Showing papers by "Thalappil Pradeep published in 2002"
TL;DR: In this article, the growth of gold, silver, and gold-silver alloy crystals of submicron dimensions was observed by Lactobacillus strains, common in buttermilk, and the growth occurs by the coalescence of clusters, and tens of crystals were found within the bacterial contour.
Abstract: Lactobacillus strains, common in buttermilk, assist the growth of gold, silver, and gold-silver alloy crystals of submicron dimensions upon exposure to the precursor ions. Several well-defined crystal morphologies are observed. Crystal growth occurs by the coalescence of clusters, and tens of crystals are found within the bacterial contour. Crystal growth does not affect the viability of the bacteria. Crystals are presumably nucleated through nanoclusters, which are formed within as well as transported into the bacteria. Biomass with the crystals can be harvested completely. Results point to potential applications in analytical chemistry, nanotechnology, medicine, and metal ion recovery. Coalescence appears to be a route by which surface area of the crystal is reduced so that it can be effectively protected to avoid biological damage.
743 citations
TL;DR: In this paper, a review of the structure, temperature-induced phase transitions, and associated dynamics of self-assembled monolayers (SAMs) can be found in the context of their own work in this area.
Abstract: Organized molecular assemblies have been one of the intensely pursued areas of contemporary chemistry. Among the various methodologies used to make organized mono- layer structures, self-assembled monolayers (SAMs) have been attractive to many materials chemists owing to the simplicity of the preparative method and high stability. Advances in various techniques and their application in the study of SAMs have significantly improved our understanding of these molecular systems. These studies have been further intensified since the successful preparation of stable metal clusters protected with monolayers. This arti- cle reviews the structure, temperature-induced phase transitions, and associated dynamics of monolayers, principally in the context of our own work in this area. Alkanethiols on Au(111) and Ag(111) are taken as archetypal systems to discuss the properties of 2D SAMs; studies from our laboratory have been on evaporated thin films. Alkanethiols on Au and Ag cluster surfaces are taken as examples of 3D SAMs. Although our principal focus will be on alkane- thiols, we will touch upon a few other adsorbate systems as well.
38 citations
TL;DR: In this paper, the rotational motions of the alkyl chains in an isolated monolayer protected cluster (MPC), AuC18 (Cn = n carbon n-alkanethiolate), and a superlattice of AgC8 MPC have been investigated by quasielastic neutron scattering (QENS) technique in the temperature range of 300−400 K.
Abstract: Dynamics of alkyl chains in an isolated monolayer protected cluster (MPC), AuC18 (Cn = n carbon n-alkanethiolate), and a superlattice of AgC8 MPC have been investigated by quasielastic neutron scattering (QENS) technique in the temperature range of 300−400 K. The results have been compared with a layered silver thiolate, AgC12, chosen to represent a planar two-dimensional monolayer. In the cluster superlattice, QENS broadening was observed even at room temperature and below the chain melting temperature (Tcm) whereas for the isolated cluster it was seen only above Tcm. In the layered silver thiolate, it was observed above the melting point. Data pertain to the rotational motions of the alkyl chains and can be best described by jump diffusion among N equivalent sites or continuous rotation about the molecular axis. At room temperature, the observed dynamics in AgC8 correspond only to the noninterdigitized molecular chains which amount to about 50% of the total. Above 340 K, contribution from the interdigit...
25 citations
TL;DR: In this article, a method of synthesis for zirconia coated silver clusters using self-assembled monolayers as templates was reported, showing that metal ions can be incorporated into the oxide layer leading to a shift in the plasmon resonance band implying the possible use of these materials as ion sensors.
Abstract: We report a method of synthesis for zirconia coated silver clusters using self-assembled monolayers as templates. Formation of the zirconia cover, as monitored with X-ray diffraction and absorption spectroscopy, suggests a continuous overlayer growth that can be inhibited at any stage. Surface plasmon resonance of the silver cluster undergoes a gradual shift and decreases in intensity upon systematic build-up of the dielectric cover. The zirconia overlayer is optically transparent for smaller coverages, but becomes opaque for thicker layers. Spectroscopic studies showed that the mercaptobenzoic acid monolayer is intact in the synthetic procedure and the surface thiolate binding is unaltered. Preliminary studies suggest that metal ions can be incorporated into the oxide layer leading to a shift in the plasmon resonance band implying the possible use of these materials as ion sensors.
15 citations
TL;DR: In this paper, the mechanism of formation of larger metal-carbon clusters was investigated by means of association reactions with H2O, and the results showed that metal carbon clusters of other compositions have also been studied.
Abstract: New metal-carbon clusters, M4C9
+ (M = Ti, V), generated using a combined thermal arc discharge evaporation set-up, have been studied with quadrupole mass spectrometry. Reactivities of these clusters have been investigated by means of association reactions with H2O. Metal-carbon clusters of other compositions have also been studied. We speculate on the mechanism of formation of larger metal-carbon clusters.