The formation of Au25@SiO2 is reported in which the quantum clusters (QCs) are embedded in a layer of silica. Polydisperse Au mSGn QCs are converted rapidly into monodisperse Au 25 QCs by the addition of (3-mercaptopropyl)trimethoxysilane (MPTS) with 7-times-higher yield when compared to the glutathione-mediated synthesis. Subsequent hydro-lysis and condensation results in the formation of Au 25@SiO2. © 2011 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

Pradeep Thalappil

Department Of Chemistry

Glutathiones

Higher yield

Monodisperse

Polydisperses

PREFERENTIAL POPULATION

QUANTUM CLUSTERS

TRIMETHOXYSILANE

Gold

Polydispersity

silica

Gold compounds

glutathione

silicon dioxide

article

chemistry

Transmission electron microscopy

Microscopy, Electron, Transmission

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Glutathione protected, silver clusters were synthesized within gel cavities, using sunlight. Compared to the conventional chemical reduction process, this method is cheaper and environmentally friendly as it involves the use of natural resources. The as-synthesized silver quantum clusters in aqueous medium show a distinct step-like behavior in their absorption profile. They have been characterized with various spectroscopic and microscopic techniques such as UV/Vis Spectroscopy, Luminescence Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), High Resolution Transmission Electron Microscopy (HRTEM), and X-ray Photoelectron Spectroscopy (XPS). Polyacrylamide gel cavities seemingly control the growth of the particles. The cluster synthesis is scalable by increasing the amount of reagents yielding hundreds of milligrams in a single step. The antibacterial properties of the as-synthesized Ag clusters were studied against a Gram negative and Gram positive organism, Escherichia coli and Staphylococcus aureus, respectively. © 2013 The Royal Society of Chemistry.

Fulltext

Journal of Materials Chemistry B

Sunlight mediated synthesis and antibacterial properties of monolayer protected silver clusters

Luminescent Ag15 clusters confined in bovine serum albumin (BSA) have been prepared by a simple wet chemical route. The luminescence, exhibiting a maximum at 685 nm, is observable to the naked eye. The chemical composition of these clusters was analyzed using matrix assisted laser desorption ionization mass spectrometry (MALDI MS), X-ray photoelectron spectroscopy (XPS), and energy dispersive analysis of X-rays (EDAX). Intact Ag15@BSA is observed by MALDI MS. Multiple charge states of the cluster are observed confirming the mass assignment. The clusters showed a quantum yield of 10.71% in water and the luminescence was stable in a pH range of 1-12. Stability of the clusters was enhanced by the addition of polyvinylpyrrolidone (PVP). The clusters showed luminescence in the solid state as well. Evolution of clusters with variation in the amount of reducing agent added shows that the cluster formation goes through an intermediate state of bound silver, formed instantaneously after the addition of Ag+, which transforms to the cluster. High yield synthesis and exciting photophysical properties make our new material interesting for various applications such as biolabeling and imaging. © 2011 The Royal Society of Chemistry.

Journal of Materials Chemistry

A fifteen atom silver cluster confined in bovine serum albumin

We synthesized fluorescent, porphyrin-anchored, Au 22 clusters in a single step, starting from well-characterized Au 25 clusters protected with glutathione (-SG) by a combined core reduction/ligand exchange protocol, at a liquid-liquid interface. The prepared cluster was characterized by UV/vis, photoluminescence, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, elemental analysis, and matrix-assisted laser desorption ionization mass spectrometry. The absence of a 672 nm intraband transition of Au 25 and the simultaneous emergence of new characteristic peaks at 520 and 635 nm indicate the formation of the Au 22 core. An increase in the binding energy of 0.4 eV in Au 4f core-level peaks confirmed the presence of a reduced core size. Quantitative XPS confirmed the Au/S ratio. The presence of a free base, tetraphenylporphyrin (H 2TPPOAS-), on the Au 22 core was confirmed by fluorimetric titrations with Cu 2+ and Zn 2+ ions. From all of these, the composition of the cluster was determined to be Au 22[(-SG) 15(-SAOPPTH 2) 2], which was supported by mass spectrometry and elemental analysis. We utilized the fluorescence nature of these water-soluble clusters for the fabrication of fluorescent patterns by soft lithography. The patterns were studied using tapping-mode atomic force microscopy and confocal fluorescence imaging. © 2009 American Chemical Society.

ACS Applied Materials and Interfaces

Functionalized Au 22 clusters: Synthesis, characterization, and patterning

Glutathione protected Au25 quantum clusters, exhibiting characteristic fluorescence, have been uniformly coated inside and outside of β-Ala-L-Ile dipeptide nanotubes. These coated structures have been imaged using the inherent fluorescence of Au25. Upon exposure to an electron beam, in a transmission electron microscope, the quantum clusters gradually transform to gold nanoparticles, of the metallic size regime. The nanoparticles grow to a size of 4.5 nm and thereafter the particle size is unaffected by electron beam exposure. The nanotubes are intact and this template is shown to control the uniformity of the size of the nanoparticles grown. The quantum clusters can be loaded selectively inside the tubes using capillarity of the nanotubes. The sizes of the nanoparticles grown are tuned using electron beam exposure. © 2009 The Royal Society of Chemistry.

Size tuning of Au nanoparticles formed by electron beam irradiation of Au25 quantum clusters anchored within and outside of dipeptide nanotubes

We report the instantaneous decomposition of the small molecular gold cluster, Au25SG18 (SG-glutathione thiolate) in the presence of externally added chloroaurate ions resulting in the instantaneous formation of the insoluble gold-glutathione polymer. The rate of decomposition, however, was much slower for the metal ions such as Ag+, Fe3+, Cu2+, Ni2+, Cd2+, Zn2+ and Sr2+. This chemical reactivity is shown to have no direct correlation with the electrochemical potential of the added ions. © 2007 Elsevier B.V. All rights reserved.

Chemical Physics Letters

Reactivity of Au25 clusters with Au3+

Angewandte Chemie International Edition

Spotlights on our sister journals: Angew. Chem. Int. Ed. 49/2010

ACS Nano

Size-Focusing Synthesis, Optical and Electrochemical Properties of Monodisperse Au38(SC2H4Ph)24Nanoclusters

Au25@SiO2: Quantum clusters of gold embedded in silica

Journal	Small
ISSN	16136810
Open Access	No