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.

Pradeep Thalappil

Department Of Chemistry

Bacteria

Escherichia coli

Fourier transform infrared spectroscopy

Photoelectrons

ultraviolet visible spectroscopy

X ray photoelectron spectroscopy

Antibacterial properties

Chemical reduction

GRAM-POSITIVE ORGANISMS

LUMINESCENCE SPECTROSCOPY

POLYACRYLAMIDE GELS

SPECTROSCOPIC AND MICROSCOPIC TECHNIQUES

Staphylococcus aureus

UV/ VIS SPECTROSCOPY

High resolution transmission electron microscopy

Fulltext

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Journal of Materials Chemistry B

Reactivity of monolayer protected atomically precise clusters of noble metals is of significant research interest. To date very few experimental data are available on the reaction thermodynamics of such clusters. Here we report a calorimetric study of the reaction of glutathione (GSH) protected silver clusters in the presence of excess ligand, GSH, using isothermal titration calorimetry (ITC). We have studied Ag11(SG)7 and Ag32(SG)19 clusters and compared their reactivity with GSH protected silver nanoparticles (AgNPs) and silver ions. Clusters show intermediate reactivity toward excess ligand compared to nanoparticles and silver ions. Several control experiments were performed to understand the degradation mechanism of these silver clusters and nanoparticles. The effect of dissolved oxygen in the degradation process was studied in detail, and it was found that it did not have a significant role, although alternate pathways of degradation with the involvement of oxygen cannot be ruled out. Direct confirmation of the fact that functionalized metal clusters fall in-between NPs and atomic systems in their stability is obtained experimentally for the first time. Several other thermophysical parameters of these clusters were also determined, including density, speed of sound, isentropic compressibility, and coefficient of thermal expansion. © 2017 American Chemical Society.

Journal of Physical Chemistry C

Reactivity of Monolayer Protected Silver Clusters toward Excess Ligand: A Calorimetric Study

The cluster Ag44SePh30, originally prepared from silver selenolate, upon oxidative decomposition by H2O2 gives the same cluster back, in an apparently reversible synthesis. Such an unusual phenomenon was not seen for the corresponding thiolate analogues. From several characterization studies such as mass spectrometry, Raman spectroscopy, etc., it has been confirmed that the degraded and as-synthesized selenolates are the same in nature, which leads to the reversible process. The possibility of making clusters from the degraded material makes cluster synthesis economical. This observation makes one to consider cluster synthesis to be a reversible chemical process, at least for selenolates. © The Royal Society of Chemistry 2014.

Nanoscale

Reversible formation of Ag44 from selenolates

A selenolate-protected Ag-Pd alloy cluster was synthesized using a one-pot solution-phase route. The crude product upon chromatographic analyses under optimized conditions gave three distinct clusters with unique optical features. One of these exhibits a molecular peak centered at m/z 2839, in its negative ion mass spectrum assigned to Ag5Pd4(SePh)12-, having an exact match with the corresponding calculated spectrum. Tandem mass spectrometry of the molecular ion peak up to MS9 was performed. Complex isotope distributions in each of the mass peaks confirmed the alloy composition. We find the Ag3Pd3- core to be highly stable. The composition was further supported by scanning electron microscopy, energy-dispersive spectroscopy, and X-ray photoelectron spectroscopy. (Graph Presented). © 2014 American Chemical Society.

Journal of Physical Chemistry Letters

Isolation and tandem mass spectrometric identification of a stable monolayer protected silver-palladium alloy cluster

A blue luminescent 11-atom platinum cluster showing step-like optical features and the absence of plasmon absorption was synthesized. The cluster was purified using high performance liquid chromatography (HPLC). Electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) mass spectrometry (MS) suggest a composition, Pt11(BBS)8, which was confirmed by a range of other experimental tools. The cluster is highly stable and compatible with many organic solvents. This journal is © the Partner Organisations 2014.

Blue emitting undecaplatinum clusters

A cluster obtained in high yield from the reduction of a silver-thiolate precursor, Ag-SCH2CH2Ph, exhibited a single sharp peak near 25 kDa in the matrix-assisted laser desorption mass spectrum (MALDI MS) and a well-defined metal core of ∼2 nm measured with transmission electron microscopy (TEM). The cluster yields a single fraction in high-performance liquid chromatography (HPLC). Increased laser fluence fragments the cluster until a new peak near 19 kDa predominates, suggesting that the parent cluster-Ag152(SCH2CH2Ph)60-evolves into a stable inorganic core-Ag152S60. Exploiting combined insights from investigations of clusters and surface science, a core-shell structure model was developed, with a 92-atom silver core having icosahedral-dodecahedral symmetry and an encapsulating protective shell containing 60 Ag atoms and 60 thiolates arranged in a network of six-membered rings resembling the geometry found in self-assembled monolayers on Ag(111). The structure is in agreement with small-angle X-ray scattering (SAXS) data. The protective layer encapsulating this silver cluster may be the smallest known three-dimensional self-assembled monolayer. First-principles electronic structure calculations show, for the geometry-optimized structure, the development of a ∼0.4 eV energy gap between the highest-occupied and lowest-unoccupied states, originating from a superatom 90-electron shell-closure and conferring stability to the cluster. The optical absorption spectrum of the cluster resembles that of plasmonic silver nanoparticles with a broad single feature peaking at 460 nm, but the luminescence spectrum shows two maxima with one attributed to the ligated shell and the other to the core. © 2012 American Chemical Society.

Nano Letters

The superstable 25 kDa monolayer protected silver nanoparticle: Measurements and interpretation as an icosahedral Ag152(SCH 2CH2Ph)60 cluster

We describe the application of a recently discovered family of materials called quantum clusters, which are sub-nanometer particles composed of a few atoms with well-defined molecular formulae, exhibiting intense absorption and emission in the visible region in metal ion sensing, taking Ag 25 as an example. The changes in the optical properties of the cluster, in both absorption and emission upon exposure to various metal ions in aqueous medium are explored. The cluster can detect Hg 2+ down to ppb levels. It can also detect 5d block ions (Pt 2+, Au 3+ and Hg 2+) down to ppm limits. Hg 2+ interacts with the metal core as well as the functional groups of the capping agents and the interaction is concentration-dependent. To understand the mechanism behind this type of specific interaction, we have used spectroscopic and microscopic techniques such as UV-vis spectroscopy, luminescence spectroscopy, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD). Specific reasons responsible for the interaction of Hg 2+ have been proposed. © 2011 Elsevier B.V.

Journal of Hazardous Materials

Luminescent sub-nanometer clusters for metal ion sensing: A new direction in nanosensors

A highly luminescent freestanding film composed of the quantum cluster, Au 15, was prepared. We studied the utility of the material for specific metal ion detection. The sensitivity of the red emission of the cluster in the composite to Cu 2+ has been used to make a freestanding metal ion sensor, similar to pH paper. The luminescence of the film was stable when exposed to several other metal ions such as Hg 2+, As 3+, and As 5+. The composite film exhibited visual sensitivity to Cu 2+ up to 1 ppm, which is below the permissible limit (1.3 ppm) in drinking water set by the U.S. environmental protection agency (EPA). The specificity of the film for Cu 2+ sensing may be due to the reduction of Cu 2+ to Cu 1+/Cu 0 by the glutathione ligand or the Au 15 core. Extended stability of the luminescence of the film makes it useful for practical applications. © 2012 American Chemical Society.

ACS Applied Materials and Interfaces

Luminescent, freestanding composite films of Au 15 for specific metal ion sensing

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.

Small

Au25@SiO2: Quantum clusters of gold embedded in silica

Biosynthesis of silver nanoparticles (AgNPs) was achieved by a novel, simple green chemistry procedure using citrus sinensis peel extract as a reducing and a capping agent. The effect of temperature on the synthesis of silver nanoparticles was carried out at room temperature (25 °C) and 60 °C. The successful formation of silver nanoparticles has been confirmed by UV-vis, FTIR, XRD, EDAX, FESEM and TEM analysis and their antibacterial activity against Escherichia coli, Pseudomonas aeruginosa (Gram-negative), and Staphylococcus aureus (Gram-positive) has been studied. The results suggest that the synthesized AgNPs act as an effective antibacterial agent. © 2011 Elsevier B.V. All rights reserved.

Journal	Data powered by TypesetJournal of Materials Chemistry B
Publisher	Data powered by TypesetRoyal Society of Chemistry
ISSN	20507518
Open Access	No