Preparation,characterization, and thermal studies of γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> and CuO dispersed polycarbonate nanocomposites

Polycarbonate with γ-Fe₂O₃ and CuO dispersions were carried out by solvent casting method to make polycarbonate-γ-Fe₂O₃ and polycarbonate-CuO composite films. These films were characterized for the molecular structure through FTIR spectroscopy and crystallinity by X-ray diffraction (XRD) measurements. The morphology of polycarbonate-γ-Fe₂O₃ was found to be different from that of polycarbonate-CuO composite films based on the scanning electron micrograph (SEM) images. The thermal traces of composites are different from that of pure polycarbonate which indicating the catalytic decomposition when compared with virgin polymer which is oxidative decomposition. An understanding of the structure, morphology, and thermal behaviour of the composite films are envisaged in the present study.     

Analgesic and anti-inflammatory properties of Thespesia populnea leaf extracts

Analgesic and anti-inflammatory activities of the aqueous and ethanol extracts of Thespesia populnea Soland. ex. Correa (Malvaceae) leaves were evaluated in animal models. Orally-administered aqueous and ethanol extracts (100, 200 and 400?mg?kg?1 bw) showed significant analgesic activity in chemical-, mechanical- and thermally-induced pain test models in mice. The extracts also reduced paw oedema induced by carrageenan in rats. The results obtained in this study suggest that Thespesia populnea extracts have analgesic and anti-inflammatory properties.     

Highly conducting π-conjugated molecular junctions covalently bonded to gold electrodes

We measure electronic conductance through single conjugated molecules bonded to Au metal electrodes with direct Au-C covalent bonds using the scanning tunneling microscope based break-junction technique. We start with molecules terminated with trimethyltin end groups that cleave off in situ, resulting in formation of a direct covalent σ bond between the carbon backbone and the gold metal electrodes. The molecular carbon backbone used in this study consist of a conjugated π system that has one terminal methylene group on each end, which bonds to the electrodes, achieving large electronic coupling of the electrodes to the π system. The junctions formed with the prototypical example of 1,4-dimethylenebenzene show a conductance approaching one conductance quantum (G(0) = 2e(2)/h). Junctions formed with methylene-terminated oligophenyls with two to four phenyl units show a 100-fold increase in conductance compared with junctions formed with amine-linked oligophenyls. The conduction mechanism for these longer oligophenyls is tunneling, as they exhibit an exponential dependence of conductance on oligomer length. In addition, density functional theory based calculations for the Au-xylylene-Au junction show near-resonant transmission, with a crossover to tunneling for the longer oligomers.     

Biosynthesis, purification and characterization of silver nanoparticles using Escherichia coli

The application of nanoscale materials and structures, usually ranging from 1 to 100 nanometers (nm), is an emerging area of nanoscience and nanotechnology. Nanomaterials may provide solutions to technological and environmental challenges in the areas of solar energy conversion, catalysis, medicine, and water-treatment. The development of techniques for the controlled synthesis of nanoparticles of well-defined size, shape and composition, to be used in the biomedical field and areas such as optics and electronics, has become a big challenge. Development of reliable and eco-friendly processes for synthesis of metallic nanoparticles is an important step in the field of application of nanotechnology. One of the options to achieve this objective is to use ‘natural factories’ such as biological systems. This study reports the optimal conditions for maximum synthesis of silver nanoparticles (AgNPs) through reduction of Ag⁺ ions by the culture supernatant of Escherichia coli. The synthesized silver nanoparticles were purified by using sucrose density gradient centrifugation. The purified sample was further characterized by UV–vis spectra, fluorescence spectroscopy and TEM. The purified solution yielded the maximum absorbance peak at 420 nm and the TEM characterization showed a uniform distribution of nanoparticles, with an average size of 50 nm. X-ray diffraction (XRD) spectrum of the silver nanoparticles exhibited 2θ values corresponding to the silver nanocrystal. The size-distribution of nanoparticles was determined using a particle-size analyzer and the average particle size was found to be 50 nm. This study also demonstrates that particle size could be controlled by varying the parameters such as temperature, pH and concentration of AgNO₃.     

σ-Ferrier rearrangement of carbohydrate derived vinylcyclopropanes: a facile approach to oxepane analogs

This article presents our work on the σ-Ferrier ring-expansion of carbohydrate derived vinylcyclopropanes (VCPs) under electrophilic conditions mediated by chloramine-T and a phase-transfer catalyst. The present work serves as the first example on the studies of the reactivity of carbohydrate VCPs towards the synthesis of densely functionalized oxepane analogues. The work elaborates on a reasonable mechanism for the product formation and our observations on the diastereoselectivity based on control experiments and gas-phase calculations.     

Bridged triarylamines: a new class of heterohelicenes

A series of bridged triarylamines, which constitute a new class of heterohelicenes, have been synthesized using a simple three-step procedure. These compounds are shown to be highly luminescent chromophores and are capable of being oxidized. The solid-state structures of these helicenes show a tendency for pi-stacking interactions into an overall zigzag motif.     

Determination of WR-1065 and WR-33278 by liquid chromatography with electrochemical detection

A liquid chromatographic method using electrochemical detection is presented for measuring the thiol WR-1065 12-(3-aminopropylamino) ethanethiol] and its symmetrical disulfide WR-33278 [NH2(CH2)3NHCH2CH2S]2. WR- 1065 is the active, radioprotective drug derived from the phosphorothioate pro-drug WR-2721 (amifostine). External standard curves for both compounds were linear over the range of 40-200 pmol injected (r2 = 0.999 and 0.996 for the thiol and disulfide, respectively). The detection and quantitation limits for WR-1065 were 9 and 18 pmol, respectively, whereas the corresponding values for WR-33278 were 30 and 59 pmol, respectively. Within- and between-day determinations of measurement Vision and accuracy for both compounds validated the suitability of this assay method.     

Partitioning of polystyrene between incompatible phases and distributional effects in the system polystyrene–polybutadiene–toluene

The average molecular weights and the molecular weight distributions of polystyrene (PS) in the conjugate incompatible phases of the ternary system of PS and polybutadiene with toluene as solvent were studied at 23°C. Gelpermeation chromatography, with ultraviolet and differential refractive index detectors, was used for analyzing the compositions of the conjugate phases and for obtaining the molecular weight averages of PS in the phases. Both narrow and broad molecular weight distribution (MWD) polymer samples were used. The effect of broad MWD polymers is seen as one of narrowing the shape of the binodal, thus effectively increasing the compatible region. The molecular weight averages of PS in the two conjugate phases do not vary significantly in the case of the narrow MWD PS sample while for broad MWD samples the average molecular weight of PS is found to be higher in the PS-rich phase than in the polybutadiene-rich phase for tie lines closer to the plait point indicating a partitioning or redistribution of the molecular weight species of PS between the incompatible phases.     

Ligand substitution reactions of W6S8L6 with tricyclohexylphosphine (L = 4-tert-butylpyridine or n-butylamine): 31P NMR and structural studies of W6S8(PCy3)n(4-tert-butylpyridine)6-n (0 < n < or = 6) complexes

The substitution reactions by bulky tricyclohexylphosphine (PCy3) ligands on W6S8L6 (L = 4-tert-butylpyridine or n-butylamine) clusters were investigated to prepare clusters with mixed axial ligands for low-dimensional cluster linking. When 4-6 equiv of PCy3 are used to react with W6S8(4-tert-butylpyridine)6 (4) in THF, cis-W6S8(PCy3)4(4-tert-butylpyridine)2 (1) is preferentially formed. But when starting with W6S8(n-butylamine)6 (2), only W6S8(PCy3)6 (3) is produced with 6 equiv of PCy3. Other conditions with fewer equivalents of PCy3 led to mixtures of partially substituted complexes in the W6S8L6-n(PCy3)n (0 < or = n < or = 6, L = 4-tert-butylpyridine or n-butylamine) series. A significantly distorted structure for 1 helps to explain its preferential formation. 1H NMR spectra were collected for clusters 1 and 2 and 31P NMR spectra for 1 and W6S8(4-tert-butylpyridine)6-n(PCy3)n complexes. P-P coupling through P-W-W-P is reported for the first time in octahedral metal clusters and shown to be very useful in identifying nearly all the W6S8L6-n(PR3)n complexes and their stereoisomers in the mixtures even before individual species are isolated.     

Two-state random walk model of lattice diffusion. 1. Self-correlation function

Diffusion with interruptions (arising from localized oscillations, or traps, or mixing between jump diffusion and fluid-like diffusion, etc.) is a very general phenomenon. Its manifestations range from superionic conductance to the behaviour of hydrogen in metals. Based on a continuous-time random walk approach, we present a comprehensive two-state random walk model for the diffusion of a particle on a lattice, incorporating arbitrary holding-time distributions for both localized residence at the sites and inter-site flights, and also the correct first-waiting-time distributions. A synthesis is thus achieved of the two extremes of jump diffusion (zero flight time) and fluid-like diffusion (zero residence time). Various earlier models emerge as special cases of our theory. Among the noteworthy results obtained are: closed-form solutions (ind dimensions, and with arbitrary directional bias) for temporally uncorrelated jump diffusion and for the ‘fluid diffusion’ counterpart; a compact, general formula for the mean square displacement; the effects of a continuous spectrum of time scales in the holding-time distributions, etc. The dynamic mobility and the structure factor for ‘oscillatory diffusion’ are taken up in part 2.