Search results for "Vinyl Compounds"
showing 10 items of 20 documents
Observation of Very Narrow Linewidths in the Fluorescence Excitation Spectra of Single Conjugated Polymer Chains at 1.2 K
2007
Fluorescence emission and excitation spectra of single poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] polymer molecules embedded in poly(methylmethacrylate) have been recorded at 1.2 K. The ubiquitous spectral diffusion causes large variations in the spectral shape and apparent linewidth in the emission spectra. Nevertheless, we find very narrow (approximately 0.1 cm(-1)) purely electronic zero-phonon lines in the excitation spectra, which are 2 orders of magnitude smaller than previous estimates of the homogeneous linewidth. These results complement the molecular description of the low energy transitions in conjugated polymers.
Single Molecule Studies of a Ladder Type Conjugated Polymer: Vibronic Spectra, Line Widths, and Energy Transfer
2014
Confocal fluorescence microscopy and spectroscopy are employed to investigate single poly(ladder-type pentaphenylene) (LPPentP) molecules dispersed in thin poly(methyl methacrylate) (PMMA) films at 1.2 K. Emission spectra of single chains show single as well as multi-chromophore emission indicating variegated communication along the chains. The vibronic structure in the emission spectra resembles the one found for other ladder-type polymers. Purely electronic zero-phonon lines in emission are substantially broadened, most probably due to fast spectral diffusion. By surmounting the limitations of emission spectroscopy, nonemitting donor chromophores, which transfer their excitation energy in…
Hemoglobin loaded polymeric nanoparticles: preparation and characterizations.
2011
In the present work polymeric nanoparticles based on Poly (maleic anhydride-alt-butyl vinyl ether) 5% grafted with m-PEG (2000) and 95% grafted with 2-methoxyethanol (VAM41-PEG) were loaded with human hemoglobin (Hb) and characterized from a physicochemical point of view. The assessment of structural and functional features of the loaded Hb was performed and the effect of the introduction of different reducing agents as aimed at minimizing Hb oxidation during the nanoparticles formulation process, was also investigated. Nanoparticles possessing an average diameter of 138 ± 10 nm and physicochemical features suitable for this kind of application were successfully obtained. Although the oxida…
Multilayered supported ionic liquids as catalysts for chemical fixation of carbon dioxide
2011
Multilayered, covalently supported ionic liquid phase (mlc-SILP) materials were synthesized by using a new approach based on the grafting of bis-vinylimidazolium salts on different types of silica or polymeric supports. The obtained materials were characterized and tested as catalysts in the reaction of supercritical carbon dioxide with various epoxides to produce cyclic carbonates. The material prepared by supporting a bromide bis-imidazolium salt on the ordered mesoporous silica SBA-15 was identified as the most active catalyst for the synthesis of cyclic carbonates and displayed improved productivity compared with known supported ionic liquid catalysts. The catalyst retained its high act…
Characteristics of haloethylene-induced acetonemia in rats.
1980
A series of halogenated ethylenes (vinyl chloride, vinylidene fluoride,cis- andtrans-1,2-dichloroethylene, perchloroethylene) induces increased acetone exhalation in rats. Exposures of differently pre-treated rats to vinylidene fluoride suggest that a metabolite of the haloethylene must be envolved in eliciting this formation of acetone. This conclusion is based on (a) dependence of acetone exhalation on the concentration of vinylidene fluoride, (b) effect of inducing agents, (c) effect of pyrazol, a metabolic inhibitor, (d) effect of cysteine, (e) effect of hypoxia and (f) the time course of acetone exhalation.
Solvent-Enhanced Diastereo- and Regioselectivity in the PdII-Catalyzed Synthesis of Six- and Eight-Membered Heterocycles viacis-Aminopalladation
2009
The Pd(II)-catalyzed intramolecular oxidative cyclization of tosyl-protected cis- and trans-N-allyl-2-aminocyclohexanecarboxamides was examined, and efficient syntheses of cyclohexane-fused pyrimidin-4-ones and 1,5-diazocin-6-ones were developed. In the course of the research, a marked solvent effect was observed on both the regio- and diastereoselectivity. Additionally, a novel Pd(II)-mediated domino oxidation, oxidative amination reaction was discovered. Our experimental and theoretical findings suggest that the reactions proceed via a cis-aminopalladation mechanism.
A DFT study of [3 + 2] cycloaddition reactions of an azomethine imine with N-vinyl pyrrole and N-vinyl tetrahydroindole
2016
The mechanism and selectivities of the [3+2] cycloaddition (32CA) reactions of azomethine imine (AI) 8 with two N-vinyl five-membered heterocycles (NVFH), 9a and 9b, have been theoretically studied using DFT methods at the MPWB1K/6-31G(d) computational level. The possible ortho/meta regio- and endo/exo stereoselective channels were explored and characterised. The low polar character of these 32CA reactions, which is the consequence of the high nucleophilic character of both reagents, as well as the non-effective reactivity of these NVFH as nucleophiles, accounts for the high calculated activation energies, 16.1 (9a) and 16.8 (9b) kcalmol-1 in chlorobenzene. Analysis of the relative electron…
Evidence of chloroethylene oxide being the reactive metabolite of vinyl chloride towards DNA: comparative studies with 2,2′ -dichloro-diethylether
1983
The roles of chloroethylene oxide (CEO) and chloroacetaldehyde (CAA) in carcinogenicity of vinyl chloride (VC) have been studied by comparing biological effects of VC exposure with those of 2,2'-dichlorodiethylether (bis(chloroethyl)ether, BCEE) as a metabolic precursor of CAA. Biological end-points investigated were covalent protein binding, nucleic acid (RNA and DNA) alkylation and the potency of the two chemicals to induce preneoplastic ATPase-deficient foci in rat liver. After exposure of rats to [1-14C]BCEE, BCEE derived radioactivity was bound to liver proteins. Analysis of hydrolysates of liver RNA and DNA gave no indication for the formation of either 7-N-(2-oxoethyl)guanine, 1,N6-e…
Copper-catalyzed regioselective synthesis of (E)-β-fluorovinyl sulfones
2019
Organofluorine compounds are finding increasing application in a variety of fields such as pharmaceutical, agrochemical, and material sciences. However, given the scarcity of fluorine-containing natural products, advancement in this area depends almost entirely on the development of new synthetic methodologies. In this article, we present the synthesis of a series of previously undescribed (E)-&beta
Enzymes involved in vinyl acetate decomposition by Pseudomonas fluorescens PCM 2123 strain
2014
Esterases are widely used in food processing industry, but there is little information concerning enzymes involved in decompositions of esters contributing to pollution of environment. Vinyl acetate (an ester of vinyl alcohol and acetic acid) is a representative of volatile organic compounds (VOCs) in decomposition, of which hydrolyses and oxidoreductases are mainly involved. Their activities under periodically changing conditions of environment are essential for the removal of dangerous VOCs. Esterase and alcohol/aldehyde dehydrogenase activities were determined in crude cell extract from Pseudomonas fluorescens PMC 2123 after vinyl acetate induction. All examined enzymes exhibit their hig…