SYNTHESIS OF GOLD NANOCLUSTERS

Gold nanoclusters are primarily used to catalyze the growth of nanowires (via VLS or SLS routes), and are also utilized for biomedical applications such as targeted drug deUvery agents. As discussed in Chapter 6, a number of techniques may be used to synthesize metallic nanoclusters. In this experiment, a gold precursor is transformed into nanoclusters with diameters 2 nm via a two-step reaction. The first step consists of phase-transfer into an organic layer where it reacts with triphenyl-phosphine. In the second step, the mixture is reduced by sodium borohydride. 

Dissolve hydrogen tetrachloroaurate trihydrate (1.00 g, 2.54 nunol) and tetraoctylammonium bromide (1.60 g, 2.93 mmol) in a degassed water/toluene mixture (50 mL/65 mL). 

When the golden color is transferred into the organic phase, add triphenylphosphine (2.32 g, 8.85 mmol) with vigorous stirring for ca. 10 min until the organic phase is white and cloudy. 

Add aqueous sodium borohydride (1.41 g, 37.3 mmol, dissolved in 10 mL of water immediately prior to use) to the organic phase. The organic phase will immediately turn dark purple. Continue to stir the solution for 3 h under a nitrogen flow. 

Separate the toluene layer, washing it with water (2 x 100 mL). Remove the solvent in vacuo, or with a stream of nitrogen to yield a black solid. 

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Abstract There have been remarkable advances in the development of gold nanoclusters protected by thiolates (Au (SR)m), and techniques for the synthesis and characterization of these materials have improved significantly, enabling Au (SR)m to be synthesized with atomic precision. Experiments on the stabilities of clusters synthesized in this way have revealed a series of magic clusters, and the structures and physical and chemical properties of these magic clusters have subsequently been elucidated. Furthermore, several methods have been established for the functionalization of magic clusters. This chapter describes recent developments in Au (SR)m cluster chemistry. 

Attention has been given to the synthesis of bimetallic silver-gold clusters [71] due to their effective catalytic properties, resistance to poisoning, and selectivity [72]. Recently molecular materials with gold and silver nanoclusters and nanowires have been synthesized. These materials are considered to be good candidates for electronic nanodevices and biosensors [73]. 

Xie J, Zheng Y, Ying JY (2009) Protein-directed synthesis of highly fluorescent gold nanoclusters. J Am Chem Soc 131 888-889... 

Lin C-AJ, Yang T-Y, Lee C-H et al (2009) Synthesis, characterization, and bioconjugation of fluorescent gold nanoclusters toward biological labeling applications. ACS Nano 3 395 101... 

Guzman J, Gates BC (2001) Gold nanoclusters supported on MgO Synthesis, characterization, and evidence of Au. Nano Lett 1 689... 

Fig. 4. Main methods for the preparation of gold GNPs. (A) Direct synthesis based on the reduction of a Au(III) salt and in situ protection of the nascent gold nanocluster with thiol-aimed glycoconjugates. (B) Ligand place exchange reactions based on the treatment of preformed gold nanoparticles with thiol-derivatized glycoconjugates. (C) Functionalization of gold nanoparticles by reaction between functional groups on gold surface and suitably derivatized carbohydrates. (See Color Plate 31.)...

P/ate 3.2. Schematic of the alkanethiol stabilized cluster synthesis. After reduction of the gold ions, the competitive processes of gold particle growth and alkanethiol surface complexation determine the size of the gold nanocluster. 

The molybdenum neopentyUdene complex Mo(CHBu )(NR)(OBu )2 is the active catalyst used in a fascinating development for the synthesis of 11-Vt semiconductor clusters (ZnS, CdS, PbS) and silver and gold nanoclusters of predictable size within microdomains in films of block copolymers prepared by ROMP. Block copolymers of norbomene and a functionalized norbomene that wiU complex with a metal-containing compound were prepared and characterized as monodisperse materials. The functionalized component (amine, alkoxide, or thiolate) then sequestered the metal and the metallated block copolymer was cast into a film which was subsequently treated with H2S to convert the metal into the sulfide. The molybdenum complexes have also featured in the development of the synthesis of side-chain liquid crystal polymers by living ROMP.98 99... 

In the field of bio-nanotechnology, dendritic disulfides made from biocompatible L-lysine building-blocks were also found as useful ligands for the controlled assembly of gold nanoparticles [66] with anion sensing properties [67]. The synthesis of CdSe dendron stabilized nanoclusters with high stability and biocompatibility (box-nanocrystals) is also noteworthy [68]. 

The synthesis of SiNWs starts from gold nanoparticles with diameters of 10, 20, or 40 nm that are distributed on a silicon substrate. The nanoclusters are required to catalyze SiNW growth. The method employs an elaborate series of steps of growth, etching, oxidation, and finally silylation to generate a perfluorophenyl-... 

Biji, R, N. K. Sarangi, and A. Patnaik. 2010. One pot hemimiceUar synthesis of amphiphilic janus gold nanoclusters for novel electronic attributes. Langmuir 26 14047-14057. 

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