Temperature dependence of trap luminescence of CdS doped glasses

The temperature dependence of the optical absorption edge and integrated luminescence of CdS semiconductor doped glasses, having similar characteristics but manufactured by different manufactures like Corning 373 and Schott 1743 has been investigated. Transmission Electron Microscope (TEM) analysis is presented for these samples to understand the contribution of the inhomogeneous distribution of nanocrystal size. The energy gap shrinkage coefficient (α) and effective phonon energy (θ) have been derived from the temperature dependence of the energy gap. The activation energy of thermal photoluminescence (PL) quenching has been derived from the temperature dependence of luminescence intensity. An anomalous behaviour of the luminescence intensity and of bandwidth in the temperature range 50-10 K has been discussed using configuration co-ordinate model. The difference in the behaviour of different samples in the range 50-10 K has been suggested to arise from the inhomogeneous size distribution, which is supported by TEM analysis.     

Studies on pyrolytically sprayed SnO2 and Sb-SnO2 thin films for LPG sensor applications

Undoped and antimony doped tin oxide thin films of different thicknesses were prepared on mineral glass substrate by spray pyrolysis method via sol-gel route. Both the films show good transmittance in the visible region. Band gap energy of both films lies between 3 to 3.5 eV. X-ray diffraction studies of undoped and antimony doped tin oxide thin films for various annealing temperature show polycrystalline tetragonal structure of SnO₂ with preferred orientation of (110) and (101), respectively and from the XRD data, grain size were also evaluated. AFM images of Undoped and antimony doped tin oxide thin films annealed at 375 °C depict the film thickness and indicate uniform surface pattern without dark pits and with strains of some ups exceeding the specified limit. The prepared films were tested in a specially developed test rig for Liquefied Petroleum Gas detection at different operating temperatures. The response characteristics of the films for LPG detection show maximum sensitivity and minimum response time at the operating temperature 400 °C. Studies indicate that antimony doped tin oxide thin film are one among the suitable candidates for LPG detection with a detection sensitivity and response time (t90) of 11 and 140 seconds, respectively. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Electrochemical preparation of copper–dendrimer nanocomposites: picomolar detection of Cu<Superscript>2+</Superscript> ions

The present work describes, for the first time, in situ electrochemical preparation of dendrimer-encapsulated Cu nanoparticles using a self-assembled monolayer of fourth-generation amine-terminated polyamidoamine (PAMAM) dendrimer as the template. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) studies of the modified surface confirmed the presence of Cu nanoparticles entrapped in dendrimer film. Au electrode modified with a monolayer of the dendrimer enables preconcentration and subsequent voltammetric detection of Cu²⁺ at picomolar concentrations. Further, Cu nanoparticles in the dendrimer monolayer could be electrochemically derivatised to Cu hexacyanoferrate, which exhibits specific crystal planes, unlike the random distribution of crystal planes in bulk-formed Cu hexacyanoferrate, which is another catalytically active material for sensor applications. Figure Electrochemical preparation of copper–dendrimer nanocomposite     

Asymmetric Reduction of Ketones Using In Situ Generated Oxazaborolidines From (1R-Camphor as Catalysts

Benzyl and 1-naphthyl derivatives of 1,2-amino alcohols derived from (1R)-(+)-camphor were made by a simple and efficient procedure and these were used for the generation of oxazaborolidines with borane. The asymmetric reductions of prochiral ketones were carried out using these in situ generated oxazaborolidines as catalysts.     

Efficient, chemoenzymatic process for manufacture of the Boceprevir bicyclic [3.1.0]proline intermediate based on amine oxidase-catalyzed desymmetrization

The key structural feature in Boceprevir, Merck's new drug treatment for hepatitis C, is the bicyclic [3.1.0]proline moiety "P2". During the discovery and development stages, the P2 fragment was produced by a classical resolution approach. As the drug candidate advanced through clinical trials and approached regulatory approval and commercialization, Codexis and Schering-Plough (now Merck) jointly developed a chemoenzymatic asymmetric synthesis of P2 where the net reaction was an oxidative Strecker reaction. The key part of this reaction sequence is an enzymatic oxidative desymmetrization of the prochiral amine substrate.     

Saturable and reverse saturable absorption in aqueous silver nanoparticles at off-resonant wavelength

Silver nano-colloid was prepared by chemical reduction method and its nonlinear absorption properties were investigated by using open aperture z-scan experiment with nanosecond laser pulses operating at 532?nm. Interestingly, a switch over from saturable absorption to reverse saturable absorption was observed when the input intensity is increased from 28.1 to 175.8?MW/cm². The underlying mechanism responsible for the observed switching behaviour is the interplay between ground state plasmon band bleaching and excited state absorption. Theoretical fitting was done by using a model in which nonlinear absorption coefficient as well as saturation intensity are incorporated.     

Multicomponent reactions involving zwitterionic intermediates for the construction of heterocyclic systems: one pot synthesis of aminofurans and iminolactones

The reaction of 1:1 zwitterionic intermediate generated in situ from dimethyl acetylenedicarboxylate (DMAD) and cyclohexyl isocyanide with aldehydes and quinones is described. The reaction of stoichiometric amounts of DMAD, isocyanide and aldehydes afforded 2-aminofurans in good yields, while the reaction with quinones gave iminolactones.     

PHOTOPHYSICAL and PHOTOCHEMICAL PROPERTIES OF COUMARIN DYES IN AMPHIPHILIC MEDIA

Abstract— Photophysical properties of coumarin dyes solubilized in aqueous detergent solutions have been investigated including measurement of absorption and fluorescence emission maxima, and fluorescence quantum yields. Use of coumarin 4 as a fluorescence probe of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) solutions led to the conclusion that the sites for dye incorporation in micelles are significantly hydrogen-bonded (hydrated). The inhibition of photochemical decomposition for detergent-solubilizcd dyes has also been observed. Electron transfer from micelle-bound dye to a water soluble acceptor, methyl viologen, has been investigated by flash photolysis.     

Synthesis of Cyclodextrin Glucosyl Transferase byBacillus cereus for the production of cyclodextrins

A potent indigenous bacillus isolate identified asBacillus cereus (RJ-30) was found to produce Cyclodextrin Glucosyl Transferase (CGTase) extracellularly. Process optimization of various fermentation parameters has been established for optimal growth of bacillus and the maximum enzyme synthesis. The organism had the highest specific growth rate (0.7μ) with a generation time of 1 h in glucose containing medium at the conditions of pH 7.0, 37°C at 300 rpm, 1.5 vvm of agitation, and aeration. At these conditions, it exhibited the maximum activity of 54 U/mL at the synthesis rate of 2.7 U/L/h. CGTase was produced from the early exponential growth and peaked during the midsporulating stage of about 16 h thereafter maintained at the same level of 50 U/mL. Saccharides containing media were better inducers than starch, and the influence of carbohydrate substrates has shown that enzyme synthesis is promoted by xylose (65 U/mL) and, more remarkably, by the supplementation of wheat bran extract in glucose medium (106 U/mL). This organism produced CGTase stably in a chemostat culturing over a period of 400 h with a maximum productivity of 5.4 kU/L/h (threefold higher than obtained in batch culturing [1.75 kU/L/h]). Comparatively, CGTase was produced by immobilized cells in a continuous fluidized bed reactor for over approx 360 h, at a relatively high dilution rate of 0.88 h⁻¹ resulting in the productivity of 23.0 kU/L/h.     

Novel heterocyclic construction via dipolar cycloadditions to 1,2‐dicarbonyl compounds

The reactivity of o‐quinones and other 1,2‐diones towards a variety of dipolar species viz‐, nitrile oxides, carbonyl ylides, betaines and mesoionic compounds has been investigated. In most cases, these reactions occur with the participation of C=O group as the dipolarophile leading to the synthesis of novel heterocyclic compounds.