) can be explored by various techniques such as x-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and x-ray photoelectron spectroscopy (XPS), as illustrated in FIGS. 3-5, respectively.

[0051] FIG. 3 illustrates the XRD patterns of (A) an exemplary as-synthesized material reacted with 1000 mg/L fluoride; (B) as-synthesized material reacted with 100 mg/L fluoride (C) as- synthesized AIOOH; and (D) chitosan. Dotted lines correspond to the standard reflections of AIOOH. The traces are shifted vertically for clarity. (Label: '+' - chitosan; '*'- AIOOH). The as-synthesized samples showed peaks corresponding to (020), (120), (013), (200) and (231) and (251) planes (FIG. 3A). All these peaks can be indexed as orthorhombic- AIOOH. The broadened XRD peaks imply that the crystallite size of the OTBN particles is very small. The mean crystallite size calculated from the Scherrer formula shows that nanocrystals are of an average size of about 3.5 nm. The presence of organic template (chitosan) is also clear from the XRD data. Fluoride reacted OTBN samples showed no change in diffraction patterns indicating that the crystal structure is intact even after fluoride adsorption (FIG. 3A). The standard reflections of orthorhombic-AlOOH are also given to validate the structure of the sample. Comparing the XRD positions of the standard sample and the as- synthesized sample, a change in intensity pattern could be seen, which can be ascribed to the effect of the organic template. The intensity of the higher index planes is higher in the nanoscale material. Recent studies on the catalytic activity of metals such as Pt have shown that high-index planes exhibit much higher catalytic activity than that of common and stable, low-index planes.

[0052] Apart from the point of view of enhanced catalytic activity, the current synthesis method can yield crystalline nanoscale- AIOOH having good green strength at much lower temperature in comparison to conventional methods. According to the current literature, AIOOH formation is possible only above 373 K, and the prior art syntheses of nanoscale- AIOOH have been done in hydrothermal conditions at temperatures above 373 K.

[0053] XRD patterns of the OTBNs prepared at various physical and chemical conditions were recorded in order to understand their effects on crystal structure of OTBN. Some of the XRD patterns recorded are shown in FIG. 3b. FIG. 3b illustrates the XRD patterns of as- synthesized materials through various starting materials: (Al) OTBN prepared using aluminum nitrate and ammonia as the starting materials, (A2) OTBN prepared using aluminum sulfate and ammonia as the starting materials, (A3) OTBN prepared using aluminum nitrate and sodium hydroxide as the starting materials, (A4 to A6) OTBN prepared using aluminum chloride and NaOH as the starting materials. All the materials except A5 and A6 were dried at 60 degree centigrade in oven. A5 was dried at room temperature and A6 was dried at 120 degree centigrade in oven. The data shows the formation of AIOOH with all the aluminum precursors and temperature range (25 to 130 degree centigrade) studied. The crystallographic structures obtained were seemingly identical.

[0054] FIG. 4 illustrates FT-IR spectra of (A) the as- synthesized OTBN and (B) fluoride adsorbed OTBN. All the absorption bands are consistent with literature values and give additional evidence for the formation of [gamma]- AIOOH. The bands at 1072 and 1154 cm<-1> are assigned to the symmetric and asymmetric stretching frequencies of Al-O-H of boehmite, respectively. The bands at 3096 and 3312 cm<-1> are assigned to Al-OOH stretching vibrations. The band at 1636 cm<-1> is assigned to the bending modes of adsorbed water and the broad band at 3429 cm<-1> is due to the O-H stretching mode of adsorbed water.

[0055] FIG. 5 illustrates the X-ray photoelectron spectroscopy (XPS) survey spectra of OTBN before and after the adsorption of the fluoride. Trace (A) and (B) in the FIG. 5(a-d) represent as-prepared OTBN and fluoride adsorbed OTBN respectively. FIG. 5(a) shows the survey spectra and (b,c,d) show the spectra of various regions of interest.These spectra confirm the existence of adsorbed fluoride along with the key elements aluminum and oxygen. For understating the chemical form of the pristine and fluoride adsorbed materials, detailed scans of specific regions of key elements (Al 2p, O ls) and adsorbed ion (F Is) were carried out and are shown in FIG. 5. The XPS spectrum of the aluminum 2p level shows a peak at 74.4 eV, which is in agreement with reported values of aluminum in AIOOH. Thus, in one aspect, fluoride adsorption does not affect the position of aluminum, but a reduction in the surface positive charge can be seen in the oxygen of Is orbital, as a result of which it appears at a lower binding energy. [0056] In another aspect, the granular composite of organic templated nanometal- oxyhydroxide prepared by the methods of the present invention can exhibit fluoride, arsenic and/or pathogen adsorption capability from water. In one aspect, a granular composite can have a fluoride adsorption capacity in excess of about 50 mg/g at an initial fluoride concentration of about 10 mg/1, and/or have an arsenic adsorption capacity in excess of about 19 mg/g at an initial arsenate concentration of about 1.0 mg/1.

[0057] In another aspect, the fluoride and/or arsenic adsorption rates of the composite of organic templated nanometal-oxyhydroxide prepared by the methods of present invention are discussed in FIGS 6 - 8.

[0058] FIG. 6a illustrates the extent of fluoride adsorption by OTBN as a function of adsorbent dose. The working volume of the contaminated water was taken to be 100 ml and the quantity of adsorbent dose is varied between 2.5 mg to 100 mg. The OTBN prepared through various starting materials were also tested to assess their capability to remove fluoride. As expected, the amount of fluoride adsorbed increased with increase in material dose from about 2.5 mg to about 50.0 mg and became more or less constant for further increase in dose. As evident from the data, the fluoride concentration reduced to a value as low as about 0.5 mg/L from an initial concentration of about 10 mg/L at optimum adsorbent dose. When the OTBN dose was further increased, there was less proportionate increase in adsorption because of the limitation of fluoride ions as compared to the adsorption sites available for the reaction. From these results it is observed that at about 10 mg/L fluoride concentration and neutral pH, the OTBN sample can remove about 53 mg/g of fluoride. This is considerably higher than the commercially available alumina or AIOOH based
nanomaterials tested so far. A recent attempt to remove fluoride from water using nanoscale- AIOOH showed a removal capacity of 3.26 mg/g, which is around 16 times less in capacity compared to the inventive OTBN sample prepared using the methods of present invention.

[0059] FIG. 6b illustrates the fluoride uptake capacity as a function of initial fluoride concentration. The working volume of the contaminated water was taken to be 100 ml and the initial fluoride concentration was varied between 5-60 mg/L. An increase in fluoride uptake capacity was observed with increase in initial fluoride concentrations and an uptake capacity in excess of about 50 mg/g was observed at initial fluoride concentration of 60 mg/L (Ce = 33.5 mg/L).

[0060] FIG. 7a illustrates fluoride uptake capacity of OTBN as a function of time.The working volume of the contaminated water was taken to be 100 ml and quantity of adsorbent used is 50 mg. Results show that fluoride uptake with OTBN sample prepared using the method of present invention is very fast and most of the removal takes place in the first 10 minutes of contact and the equilibrium is reached in 60 min. The fluoride uptake kinetics observed in the case of OTBN is much superior to the commercially available alumina and many other adsorbents used for scavenging fluoride, which has large implications in practical applications.

[0061] To understand the process kinetics better, kinetic data of fluoride adsorption by OTBN was analyzed with various reaction kinetic models, including Lagergren pseudo-first-order, and Ho's pseudo-second-order reaction rate models. While not wishing to be bound by theory, mathematical representations of these models are given in equations 1 and 2.

Pseudo-first-order equation:
(1)
Pseudo- second-order equation:

where qt is the amount of fluoride removed from aqueous solution at time t (mg/g); qe is the amount of fluoride removed from aqueous solution at equilibrium (mg/g); Ki is the pseudo- first-order rate constant of adsorption (1/min); K2 is the pseudo-second-order rate constant of adsorption (g/mg.min); and t is the time (min).

[0062] The best-fit model plots (pseudo-second-order reaction model) along with experimental plots are illustrated in FIG. 7b. The kinetic rate constant, K2 for 10 mg/L and 5 mg/L of fluoride were calculated to be 0.049 and 0.098 g/mg.min, respectively.

[0063] FIG. 8a illustrates the extent of arsenic adsorption by OTBN as a function of adsorbent dose. OTBN dose was varied over a range of 5 to 100 mg. The working volume of the contaminated water was taken to be 100 ml. Studies were conducted with an initial arsenic concentration of about 1.1 mg/L and at pH of 7 + 0.2. As evident from the data, the OTBN (25 mg) could reduce the arsenic concentration to a value below detectable limits of current techniques, such as inductively coupled plasma (ICP-OES) (< 0.05 mg/L).

[0064] In another aspect, an equilibrium adsorption study of arsenic by OTBN was carried out at 30 + 2 [deg.]C and neutral pH. The initial arsenic concentrations were varied over a wide range (5 - 100 mg/L). The working volume of the contaminated water was taken to be 100 ml. The results obtained from this study are shown in FIG. 8b. As evident from the data, the uptake capacity increased with increase in arsenic concentrations. An adsorption capacity of 183 mg/g is observed at initial arsenic concentration of 100 mg/L. This shows that the OTBN prepared using the method of the present invention has high affinity to arsenic and is better than any other aluminum based material reported for arsenic removal at similar equilibrium concentrations studied.

[0065] In yet other aspects, the present invention provides methods for using a granular composite, such as, for example, to remove at least a portion of fluoride and/or arsenic that can be present in a water source. In such an aspect, the present invention can serve as an adsorption media in a water purification technology, such as, for example, a water filter. In various aspects, the inventive granular composite can reduce the concentration of fluoride, arsenic, pathogens, and/or other contaminants in a water source.

EXAMPLES

[0066] The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, articles, devices and/or methods claimed herein are made and evaluated, and are intended to be purely exemplary of the invention and are not intended to limit the scope of what the inventors regard as their invention. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in [deg.]C or is at ambient temperature, and pressure is at or near atmospheric.

Example 1

[0067] This example describes low temperature synthesis of nanoscale-[Alpha][Iota][Omicron][Omicron][Eta] through a simple soft chemistry route. The synthesis procedure comprises mixing an aluminum precursor solution with chitosan (dissolved in 1 - 5 % glacial acetic acid or HC1 or combination thereof) with vigorous stirring. In a general procedure, a solution of aluminum precursor, such as aluminum nitrate was added slowly into the chitosan solution with vigorous stirring for 60 minutes and was kept overnight without agitation. Aqueous ammonia or NaOH solution was slowly added into the metal-chitosan solution with vigorous stirring to facilitate the precipitation of the metal-chitosan composites (pH 7 - 8.0). All these steps were carried out at temperature below 30 [deg.]C. Stirring was continued for two hours. The precipitate was filtered, washed to remove any unwanted impurities, converted in the shape of beads and dried at various conditions.

Example 2

[0068] This example describes the use of other biopolymers for the preparation of OTBN through a simple soft chemistry route. The synthesis procedure comprises mixing the aluminum precursor solution with cellulose with vigorous stirring. In a general procedure, a solution of aluminum precursor such as aluminum nitrate was added slowly into the polymer solution with vigorous stirring for 60 minutes and was kept overnight without agitation. Aqueous ammonia or NaOH solution was slowly added into the metal-cellulose solution with vigorous stirring to facilitate the precipitation of the metal-cellulose composites (pH 7 - 8.0). All these steps were carried out at temperature below 30 [deg.]C. Stirring was continued for two hours. The precipitate was filtered, washed to remove any unwanted impurities, converted in the shape of beads and dried at various conditions.

Example 3

[0069] This example describes the use of a mixture of biopolymers for the preparation of OTBN through a simple soft chemistry route. The biopolymers used for the study are chitosan and cellulose. Cellulose powder was added to the chitosan solution (chitosan dissolved in 1% acetic acid). The weight ratio of chitosan to cellulose is 1: 1. Further, aluminum nitrate solution was added slowly into the biopolymer solution with vigorous stirring for 60 minutes and was kept overnight without agitation. Aqueous ammonia or NaOH solution was slowly added into the metal-chitosan solution with vigorous stirring to facilitate the precipitation of the metal-cellulose-chitosan composites (pH 7 - 8.0). All these steps were carried out at temperature below 30 [deg.]C. Stirring was continued for two hours. The precipitate was filtered, washed to remove any unwanted impurities, converted in the shape of beads and dried at various conditions.

Example 4

[0070] This example describes the low temperature synthesis of metal ion doped nanoscale- AIOOH through a simple soft chemistry route. A mixture of aluminum nitrate and ferric nitrate is prepared in the molar ratio of 3: 1 (Al:Fe). The mixture is then slowly added into the chitosan solution (prepared in 1-5% nitric acid) with vigorous stirring for 60 minutes and was kept overnight without agitation. Aqueous ammonia or NaOH solution was slowly added into the metal-chitosan solution with vigorous stirring to facilitate the precipitation of the metal- chitosan composites (pH 7 - 8.0). All these steps were carried out at temperature below 30 [deg.]C. Stirring was continued for two hours. The precipitate was filtered, washed to remove any unwanted impurities, converted in the shape of beads and dried at various conditions.

Example 5

[0071] This example describes the variation in the size of nanoscale-[Alpha][Iota][Omicron][Omicron][Eta] by varying the ratio of Akchitosan. The quantity of chitosan in the OTBN is increased to 40%. The presence of higher quantity of chitosan helps in further reducing the size of the nanoscale-[Alpha][Iota][Omicron][Omicron][Eta]. A solution of aluminum precursor such as aluminum nitrate was added slowly into the chitosan solution with vigorous stirring for 60 minutes and was kept overnight without agitation. Aqueous ammonia or NaOH solution was slowly added into the metal-chitosan solution with vigorous stirring to facilitate the precipitation of the metal-chitosan composites (pH 7 - 8.0). All these steps were carried out at temperature below 30 [deg.]C. Stirring was continued for two hours. The precipitate was filtered, washed to remove any unwanted impurities, converted in the shape of beads and dried under various conditions.

[0072] It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.



WO2012140520
SUSTAINED SILVER RELEASE COMPOSITION FOR WATER PURIFICATION  

Description

BACKGROUND

TECHNICAL FIELD

[0001] The present disclosure relates to the field of water purification and specifically to compositions and methods related to sustained silver release for water purification.

TECHNICAL BACKGROUND

[0002] Contamination of drinking water is a major health concern across the world, especially in the developing and under-developed countries. A number of contaminants affect the water quality including biological (e.g. bacteria and virus), inorganic (e.g. fluoride, arsenic, iron) and organic (e.g. pesticides, volatile organics) species. These contaminants in water are a source of a number of diseases for a large population of the world. A significant cost burden associated with health effects of the contaminated water still rests on the shoulders of the poor. This problem can be addressed by developing affordable and effective solutions for removal of these contaminants.

[0003] Silver is widely known for its antibacterial property and has been employed as an inorganic silver salt, as an organic silver salt and as colloids of its salt, oxide, and in metallic states for treatment of contaminated water. Although it is well known that silver is a good antibacterial agent, the nature of silver present in the water determines its antibacterial efficiency. Recently, silver has been extensively used in the form of metallic nanoparticles. The antibacterial property of silver nanoparticles emerges either from nanoparticle-bacteria surface interaction or from released silver ions from nanoparticles or both.

[0004] Antibacterial property of silver nanoparticles has been discussed in a number of patent applications, wherein improvements to method of synthesis of silver nanoparticles have been disclosed (Pal et. al. in Appl Environ Microbiol, 2007, 73(6), 1712; De Windt et. al. in United States Patent Application 20100272770; Sastry et. al. in 936/MUM/2008), methods for their synthesis in media other than water have been used (Chen et. al. in United States Patent 7329301), and methods for loading silver nanoparticles on various substrates have been discussed (Rautaray et. al. in Indian patent application 1571/MUM/2008). The enhanced antibacterial property of silver nanoparticles is due to size confinement of silver metal. Although a number of methods have been developed for the synthesis of silver nanoparticles, keeping reactive particles in nanometer size for a long time in real water composed of various species is very difficult. This is due to ion induced aggregation, surface modification, salt deposition and so forth. Therefore, an important requirement while employing reactive silver nanoparticles in water purification is size stabilization and preventing surface modification over extended periods.

[0005] Another important aspect of use of silver nanoparticles for anti-bacterial performance is the fraction of silver ions released (quantity of silver ions released/quantity of silver nanoparticle used). It is known that although significant quantities of silver nanoparticles are used, a small amount of silver ions are released into the contaminated water. For example, Hoek et al. (Environ. Sci. Technol. 2010, 44, 7321) reported that in reproduced real water having total dissolved solids (TDS) of around 340 parts per million (ppm), the fraction of dissolved silver is less than 0.1% of the total mass of silver added, regardless of the initial source, i.e., AgN03 or silver nanoparticles. This phenomenon is attributed to the presence of various anions in water, such as chlorides (many silver salts have very low solubility). Hence, the quantity of silver nanoparticles used in water filters is more than the optimum and results in an increase in the filter size and the cost of the device.

[0006] The release rate of silver ion from the nanoparticles determines how long the nanoparticels can be used as an antimicrobial agent. Constant release of silver ions from silver nanoparticles for longer time is essential for effective use in water filters. This ensures consistent anti-microbial performance and release of silver ions below permissible limit as prescribed by the World Health Organization (WHO). The rate of silver ion release has been discussed in the literature. For example, Epple et al. (Chem. Mater. 2010, 22, 4548 and Hurt et al. Environ. Sci. Technol. 2010, 44, 2169) demonstrated that the release of silver ions from silver nanoparticles in distilled water depends on temperature, incubation days, and species present in the water such as dissolved oxygen level, salt, and organic matter. The rate of dissolution is not constant with time and attains saturation in a short period.

[0007] Hence, stability of reactive nanoparticles for prolonged periods in water is essential for controlled release of silver ions. Metal oxides have been widely considered as good substrates. Silver nanoparticles have been ex-situ and in-situ loaded in/on metal oxides. In-situ loading in metal oxide has shown promising stability even at high loading percentage. For example, in-situ syntheses of silver nanoparticles in metal oxide matrices have been reported earlier. Chen et al. Environ. Sci. Technol. 2009, 43, 2905 demonstrated the sol-gel synthesis of silver nanoparticles (<5 nm) loaded onto Ti02 nanocomposite where Ti02 particles act as anti-aggregation support and showed that 7.4 wt% Ag loading in Ti02 had highly potent antibacterial properties against E. coli. Similar results were obtained by the use of rice husk ash (Rautaray et. al. 157 l/MUM/2008). Results obtained by this group indicates that the leached silver concentration varied in a wide range of 1.3 ppb - 65 ppb (measured over a volume of 3000L).

[0008] Various attempts have been made to synthesize silver nanoparticles on low-cost substrates. For example, Shankar et al. (J Chem Technol Biotechnol. 2008, 83, 1177) loaded silver on activated carbon at high silver loading percentage. An optimum of 9-10.5 wt% of Ag loaded in activated carbon (5 g) is necessary to have effective anti-bacterial properties against E. coli (concentration: 10<3> CFU/ml) in the contact-mode for up to 350 L of flowing water (flow rate: 50 mL/min). Accordingly, -0.5 g of silver for 350 L of bacteria free water should be used which has a cost of lOpaise/liter (US$.0088/gallon) water .

[0009] As described above, current systems fail to address the problem of stabilization of silver nanoparticles on a supporting matrix. Further, the surface chemistry is altered in controlled silver ion release systems over extended periods, thereby requiring the use of large quantities of silver. Controlled constant silver release determines the long term use, effectiveness, and the life time of a device and low cost.

[0010] The above referenced shortcomings are resolved by the compositions and methods described herein.

SUMMARY

[0011] The compositions and methods described herein, in one aspect, relates to water purification. Particularly, the disclosure compositions and methods described herein relates to a sustained silver release composition for water purification.

[0012] An object of the compositions and methods described herein is to provide dissolution of silver ions from silver nanoparticles in water, for prolonged use (composition for a sustained silver ion release). [0013] Another object of the compositions and methods described herein is to increase the volume of water that can be treated with silver nanoparticles while maintaining a substantially constant concentration of silver ions in the water derived from the silver nanoparticles. The silver nanoparticles can be loaded on organic polymer-metal oxide/hydroxide compositesuch as an organic-templated-boehmite nanoarchitecture (OTBN).

[0014] Yet another object of the compositions and methods described herein is to use organic polymer-metal oxide/hydroxide composites as a dual stabilizing agent for the synthesis of highly dispersed and stable silver nanoparticles. The silver nanoparticles can be antimicrobial, for example antibacterial, at a loading of about 0.1-1 wt%.

[0015] The compositions and methods described herein release at least 10% of the silver present in nanoparticles into the water with moderately high TDS from silver nanoparticles loaded OTBN over an extended period. An aspect of the compositions and methods described herein includes the volume of water treated and time independent constant release of silver ion from a Ag-OTBN matrix.

[0016] In one aspect, a method is disclosed for preparing an adsorbent composition. The method comprises impregnating silver nanoparticles on an organic-templated-nanometal oxyhydroxide. Particle size of the silver nanoparticles can be less than about 50 nm. The adsorbent composition has antimicrobial properties in water. In an aspect, the organic-templated-nanometal oxyhydroxide can be organic-templated-boehmite nanoarchitecture (OTBN).

[0017] In the compositions and methods described herein, the potent antibacterial material for long term use is obtained when silver nanoparticles are synthesized in organic-templated metal oxide/hydroxide nanoarchitecture. Stability of silver nanoparticles in water for longer time determines its antibacterial properties over time. Stable silver nanoparticles can be achieved via a in-situ syntheses of the nanoparticles in the OTBN matrix. Disclosed herein is an OTBN matrix that enhances the antimicrobial (i.e. antibacterial) property of silver nanoparticles in water. The matrix controls the size and stabilizes the particles from aggregation, and prevents the adsorption/deposition/scaling of soluble ligands, organic matters and dissolved solids on the silver nanoparticles.

[0018] The surface reactivity of silver nanoparticles can be maintained by both chitosan and metal oxide/hydroxide. Silver nanoparticles encapsulated by chitosan, can be dispersed in metal oxide support and vice-versa. The dual stabilization prevents the surface modification and also salt deposition over a period of time. This is further explained through the material
characterization studies.

[0019] In one aspect, the compositions disclosed herein can contain 0.5 wt% Ag loaded in OTBN with antimicrobial properties. For example the compositions and methods can kill 10<5> CFU/mL of E.coli in the contact-mode using several hundred liters, for example 100, 200, 300, 400, 500, 600 or 700 liters, of flowing water at very high flow rate. This is achieved through controlled constant release of silver ion for long time, for example 50 mL/min, 100 mL/min, 200 ml/min, 300 ml/min, 400 ml/min, 500ml/min or 1000 ml/min.

[0020] In one aspect the silver nanoparticles described herein can kill 10<5> CFU/mL of E.coli in tap water. In another aspect, killing microorganism with the disclosed compositions and methods does not require contact between the microorganisms and the nanoparticels.

[0021] In another aspect, a water purification device that includes a water filter is disclosed. The water filter can be made of an adsorbent composition prepared by impregnating silver nanoparticles on an organic-templated-nanometal oxyhydroxide, wherein a particle size of the silver nanoparticles is less than about 50 nm. The adsorbent composition can kill microorganisms, i.e have antimicrobial properties, in water. The water filter can be in the form of a candle, a molded porous block, a filter bed and a column. In another aspect, the water filter can be in the form of a sachet or porous bag.

[0022] Additional aspects and advantages of the invention will be set forth, in part, in the detailed description and any claims which follow, and in part will be derived from the detailed description or can be learned by practice of the invention. The advantages described below will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as disclosed.

BRIEF DESCRIPTION OF THE FIGURES

[0023] The accompanying figures, which are incorporated in and constitute a part of this specification, illustrate several aspects and together with the description serve to explain the principles of the invention.

[0024] FIG. 1 is a schematic representation of chemical reactions involved in the method for preparation of silver nanoparticles loaded organic-templated-boehmite nanoarchitecture (OTBN), in accordance with an embodiment of the present invention.

[0025] FIG. 2 depicts X-ray diffraction patterns of an organic-templated-boehmite
nanoarchitecture (OTBN) and silver nanoparticles loaded OTBN, in accordance with various aspects of the present disclosure.

[0026] FIG. 3 depicts high-resolution transmission electron microscopic (HRTEM) micrographs of silver nanoparticles loaded OTBN system and an energy-dispersive X-ray (ED AX) spectrum of silver nanoparticles loaded OTBN, in accordance with various aspects of the present disclosure.

[0027] FIG. 4 depicts TEM-EDAX elemental imaging of silver nanoparticles loaded OTBN matrix, in accordance with various aspects of the present disclosure.

[0028] FIG. 5 depicts FESEM image of silver nanoparticles loaded OTBN, SEM image of granular composite and corresponding SEM-EDAX based elemental composition.

[0029] FIG. 6depicts antibacterial activity of silver nanoparticles loaded OTBN tested in batch mode, in accordance with various aspects of the present disclosure.

[0030] FIG. 7depicts antibacterial activity of silver nanoparticles loaded OTBN tested in column mode, in accordance with various aspects of the present disclosure.

[0031] FIG. 8 depicts inductively coupled plasma optical emission spectrometry (ICP-OES) data for silver ion leaching in E. coli contaminated water, in accordance with various aspects of the present disclosure. [0032] FIG. 9 depicts antiviral activity of silver nanoparticles loaded OTBN tested in batch mode, in accordance with various aspects of the present disclosure.

DESCRIPTION

[0033] The present invention can be understood more readily by reference to the following detailed description of the invention and the examples included therein.

[0034] Before the present compounds, compositions, articles, systems, devices, and/or methods are disclosed and described, it is to be understood that they are not limited to specific synthetic methods unless otherwise specified, or to particular reagents unless otherwise specified, as such can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, example methods and materials are now described.

[0035] All publications mentioned herein are incorporated by reference to disclose and describe the methods and/or materials in connection with which the publications are cited.

DEFINITIONS

[0036] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, example methods and materials are now described.

[0037] As used in the specification and the appended claims, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a metal" includes mixtures of two or more metals.

[0038] Ranges can be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as "about" that particular value in addition to the value itself. For example, if the value "10" is disclosed, then "about 10" is also disclosed. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.

[0039] As used herein, the terms "optional" or "optionally" means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.

[0040] Disclosed are the components to be used to prepare the compositions of the invention as well as the compositions themselves to be used within the methods disclosed herein. These and other materials are disclosed herein, and it is understood that when combinations, subsets, interactions, groups, etc. of these materials are disclosed that while specific reference of each various individual and collective combinations and permutation of these compounds cannot be explicitly disclosed, each is specifically contemplated and described herein. For example, if a particular compound is disclosed and discussed and a number of modifications that can be made to a number of molecules including the compounds are discussed, specifically contemplated is each and every combination and permutation of the compound and the modifications that are possible unless specifically indicated to the contrary. Thus, if a class of molecules A, B, and C are disclosed as well as a class of molecules D, E, and F and an example of a combination molecule, A-D is disclosed, then even if each is not individually recited each is individually and collectively contemplated meaning combinations, A-E, A-F, B-D, B-E, B-F, C-D, C-E, and C-F are considered disclosed. Likewise, any subset or combination of these is also disclosed. Thus, for example, the sub-group of A-E, B-F, and C- E would be considered disclosed. This concept applies to all aspects of this application including, but not limited to, steps in methods of making and using the compositions of the invention. Thus, if there are a variety of additional steps that can be performed it is understood that each of these additional steps can be performed with any specific embodiment or combination of embodiments of the methods of the invention. [0041] Each of the materials disclosed herein is either commercially available and/or the methods for the production thereof are known to those of skill in the art.

[0042] It is understood that the compositions disclosed herein have certain functions. Disclosed herein are certain structural requirements for performing the disclosed functions and it is understood that there are a variety of structures that can perform the same function that are related to the disclosed structures, and that these structures will typically achieve the same result.

[0043] In one aspect, synthesis, characterization and application of silver nanoparticles impregnatedorganic-templated-boehmite-nanoarchitecture (Ag-OTBN) are described. Impregnation of silver nanoparticles in OTBN is demonstrated using a number of procedures. The as-synthesized Ag-OTBN composition is characterized by a number of spectroscopic and microscopic techniques. The capability of Ag-OTBN to remove microorganisms from drinking water is demonstrated through the use of E. coli and MS2 bacteriophage as model organisms for bacteria and virus, respectively.

[0044] The silver nanoparticles can be impregnated in p-block, transition and rare-earth metal doped organic template metal oxyhydroxide compositions. It should also be noted that it can be of mixed metal oxide/hydroxide/oxyhydroxide nanoarchitecture. The mixture can be binary or a mixture of all the above mentioned metal oxide/hydroxide/oxyhydroxide.

[0045] In an aspect, the Ag-OTBN defined in the present invention can have chitosan polymer to metal oxide/hydroxide weight ratio between 5%and 50%. In another aspect, Ag to OTBN weight ratio can be between 0.1 to 10 %.

[0046] In another aspect, the silver nanoparticles can be synthesized in OTBN using any reducing agent at any temperature for any application. In one aspect, the reducing agent can be ascorbic acid, tri sodium citrate, dextrose, hydrazine, etc., and at a temperature between 40 to 200[deg.]C.

[0047] FIG 1 illustrates the scheme 100 utilized for the preparation of granular composite of silver nanoparticles loaded metal oxyhydroxide particles-biopolymer. Steps 101-106 have been described in the PCT application PCT/IB2011/001551 by Pradeep et al.\, its entire contents of which is hereby incorporated by reference. The filtered composite gel 106 is thereafter homogeneously dispersed in distilled water. Silver precursor solution 107 is then added to metal oxyhydroxide particles-biopolymer composite 106. Metal oxyhydroxide particles-biopolymer composite 106 and silver ions of silver precursor solution 107 interact with each other through a number of functional groups to obtain silver ion complexed metal oxyhydroxide particles- biopolymer composite 108. Further, reducing agent 109 is added to 108. Upon addition of reducing agent 109, silver particles in the precursor solution 107undergo reduction and nucleate on metal oxyhydroxide particles-biopolymer composite 108 to form silver nanoparticles loaded metal oxyhydroxide particles-biopolymer composite. Eventually, a semi solid precipitate 110 is obtained, which is washed with copious amounts of water and is dried at a temperature between 30-60 [deg.]C.

[0048] FIG. 2 shows X-ray diffraction patterns of an organic-templated-boehmite nanoarchitecture (OTBN) and silver nanoparticles loaded OTBN are shown, in accordance with various aspects of the present disclosure. In FIG. 2, the peaks marked by * correspond to the organic template i.e., chitosan.

[0049] The as-synthesized OTBN shows peaks corresponding to (120), (013), (051), (151), (200), (231) and (251) planes (refer to curve (a)). These peaks can be indexed as orthorhombic- AIOOH (JCPDS 21-1307). The broadened XRD peaks imply that the crystallite size of OTBN particles is very small. The mean crystallite size calculated from the Scherrer formula shows that nanocrystals have an average size of 3.5 nm. The presence of organic template (i.e., chitosan) can also been seen in the XRD data. The peaks marked by * in FIG.2 corresponding to 2[Theta] (in degrees) = 18.7[deg.], 20.6[deg.], and 41.2[deg.] are attributed to the presence of the organic template. It is clear that there is a definite difference in the full-width at half maxima (FWHM) for the peaks corresponding to AIOOH and organic template.

[0050] Upon impregnation of silver nanoparticles in the OTBN, there are no new peaks observed in the diffraction pattern (refer to curve (b)). This is attributed to the low loading percentage of silver nanoparticles and homogeneous distribution of silver nanoparticles in OTBN. Comparing the diffraction peaks of OTBN and silver nanoparticles impregnated OTBN, a negative shift in the 2[Theta] value is observed. The interplanar distance of OTBN increases after loading of silver nanoparticles. This is a clear evidence of the loading of an external material which increases the interplanar spacing. [0051] FIG. 3 shows high-resolution transmission electron microscopic(HRTEM) micrographs of silver nanoparticles loaded OTBN system and an energy-dispersive X-ray (ED AX) spectrum of silver nanoparticles loaded OTBN, in accordance with various aspects of the present disclosure. FIG.3(a) to 3(c) show HRTEM micrographs of Ag nanoparticles loaded OTBN system and spectrum 3(d) shows the EDAX spectrum of Ag nanoparticles loaded OTBN.

[0052] In order to determine the interaction between OTBN and silver nanoparticles, silver nanoparticles impregnated OTBN matrix was analyzed under transmission electron microscope. The TEM image shows the three components i.e., silver nanoparticles, organic polymers and metal oxide/hydroxide nanoparticles in the Ag-OTBN. The OTBN matrix stabilizes the silver nanoparticles from aggregation, which results in the homogenous distribution of silver nanoparticles in the matrix. It is clear from the TEM images that homogenously sized silver nanoparticles are anchored in the organic polymer-metal oxide/hydroxide nanoparticle matrix (pictures (b) and (c)) and the silver nanoparticles are of 5-10 nm in size (picture (c)). The sheetlike organic polymer chitosan is seen clearly (Figs 3 (a), (b) and (c)). Such homogeneity is difficult in unprotected silver nanoparticles. Typically, homogeneity is brought about by monolayer protection.

[0053] This HRTEM of the composition also shows that silver nanoparticles are trapped in the biopolymer-metal oxyhydroxide cages. This allows nanoparticles to be preserved by reducing contact with the scale forming chemical species while allowing sufficient interaction with water, which results in sustained release of Ag<+>ions.

[0054] Graph (d) shows the EDAX spectrum measured from the area shown in picture (b). From this,the presence of silver is confirmed.

[0055] FIG. 4 shows EDAX elemental imaging of silver nanoparticles loaded OTBN matrix, in accordance with various aspects of the present disclosure. In FIG. 4, the top left extreme is the TEM image and others are elemental maps from the region.

[0056] EDAX coupled with TEM was used to image the elemental mapping of Ag loaded OTBN. Elements present in the Ag-OTBN such as C, N, O, Al and Ag were mapped. The presence of three components i.e., chitosan (C, N and O), boehmite (Al and O) and silver nanoparticles (Ag) was confirmed. [0057] FIG. 5 shows the SEM micrograph of silver nanoparticles loaded OTBN and its chemical composition. Silver nanoparticles are not visible on the surface of the composition (note: particles of similar size (10-30 nm) from substrate (Indium tin oxide) are clearly observable in the highlighted red circle) (FIG. 5(a)). This confirms that silver nanoparticles are embedded and well-protected in the OTBN matrix. Granular form of the composition is also visible (FIG. 5(b)). Elemental composition confirms the presence of essential elements: carbon, nitrogen, oxygen, aluminum and silver (FIG. 5(c)). Insets show the elemental composition for an illustrative silver nanoparticles impregnated OTBN and expanded region of ED AX spectrum around 3 keV, confirming the presence of silver (note: carbon content is higher due to presence of conducting carbon tape in the background).

[0058] FIG. 6 shows an antibacterial activity of silver nanoparticles loaded OTBN tested in batch mode, in accordance with various aspects of the present disclosure. In FIG. 6 curve (a) depicts the input E. coli concentration and curve (b) depicts the output E. coli concentration.

[0059] The Ag-OTBN material as explained in example 1 was used for batch study. As explained in the example 7, the antibacterial activity was tested for batch mode. FIG. 6 shows the antibacterial efficiency of Ag-OTBN with number of trials. Curve (a) in shows the input concentration of E. coli and curve (b) shows the number of E. coli colonies after 1 hour of shaking. It is confirmed from curve (b) that the Ag-OTBN completely kills the E. coli present in the water. For up to 30 trials, complete killing of E. coli was seen. It should be noted that the number of trials or the output E. coli counts do not indicate the saturation point of the Ag-OTBN material, but show the continuous release of silver ions at constant rate. It should also be noted that the concentration of released silver ions from silver nanoparticles is higher under shaking for an hour. The antibacterial activity of Ag-OTBN in batch mode indirectly demonstrates the promising long-time antibacterial activity of Ag-OTBN in column mode.

[0060] The material was also tested for antibacterial study without contact mode. The 100 mL of the shaken water was filtered and 1 x 10<5>CFU/mL of bacterial load was added to the water. It was plated as described in the foregoing specification. The performance of the material tested without contact mode is similar to the material tested with contact mode (data not shown). It showed that the antibacterial property is due to the released silver ions from silver nanoparticles. [0061] FIG. 7 depicts an antibacterial activity of silver nanoparticles loaded OTBN tested in column mode, in accordance with various aspects of the present disclosure. In FIG. 7, curve (a) depicts the input E. coli concentration and curve (b) depicts the output E. coli concentration.As explained in the example 8, the antibacterial activity was tested for a column filled with Ag- OTBN. FIG. 7 shows the antibacterial efficiency of Ag-OTBN with volume of contaminated water passed. Curve (a) in Fig6 shows the input concentration of 10<5> CFU/mL E. coli and curve (b) shows the number of surviving E. coli colonies after filtration. Curve (b) shows that the Ag- OTBN material kills E. coli for 1500 L at 1000 mL/min flow rate. It should be noted that complete killingwas observed at 10 mL/min, 100 mL/min and 1000 mL/min flow rate, separately. Hence, the present invention demonstrates that the complete killing of E. coli at the concentration of ~10<5> CFU/mL can be achieved using Ag-OTBN material even at very high flow rate such as -1000 mL/min.

[0062] FIG. 8 depicts inductively coupled plasma optical emission spectrometer(ICP-OES) data for silver ion leaching in E. coli contaminated water, in accordance with various aspects of the present disclosure. In FIG. 8,curve (a) shows the allowed silver ion concentration in drinking water as per WHO norms and curve (b) shows the released silver ion concentration in output water, in accordance with an aspect of the present invention.
[0063] The Ag-OTBN material as explained in example 1 was used for column study. As explained in the example 8, the antibacterial activity was tested for Ag-OTBN in column mode. E. coli concentration of lxl 0<5> CFU/mL was periodically spiked in challenge water at the passage of 0, 250, 500, 750, 1000, 1250 and 1500L. Contaminated water was passed at a flow rate of 10- 2000 mL/min, preferably at 1000 mL/min. At regular intervals, the microbial de-contaminated output water was collected. Quantitative detection of concentration of silver ions released from the Ag-OTBN material was performed using Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES). FIG. 8 shows the relation between the concentration of silver ions released into the contaminated challenge water and the volume of water passed. Curve (a) in FIG. 8 shows the allowed silver ion concentration in drinking water and curve (b) shows the released silver ion concentration from Ag-OTBN. FIG. 8 shows that silver ions are continuously released into the contaminated challenge water at a constant rate and the concentration found was significantly below the permitted level of silver ions in drinking water. The present invention demonstrates that the silver ions released from Ag-OTBN into the challenge water areenough for killing all E. coli present in the water. From the ICP-OES, it was found that more than 10% of silver from Ag-OTBN released into water upon passage of 1500L of challenge water.

[0064] FIG. 9 shows an antiviral activity of silver nanoparticles loaded OTBN tested in batch mode, in accordance with various aspects of the present disclosure. In FIG. 9, curve (a) depicts the input MS2 coliphage concentration and curve (b) depicts the output MS2 coliphage concentration. The Ag-OTBN material as explained in example 1 was used for batch study and the antiviral activity was tested as explained in the example 9. FIG. 9 shows the antiviral efficiency of Ag-OTBN with number of trials. Curve (a) in Fig8 shows the input concentration of MS2 coliphage and curve (b) shows the number of MS2 coliphage plaques after 1 hour of shaking. It is confirmed from curve (b) that the MS2 coliphage is completely removed from the water. For up to 35 trials, complete removal of MS2 coliphage was observed. It should be noted that the number of trials or the output counts do not indicate the saturation point of the Ag- OTBN material, but show the continuous performance of its antiviral property. Antiviral activity of Ag-OTBN in batch mode indirectly demonstrates the promising long-time performance of Ag- OTBN in column mode.

[0065] In an aspect of the present invention, a method for preparing an antimicrobial composition for water purification is provided. Silver nanoparticles are impregnated on an organic-templated-nanometal oxyhydroxide, such as OTBN. The particle size of the silver nanoparticles is preferably less than about 50 nm. Sizes include, but are not limited to, less than 50nm, 40nm, 30nm, 20nm, lOnm, and 5nm. The antimicrobial composition is used for killing microorganisms in water as explained in the foregoing specification. The silver ions are impregnated with OTBN in gel or solid states. The method also includes reduction of the silver ions to a zerovalent state by using a reducing agent, such as sodium borohydride, ascorbic acid, tri-sodium citrate, hydrazine hydrate or combinations thereof. In an aspect, the concentration of the reducing agent is kept in the range of about 0.001 M to about 1 M. In a preferred aspect, the concentration of the reducing agent is kept at 0.001 M to 0.05 M. Further, organic templates such as chitosan, banana silk and cellulose can be used. The invention supports following precursors: silver nitrate, silver fluoride, silver acetate, silver sulfate, silver nitrite and combinations thereof.

[0066] In one aspect, the compositions and methods release for silver ion into water for a prolonged period of time. For example, the compositions and methods can release a silver ions at a constant or substantially constant rate for at least 1 day, 1 week, 1 month, 3 months, 6 months, 1 year or 3 years.

[0067] In another aspect, a water purification system that includes a filter prepared by the method described herein is provided. The filter can be realized in the form of a candle, a molded porous block, a filter bed and a column. In another aspect, a water purification system can comprise the compositions described herein, for example, a silver impregnated boehmite structure, disposed in a sachet or porous bag, such that the sachet can be placed in contaminated water and the water allowed to flow through the sachet to contact the composition. A skilled artisan will appreciate that such forms of filters are well known in the art and their description has been omitted so as not to obfuscate the present disclosure.

[0068] The described aspects are illustrative of the compositions and methods and are not restrictive. Modifications of design, methods, structure, sequence, materials and the like that are apparent to those skilled in the art, also fall within the scope of the compositions and methods described herein.

EXAMPLES

Experimental methods Material characterization

[0069] The identification of the phase(s) of the as-prepared sample was carried out by X-ray powder diffraction (using D8 Discover of Bruker AXS, USA) using Cu-[Kappa][alpha] radiation at [lambda] = 1.5418 A. Surface examination was carried out using Field Emission Scanning Electron
Microscope (using FEI Nova NanoSEM 600 instrument). For this, the sample was re-suspended in water by sonication for 10 minutes and drop-casted on an indium tin oxide (ITO) conducting glass. The sample was subsequently dried. Surface morphology, elemental analysis and elemental mapping studies were carried out using a Scanning Electron Microscope (SEM) equipped with Energy Dispersive Analysis of X-rays (EDAX) (using FEI Quanta 200 scanning electron microscope). Granular composition was imaged by attaching it on a conducting carbon tape. High resolution Transmission Electron Microscopy (HRTEM) images of the sample were obtained with JEM 3010 (JEOL, Japan). The samples prepared as above were spotted on amorphous carbon films supported on copper grids and dried at room temperature. X-ray Photoelectron Spectroscopic (XPS) analysis was performed using ESCA Probe TPD of Omicron Nanotechnology. Polychromatic Mg Ka was used as the X-ray source (hv = 1253.6 eV). Spectra in the required binding energy range were collected and an average was taken. Beam induced damage of the sample was reduced by adjusting the X-ray flux. Binding energy was calibrated with respect to C Is at 284.5 eV. Silver ion concentration in the water was detected using inductively coupled plasma optical emission spectrometry (ICP-OES).

[0070] The following are a few examples that illustrate the methods and compositions described herein. The examples should not be construed as limiting the scope of the methods and compositions described herein.

Example 1

[0071] This example describes the in-situ impregnation of silver nanoparticles on OTBN. In an aspect, OTBN was prepared as reported in the previous Indian patent application 1529/CHE/2010, entire contents of which are herein incorporated by reference. The OTBN gel obtained after washing the salt content was used for the formation of silver nanoparticles. The OTBN gel was again re-dispersed in water, to which 1 mM silver precursor (silver nitrate, silver fluoride, silver acetate, silver permanganate, silver sulfate, silver nitrite, silver bromate, silver salicylate or any combination of the above) was added drop-wise. The weight ratio of Ag to OTBN can be varied anywhere between 0.1-1.5%. After stirring the solution overnight, 10 mM sodium borohydride was added to the solution drop wise (in ice-cold condition, temperature < 5[deg.] C). Thereafter, the solution was allowed to stir for half an hour, filtered and washed with copious amount of water. The obtained gel was then dried at room temperature.

Example 2

[0072] This example describes the in-situ impregnation of silver nanoparticles on OTBN powder. In an aspect, the dried OTBN powder was crushed to a particle size of 100-150 micron. The powder was stirred in water, using an appropriate shaker. 1 mM silver precursor solution was then slowly added. The weight ratio of Ag to OTBN can be varied anywhere between 0.1- 1.5%. After stirring the mixture overnight, 10 mM sodium borohydride was added to the mixture drop-wise (in ice-cold condition, temperature < 5[deg.] C). Thereafter, the mixture was allowed to stir for half an hour, filtered and washed with copious amount of water. The obtained powder is then dried at room temperature.

Example 3

[0073] This example describes the ex-situ impregnation of silver nanoparticles on OTBN. In an aspect, the OTBN gel obtained after washing the salt content was used for the impregnation of silver nanoparticles. The OTBN gel was again re-dispersed in water, to which 1 mM silver nanoparticles solution (prepared by any route reported in the literature) was added drop-wise. The weight ratio of Ag to OTBN can be varied anywhere between 0.1-1.5%. After stirring the solution overnight, it was filtered and washed with copious amount of water. The obtained gel is then dried at room temperature.

Example 4

[0074] This example describes the ex-situ impregnation of silver nanoparticles on OTBN powder. In an aspect, the dried OTBN powder was crushed to a particle size of 100-150 [mu][iota][eta]. The powder was stirred in water, using a shaker. 1 mM silver nanoparticles solution (prepared by any route reported in the literature) was added drop-wise. The weight ratio of Ag to OTBN can be varied anywhere between 0.1-1.5%. After stirring the solution overnight, it was filtered and washed with copious amount of water. The obtained powder was then dried at room temperature.

Example 5

[0075] The organic templated metal oxyhydroxide/oxide/hydroxide matrix defined in the methods and compositions described herein, is such that the metal is chosen from amongst p- block, transition and rare-earth metal series. The metal precursor can be Fe(II), Fe(III), Al(III), Si(IV), Ti(IV), Ce(IV), Zn(II), La(III), Mn(II), Mn(III), Mn(IV), Cu(II) or a combination thereof. And the metal oxide/hydroxide/oxyhydroxide nanoparticle may serve as an inert filler material or an active filtration medium.

[0076] This example describes the silver nanoparticles impregnation in p-block, transitionand rare-earth metal doped organic templated metal oxyhydroxide composition (as disclosed in the previous Indian patent application 1529/CHE/2010, entire contents of which are herein incorporated by reference). P-block, transition and rare-earth metals were chosen from the following: aluminum, manganese, iron, titanium, zinc, zirconium, lanthanum, cerium, silicon. The synthesis procedure for composition is as follows: the chosen metal (eg: La) salt was mixed with the ferric nitrate salt solution in an appropriate ratio, preferably 1 :9 (wt/wt). The salt solution was added slowly to the chitosan solution (dissolved in 1 - 5 % glacial acetic acid or HC1 or combination thereof) with vigorous stirring for 60 minutes and was kept overnight.

Aqueous ammonia or NaOH solution was slowly added into the La-Fe-chitosan solution with vigorous stirring to facilitate the precipitation of the metal-chitosan composites. Stirring was continued for two hours. The precipitate was filtered, washed to remove any unwanted impurities and dried.
[0077] The as-synthesized precipitategel was again re-dispersed in water, to which 1 mM silver precursor was added drop-wise. The weight ratio of Ag to OTBN can be varied anywhere between 0.1-1.5%. After stirring the solution overnight, 10 mM sodium borohydride was added to the solution drop-wise (in ice-cold condition). Thereafter, the solution was allowed to stir for half an hour, filtered and washed with copious amount of water. The obtained gel was then dried at room temperature.

Example 6

[0078] This example describes the doping of p-block, transition and rare-earth metal precursor in the composition. The procedure is similar to that described in example 5, with a change that gel or dried powder obtained after silver nanoparticles impregnation is soaked with metal precursor chosen from p-block, transition and rare-earth metal series.

Example 7

[0079] This example describes the testing protocol in batch for antibacterial activity of silver nanoparticles impregnated OTBN composition. In an aspect, 100 mL of water was shaken with the material and 1 x 10<5> CFU/mL of bacterial load was added to the water. Challenge water having the specific ions concentration similar to prescribed by US NSF for contaminant removal claim was used in the study. After one hour of shaking, 1 mL of the sample along with nutrient agar was plated on sterile petridish using the pour plate method. After 48 hours of incubation at 37 [deg.]C, the colonies were counted and recorded. This procedure was repeated 25 to 30 times.

Example 8

[0080] This example describes the testing protocol for antibacterial activity of silver nanoparticles impregnated OTBN powder packed in a column. In an aspect, the column in which a known quantity of the material is packed has a diameter between about 35 mm to about 55 mm. The feed water was passed at a flow rate in the range of 10 mL/min to 2000 mL/min. The challenge water was periodically subjected to anE. coli load of 1 x 10<5> CFU/mL. The output water collected from the column was screened for bacterial presence by pour plate method. The bacterial colonies were counted and recorded after 48 hours of incubation at 37[deg.]C.

Example 9

[0081] This example describes the testing protocol in batch for antiviral activity of silver nanoparticles impregnated OTBN composition. In an aspect, 100 mL of water was shaken with the material and 1 x 10<3> PFU/mL of MS2 coliphage load was added to the water. The challenge water having specific ions concentration similar to prescribed by US NSF for contaminant removal claim was used in the study. After one hour of shaking, virus count was obtained by plaque assay method. After 24 hours of incubation at 37 [deg.]C, the plaques were counted and recorded. This procedure was repeated for 35 to 40 times.



WO2012090034
GOLD AND SILVER QUANTUM CLUSTERS AND METHODS FOR THEIR PREPARATION AND USE  

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001 ] This application claims the benefit of India Patent Application
No. 4036/CHE/2010, filed December 30, 2010, which is incorporated herein by reference in its entirety for any and all purposes.

FIELD

[0002] The present technology generally relates to quantum clusters. In particular, the present technology refers to quantum clusters made of gold or silver.

BACKGROUND

[0003] Quantum clusters are materials having very few atoms; with core sizes in the sub-nanometer range and which exhibit novel properties. Compared to metal nanoparticles, quantum clusters do not have a continuous density of states but are characterized by discrete electronic energy levels. Quantum clusters act as a bridge between atomic and nanoparticle behaviors and therefore exhibit properties different from both these.

SUMMARY

[0004] In one aspect, a composition is provided including a quantum cluster with Agm, Au", or AgmAun where m and n are from 2 to 100, one or more protector molecules and a molecular cavity partially or wholly surrounding the quantum cluster. In some embodiments, the protector molecule is a thiol. In some embodiments, thiol is glutathione, cysteine, mercaptosuccinic acid, dimercaptosuccinic acid, phenylethane thiol and other aliphatic and aromatic thiols. In some embodiments, the molecular cavity includes a cyclodextrin, calixirane, or a crown ether. [0005] In some embodiments, the composition is luminescent. In some embodiments, the luminescence of the composition is medium-dependent, liquid- solvent dependent or solvent vapor-dependent.

[0006] In one aspect, a method is provided including adding a first amount of glutathione to a gold salt, a silver salt, or a mixture thereof to form a mixture. The method includes adding a reducing agent to the mixture to form a precipitate, and mixing the precipitate with a second amount of glutathione and a cyclodextrin to form a composition. In some embodiments, the method includes having a molar ratio of the first amount of glutathione to the amount of the gold salt, the silver salt, or the mixture thereof of from about 1 :2 to about 1 :8. In some embodiments, the precipitate comprises a) a quantum cluster of, Agm, Aun, or AgmAu"; and b) glutathione, where m and n are independently from 2 to 100. In some embodiments, m and n are from 2 to 50. In some other embodiments, m and n are independently from 10 to 40. In some embodiments, the gold salt is a trivalent gold source. In some embodiments, the gold salt is HAuCl4-3H20, AuCU, or a mixture thereof. In some embodiments, the reducing agent is NaBRj, L1BH4, or a mixture thereof.

[0007] In one aspect, a device is provided with a substrate; and a composition coated on the substrate; where the composition includes a quantum cluster, a protector compound, and a molecular cavity and the device exhibits solvent-dependent luminescence when exposed to a liquid solvent or a solvent vapor. In some embodiments, the substrate comprises S1O2, glass, conducting glass, quartz, silicon, or functionalized polymers.

[0008] In one aspect, a method is provided including the steps of: providing a substrate coated with a composition comprising a quantum cluster, a protector compound, and a molecular cavity; exposing the substrate to a first solvent; where the first solvent induces a luminescent response from the composition; the composition is coated on the substrate in a pattern; and the first solvent comprises a liquid solvent or solvent vapor. In some embodiments, the methods includes removing the first solvent, wherein the composition does not luminesce, or exhibits a luminescence of reduced intensity, after the first solvent is removed. In some embodiments, removing the solvent includes exposing the substrate to a second solvent, wherein the second solvent does not produce a luminescent response from the composition, and contacting the substrate with the second solvent quenches the luminescent response induced by the first solvent. In some embodiments, the removing includes allowing the first solvent to evaporate from the substrate. The method can further comprise detecting the presence or absence of the luminescent response.

[0009] In one aspect, a composition is provided with a core comprising 15 Au atoms, one or more glutathione molecules, and one or more cyclodextrin molecules wherein the cyclodextrin molecules at least partially surround the Au atoms. In some embodiments, two molecules of cyclodextrin partially or wholly surround the Au atoms. In some embodiments, the cyclodextrin is b-, or Q -cyclodextrin.

[0010] In one aspect, a labeling system is provided including a substrate having a coating comprising a quantum cluster, a protector compound, and a molecular cavity. The coating on the substrate is in a pattern and the pattern is luminescent when exposed to solvent. The labeling system includes a means for detecting the pattern on the substrate. In some embodiments, the pattern includes letters, numbers, symbols, pictures, or barcodes. In some embodiments, the substrate is attached to currency, financial and legal documents, shipping containers, electronics, medical device, pharmaceutical packaging, packaging on consumer items or biological compounds.

[0011] In one aspect, a method of authentication is provided including exposing a patterned coating to a solvent and detecting the patterned coating. In some embodiments, the coating includes a quantum cluster, a protector compound, and a molecular cavity. In some embodiments, the coating is luminescent when exposed to the solvent and luminescence intensity is reduced when the solvent is removed. In some embodiments, the patterned coating encodes the authenticity of an object to which the coating is applied. In some embodiments, the patterned coating comprises letters, numbers, symbols, pictures, or barcodes. In some embodiments, the object is currency, a financial document, a legal document, a shipping container, an electronic object, an envelope, or packaging. The method can include detecting the presence or absence of the patterned coating on the object. In some embodiments, the method includes verifying authenticity of the object by correlating the presence of the patterned coating with authenticity of the object.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a schematic of the process for making the cluster composition, according to one embodiment.

[0013] FIG. 2 is a schematic showing the interaction of the SG ligand of the cluster with the CD molecule, according to one embodiment.

[0014] FIG. 3A is the UV-Vis spectra of Aui5@aCD, Aui5@ CD and AU15@YCD clusters, according to the examples. [0015] FIG. 3 B is the natural logarithm of Jacobian factor-corrected absorbance versus the wavelength of Aui5@aCD, Au15@pCD, and Aui5@yCD, according to the examples.

[0016] FIG. 3C is a graph of the absorption profiles of pure GSH and a-CD, according to the examples. [0017] FIG. 3D is a graph of the luminescence spectra of three of the quantum compositions- Aui5@aCD; Au15@ CD; Aui5@yCD, according to the examples.

[0018] FIG. 4 A is the circular dichroism spectra of Aui5@aCD, Au15@ CD Au15@yCD clusters along with pure GSH and Au25SGi8, according to the examples.

[0019] FIG. 4B shows the combined plot of absorption and circular dichroism (CD) spectra for Au]5@aC, according to the examples.

[0020] FIG. 5 is a luminescence spectra of a TLC plate coated with Au@CD, when contacted with various solvents, according to the examples.

[0021] FIG. 6 A is an ED AX spectrum of the gel formed by cluster compositions, according to the examples. [0022] FIG. 6B is an SEM image of the gel formed by the cluster compositions, according to the examples.

[0023] FIG. 6C is an ED AX mapping of the gel using Aun, corresponding to SEM image in 6A, according to the examples.

[0024] FIG. 6D is a TEM image of the gel shows the self assembly and fiber- like morphology, according to the examples.

[0025] FIG. 7A & 7B are UV- Vis spectra of Aui5@aCD cluster before and after the addition of Cu<2+>, according to the examples.

DETAILED DESCRIPTION

[0026] In the following detailed description, reference is made to the accompanying drawings, which form a part thereof. The illustrative embodiments described in the detailed description, drawings and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. The present technology is also illustrated by the examples herein, which should not be construed as limiting in any way.

[0027] In general, compositions are provided which include Agm, Au", or AgmAun quantum clusters are provided by combining host-guest chemistry with core- etching. Such compositions exhibit luminescence that is dependent upon the environment in which the quantum cluster is located. Such compositions may also be useful in authentification processes. The compositions, devices, and methods are all described in greater detail below. As used herein, "core etching" refers to treatment of the metal quantum clusters with excess of protector molecules. As used herein, "host-guest chemistry" refers to partial or whole containment of the metal quantum clusters in the molecular cavity.

[0028] In one aspect, compositions including Agm, Au", or AgmAun quantum clusters are provided. In some embodiments, the composition includes one or more protector molecules surrounding the metal atoms, and m and n are from 2 to 100. In some embodiments, n is from 5 to 50, or from 10 to 20. In some embodiments, n is 15. Specific examples of n include 2, 3, 4, 5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, and ranges between any two of these values. In some embodiments, the quantum cluster comprises Au". In other embodiments, the quantum cluster comprises Agm.

[0029] In some embodiments, the protector molecule is a thiol. The protector molecule can bind to the surface of the quantum cluster, thereby forming a layer partially or fully around the cluster and protecting the cluster. In some embodiments, the protector molecules may include glutathione (GSH), cysteine, homocysteine, mercaptosuccinic acid, dimercaptosuccinic acid, phenylethane thiol, or other alkyl or aryl thiols. Generally, where the protector molecule is a mono thiol, it will reduce the Au<3+> to Au<1+>. Further reduction may be carried out by the addition of a reducing agent. In contrast, where the protector molecule is a dithiol, for example the dimercaptosuccinic acid, one of the thiol groups will act as reducing agent (i.e. one of the groups is oxidized) and the other will act as a protecting agent (i.e. it is reduced). In some embodiments, the protector molecule is a reduced form of the protector molecule; such as reduced glutathione. Clusters of Au atoms with the glutathione ligand (-SG) may be represented as Au@SG for convenience.

[0030] In some embodiments, a molecular cavity partially or wholly surrounds the metal cluster with the protector molecule, e.g., Au@SG. Such molecular cavities may include one or more molecules of cyclodextrin, calixirane, or a crown ether. In addition, it may be possible to create cluster compositions within other molecular cavities such as PAMAM, BSA, and the like.

[0031] Cyclodextrins are a family of compounds made up of sugar molecules bound together in a ring. In some embodiments, [alpha]-, [beta]-, or [gamma]-cyclodextrin ([alpha]-, [beta]-, or [gamma]- CD) molecules are used to form the cluster composition represented as Au@aCD, Au15@pCD or AU15@YCD. Cyclodextrins are bowl-shaped molecules which may "trap" or "encapsulate" other molecules of an appropriate size which will fit into the bowl.

[0032] As noted, the above compositions exhibit luminescence. Such luminescence may be medium-dependent, liquid solvent-dependent, or solvent vapor-dependent. For example, when the composition is exposed to some media, the luminescence is increased. In some embodiments, the solvent is, but not limited to, an alcohol, methanol, ethanol, or propanol; water; acetonitrile; acetone; dichloromethane; carbon tetrachloride; chloroform; toluene; hexane; or a mixture of any two or more thereof. In some cases, it is observed that the more hydrogen bonding between the cluster ligands and the solvent, the greater the luminescence. Accordingly, the luminescence of the composition in the presence of either methanol or ethanol is greater than that for propanol. In some embodiments, where the composition is placed in water, luminescent emission at 318 nm, 458 nm and 580 nm is observed

[0033] In another aspect a method of preparing the compositions is provided. In one embodiment, a gold or silver salt is mixed with the thiol protector molecule to precipitate a protected metal cluster, . In some embodiments, where it is a gold slat that is used, and the protector molecule is glutathione, the cluster particles (referred to as Au@SG) may be precipitated from the mixture in the presence of a reducing agent. It is understood that gold salts such as HAuCL^FkO, AuCl3, or other trivalent gold salts may be used in the methods. Suitable reducing agents include, but are not limited to NaBFLj and L1BH4, as well as other known reducing agents, or a mixture of any two or more reducing agents. In some embodiments, the amount of gold or silver salt to protector molecule ranges from about 1 :2 to about 1 :8. In other embodiments, the metal cluster has formula Agm, Aun, or AgmAun where m and n are from 2 to 100. In some embodiments, n is from 5 to 50, or from 10 to 20. Specific examples of n include 2, 3, 4, 5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, and ranges between any two of these values. In some embodiments, n is 15. In some embodiments, n is from 5 to 50, or from 10 to 20. Specific examples of n include 2, 3, 4, 5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, and ranges between any two of these values. In some embodiments, n is 15.
 
[0034] After preparation of the protected metal cluster, it is then mixed with the molecule that is to form the molecular cavity to form the composition of the protected metal cluster partially or fully surrounded by the molecular cavity. For example, where the protected metal cluster is Au@SG, it may be processed with an a-, [beta]-, or [gamma]-cyclodextrin (CD) molecule to form the cluster composition, Aui5@CD. In one embodiment, the Au@SG precipitate is dissolved in aqueous solution and mixed with CD and excess GSH. The Au15@CD cluster composition may be collected from the solution by any known method of separation. Such separation may include centrifugation in some embodiments.

[0035] In another aspect, a device is provided which includes any one of the above compositions deposited on a substrate. Suitable substrates include, but are not limited to Si02, glass, conducting glass, quartz, silicon or functionalized polymers. For example, in one embodiment, the substrate is a thin layer chromatography (TLC) plate coated with a S1O2 stationary phase. In other embodiments, the substrate is a chitosan, a carbon nanotube, activated carbon, alumina, or the like. Such substrates may be sequestered on a surface, or the substrate may be a powder or suspension. In some embodiments, the cluster compositions are uniformly coated on the substrate. In some embodiments, the cluster compositions are coated on the substrate in a pattern. The devices coated with the compositions exhibit a solvent- or medium- dependent luminescence as described above for the compositions.

[0036] Any solvent may be used to produce luminescence including methanol, ethanol, 2-propanol, water, acetonitrile, acetone, dichloromethane, carbon tetrachloride, chloroform, toluene, hexane or a mixture. As used herein, "solvent" may be a liquid solvent or solvent vapors.

[0037] In some embodiments, the luminescence of the substrate may be reduced or eliminated when the solvent is removed by either evaporation of the first solvent or exposure to a second solvent. In some embodiments, exposure to a first solvent produces luminescence of a cluster composition coated substrate and exposure to a second solvent quenches the luminescence. In some embodiments, the intensity of the luminescence is a dependant on the concentration of the solvent. In some embodiments, a device which includes a cluster composition coated substrate may be used to monitor or identify solvent vapors in the air. The cluster composition may also be used for the selective detection of metal ions as described in Example 8.

 [0038] Useful information about a product may be contained in a label including the cluster compositions. In some embodiments, a labeling system is provided having a substrate coated with the cluster compositions in a pattern and the pattern is luminescent when exposed to solvents. The labeling system may also include a detection system or means for detecting the pattern on the substrate, or it may be observed visually. The pattern on the substrate may include letters, numbers, symbols, pictures or barcodes that can capture information. The substrate may be attached to currency, financial and legal documents, shipping containers, electronics, medical device, pharmaceutical packaging, packaging on consumer items, biological compounds or other items that should be labeled. For example, the composition may be used to label an article or an object, either with a physical label, or through direct application of the composition to form a label. In some embodiments, the label is invisible to naked eye, but when exposed to a substance, such as a solvent liquid or vapor, the luminescence of the composition is altered, and the label may be visualized.

[0039] The detection system or "means for detecting" may be a device that can capture the luminescent pattern including a camera, a UV-Vis detector, a scanner, and the like. As used herein, "coating" of the cluster compositions is understood to include attachment, embedment or other means of binding or association.

[0040] In some embodiments, the cluster composition is used in a method for authentication. The cluster composition may be coated on an object in a particular pattern where the authenticity of the object is encoded in the pattern. When the object is exposed to a solvent, the pattern becomes luminescent and the luminescence intensity is reduced when the solvent is removed. In some embodiments, the pattern will be detected with a device such as a camera, UV-Vis detector or the human eye upon contact with the solvent, but the pattern is not detectable, or it is invisible to the naked eye in the absence of the solvent.

[0041 ] In some embodiments, the object may be any item that may need authentication such as currency, financial or legal document, a shipping container, an electronic object, medical device, pharmaceutical packaging, an envelope, packaging or other item. In some embodiments, authenticity of the object will be verified by checking the presence or absence of the pattern of luminescence. Thus, in one embodiment, a method of authentication includes exposing a patterned coating to a solvent, where the patterned coating includes a composition as described above. The method also includes detecting the patterned coating. In such methods, the coating is luminescent when exposed to the solvent and is not luminescent when the solvent is removed; and the patterned coating encodes the authenticity of an object to which the coating is applied. The method may also then include verifying the authenticity of the object. Such authentifications may include the patterned coating being in the form of letters, numbers, symbols, pictures, or barcodes. Thus, the verification may be based upon coding, a standard message, or the like.

[0042] As used herein, the following definitions of terms shall apply unless otherwise indicated.

[0043] As used herein, "about" will be understood by persons of ordinary skill in the art and will vary to some extent depending upon the context in which it is used. If there are uses of the term which are not clear to persons of ordinary skill in the art, given the context in which it is used, "about" will mean up to plus or minus 10% of the particular term.

[0044] The use of the terms "a" and "an" and "the" and similar referents in the context of describing the elements (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the embodiments and does not pose a limitation on the scope of the claims unless otherwise stated. No language in the specification should be construed as indicating any non-claimed element as essential. [0045] The embodiments, illustratively described herein may suitably be practiced in the absence of any element or elements, limitation or limitations, not specifically disclosed herein. Thus, for example, the terms "comprising," "including," "containing," etc. shall be read expansively and without limitation.

Additionally, the terms and expressions employed herein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the claimed technology. Additionally, the phrase "consisting essentially of will be understood to include those elements specifically recited and those additional elements that do not materially affect the basic and novel characteristics of the claimed technology. The phrase "consisting of excludes any element not specified.

[0046] As used herein, "thiols" are compounds with an "SH" functional group represented by R-SH where R may be H, an alkyl, or aryl group.

[0047] Alkyl groups include straight chain, branched chain, or cyclic alkyl groups having from 1 to 20 carbon atoms or, in some embodiments, from 1 to 12, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. Examples of straight chain alkyl groups include those with from 1 to 8 carbon atoms such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, and n-octyl groups. Examples of branched alkyl groups include, but are not limited to, isopropyl, iso-butyl, sec-butyl, tert-butyl, neopentyl, isopentyl, and 2,2-dimethylpropyl groups. Representative substituted alkyl groups may be substituted one or more times with substituents such as those listed above. Where the term haloalkyl is used, the alkyl group is substituted with one or more halogen atoms.

[0048] Cycloalkyl groups are cyclic alkyl groups such as, but not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl groups. In some embodiments, the cycloalkyl group has 3 to 8 ring members, whereas in other embodiments the number of ring carbon atoms range from 3 to 5, 3 to 6, or 3 to 7.

Cycloalkyl groups further include mono-, bicyclic and polycyclic ring systems, such as, for example bridged cycloalkyl groups as described below, and fused rings, such as, but not limited to, decalinyl, and the like. In some embodiments, polycyclic cycloalkyl groups have three rings. Substituted cycloalkyl groups may be substituted one or more times with, non-hydrogen and non-carbon groups as defined above. However, substituted cycloalkyl groups also include rings that are substituted with straight or branched chain alkyl groups as defined above. Representative substituted cycloalkyl groups may be mono-substituted or substituted more than once, such as, but not limited to, 2,2-, 2,3-, 2,4- 2,5- or 2,6-disubstituted cyclohexyl groups, which may be substituted with substituents such as those listed above.

[0049] Aryl, or arene, groups are cyclic aromatic hydrocarbons that do not contain heteroatoms. Aryl groups include monocyclic, bicyclic and polycyclic ring systems. Thus, aryl groups include, but are not limited to, phenyl, azulenyl, heptalenyl, biphenylenyl, indacenyl, fluorenyl, phenanthrenyl, triphenylenyl, pyrenyl, naphthacenyl, chrysenyl, biphenyl, anthracenyl, indenyl, indanyl, pentalenyl, and naphthyl groups. In some embodiments, aryl groups contain 6-14 carbons, and in others from 6 to 12 or even 6-10 carbon atoms in the ring portions of the groups. Although the phrase "aryl groups" includes groups containing fused rings, such as fused aromatic-aliphatic ring systems (e.g., indanyl, tetrahydronaphthyl, and the like), it does not include aryl groups that have other groups, such as alkyl or halo groups, bonded to one of the ring members. Rather, groups such as tolyl are referred to as substituted aryl groups. Representative substituted aryl groups may be mono- substituted or substituted more than once. For example, monosubstituted aryl groups include, but are not limited to, 2-, 3-, 4-, 5-, or 6-substituted phenyl or naphthyl groups, which may be substituted with substituents such as those listed above.

[0050] In general, "substituted" refers to a group, as defined above (e.g., an alkyl or aryl group) in which one or more bonds to a hydrogen atom contained therein are replaced by a bond to non-hydrogen or non-carbon atoms. Substituted groups also include groups in which one or more bonds to a carbon(s) or hydrogen(s) atom are replaced by one or more bonds, including double or triple bonds, to a heteroatom. Thus, a substituted group will be substituted with one or more substituents, unless otherwise specified. In some embodiments, a substituted group is substituted with 1 , 2, 3, 4, 5, or 6 substituents. Examples of substituent groups include: halogens (i.e., F, CI, Br, and I); hydroxyls; alkoxy, alkenoxy, alkynoxy, aryloxy, aralkyloxy, carbonyls(oxo), carboxyls, esters, urethanes, thiols, sulfides, sulfoxides, sulfones, sulfonyls, sulfonamides, amines, isocyanates, isothiocyanates, cyanates, thiocyanates, nitro groups, nitriles (i.e., CN), and the like.

[0051 ] The present technology, thus generally described, will be understood more readily by reference to the following example, which is provided by way of illustration and is not intended to limit the present technology.

EXAMPLES

[0052] Example 1. Synthesis of Au@SG. To a 50 mL methanolic solution (0.5 mM) of HAuC-4.3H20, 1.0 mM GSH was added (1 :2 molar ratio, total volume of methanol was 50 mL). The mixture was cooled to 0 [deg.]C in an ice bath for 30 minutes. An aqueous solution of NaBHt (0.2 M, 12.5 mL), cooled to 0[deg.]C, was injected rapidly into the above mixture under vigorous stirring. The mixture was allowed to react for another hour. The resulting precipitate was collected and washed repeatedly with methanol through centrifugal precipitation. Finally, the Au@SG precipitate was dried and collected as a dark brown powder. The size of Au@SG particles was in the range of2-3 nm.

[0053] Example 2. Cyclodextrin assisted synthesis of Au15 clusters. The above nanoparticles (50 mg) were dissolved in 40 mL of de-ionized water containing 1.6 mole of GSH and 2.2x10^ mole of cyclodextrin (the three CD molecules were used separately). The mixture was heated at 70[deg.]C for 48 hours. The completion of the reaction was monitored by checking the red emission of the cluster under UV light. Intense red emission from the sample indicates the formation of the desired cluster. The entire solution was centrifuged at 5000 rpm for 10 minutes. The whitish brown precipitate of Au(l)thiolate was discarded. The supernatant was then transferred to a plastic vial and freeze dried to obtain a brown powder with intense red emission in the solid state. The same method was used for all the three CD molecules ([alpha]-, [beta]-, and [gamma]-cyclodextrin) resulting in three separate cluster products. The material was washed twice with ethanol to remove excess GSH. Analysis was done with energy dispersive analysis of X-rays (ED AX). The sample becomes a gel if the solution is allowed to dry in air. [0054] FIG. 1 is a schematic of the process for synthesizing some
embodiments of the cluster compositions. A Au nanoparticle 10 interacts with one or more protector molecules 20. In some embodiments, the protector molecules are glutathione (-SG) ligands. The Au cluster 10 and the- SG ligand 20 form the Au@SG particle 25. The Au@SG clusters are then mixed with a molecular cavity 30, which may be one or more cyclodextrin (CD) molecules, in the presence of reduced glutathione molecules (GSH) 40. As shown in FIG. 1 , various cluster compositions may form during this process including - the Au cluster is partially or wholly surrounded by one CD molecule as in 50, which is an illustration of an Aui5SGi3@CD cavity. It is believed that the -SG ligand 20 interacts with the CD molecules 30 (partially shown) in the cluster composition 50 as shown in FIG. 2A. In particular, the proton 'e' of the -SG ligand 20 interacts with the [Eta]3' proton of the CD molecule 30. This was confirmed by 2D 1H NMR (ROESY) of Aui5@aCD, which showed cross peaks for the H3 and e protons. <l>H NMR of Aui5@aCD suggests that the -SG ligands near the surface of the cluster compositions are in two different environments - inside or outside the CD molecules. In addition, the -SG peaks are shifted from the peak for the parent GSH suggesting that there are no free GSH molecules.
[0055] Example 3. UV-Vis spectra were recorded using a Perkin Elmer Lambda 25 spectrophotometer. The experimentally obtained intensities in
absorbance, as a function of wavelength [I(W)], have been converted to energy- dependent values [1(E)] using the expression 1(E) = I(W)l(dEldW) a I(W)*W<2>, where dEldw represents the Jacobian factor. The photoexcitation and luminescence studies were done using a NanoLog HORIBA JOBINYVON spectrofluorimeter with a 100 W xenon lamp as the excitation source, at a scan speed of 240 nm/sec. Band pass for both excitation and emission monochromators was kept at 5 nm. Metal ion detection was studied at ppm concentrations. Acetates (Cu and Hg ), nitrates (Ag , Cd and Zn<2+>) and chlorides (Fe<34>) were used for metal ion detection studies. XPS measurements were done using an Omicron Nanotechnology spectrometer with polychromatic Al Ka X-rays (hv = 1486.6 eV). At least ten spectra in the desired binding energy range were collected and an average was taken. The samples were spotted as drop cast films on the sample stub and dried under vacuum. X-ray flux was adjusted to reduce the beam induced damage of the sample. The energy resolution of the spectrometer was set at 1.1 eV, at a pass energy of 50 eV. Binding energy (BE) was calibrated with respect to Cl s at 285.0 eV. Luminescence transients were measured and fitted using a commercially available spectrometer (Lifespec-ps) from Edinburgh instrument, U.K. (80 ps instrument response function (IRF)). 1H NMR and 2D 1H NMR (ROES Y) spectra were measured with a 500 MHz Briiker Advance III spectrometer operating at 500.13 MHz for 1H NMR and equipped with a 5 mm triple- resonance PFG probe. Solutions were made in 99.98 % D20 (Aldrich) and sealed immediately. The signal of the solvent served as the reference for the field-frequency lock. All experiments were performed at a temperature of 25 [deg.]C unless specified. Standard Bruker pulse programs (Topspin 2.1) were employed throughout. The ID spectra were acquired with 32 K data points. The data for phase sensitive ROES Y experiments were acquired with a sweep width of 5600 Hz in both dimensions. For each spectrum, 16 transients of 2048 complex points were accumulated for 256 ti- increments and a relaxation delay of 2s was used. A CW spin lock mixing time of 200 ms was employed. Prior to Fourier transformation, zero filling to 2K x 2K complex points was performed, and apodized with a weighted function (QSINE) in both dimensions. All the data were processed on a HP workstation using Topspin 2.1 software. Mass spectrometric studies were conducted using an electrospray (ESI-MS) system, 3200 Q-TRAP LC/MS/MS (Applied Biosystems). Samples of 15 ppm concentration, taken in 1 : 1 water/methanol mixture were electrosprayed at a flow rate of [Iota][Omicron][mu][iota]/[iota][eta][iota][eta] and ion spray voltage of 5 kV. Circular dichroism studies were measured using a JASCO J-810 circular dichroism spectropolarimeter. Limit of detection (LOD) of GSH in circular dichroism is approximately 0.1 mg/mL. The optical polarization image was measured using a Nikon Eclipse LV100 POL polarizing microscope. Dynamic light scattering (DLS) measurements were carried out with Nano-S Malvera-instrument employing a 4 mW He-Ne laser ([lambda] = 632.8 ran) equipped with a thermostated sample chamber. All the scattered photons were collected at 173[deg.] scattering angle. The scattering intensity data were processed using the instrumental software to obtain the hydrodynamic diameter (dn) and the size distribution of the scatterer in each sample. [0056] Example 4. Dynamic light scattering (DLS) measurements were performed to understand the size of the cluster compositions in solution. DLS measurements were carried out with Nano-S Malvem-instrument employing a 4 mW He-Ne laser ([lambda] = 632.8 nm) equipped with a thermostated sample chamber. All the scattered photons were collected at 173[deg.] scattering angle. The scattering intensity data were processed using the instrumental software to obtain the hydrodynamic diameter (dn) and the size distribution of the scatterer in each sample.

[0057] The hydrodynamic diameter of the cluster compositions were observed to be 3-4 nm, which implies the presence of one cluster per CD molecule with water of hydration (see 50 in FIG. 1 ).

[0058] Although the structure of Au15 core is not available from single crystal XRD studies, calculations suggest it to have a symmetric, shell-like flat cage structure with a pointed tip. It is possible that a part of the core or monolayers can penetrate into the CD cavity. The inner core diameter is in the range of 0.6-0.9 nm for [alpha], [beta] or [gamma] CDs, respectively, sufficiently large enough to partially accommodate Au15 cluster compositions.

[0059] The nature of the metal core in these cluster compositions was confirmed by XPS analysis. XPS measurements were done using an Omicron Nanotechnology spectrometer with polychromatic Al K" X-rays (hv = 1486.6 eV). At least ten spectra in the desired binding energy range were collected and an average was taken. The samples were spotted as drop cast films on the sample stub and dried under vacuum. X-ray flux was adjusted to reduce the beam induced damage of the sample. The energy resolution of the spectrometer was set at 1.1 eV, at a pass energy of 50 eV. Binding energy (BE) was calibrated with respect to Cls at 285.0 eV. The 4f7/2 and 4f5 2 BEs of Au in all these cluster compositions appear at 85.2 and 89.2 eV.

[0060] The S 2p, N Is and C ls core level spectra of these cluster compositions were also measured. The Au/S atomic ratio measured from XPS is 1.150, which is in agreement with a composition of AuisSn (theoretical value is 1.1538). The Au15 core reported is with 13 -SG ligands. The S 2p occurs at a slightly higher BE (163.1 eV) than typical thiolates (-162.0 eV) suggesting that the -SG protection is intact. The N Is spectrum shows two peaks at 399.5 eV and 401.3eV BE, indicating the presence of -NH and -NH3<+>, respectively.

[0061] Example s. Three samples of cluster compositions- Aui5@aCD;
Aui5@pCD; Aui5@yCD were prepared according to Example 2 each with [alpha], [beta] or [gamma] CDs. FIG. 3 A is a UV-Vis spectra of Aui5@aCD, Aui5@ CD, and Au15@yCD. FIG. 3 A indicates that the absorption wavelengths for Aui5@aCD, Aui5@ CD, and Aui5@yCD exhibit the same features. The distinct features of the Aui5 core are indicated by the ellipses. The UV-Vis spectra were recorded using a Perkin Elmer Lambda 25 spectrophotometer. The experimentally obtained intensities in absorbance, as a function of wavelength [I(W)]t have been converted to energy-dependent values [1(E)] using the expression 1(E) = I(W)l(dEldW) a I(W)* W<2>, where dEldw represents the Jacobian factor.

[0062] The three varieties of the quantum composition have characteristic absorption features at 318, 458 and 580 nm, where there are no features for GSH as well as CD. FIG. 3B gives the plot of the natural logarithm of the Jacobian factor versus the wavelength of all the three clusters to show the molecular features more clearly (well-defined absorption features are marked by arrows). FIG. 3C provides the absorption profiles of pure GSH and a-CD.

[0063] FIG. 3D is the luminescence spectra of quantum compositions Au15@aCD, Au15@pCD, and Auis@yCD. The photoexcitation and luminescence studies were done using a NanoLog HORIBA JOBINYVON spectrofluorimeter with a 100 W xenon lamp as the excitation source, at a scan speed of 240 nm/sec. Band pass for both excitation and emission monochromators was kept at 5 nm. The samples were excited at 375 nm and the emission was observed at 690 nm. These values are consistent with reported numbers for such as Au22, Au^, and Auio.

[0064] Lifetime values of the clusters were obtained by numerical fitting of the luminescence at 690 nm. They are 0.029 ns (83.50%), 1.50 ns (5.90%), 14.80 ns (2.60%) and 181 ns (8.0%) for Aui5@aCD; 0.071 ns (76.6%), 1.15 ns (1 1.8%), 1 1.10 ns (4.5%) and 163 ns (7.1%) for Au15@ CD and 0.024 ns (84.7%), 1.23 ns (7.6%), 13.90 ns (3.0%) and 172 ns (4.7%) for Aui5@yCD. The fast lifetime component is present in several clusters investigated so far which also show an extremely slow component with reduced weight. For example, the Au22 system shows a fast life time component of 0.05 ns (86.50%) and a slow component of 141.80 ns (3.40%).<14> The quantum yields of the cluster compositions were approximately 6.7% (Aui5@aCD), 6.5% (Aui5@ CD) and 7 % (Aui5@yCD) at room temperature, using ethidium bromide as the reference. In comparison to other similar clusters such as Au22 (4%) and Au23 (1.3%), the quantum yield for the cluster compositions here are substantially larger.

[0065] FIG. 4A shows circular dichroism spectra for the cluster compositions with [alpha], [beta] and [gamma] -CDs. Circular dichroism was measured using a J ASCO J-810 circular dichroism spectropolarimeter. Limit of detection (LOD) of GSH in circular dichroism is approximately 0.1 mg/mL. In addition, the spectra for pure GSH another cluster Au^SGig have been included in FIG. 4A as a comparison. GSH is a chiral compound with a negative Cotton peak around 237 nm. The absence of this peak in the cluster and the cluster composition suggest that there is no free GSH.

[0066] As seen in FIG. 4A, the spectrum of the cluster compositions are different from the spectra for the AU25SG18 cluster. FIG. 4A suggests that the cluster compositions exhibit induced circular dichroism. The cluster compositions have a positive Cotton peak around 330-380 nm and a negative Cotton peak around 400-455 nm, which may be attributed to the cluster core. FIG. 4B shows the combined plot of absorption and circular dichroism (CD) spectra for Aui5@aCD.

[0067] Example 6. Aui5@aCD was stored in a glass vial for 24 hours and the solution was decanted. The glass vial retains a thin layer of cluster composition even with water sonication for 10 minutes. The cluster compositions remain intact and coat on the glass. Although not bound by theory, it is believed that the cluster compositions may bind with the Si-OH of the glass.

[0068] A thin layer chromatography (TLC) plate with bulk S1O2 coating was coated with the cluster composition solution of two different concentrations. The plate with the high and low concentration of cluster composition shows red and rose emissions, respectively, under UV light. The cluster composition-coated TLC plate can be used as a substrate for checking the solvent dependency of photoluminescence. The emission from the TLC plate was collected with 375 nm excitation. Then 2- propanol was sprayed over the plate using a sprayer. Immediately after spraying, emission was collected using the same excitation. There is a slight enhancement of the luminescence intensity. The plate was then allowed to dry completely resulting in the reversal of luminescence. A few other alcohols such as methanol and ethanol were sprayed. Luminescence increased in the order, propanol < methanol ~ ethanol. However, exposure of water on the TLC plate drastically reduced the luminescence intensity. No shift in the emission wavelength was observed. The emission data are presented in FIG. 5.

[0069] The solvent dependency of emission is currently believed to be attributed to hydrogen bonding of the solvent molecules with ligands on the cluster. As a result, the non-radiative rate of decay will reduce and this will enhance the emission. In addition to the cluster composition emission, FIG. 5 shows a peak at 725 nm which is attributed to the emission from the TLC plate. Asterisk (*) corresponds to regions where higher order line of the grating mask the spectrum and dollar ($) corresponds to the emission coming from Si02.

[0070] The solvent dependency of the emission was used to write letters on the TLC plate. In this approach; the TLC plate was coated with a given concentration of the cluster composition. In one embodiment, a low concentration of cluster composition was used to coat the TLC place such that the emission intensity is weak (and the plate is rose in color). When solvent contacts the plate, it enhances luminescence intensity and the solvent exposed regions appear with brighter luminescence. As the solvent evaporates, the parent luminescence reappears bringing the plate to the original state.

[0071] Example 7. At higher concentrations, QCs have a tendency to form a gel-like material with intense emission. Self assembly of the CD and -SG molecules at high concentration may result in gelation. This appears to be the first report of a gel using QCs. These materials were analyzed by SEM and HRTEM. The microstructure of the gel is composed of fibers of ~8 [mu][pi][iota] diameter (FIG. 6B). In order to study the spatial distribution of gold in the gels formed by QCs, elemental mapping was carried out using energy dispersive analysis of X-rays (ED AX). FIG. 6A shows the ED AX spectrum collected from the gel shown in FIG. 6B. ED AX mapping was done using Au Ma and the image is given in FIG. 6C. The detailed structure of the fibers was examined by TEM (FIG. 6D). The isolated clusters are not seen in [Tau][Epsilon][Mu], as mentioned before. Both in TEM and SEM, a fiber-like morphology is observed. Cyclodextrins and their derivatives have been extensively used as host molecules in supramolecular chemistry. Inclusion complexes (ICs) of CDs and guest molecules may result in supramolecular nanostructures (nanogels). Such complexes may find applications in drug delivery and diagnosis, especially in view of the low metallic content of the cluster and its high solubility in water in conjunction with
luminescence.

[0072] Example 8. The cluster composition may be used for the selective detection of metal ions such as Cu<2+>. An aqueous solution of the cluster composition was prepared. Metal ions were added individually under UV light. With the addition ofCu<2+> ions, there was a drastic change in luminescence- disappearance of red emission followed by the emergence of yellow emission (within a few minutes). The UV-Vis and luminescence spectra of cluster solution before and after addition of Cu are given in Figure 7 A and 7B. Even after the addition of Cu , the molecular absorption features are still intact (FIG. 7A), suggesting that the cluster composition is stable. But by looking into the PL spectra of cluster composition before and after the addition of Cu<2+>, a drastic change of emission maximum was observed (a blue shift of -100 run).

EQUIVALENTS

[0073] While certain embodiments have been illustrated and described, it should be understood that changes and modifications can be made therein in accordance with ordinary skill in the art without departing from the technology in its broader aspects as defined in the following claims.

[0074] The use of the terms "a" and "an" and "the" and similar referents in the context of describing the elements (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms "comprising," "having," "including," and "containing" are to be construed as open-ended terms (i.e., meaning "including, but not limited to,") unless otherwise noted. Additionally, the terms and expressions employed herein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Additionally the phrase "consisting essentially of will be understood to include those elements specifically recited and those additional elements that do not materially affect the basic and novel characteristics of the claimed invention. The phrase "consisting of excludes any element not specifically specified.

[0075] The present disclosure is not to be limited in terms of the particular embodiments described in this application. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and compositions within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, reagents, compounds compositions or biological systems, which can of course vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0076] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

[0077] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as "up to," "at least," "greater than," "less than," and the like, include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member.



US2012052513
GOLD SUB-NANOCLUSTERS AND USES THEREOF  

Description

BACKGROUND

[0001] Sub-nanoclusters of noble metals differ substantially from metallic nanoparticles of the same element in both structure and physical properties. While metal nanoparticles may range from a few nanometers (nm) to hundreds of nm in size, sub-nanoclusters have dimensions of about 1 nm or less and include relatively few atoms of metal. Due to the sub-nanometer core size, sub-nanoclusters cannot possess continuous density of states but have discrete electronic energy levels. They show "molecule-like" optical transitions in absorption and emission and therefore show characteristic features different not only from those of nanoparticles but from individual atoms as well.

[0002] The absorption profiles of sub-nanoclusters of various sizes can be distinguished from each other and from nanoparticles. Sub-nanoclusters exhibit strong photoluminescence and their luminescence ranges from the near-infrared (NIR) region to the ultraviolet as core size decreases. While metal nanoparticles of 2-3 nm exhibit very weak luminescence with quantum yields of about 10<-4 >to 10<-5>, sub-nanoclusters can exhibit luminescence with quantum yields in the range of 10<-1 >to 10<-3>. Moreover, sub-nanoclusters may be readily conjugated to biological molecules and their low metal content makes them more biocompatible than nanoparticles. Such properties allow for the use of sub-nanoclusters in imaging and detection, especially medical imaging and in conjunction with therapeutics.

[0003] Discovery and use of metal sub-nanoclusters remain an empirical enterprise. While current techniques have allowed for the preparation of a variety of sizes of sub-nanoclusters, not all sizes have proven accessible. Some sub-nanoclusters are thermodynamically unstable and luminescence quantum yields vary between sub-nanoclusters. In addition, methods such as the reduction of Au<3+> ions in the presence of glutathione provide a complex mixture of sub-nanoclusters that must be separated by, e.g., polyacrylamide gel electrophoresis (PAGE).

SUMMARY

[0004] The present technology provides gold sub-nanoclusters with good thermodynamic stability and luminescence quantum yields and reliable methods of making such sub-nanoclusters. The present technology further provides conjugates and compositions including such sub-nanoclusters and methods of using the same.

[0005] In one aspect, the present technology provides gold sub-nanoclusters including a gold core and one or more thiolates bound to the gold core. In some embodiments, the gold core includes or consists essentially of 23 gold atoms. In some embodiments, the one or more thiolates are selected from glutathione thiolate, 3-mercaptopropyl trimethoxy silane, octanethiolate and a mixture of any two or more thereof. In some embodiments, the one or more thiolates is glutathione thiolate. In an illustrative embodiment, the gold sub-nanocluster has the formula Au23(SG)18 wherein SG is glutathione thiolate.

[0006] In some embodiments of the present technology, the gold sub-nanoclusters further include one or more amine or phosphine ligands. In some embodiments of the present technology, the gold sub-nanoclusters further include one or more fluorescent ligands selected from dansyl, fluorescein isothiocyanate (FITC), green fluorescent protein, coumarin, fluorescein, and cyanine dyes.

[0007] In other embodiments, the gold sub-nanocluster of the present technology may be conjugated to a targeting molecule selected from the group consisting of a protein, a polynucleotide, or a ligand that binds to a protein or polynucleotide. Illustrative targeting molecules include but are not limited to streptavidin, biotin, an antibody, folic acid, lactoferrin, transferrin, or tat protein.

[0008] In another aspect, the present technology provides a composition including an aqueous solution, an organic solution or a mixture thereof that includes one or more gold sub-nanoclusters as described herein.

[0009] In yet another aspect, the present technology provides methods of making gold sub-nanoclusters. The methods include core etching of one or more Au25SG18 sub-nanoclusters using a molar excess of thiolate relative to the molar amount of SG, to provide one or more gold sub-nanoclusters, wherein SG is glutathione thiolate. In some embodiments of the methods, the one or more Au25SG18 sub-nanoclusters are dissolved in an aqueous solution and the excess thiolates are dissolved in an organic solvent that forms a two-phase system with the aqueous solution. The organic solvent may, e.g., be selected from toluene and xylene. In some embodiments of the methods, the thiolate may be selected from glutathione thiolate, octanethiolate, 3-mercaptopropyl trimethoxy silane thiolate and a mixture of any two or more thereof.

[0010] Various gold nanoclusters may be produced by the present methods. In some embodiments of the methods, the gold sub-nanocluster produced consists essentially of 23 atoms of gold and one or more thiolates such as, e.g., glutathione thiolate. In some embodiments, the gold sub-nanocluster produced has the formula Au23SG18 (wherein SG is glutathione thiolate). In other embodiments, the gold sub-nanocluster produced contains 22 or 33 gold atoms. In some embodiments, the gold sub-nanoclusters produced have the formula Au22(MPTS)10(SG)7 or Au33OT22.

[0011] In another aspect, there are provided methods of using the sub-nanoclusters of the present technology. The methods include labeling a biological target with a conjugate of a gold sub-nanocluster as described herein, and detecting the conjugate by luminescence. In some embodiments of the present methods, the biological target may be a cancer cell. In other embodiments, the luminescence may be excited at a wavelength from about 400 to about 550 nm and the emission may be detected at a wavelength from about 600 nm to about 800 nm.

[0012] In yet another aspect of the present technology, there are provided methods of detecting Cu<2+> ions in an aqueous sample. The methods include treating an aqueous sample to be tested for Cu<2+> ions with an effective amount of gold sub-nanoclusters and measuring the decrease in fluorescence of the treated sample, wherein the gold sub-nanocluster includes a gold core and one or more thiolates bound to the gold core, and wherein the gold core consists essentially of 23 gold atoms.

[0013] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1A-C show mass spectra of an illustrative embodiment of the present technology: A) MALDI-MS of the gold sub-nanoclusters showing peaks due to gold thiolate clusters (in which only AumSn clusters are visible since the laser irradiation cleaves the S-C bond of thiolate ligands); B) a group of peaks with m/z spacing of 197 or 229 between the major peaks of the adjacent group of peaks; and C) expanded view of peaks due to Au23S18-23.

[0015] FIG. 2A-D show Fourier Transform Infrared (FTIR) spectra of illustrative embodiments of the starting material, Au25(SG)18, as well as the gold sub-nanoclusters of the present technology and the corresponding thiols used for etching,

[0016] FIG. 3A-B show inherent luminescence of illustrative embodiments of subnanoclusters of the present technology, including (A) Au22 and (B) Au23 collected by spectroscopic mapping at an excitation wavelength of 532 nm. Light regions represent the pixels where the signal (used for the mapping) is at a maximum, the minima being represented with black. The scan area was 40 [mu]m*40 [mu]m.

[0017] FIG. 4A-C show an illustrative embodiment of (A) fluorescent, (B) bright field, and (C) overlay of fluorescent and bright field images of human hepatoma cells stained with streptavidin-conjugated Au23.

DETAILED DESCRIPTION

[0018] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here.

[0019] The present technology provides gold sub-nanoclusters, compositions and conjugates of such sub-nanoclusters and methods of making and using the same. Such sub-nanoclusters are luminescent, e.g., fluorescent in the near infrared, may be coated with thiolate, are relatively non-toxic and are therefore useful in various imaging applications, including, e.g., fluorescent patterns for soft lithography, protein chips, medical imaging and in conjunction with therapy. In particular, such sub-nanoclusters may be derivatized with ligands that selectively bind to biological targets and allow them to be used as fluorescent labels for the biological targets.

[0020] In one aspect, the present technology provides gold sub-nanoclusters including a gold core and one or more thiolates bound to the gold core. The gold core refers to the gold atoms in the sub-nanocluster, but does not include any surface modifications of the gold atoms such as thiolates or other molecules which are bound to the surfaces of the gold atoms. Gold sub-nanoclusters of the present technology include Au22, Au23, and Au33 cores. The luminescence quantum yields of the Au22 and Au23 cores are 2.5% and 1.3%, respectively, making them significantly brighter fluorescent labels than the similar Au25 cores (about 0.1% quantum yield).

[0021] Gold sub-nanoclusters of the present technology may include thiolates bound to the gold core. A thiolate is the anionic form (-S<->) of the chemical group, thiol (-SH). Both water soluble and non-water soluble thiolates may be used. Thiolates that may be bound to the gold core include but are not limited to glutathione thiolate (SG), 3-mercaptopropyl trimethoxy silane (MPTS), octanethiolate (OT) and a mixture of any two or more thereof. In some embodiments, the gold sub-nanoclusters include, consist of or consist essentially of 23 gold atoms and glutathione thiolate, for example, Au23(SG)18. Other illustrative embodiments include but are not limited to Au22(MPTS)10(SG)7 and Au33(OT)22.

[0022] In still other embodiments, amine and phosphine ligands may be bound to the gold core in addition to or in place of thiolates through, e.g., interfacial ligand exchange involving two or more immiscible phases such as two immiscible liquids or solid-liquid phases, and the like. For example, alkyl amines including but not limited to 1-butylamine, 1-hexylamine, and 1-octylamine as well as amino acids with amine side-chains such as lysine or ornithine may be exchanged onto the surface of gold sub-nanoclusters of the present technology. Likewise, phosphines including but not limited to triphenylphosphines, salts of sulfonated phosphines (e.g., 4-(diphenylphosphino)benzenesulfonic acid), and the like.

[0023] Gold sub-nanoclusters of the present technology may also include one or more fluorescent ligands. Suitable ligands include but are not limited to dansyl, fluorescein isothiocyanate (FITC), green fluorescent protein, coumarin, fluorescein, and cyanine dyes. In illustrative embodiments, ligands include but are not limited to acridine, 7-amino-4-methyl coumarin-3-acetic acid (AMCA), boron dipyrrolemethene (BODIPY), Cascade Blue, Cy2, Cy3, Cy5, Cy7, Edans, Eosin, Erythrosin, 6-Fam, Tet, Joe, Hex, Oregon Green, Rhodamine, Rhodol Green, Tamra, Rox, and Texas Red.

[0024] Such fluorescent ligands may be readily attached to suitably functionalized thiolates. By way of non-limiting example, fluorescent ligands containing amino or carboxyl groups may be coupled to a thiolate bearing a carboxyl or amino group, respectively, using standard procedures for amide bond formation (see, e.g., S-Y. Han and Y-A. Kim, Recent development of peptide coupling reagents in organic synthesis. Tetrahedron, 2004, 60, 2447). Thus, coupling agents (e.g., EDC), active esters (e.g., pentafluorophenol), mixed anhydrides and the like may all be used to form amide bonds between, e.g., a carboxyl-bearing thiolate of the sub-nanocluster and an amino-bearing ligand. Other types of linkages such as urethane and thiourea may also be formed from, e.g., isocyanates with amines or thiols. Similarly, click chemistry such as, e.g., the copper catalyzed Huisgen azide-alkyne reaction, may be used to attach fluorescent ligands to suitable functional groups on the thiolates. Depending on the type of chemistry, the reactions may be carried out directly on the sub-nanoclusters, or thiolates of the sub-nanoclusters may be exchanged for fluorescent-containing thiolates prepared according to the reactions described above.

[0025] Gold sub-nanoclusters may be conjugates that include a targeting molecule. By "targeting molecule" is meant a molecule that specifically binds to another molecule, i.e. has a binding constant with its partner of about 10 [mu]M or less, and in some embodiments, 1 [mu]M or less, 0.1 [mu]M or less, or even 0.01 [mu]M or less. A targeting molecule may be a protein, a polynucleotide, or a ligand that binds to a protein or polynucleotide. Such ligands include not only large biological macromolecules, such as but not limited to antibodies, receptors, enzymes, oligonucleic acids, and aptamers, but small organic molecules, such as but not limited to folic acid and cofactors, such as but not limited to, biotin. Thus, in illustrative embodiments, targeting molecules include but are not limited to streptavidin, biotin, antibodies, folic acid, lactoferrin, transferrin, or tat protein.

[0026] Such conjugates may be prepared by coupling a suitably functionalized thiolate to the targeting molecule in much the same way that fluorescent ligands may be attached to thiolates as described above. For example, antibodies, other proteins and small molecules bearing carboxyl or amino groups may be linked, respectively, to the amino or a carboxyl group of glutathione via amide bond formation as described herein for fluorescent ligands. Likewise, urethanes, thiourethanes, and thioureas may also be formed from suitably functionalized thiolates and targeting molecules. Click chemistry may also be employed to prepare such conjugates.

[0027] In one aspect, the present technology provides compositions including aqueous solutions, organic solutions or mixtures thereof that include one or more gold sub-nanoclusters described herein. Such compositions may be useful in imaging applications and may be readily prepared using water or organic solvents as appropriate to the particular application at hand. Aqueous solutions of, e.g., Au23SG18, may be used to stain cells in vitro or in vivo. Organic solutions of, e.g., Au33(OT)22 may be used for catalysis of chemical reactions. Particularly with respect to in vivo use, aqueous solutions may include pharmaceutically acceptable carriers. As used herein the term "pharmaceutically acceptable carrier" includes saline, solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents, and the like, compatible with pharmaceutical administration. Supplementary active compounds can also be incorporated into the compositions.

[0028] The gold sub-nanoclusters described herein may be prepared by core etching (also known as "interfacial etching") one or more Au25SG18 sub-nanoclusters using a molar excess of thiol relative to the molar amount of SG. The types of gold sub-nanoclusters that may be made will vary with the conditions used. In some embodiments of the methods, the Au25SG18 sub-nanoclusters are dissolved in an aqueous solution and the excess thiols (which form thiolates) are dissolved in an organic solvent that forms a two-phase system with the aqueous solution. The organic solvent may, e.g., be selected from aromatic solvents such as, but not limited to, toluene and xylene, chlorocarbons, such as but not limited to chloroform and dichloromethane. Various thiols may be used including but not limited to hexane thiol, decane thiol, phenylethane thiol, mercaptopropionic acid, mercaptosuccinic acid, glutathione, octanethiol, 3-mercaptopropyl trimethoxy silane thiol and a mixture of any two or more thereof. The molar excess of thiol may range, e.g., from about 2 to about 4, about 6 or about 8 equivalents per mole of SG in the Au25SG18 sub-nanoclusters. In some embodiments, the excess thiol may range from about 2 to about 100, about 2 to about 50, about 2 to about 30, about 2 to about 15, or about 2 to about 10 equivalents. The core-etching may be carried out at or near room temperature (e.g., about 20[deg.] C. to about 30[deg.] C., or at about 25[deg.] C.) or at an elevated temperature, e.g., about 50[deg.] C. to about 60[deg.] C. or about 55[deg.] C. In general, lower temperatures may be used to produce smaller clusters, while higher temperatures may be used to produce larger clusters. The reaction time may range from a few minutes to a few hours, including but not limited to, about 5 minutes to about 24 hours, about 10 minutes to about 12 hours, about 30 minutes to about 1, 2, 3, 4, 5, or 6 hours.

[0029] In other methods, the Au25SG18 sub-nanoclusters are dissolved in aqueous solution. Excess thiol is added (e.g., up to about 4 equivalents or from about 1.5 equivalents to about 3 equivalents, or about 2 equivalents per mole of SG in the Au25SG18 sub-nanoclusters) and the reaction mixture stirred for several hours at or near room temperature (e.g., about 20[deg.] C. to about 30[deg.] C., or at about 25[deg.] C.). The thiol, such as MPTS, should be readily soluble in water. Reaction times similar to those for the two-phase system may be used.

[0030] Core-etching methods typically provide predominantly a single species of sub-nanoclusters rather than the spectrum of species that result from some other methods. However, in the event that further purification is needed, PAGE may be used. Purity may also be assessed using PAGE, optical absorption spectroscopy, and/or mass spectrometry.

[0031] Various gold nanoclusters may be produced by the present methods. In some embodiments of the methods, the gold sub-nanocluster produced consists essentially of 23 atoms of gold and one or more thiolates such as, e.g., glutathione thiolate. In some embodiments, the gold sub-nanocluster produced has the formula Au23SG18. In other embodiments, the gold sub-nanocluster produced contains 22 or 33 gold atoms. In some embodiments, the gold sub-nanoclusters produced have the formula Au22(MPTS)10(SG)7 or Au33OT22.

[0032] The gold sub-nanoclusters of the present technology may be used for detection and imaging of biological and other targets. The methods include labeling a biological target with a conjugate of a gold sub-nanocluster as described herein, and detecting the conjugate by luminescence including but not limited to fluorescence and infrared. In addition, such conjugates may be detected using one or more of Raman resonance, NMR, EPR, mass and optical spectra. Such conjugates may also be labeled with a radionuclide emitting alpha, beta, and/or gamma particles. Thus, optical, electronic, ionic and radioactive signatures may be used to capture information.

[0033] In some embodiments of the present methods, the biological target may be a cancer cell such as, e.g., hepatoma. Many types of cancer cells may be targeted using target molecules of the present technology. For example, cancer cells containing folic acid receptors can be stained using clusters conjugated with folic acid. Thus, in some embodiments, the biological target is ovarian, kidney, brain, lung or breast cancer cells.

[0034] Standard fluorescence techniques may be used for detection of the luminescent sub-nanoclusters in the present methods. For example, confocal fluorescence microscopy may be used in vitro to examine a suitable prepared sample. By way of non-limiting example, cells to be examined may be washed free of growth medium, fixed in a paraformaldehyde solution (e.g., 3%) and exposed to a solution of the present gold sub-nanoclusters. After the cells have been stained, they are washed and imaged with the confocal fluorescence microscope. The luminescence may be excited at any suitable wavelength such as one from about 400 to about 550 nm and the emission may be detected at a wavelength from about 600 nm to about 800 nm.

[0035] The present technology may also be used for sensing certain types of metal ions in aqueous samples. Such samples may include, e.g., ground water, well water, or wastewater and may be performed in the context of pollution detection or other purposes. In particular, low concentrations of Cu<2+> in, e.g., the ppm range, may be selectively detected in water versus Ag<3+>, Ag<+>, Ni<2+>, Ca<2+>, Mg<2+>, Na<+>, Pb<2+>, Hg<2+> and Cd<2+>. When a sample containing Cu<2+> ions is treated with an effective amount of Au23 sub-nanoclusters of the present technology, the luminescence of the sample is decreased or even quenched. Thus, in some embodiments, a decrease in luminescence (e.g., fluorescence) indicates the presence of Cu<2+> ions in the sample. By "effective amount of gold sub-nanoclusters" is meant an amount sufficient (in comparison to the amount of Cu<2+> ions in the sample) to produce a detectable change in luminescence of the sample. In some embodiments, the luminescence of the test sample is compared to that of a control sample. The control sample may include the gold sub-nanoclusters but no Cu<2+> ions.

[0036] Luminescence of gold sub-nanoclusters of the present technology may be further enhanced upon phase transfer (e.g., with tetraoctylammonium bromide) from aqueous solution to an organic solution. The luminescence of the phase transferred cluster in toluene may be further enhanced upon the addition of alcohols. The luminescence intensity was enhanced according to the series: methanol<ethanol<propanol<butanol. Thus, in some embodiments of the methods herein, the methods further include treating an aqueous solution of the gold sub-nanoclusters with a water-immiscible organic solvent (e.g., an aromatic solvent such as toluene, benzene or xylene) and a phase transfer catalyst. The luminescence of such phase-transferred gold sub-nanoclusters may be detected as described herein, optionally in the presence of alcohols, e.g., C1-4 alcohols.

EXAMPLES

[0037] The present technology is further illustrated by the following examples, which should not be construed as limiting in any way.

[0038] Materials. Tetrachloroauric acid trihydrate (HAuCl2.3H2O) was purchased from CDH, India. Glutathione (GSH), 1-octanethiol (OT), 3-mercaptopropyl trimethoxysilane (MPTS), tetraoctyl ammonium bromide (TOABr), and sodium borohydride (NaBH4) were purchased from Sigma-Aldrich. Streptavidin was purchased from Hi-Media Chemicals, India. All chemicals were used as such without further purification. Triply distilled water was used throughout the experiments. Solvents were analytical grade.

Example 1

[0039] Synthesis of glutathione-capped gold (AuSG) clusters. Glutathione capped gold clusters were synthesized according to a reported method. (Negishi, Y., et al. J. Am. Chem. Soc. (2005) 127, 5261, the entire contents of which are incorporated herein by reference.) Reduced glutathione (GSH; 20 mM) was added to a solution of HAuCl4.3H2O (100 mL, 5 mM) in methanol. The mixture was then cooled to 0[deg.] C. in an ice bath for 30 minutes (min). An aqueous solution of NaBH4 (25 mL, 0.2 M), cooled at 0[deg.] C., was injected rapidly into this mixture under vigorous stirring. The mixture was allowed to react for another hour. The resulting precipitate was collected and washed repeatedly with methanol/water (3:1) through centrifugal precipitation and dried to obtain the Au@SG clusters as a dark brown powder. This product is a mixture of small nanoparticles and different clusters.

Example 2

[0040] Synthesis Au25SG18, Au25SG18 was synthesized from the as-prepared Au@SG clusters by core etching according to the literature procedure. (Shichibu, Y., et al. Small (2007) 3, 835; Habeeb, Muhammed, M. A., et al. Chem. Phys. Lett. (2007) 449, 186; Shibu, E. S., et al., J. Phys. Chem. C. (2008) 112, 12168; Habeeb Muhammed, M. A. et al., J. Phys. Chem. C. (2008) 112, 14324; the entire contents of each of the foregoing are incorporated herein by reference.) Briefly, the as-prepared Au@SG clusters were dissolved in water (25 mL). GSH was added (614 mg) and stirred at 55[deg.] C. The reaction was monitored by optical absorption spectroscopy. Heating was discontinued when the absorption features of Au25SG18 appeared in the UV/Vis spectrum. This typically took 12 hours (h) of heating. The solution was centrifuged and methanol was added to the supernatant to precipitate the cluster. The precipitate was dried to obtain Au25SG18 clusters in the powder form. The prepared Au25SG18 showed the characteristic UVN is (at 672 nm), FTIR, TEM, and NMR spectroscopic features described in the literature.

Example 3

[0041] Synthesis of Au23 clusters. The cluster was synthesized by interfacial etching. Au25SG18 clusters (10 mg) were dissolved in distilled water (10 mL). Octanethiol (8 times more than the amount of GSH present in Au25SG18) in toluene was mixed with the aqueous solution of Au25SG18 clusters. The biphasic mixture was stirred for 5 h at 25[deg.] C. During this time the absorption feature at 672 nm in the aqueous layer decreased and a new feature at 630 nm appeared. The aqueous and organic phases were separated and centrifuged. The aqueous layer contained Au23SG18 sub-nanoclusters (temporarily assigned as AuxSGy), while the residue was Au'SG polymer formed from the etched gold atoms. The organic layer was almost colorless and did not show any significant absorption feature. PAGE analysis of the aqueous layer showed only one fluorescent band, suggesting the presence of a single well-defined sub-nanocluster.

Example 4

[0042] Synthesis of Au33 clusters. The cluster was also synthesized by interfacial etching. Au25SG18 clusters (10 mg) were dissolved in distilled water (10 mL). Octanethiol (8 times more than the amount of GSH present in Au25SG18) in toluene was mixed with the aqueous solution of Au25SG18 clusters. The biphasic mixture was stirred for 1 h at 55[deg.] C. The organic layer, which was initially colorless, turned dark brown. The aqueous and organic phases were separated and centrifuged. The toluene layer displayed an absorption maximum of 709 nm, similar to that at 710 nm displayed by Au33SG22. After centrifugation, the aqueous layer contained only a deposit of Au<I>SG polymer. The isolated sub-nanocluster was temporarily assigned the formula Aux(OTy).

Example 5

[0043] Synthesis of Au22 clusters. The synthesis was carried out by single-phase etching. Au25SG18 clusters (10 mg) were dissolved in distilled water (10 mL). 3-Mercaptopropyl trimethoxysilane was added to the cluster solution (2 times more than the amount of GSH present in Au25SG18). The mixture was stirred for 7 h. During etching, the color of the aqueous layer became increasingly reddish compared with that of Au25. The solution showed an absorption feature of 540 nm and the characteristic absorption features of Au25 had disappeared completely. The solution was centrifuged and the supernatant separated from the insoluble gold thiolate. The absorption feature of the sub-nanoclusters is similar to that for Au22(SG)17, also at 540 nm. The isolated sub-nanocluster was temporarily assigned the formula Aux(MPTS)y.

Example 6

[0044] Mass Spectrometric Analysis of Gold Sub-Nanoclusters. The sub-nanoclusters of Examples 3-5 were examined using matrix desorption ionization (MALDI) mass spectrometry (Voyager DE Pro mass spectrometer of Applied Biosystems Inc). [alpha]-Cyano-4-hydroxycinnamic acid (CHCA) was used as the matrix. The spectrum was collected in the negative mode. The mass spectrum shows peaks with m/z values ranging from 100 to 10,000 (FIG. 1A). Peaks at low m/z regions are very intense with huge background signals when compared to those at higher m/z values. There is a pattern of peaks between m/z 1800 and 5300 and another pattern from m/z 5500 to 9000. The second set of peaks can be due to the clustering of ions detected in the lower m/z values. Clustering of clusters was observed in MALDI-MS studies of clusters. (Cyriac, J., et al., Chem. Phys. Lett. (2004) 390, 181, the entire contents of which are incorporated herein by reference.) The mass spectrum is composed of several groups of peaks with spacing of m/z 197 or 229 between the major peaks, as shown in FIG. 1B. This corresponds to the loss of Au or AuS. The m/z spacing between isolated peaks in each cluster of peaks is 32 on account of sulfur. These results are consistent with the earlier reports of laser-desorption mass spectrometry of gold clusters protected with thiolates. (see, e.g., Schaaff, T. G., Anal. Chem. (2004) 76, 6187, the entire contents of which are incorporated herein by reference.) Each bunch of peaks can be assigned as [AumSn]<->. Since laser irradiation cleaves the S-C bond of the ligands, we can observe only peaks due to Aum clusters covered with S, and not the entire ligand. The last group of peaks of pattern 1 is due to Au23S18-23 (FIG. 1A). It is worth noting that after the peak due to Au23, the intensity drops drastically. The major peak at m/z 5140 can be assigned to [(Au23S18)S]<->; then addition of S leads to [(Au23S19)S]<->, [(Au23S20)S]<->, and so on (FIG. 1C). Such additions are observed in MALDI and laser desorption ionization (LDI). From these, we can tentatively assign a core of Au23 for the AuxSGy cluster.

Example 7

FTIR Analysis of Gold Sub-Nanoclusters.

[0045] FTIR was carried out on the sub-nanoclusters of Examples 3-5. The FTIR spectra were measured using a Perkin-Elmer Spectrum One instrument. KBr crystals were used as the matrix for preparing the samples, which were at 5 wt % in KBr. FTIR spectra of the three clusters were compared with those of parent Au25SG18 and the ligands used for etching (FIG. 2A-D). FTIR spectra of the ligands bound on the cluster surface are less intense than the free ligands, owing to the fact that these ligands are linked to the cluster surface through covalent bonds. They are also distributed non-uniformly on the cluster surfaces, hence their vibrational features are masked to some extent. FTIR spectra of Au25SG18 and AuxSGy match exactly with each other and therefore it can be concluded that the AuxSGy clusters are protected completely with glutathione as in Au25SG18, which makes them water soluble. The peak at 2526 cm<-1 >due to the -SH stretching of glutathione disappeared both in Au25SG18 and in AuxSGy, thereby suggesting the covalent bonding of glutathione with the cluster core through the thiolate link. The FTIR spectrum of AuxSGy shows features due to octanethiol. The peak at 2568 cm<-1 >due to the -S-H stretching mode of octanethiol disappeared in AuxOTy confirming the covalent binding of octanethiol with the cluster core through the -SH group. The presence of OT on the cluster surface can also be confirmed by the large intensity of the -CH2 stretching modes at 2846 and 2918 cm<-1>. Since single-phase etching was carried out in water, 3-mercaptopropyl trimethoxysilane underwent hydrolysis to 3-mercaptopropyl trisilanol. FTIR spectra of AuxMPTSy showed features due to both 3-mercaptopropyl trisilanol and glutathione, which suggested that the cluster is protected with a mixed monolayer of 3-mercaptopropyl trimethoxysilanol and glutathione. The features due to 3-mercaptopropyl trisilanol were more significant compared with the glutathione features. The ligand protection of the clusters can now be summarized as follows.

Example 8

[0046] Elemental Analysis of Gold Sub-Nanoclusters. Whereas AuxSGy is protected with glutathione, AuxMPTSy is protected with a mixed monolayer of 3-mercaptopropyl trisilanol and glutathione. AuxOTy is covered by octanethiol (all in thiolate form). To check the presence of gold and other elements, energy dispersive analysis of X-ray (EDAX) was carried out (data not shown) by drop-casting the aqueous solution of AuxSGy and solution of AuxOTy in toluene on indium-tin oxide (ITO) glass plates. Since AuxMPTSy was expected to have silicon, the EDAX measurements were carried out by pasting the powder of the cluster on a carbon tape. The elements present in the clusters were mapped. Whereas AuxSGy contained Au, C, N, O, and S, the elements present in AuxMPTSy were Au, C, N, O, S, and Si. The elements present in AuxOTy were Au, C, and S. Based on that information, the core and ligand protection of all three clusters are known. To assign chemical compositions to the clusters, elemental analyses (CHNS) were carried out. The results are given in the Table below. The molecular formulae of the clusters were found to be Au22(MPTS)10(SG)7, Au23(SG)18, and Au33(OT)22.

[0000]

    % of element  % of element   Molecular

Sample  Element  (Experimental)  (Calculated)  formula

AuxMPTSy  N  03.85  03.68  Au22(MPTS)10(SG)7

  C  15.29  15.03  

  H  02.71  02.62  

  S  06.31  06.81  

AuxSGx  N  07.75  07.53  Au23SG18

  C  20.68  21.52  

  H  03.45  02.87  

  S  05.48  05.74  

AuxOTy  N  00.00  00.00  Au33OT22

  C  22.01  21.78  

  H  04.15  03.86  

  S  07.18  07.26

Example 9

[0047] Luminescence of Gold Sub-Nanomolar Clusters. The sub-nanomolar clusters can be imaged using their inherent luminescence. Luminescence images of drop-casted Au23 and Au22 solid films were recorded using a confocal Raman spectrometer equipped with 532 nm excitation. The images in FIG. 3 show luminescence from Au23 and Au22 rich regions. Although there was luminescence from the red (bright) spots, there was no luminescence from the dark areas. The red spots are the islands of Au22 or Au23 clusters. These images show that the clusters are also luminescent in the solid state. Since Au23 is a completely new cluster and is brightly luminescent and water soluble, further investigation of its properties were undertaken.

Example 10

[0048] Conjugation of streptavidin with Au23. Conjugation of streptavidin with glutathione-protected Au23 was carried out using 1-ethyl-3-(3-dimethyl-aminopropyl)carbodiimide (EDC) as the coupling agent. EDC (25 [mu]L of 10 mM) prepared in triply distilled water was added to a mixture of Au23 (2 mg) and streptavidin (1 mg) in triply distilled water (1 mL). The mixture was stirred for 3 h. The streptavidin-coated Au23 was subjected to dialysis for 2 d with a water change after every 6 h.

Example 11

[0049] Imaging of Hepatoma Cells with Streptavidin-conjugated Au23. Conjugated gold sub-nanoclusters of Example 10 were used to image human hepatoma cells (HepG2). These cancerous cells contain large amounts of biotin on their surfaces. Since biotin strongly binds with streptavidin, the cells can be imaged using the luminescence of the sub-nanoclusters in the form of a conjugate with streptavidin.

[0050] HepG2 cells were allowed to grow to 80% confluency starting with 2*10<4 >cells per well in 24-well tissue culture plates (in Dulbecco's Modified Eagle Medium (DMEM) supplemented with 10% fetal bovine serum (FBS) and incubated at 37[deg.] C. in humidified atmosphere containing 5% CO2). For the imaging experiment, the growth medium was removed and the cells were washed twice with phosphate buffered saline (PBS) to remove the dye phenol red and various chemical reagents such as salts and glucose present in the growth medium. After this, the cells were fixed with 3% paraformaldehyde. Two-hundred microliters of a concentrated aqueous solution of streptavidin-conjugated Au23 was added and incubated for 2 h at room temperature. After incubation the cells were washed several times with PBS to remove the unbound clusters and were imaged by confocal fluorescence microscopy. A very intense red luminescence was observed from the cells (see FIG. 4A-C). A control experiment was carried out to confirm the specificity of the streptavidin-biotin interaction. For this the fixed HepG2 cells were incubated with Au23 clusters without any streptavidin conjugation for the same period. No luminescence was observed from the cells after washing (not shown). This experiment confirms that the specific interaction of streptavidin and biotin allows the cluster to stain the cells.

Example 12

Detection of Cu<2+> Ions in an Aqueous Solution

[0051] The effect of fluorescence of Au23 in the presence of various metal ions was studied. The ions selected were Au<3+>, Ag<+>, Cu<2+>, Ni<2+>, Ca<2+>, Mg<2+>, Na<+>, Pb<2+>, Hg<2+>, and Cd<2+> as their nitrates or chlorides. Next, 50 ppm of the aqueous solutions of Au23 was treated with metal ions so that the final concentration was 10 ppm, and the emissions of the clusters were measured immediately after the addition of ions. Au23 was found to be reactive towards Cu<2+>. The emission of the cluster quenched significantly (from an intensity of 4*10<6 >to essentially zero). Although cluster emission enhanced a bit in the presence of Ag ions (from an intensity of 4*10<6 >to a little more than 5*10<6>), it remained unaltered in the presence of other metal ions.

EQUIVALENTS

[0052] The present disclosure is not to be limited in terms of the particular embodiments described in this application. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, reagents, compounds compositions or biological systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0053] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

[0054] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as "up to," "at least," "greater than," "less than," and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member. Thus, for example, a group having 1-3 cells refers to groups having 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers to groups having 1, 2, 3, 4, or 5 cells, and so forth.




Your Support Maintains this Service --

BUY

The Rex Research Civilization Kit

... It's Your Best Bet & Investment in Sustainable Humanity on Earth ...
Ensure & Enhance Your Survival & Genome Transmission ...
Everything @ rexresearch.com on a Data DVD !

ORDER PAGE