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PubMedDate not supplied

A study on the random distribution of a red acrylic target fibre.

This project was a target fibre study carried out by the European Fibres Group. Thirty-eight participating laboratories in nineteen countries searched four hundred and thirty five randomly selected top outer garments. The acrylonitrile/vinyl acetate co-polymer target fibre matched those in a red acrylic scarf, marketed in nine of those countries. The sales figures for the last five years were between 5- and 10,000 scarves annually. Matching fibres were found on only two garments, one fibre per garment. The possible origin of these two fibres is discussed. The result showed that the chances of finding a 'collective' of target fibres on a piece of clothing selected at random can be said to be extremely remote.

Acrylonitrile↗
PubMed2002

Photophysical processes of a copolymer containing 1,1'-binaphthyl-2,2'-diamino and carbazolyl units.

The photophysical processes of copolymer formed by copolymerization of 2,2'-dimethacrylamido-1,1'-binaphthyl (DMBN) with vinylcarbazole (VCZ) have been carefully studied. The results show that when the solution of copolymer (DMBN-VCZ) in THF located in low concentration range (< 10(-3) mg/ml), the fluorescence emission is in good agreement with that of DMBN monomer and the excimer is formed with gradual increase in concentration of copolymer (DMBN-VCZ). The fluorescence of copolymer (DMBN-VCZ) can be quenched both by electron donors and acceptors where the quenching effects follow the Stern-Volmer equation. The dimolecular exciplex between copolymer (DMBN-VCZ) and N,N-dimethylaniline (DMA) are formed and the triple exciplexes are also observed in the same system.

Amines↗
PubMed2000

Infrared and Raman spectra, conformational stability, barriers to internal rotation, normal-coordinate calculations and vibrational assignments for vinyl silyl bromide.

The infrared (3200-30 cm(-1) spectra of gaseous and solid, the Raman spectra (3200-30 cm(-1)) of the liquid and solid vinyl silyl bromide, CH2CHSiH2Br, have been recorded. Additionally, quantitative depolarization values have been obtained. Both the gauche and cis conformers have been identified in the fluid phases but only the gauche conformer remains in the solid. Variable temperature studies from 0 to -87 degrees C of the Raman spectrum of the liquid was carried out. From these data, the enthalpy difference has been determined to be 22 +/- 6 cm(-1) (0.26 +/- 0.08 kJ/mol), with the gauche conformer being the more stable form. The predictions from the ab initio calculations up to MP2/6-311 + + G(2d,2p) basis set favor the gauche as the more stable form. A complete vibrational assignment is proposed for both the gauche and cis conformers based on infrared band contours, relative intensities, depolarization values and group frequencies. The vibrational assignments are supported by normal coordinate calculations utilizing the force constants from ab initio MP2/6-31G(d) calculations and the potential energy terms for the conformer interconversion have been obtained from the same calculations. Complete equilibrium geometries have been determined for both rotamers by ab initio calculations employing a variety of basis sets up to 6-311 + + G(2d,2p) at levels of restricted Hartree-Fock (RHF) and/or Moller-Plesset (MP) to second order. The results are discussed and compared to those obtained for some similar molecules.

Molecular Conformation↗
PubMed2001

Lipase-catalysed hydrolysis of short-chain substrates in solution and in emulsion: a kinetic study.

We have studied the enzymatic hydrolysis of solutions and emulsions of vinyl propionate, vinyl butyrate and tripropionin by lipases of various origin and specificity. Kinetic studies of the hydrolysis of short-chain substrates by microbial triacylglycerol lipases from Rhizopus oryzae, Mucor miehei, Candida rugosa, Candida antarctica A and by (phospho)lipase from guinea-pig pancreas show that these lipolytic enzymes follow the Michaelis-Menten model. Surprisingly, the activity against solutions of tripropionin and vinyl esters ranges from 70% to 90% of that determined against emulsions. In contrast, a non-hyperbolic (sigmoidal) dependence of enzyme activity on ester concentration is found with human pancreatic lipase, triacylglycerol lipase from Humicola lanuginosa (Thermomyces lanuginosa) and partial acylglycerol lipase from Penicillium camembertii and the same substrates. In all cases, no abrupt jump in activity (interfacial activation) is observed at substrate concentration corresponding to the solubility limit of the esters. Maximal lipolytic activity is always obtained in the presence of emulsified ester. Despite progress in the understanding of structure-function of lipases, interpretation of the mode of action of lipases active against solutions of short-chain substrates remains difficult. Actually, it is not known whether these enzymes, which possess a lid structure, are in open or/and closed conformation in the bulk phase and whether the opening of the lid that gives access to the catalytic triad is triggered by interaction of the enzyme molecule with monomeric substrates or/and multimolecular aggregates (micelles) both present in the bulk phase. From the comparison of the behaviour of lipases used in this study which, in some cases, follow the Michaelis-Menten model and, in others, deviate from classical kinetics, it appears that the activity of classical lipases against soluble short-chain vinyl esters and tripropionin depends not only on specific interaction with single substrate molecules at the catalytic site of the enzyme but also on physico-chemical parameters related to the state of association of the substrate dispersed in the aqueous phase. It is assumed that the interaction of lipase with soluble multimolecular aggregates of tripropionin or short-chain vinyl esters or the formation of enzyme-substrate mixed micelles with ester bound to lipase, might represent a crucial step that triggers the structural transition to the open enzyme conformation by displacement of the lid.

Animals↗
PubMed2002

A decade of high-resolution liquid chromatography of nucleic acids on styrene-divinylbenzene copolymers.

The introduction of alkylated, nonporous poly-(styrene-divinylbenzene) microparticles in 1992 enabled the subsequent development of denaturing HPLC that has emerged as the most sensitive screening method for mutations to date. Denaturing HPLC has provided unprecedented insight into human origins and prehistoric migrations, accelerated the cloning of genes involved in mono- and polygenic traits, and facilitated the mutational analysis of more than a hundred candidate genes of human disease. A significant step toward increased sample-throughput and information content was accomplished by the recent introduction of monolithic poly(styrene-divinylbenzene) capillary columns. They have enabled the construction of capillary arrays amenable to multiplex analysis of fluorescent dye-labeled nucleic acids by laser-induced fluorescence detection. Hyphenation of denaturing HPLC with electrospray ionization mass spectrometry, on the other hand, has allowed the direct elucidation of the chemical nature of DNA variation and determination of phase of multiple alleles on a chromosome.

Chromatography, High Pressure Liquid↗
PubMed1985

Selective retention of oxygen using chromatographic columns containing metal chelate polymers.

Porous polymers containing various metal chelates bonded to nitrogen functionalities on the surface of the polymer have been synthesized and found to bind oxygen reversibly. The stationary phases containing [5,5'-(1,2-ethanediyldinitrilo)-bis(2,2,7-trimethyl-3-octanonato)]cobalt(II) were found to be the most suitable of the phases investigated for separating oxygen for argon, nitrogen, and carbon monoxide. At ambient temperatures, near 25 degrees C, the reversible interaction of molecular oxygen with the transition-metal complex bonded to the stationary phase results in a marked increase in the retention time of oxygen, relative to species that have similar retention times in columns that do not contain the metal chelate. The stationary phase can be used alone to achieve the separation of low molecular weight gases or in series with another column. The metal chelate stationary phase is selective for oxygen and little change in the retention time of oxygen is observed after hundreds of injections over a several-month period, indicating that no appreciable degradation of the stationary phase had taken place under these conditions.

Argon↗
PubMed2001

A study of the Lewis acid-base interactions of vinylphosphonic acid-modified polybutadiene-coated zirconia.

Polybutadiene-coated zirconia (PBD-ZrO2) is very useful for reversed-phase separations under a wide variety of conditions. Its excellent chemical (pH = 1-13) and thermal (up to 150 degrees C) stability distinguish it from silica-based reversed phases. Just as with silica-based phases, zirconia's surface chemistry significantly influences the chromatography of certain classes of analytes. Zirconia's hard Lewis acid sites can be chromatographically problematic. Analytes such as carboxylic acids strongly interact with these sites on PBD-ZrO2 and do not elute. Addition of phosphate or other strong, hard Lewis bases to the eluent brings about elution, but the resulting peak is often tailed and broad. Typically, cationic solutes are more retained in the presence of phosphate or fluoride due to adsorption of the Lewis base additives and the concomitant development of a negative charge on the surface. This Coulombic interaction can be used to optimize selectivity, but the reversed-phase-cation-exchange retention can produce broad peaks with excessive retention. As an alternative to adding Lewis bases to the eluent, we studied the effect of permanently modifying PBD-ZrO2 by covalently attaching vinylphosphonic acid (VPA) to PBD which was predeposited in the pores of zirconia. We have investigated the chromatography of acids, bases, and small peptides on VPA-modified PBD-ZrO2 (VPA-PBD-ZrO2) and compared it to PBD-ZrO2. VPA-PBD-ZrO2 is a reversed-cation-exchange phase with properties quite different from PBD-ZrO2. The chemical stability of both phases led us to explore how low-pH (1.5-3), ultralow-pH (0), and high-pH (12) eluents effect the retention properties of these mixed-mode phases. Ultralow-pH eluents effectively separate small peptides on both phases. This approach gives lower retention, without sacrificing resolution, and much higher efficiency for small peptides than previously reported.

Anions↗
PubMed2001

High spatial resolution imaging with near-field scanning optical microscopy in liquids.

The mechanism of tuning fork-based shear-force near-field scanning optical microscopy is investigated to determine optimal experimental conditions for imaging soft samples immersed in liquid. High feedback sensitivity and stability are obtained when only the fiber probe, i.e., excluding the tuning fork prongs, is immersed in solution, which also avoids electrical shorting in conductive (i.e., buffer) solutions. Images of MEH-PPV were obtained with comparable spatial resolution in both air and water. High optical resolution (approximately160 nm fwhm) was observed.

Ethylenes↗
PubMed2000

Oligothienylenevinylenes as a new class of multinanometer linear pi-conjugated systems for micro- and nanoelectronics.

This Account deals with the synthesis and characterization of monodisperse soluble oligothienylenevinylenes with chain lengths up to 100 A. The chain length dependence of the electronic and electrochemical properties both in solution and in the solid state are analyzed and discussed in the context of the potential use of oligothienylenevinylenes as molecular wires. Problems related to interchain interactions are illustrated by the analysis of the effects of structure on the reversible dimerization of cation radicals and by the synthesis of new series of end-substituted oligomers.

Electrochemistry↗
PubMedDate not supplied

Psoralen-containing vinyl monomer for conjugation of double-helical DNA with vinyl polymers.

We have synthesized a vinyl monomer having a psoralen moiety, which can form a photoadduct with double-helical DNA. The monomer 1 was proved to have an ability to crosslink DNA double strands through a photochemical reaction when irradiated by UV light. The resulting DNA having vinyl groups was copolymerized with a comonomer such as acrylamide and N-isopropylacrylamide to give rise to a DNA-vinyl polymer conjugate. A conjugation based on covalent bondings was verified by using gel electrophoresis; the conjugation efficiency was found to be dependent upon concentration of the monomer which had been used in the antecedent photochemical reaction. This monomer will be a useful tool when anchoring double-helical DNA on polymeric materials for separating and sensing DNA-binding substances.

Acrylic Resins↗