Hydrogen catalysis and scavenging action of Pd-POSS nanoparticles

Prompted by the need for a self-supported, chemically stable, and functionally flexible catalytic nanoparticle system, we explore a system involving Pd clusters coated with a monolayer of polyhedral oligomeric silsesquioxane (POSS) cages. With an initial theoretical focus on hydrogen catalysis and sequestration in the Pd-POSS system, we report density functional theory (DFT) results on POSS binding energies to the Pd(1 1 0) surface, hydrogen storing ability of POSS, and possible pathways of hydrogen radicals from the catalyst surface to unsaturated bonds away from the surface.     

Complex formation between cationically modified gold nanoparticles and DNA: an atomic force microscopic study

Atomic force microscopy has been used for direct visualization of the wrapping of DNA around 30-nm-sized functionalized gold nanoparticles for the first time. The morphology of the complexes seems to be dictated by the relative concentration of the nanoparticles and DNA. A higher concentration of the former leads to the formation of a network of nanoparticles assembled on DNA. This assembly pattern seems to be significantly different from the manner in which cationically modified gold nanoparticles of smaller size (< 5 nm) arrange linearly on DNA, as shown in the literature. A DNA-gold nanoparticle can be developed as a model system for in vitro studies on the mechanism of DNA condensation and also for developing novel methods of nanoparticle self-assembly on the DNA template.     

Time-resolved fluorescence of tryptophans in yeast hexokinase-PI: effect of subunit dimerization and ligand binding

Time-resolved and steady-state fluorescence measurements have been performed on monomeric and dimeric forms of yeast hexokinase-PI. Observation of similar emission spectra and fluorescence decay parameters for both the forms of the enzyme suggests that tryptophan residue(s) are not likely to be present at the subunit-subunit interface and the process of dimerization does not perturb the local environment of tryptophan(s). The fluorescence decay of tryptophans in enzyme could be fitted to a bi-exponential function with two lifetime components, tau1 approximately 2.2 ns and tau2 approximately 3.9 ns. Binding of glucose, which is known to convert the 'open' conformation of the enzyme to a 'closed' active conformation, results in approximately 30% reduction in emission intensity and a selective decrease in tau1 from approximately 2.2 to approximately 1.1 ns. These effects can be reversed by the addition of trehalose 6-phosphate (an inhibitor of yeast hexokinase), suggesting that the trehalose 6-phosphate inhibits the enzyme by binding to its 'open' inactive conformation rather than competing with glucose to bind to the 'closed' active conformation. Binding of nucleotide ligands (ATP, ADP and adenyl-(beta,gamma-methylene)-diphosphate (AMPPCP)) to the monomeric or dimeric form of enzyme quenched the steady-state fluorescence by approximately 4-8%, but had no measurable effect on the distribution of lifetimes or on their magnitudes. Addition of nucleotides to the enzyme-glucose complex also did not produce any further change in fluorescence decay parameters. These results indicate that it is highly unlikely that the formation of a ternary enzyme-glucose-nucleotide complex from the binary enzyme-glucose complex is accompanied by a large conformational change in the enzyme, as has been surmised in some earlier studies.     

Facile catalyzed acylation of heteroatoms using BiCl3 generated in situ from the procatalyst BiOCl and acetyl chloride

Acylation of a variety of alcohols, phenols, aliphatic and aromatic amines, a thiol and a thiophenol proceeds efficiently using BiCl₃ generated in situ from the procatalyst BiOCl and acetyl chloride in a solvent or under solventless conditions, furnishing the corresponding acylated derivatives in very good to excellent yields.     

Phosphorus based epoxy terminated structural adhesive 2. Curing, adhesive strength and thermal stability

The curing behavior of phosphorus based epoxy terminated polymers was studied using diaminodiphenyl ether, diaminodiphenyl sulfone, benzophenone tetracarboxylic dianhydride and the commercial hardener of Ciba-Geigy's two-pack araldite, as curing agent. The adhesive strength of these adhesives was measured by various ASTM methods like lap-shear, peel, and cohesive tests on metal-metal, wood-wood and wood-metal interfaces. All these results were compared with the synthesized epoxy resins prepared from bisphenol-A and epichlorohydrin having the epoxy equivalent value of 0.519. The thermal stability of both the virgin resin and its cured form was also studied by thermogravimetric analysis.     

New block copolymers V. Synthesis,characterization and morphological studies of poly(pentamethylene terephthalate)-b-(acrylonitrile butadiene rubber)

A block copolymer was prepared by low temperature polycondensation between (acid chloride)-terminated poly(pentamethylene terephthalate) as the hard block, and amine-terminated acrylonitrile-butadiene rubber, as the soft block. The polymer was characterized by nitrogen analysis, IR and NMR spectroscopy. The polymer showed two glass transition temperatures (T _g ) and exhibited two-phase morphology.     

Oxocation complexes,Part X. Oxomolybdenum(V) and dioxomolybdenum(VI) complexes with tri- and tetra-dentate Schiff bases

Summary Many new oxomolybdenum(V) and dioxomolybdenum(VI) complexes have been synthesized with tri- and tetradentate Schiff bases derived by the condensation of salicylaldehyde, thiosalicylaldehyde,o-hydroxyacetophenone, 3-carboxysalicyclaldehyde or acetylacetone with aminoalcohols, polymethylenediamines ando-phenylenediamines. Mononuclear oxothiolato Schiff base complexes of molybdenum(V) have been prepared for the first time. Quadridentate Schiff bases derived from salicylaldehyde and substituted salicylaldehydes ando-phenylenediamine have also been successfully employed to isolate dioxomolybdenum(VI) complexes in the solid state, in which two oxygen atoms of the MoO₂ group arecis- to each other, similar to the situation observed for other dioxomolybdenum(VI) complexes of salicylaldehyde-polymethylenediamine Schiff base ligands.Structures have been determined with the help of elemental analyses, magnetic susceptibilities, molar conductances, i.r., electronic and¹H n.m.r. spectral data.For Part IX, K. Dey, R. K. Maiti and J. K. Bhar,Indian J. Chem., in press.     

Determination of iodate and sulphate in iodized common salt by ion chromatography with conductivity detection

A simple, rapid and accurate method for the determination of iodate in iodized common salts has been developed. The quantitative determination of iodate was accomplished by anion exchange chromatography with conductimetric detection. The method requires a sample pretreatment for the removal of large excess of chloride from the sample matrix. Onguard silver cartridges were found most suitable for this purpose. The sulphate content in the salt was simultaneously determined. The lower limits for the determination of iodate and sulphate in solution are 0.5 and 0.05 mug ml(-1), respectively. Quantitative recovery of the anions in synthetic samples has been obtained and the interferences from different cations and anions have been studied. The method has been successfully applied to the determination of iodate and sulphate in the commercially available salts. The concentrations of iodate measured by this method are in good agreement with those claimed by the manufacturer.     

Studies on cross-linkable copolyimides

Some new flexible and cross-linkable copolyimides containing rubbery unsaturated aliphatic chain moiety (CPLA) were prepared by low temperature polycondensation betweenm-phenylene diamine,bis- 3(4 carboxy phthalimido) benzene, and liquid, bis [2-(4 piperazinyl) ethyl aminocarbonyl] poly-(butadiene-co-acrylonitrile) (ATBN) in (DMAC) solution. The effect of rubbery aliphatic moiety in these copolyimides on the polymer properties has been reported. A comparative study on the properties of these copolyimides (CPLA) with the mixture of ATBN and a low molecular-weight cross-linkable copolyimide possessing the same molecular structure as the aromatic moiety of CPLA polymers has been made.     

Redox‐Active Peptide‐Functionalized Quinquethiophene‐Based Electrochromic π‐Gel

An electrochromic system based on a self‐assembled dipeptide‐appended redox‐active quinquethiophene π‐gel is reported. The designed peptide‐quinquethiophene consists of a symmetric bolaamphiphile that has two segments: a redox‐active π‐conjugated quinquethiophene core for electrochromism, and peptide motif for the involvement of molecular self‐assembly. Investigations reveal that self‐assembly and electrochromic properties of the π‐gel are strongly dependent on the relative orientation of peptidic and quinquethiophene scaffolds in the self‐assembly system. The colors of the π‐gel film are very stable with fast and controlled switching speed at room temperature.