Synthese anionique de polymeres comportant une fonction vinylsilane a l'une ou aux deux extremites de la chaine macromoleculaire

The reaction of vinyldimethylchlorosilane with a living polymer (ω or α,ω carbanionic) leads under certain conditions to the quantitative formation of a vinylsilane group to one or two ends of the macromolecular chain.     

Aggregation of sensitizing dyes in solution and their adsorption onto silver halides

The formation of dye dimers and higher aggregates in solution as a function of dye structure and environmental variables are considered. These factors, together with silver halide composition and crystal habit, are also examined in regard to their influence on surface spectra, dye orientation and forces involved in adsorption of dyes at silver halide substrates.     

Novel long-chain anteiso-alkanes and anteiso-alkanoic acids in Antarctic rocks colonized by living and fossil cryptoendolithic microorganisms

Saponified extracts of rock samples colonized by cryptoendolithic microbial communities from the McMurdo Dry Valleys of Southern Victoria Land, Antarctica, were separated into hydrocarbon and fatty acid fractions by silica gel column chromatography. Hydrocarbons and methyl esters of fatty acids were analyzed by capillary gas chromatography-mass spectrometry. Unusually, a suite of long-chain anteiso-alkanes (a-C20 to a-C30) and anteiso-alkanoic acids (a-C20 to a-C30) were detected in many samples, together with straight-chain, branched and/or cyclic and acyclic isoprenoid compounds. These novel compounds are probably derived from unidentified heterotrophic bacteria or symbiotic processes in a unique microbial community in the Antarctic cold desert and suggest the occurrence of a special biosynthetic pathway. Long-chain anteiso-alkanes are probably formed through microbial decarboxylation of corresponding anteiso-alkanoic acids. They may serve as new biomarkers in environmental and geochemical studies.     

Etude de la reaction d'addition de polystyrenes ω-vinylsilane avec une molecule-modele des α,ω-dihydrogeno-polydimethylsiloxanes

Three-block copolymers polystyrene-polydimethylsiloxane-polystyrene can be obtained by a hydrosilylation reaction between α,ω-dihydrogeno polydimethylsiloxane and ω-vinylsilane polystyrene molecules.The purpose of the present investigation was to establish by use of a model system, the optical conditions for the synthesis of three-block and multiblock copolymers: reaction temperature and concentrations of reactants and catalyst.     

Polymerization of Cyclic Imino Ethers. X. Kinetics,Chain Transfer,and Repolymerization

The main conclusions in studies on polymerization catalysts and the nature of chain transfer in the polymerization of cyclic imino ethers were that there is extensive chain transfer in the 2-alkyl oxazolines to produce polymer with a reactive end. Toward the end of polymerization, these chain-transferred molecules repolymerize back on the active center producing a multibranched star polymer. A theory for the data was developed.     

Protein Allostery at Atomic Resolution

Protein allostery is a phenomenon involving the long range coupling between two distal sites in a protein. In order to elucidate allostery at atomic resoluion on the ligand-binding WW domain of the enzyme Pin1, multistate structures were calculated from exact nuclear Overhauser effect (eNOE). In its free form, the protein undergoes a microsecond exchange between two states, one of which is predisposed to interact with its parent catalytic domain. In presence of the positive allosteric ligand, the equilibrium between the two states is shifted towards domain–domain interaction, suggesting a population shift model. In contrast, the allostery-suppressing ligand decouples the side-chain arrangement at the inter-domain interface thereby reducing the inter-domain interaction. As such, this mechanism is an example of dynamic allostery. The presented distinct modes of action highlight the power of the interplay between dynamics and function in the biological activity of proteins.     

Influence of the number of flights on the dilute phase ratio in flighted rotating drums by PTV measurements and DEM simulations

Particle distribution in the cross-section of the flighted rotating drum(FRD)is critical to the analysis of heat and mass transfer between gas and solids.In thi...