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Radical Process (radical + process)
Selected AbstractsAddition of sec-Alcohols to Alkynes Through a Radical Process Using NHPI/Co(II)/O2 System.CHEMINFORM, Issue 8 2007Ryouhei Oka Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Simulation of Styrene Polymerization by Monomolecular and Bimolecular Nitroxide-Mediated Radical Processes over a Range of Reaction ConditionsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2007Juliana Belincanta-Ximenes Abstract Simulations of polymerization rate, molecular weight development and evolution of the concentrations of species participating in the reaction mechanism over a range of operating conditions, and a parameter sensitivity analysis showing the effects of temperature, activation/deactivation equilibrium constant and initial concentrations of controller and initiator (if present) on these variables are presented for the nitroxide-mediated radical polymerization of styrene. The simulations were performed with a computer program based on a detailed reaction mechanism. The simulated profiles of conversion, number average molecular weight (), and polydispersity agree well with experimental data. Previously unknown activation energies for reactions involved in the mechanism are estimated. The temperature dependence of the kinetic rate constants obtained in this study will be useful for future modeling and optimization studies. [source] Synthesis and Activity on Free Radical Processes and Inflammation of 9,10-Dihydro-5,8-dimethoxy-triptycene-quinones.CHEMINFORM, Issue 42 2003Nikoletta J. Xanthopoulou Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Stereocontrol in Radical Processes Through the Exocyclic Effect: Dual Role of Triethylboron as Radical Initiator and in situ Derivatization Agent.CHEMINFORM, Issue 34 2001Jean-Pierre Bouvier Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Radical copolymerization of vinylidene cyanide with 2,2,2-trifluoroethyl methacrylate: Structure and characterization,JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2010Mustapha Raihane Abstract A novel copolymer of vinylidene cyanide (VCN) and 2,2,2-trifluoroethyl methacrylate (MATRIF) was synthesized by bulk free radical process in a 52% yield from an equimolar comonomer feed. The copolymer's composition and microstructure were analyzed by FTIR, 1H- and 13C-NMR spectroscopy, SEC, and elemental analysis. The reactivity ratios calculated from both the Q-e Alfrey-Price parameters and the Jenkins' Patterns Scheme indicate a tendency to alternation in the copolymerization, the latter method suggesting that MATRIF homopropagation be slightly favoured (rV = r12 = 0.1, rM = r21 = 0.3). The molar incorporation of VCN in the copolymer was only 42 mol % according to the 9.0 wt % nitrogen content determined by elemental analysis, in good agreement with the value obtained by 1H-NMR. High-resolution 1H and 13C-NMR spectra were used to study the microstructure of the copolymer. As an example, the three well-resolved carbonyl resonances in the 13C-NMR spectrum were assigned to the MATRIF-centered triads VMV, VMM, and MMM, respectively, (V and M stand for VCN and MATRIF, respectively). The presence of VCN dyads (e.g., in VVM and VVV sequences) was shown to be marginal or absent altogether. Thermogravimetric analysis of poly(VCN- co -MATRIF) copolymer showed good thermal stability, and its main pyrolytic degradation taking place only above 368 °C. A 4% weight loss at about 222 °C suggested the presence of a few VCN homodyads, possibly inducing thermal depolymerization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 [source] Free-radical copolymerization of 2,2,2-trifluoroethyl methacrylate and 2,2,2-trichloroethyl ,-fluoroacrylate: Synthesis, kinetics of copolymerization, and characterizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2010Jean-Marc Cracowski Abstract Copolymers based on 2,2,2-trifluoroethyl methacrylate (MATRIFE) and 2,2,2-trichlororoethyl ,-fluoroacrylate (FATRICE) were synthesized in good yields by radical process initiated by tert -butyl 2,2-dimethylperoxypropanoate. Molar composition of the obtained poly(MATRIFE- co -FATRICE) copolymers were assessed by means of 1H and 19F nuclear magnetic resonance spectroscopy and by elemental analysis. The reactivity ratios, ri, of both comonomers were determined from the Kelen-Tüdos and Finneman-Ross methods (rMATRIFE = 1.52 ± 0.03 and rFATRICE = 0.61 ± 0.03 at 74 °C) showing unexpectedly that MATRIFE is the more reactive monomer in copolymerization. Molecular weights and polydispersity indexes of poly(MATRIFE- co -FATRICE) copolymers were ranging between 1.47 and 2.68 × 104 g·mol,1 and from 1.44 to 2.21, respectively. Thermal properties of the resulting polymers were examined and thermogravimetric analyses showed a satisfactory thermal stability, a thermal decomposition occurring from 220 to 295 °C as the molar ratio of FATRICE increased in the copolymer. Moreover, the glass transition temperatures of copolymers varied from 66 to 108 °C and also increased with FATRICE molar ratio in the copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2154,2161, 2010 [source] Cyclometalated 2-phenylpyridine complex [RuII(o -C6H4 -py)(MeCN)4]PF6 as a tunable catalyst for living radical polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2008F. Diaz Camacho Abstract The cyclometalated complex [RuII(o -C6H4 -py)(MeCN)4]PF6 (1) with a ,-RuC bond and four substitutionally labile acetonitrile ligands mediates radical polymerization of different vinyl monomers, viz. n -butyl acrylate, methyl methacrylate, and styrene, initiated by three alkyl bromides: ethyl 2-bromoisobutyrate, methyl 2-bromopropionate, and 1-phenylethyl bromide. The polymerization requires the presence of Al(OiPr)3 and occurs uncontrollably as a conventional radical process. The variation of the molar ratio of the components of the reaction mixture, such as initiator, Al(OiPr)3 and catalyst, affected the polymerization rates and the molecular weights but did not improve the control. A certain level of control has been achieved by adding 0.5 eq of SnCl2 as a reducing agent. Tin(II) chloride decreased the rate of polymerization and simultaneously the molecular weights became conversion-dependent and the polydispersities were also narrowed. Remarkably, the level of control was radically improved in the presence of excess of the poorly soluble catalyst (1), when the added amount of (1) was not soluble any more, i.e., under heterogeneous conditions, the system became adjustable and the living polymerization of all three monomers was finally achieved. Possible mechanisms of the (1)-catalyzed polymerization are discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4193,4204, 2008 [source] The Effect of Persistent TEMPO Radicals on the Gilch PolymerizationMACROMOLECULAR RAPID COMMUNICATIONS, Issue 1 2007Jens Wiesecke Abstract The mechanism of the Gilch polymerization leading to poly(p -phenylene vinylenes) is still a matter of controversial discussion. Similar to some other research groups, we strongly favor a basically radical process. Moreover, we believe it is initiated by spontaneously formed diradicals. Here, we describe further experimental evidence which clearly supports the assumed initiation step: it is shown how the polymerization process is affected quantitatively when different amounts of 2,2,6,6-tetramethylpiperidine- N -oxyl (TEMPO) are added as a scavenger. In full agreement with our expectations, the chain growth is either retarded or completely prevented, depending on the respective molar ratio of monomer and scavenger. [source] Biological significance and development of practical synthesis of biotinMEDICINAL RESEARCH REVIEWS, Issue 4 2006Masahiko Seki Abstract Biotin (1), a water-soluble B series vitamin, distributes widely in microorganisms, plants, and animals. Biosynthesis of 1 involves five steps sequence starting from pimelic acid. The last step, a transformation from dethiobiotin (DTB) to 1, includes an iron clusters-mediated radical process. The compound 1 is a cofactor of carboxylation enzymes and plays crucial roles in the metabolism of fatty acids, sugars, and ,-amino acids. In addition to the increasing application to feed additives, recent reports have revealed that 1 enhances insulin secretion in animals, suggesting it for a promising therapeutic candidate for an anti-diabetes drug. The remarkably strong affinity of 1 with avidin and streptavidin has been extensively applied for such technologies as photoaffinity labeling. Among the number of approaches to 1 so far developed in 50 years, a synthesis using L -cysteine and thiolactone as a starting material and a key intermediate, respectively, represents one of the best routes leading to 1, because of short steps, high yield, use of inexpensive reagents, and ease of operation. © 2006 Wiley Periodicals, Inc. Med Res Rev, 26, No. 4, 434,482, 2006 [source] Theoretical Exploration of the Oxidative Properties of a [(trenMe1)CuO2]+ Adduct Relevant to Copper Monooxygenase Enzymes: Insights into Competitive Dehydrogenation versus Hydroxylation Reaction PathwaysCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2008Aurélien de, Lande Dr. Abstract Singlet and triplet H-transfer reaction paths from CH and NH bonds were examined by means of DFT and spin-flip TD-DFT computations on the [(trenMe1)CuO2]+ adduct. The singlet energy surfaces allow its evolution towards H2O2 and an imine species. Whereas NH cleavage appears to be a radical process, CH rupture results in a carbocation intermediate stabilized by an adjacent N atom and an electrostatic interaction with the [CuIOOH] metal core. Upon injection of an additional electron, the latter species straightforwardly forms a hydroxylated product. Based on these computational results, a new mechanistic description of the reactivity of copper monooxygenases is proposed. [source] Multiple Mechanisms Of Early Hyperglycaemic Injury Of The Rat Intestinal MicrocirculationCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 1-2 2002H Glenn Bohlen SUMMARY 1. Hyperglycaemia in the vast majority of humans with diabetes mellitus is the end result of profound insulin resistance secondary to obesity. For patients in treatment, hyperglycaemia is usually not sustained but, rather, occurs intermittently. In in vivo studies of the rat intestinal microcirculation, endothelial impairment occurs within 30 min at D -glucose concentrations , 300 mg/dL. Endothelial-dependent dilation to acetylcholine and constriction to noradrenaline is impaired. Vasodilation to exogenous nitric oxide (NO) remains normal. 2. When initiated before hyperglycaemia, suppression of oxygen radicals by both scavenging and pretreatment with cyclo-oxygenase blockade to prevent oxygen radical formation minimized endothelial impairments during hyperglycaemia. Neither treatment was effective in restoring endothelial function once it was damaged by hyperglycaemia. 3. A mechanism that may initiate the arachidonic acid, oxygen radical process is activation of specific isoforms of protein kinase C (PKC). De novo formation of diacylglycerol during hyperglycaemia activates PKC. Blockade of the ,II PKC isoform with LY-333531 prior to hyperglycaemia protected NO formation within the arteriolar wall, as judged with NO-sensitive microelectrodes. Furthermore, once suppression of endothelial dilation was present in untreated animals, PKC blockade could substantially restore endothelial-dependent dilation. 4. These results indicate that acute hyperglycaemia is far from benign and, in the rat, causes rapid endothelial impairment. Both oxygen radical scavenging and cyclo-oxygenase blockade prior to bouts of hyperglycaemia minimize endothelial impairment with limited side effects. Blockade of specific PKC isozymes protects endothelial function both as a pre- or post-treatment during moderately severe hyperglycaemia. [source] Stereoelectronic effects in radical processes,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8-9 2006Paolo Brandi Abstract A kinetic study of the H-abstraction reaction from cyclic and acyclic alkylarene substrates by the nitroxyl radical (dubbed BTNO) of 1-hydroxy-benzotriazole (HBT) has been carried out in MeCN solution at 25°C. BTNO was generated from one-electron oxidation of HBT by cerium(IV) ammonium nitrate. The H-abstraction reactivity measured with the cyclic alkylarenes is invariably higher than that with the acyclic counterparts. This is explained as the contribution of hyperconjugation between the aromatic ,-system and the scissile benzylic CH bond of the substrate, which weakens the CH bond in the transition state and promotes its cleavage. Stereoelectronic considerations enable to appreciate why the weakening effect is more pronounced in the cyclic system than in the acyclic counterpart, thereby justifying the higher reactivity of the former. Evidence for the intervention of stereoelectronic effects is embodied by the dissociation energies of the CH bonds, having always lower values for the cyclic substrates investigated. Copyright © 2006 John Wiley & Sons, Ltd. [source] | |||||||||||||