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Transfer Process. (transfer + process)
Selected AbstractsNMR Quantification of Tautomeric Populations in Biogenic Purine BasesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2009Bartl Abstract Purine bases such as purine, adenine, hypoxanthine, and mercaptopurine are known to exist in several tautomeric forms. Characterization of their tautomeric equilibria is important not only for predicting the regioselectivity of their N -alkylation reactions, but also for gaining knowledge of the patterns with which these compounds of significant biological activity form hydrogen bonds with their biological targets. The tautomeric equilibria of purine and some purine derivatives in methanol and N,N -dimethylformamide solutions were investigated by low-temperature 1H and 13C NMR spectroscopy. The N(7)H and N(9)H tautomeric forms were quantified by integrating the individual 1H NMR signals at low temperatures. The Gibbs free energy differences were calculated and the effects of substitution on the N(7)H/N(9)H ratio discussed. A previously published theoretically predicted mechanism of the tautomeric exchange is compared with our measurements in deuteriated solvents. The influence of concentration on the temperature of coalescence indicates that supramolecular clusters play a significant role in this proton transfer process. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Kinetic investigation on the oxidation of nitrite by oxochromium(V) ion in aqueous and micellar systemsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2004Mookandi Kanthimathi The kinetics of oxidation of nitrite by [O = CrV (5-chlorosalen)]+ complex has been studied spectrophotometrically at [CrV] = 0.5 × 10,3 M, [NO2,] = 0.01,0.1 M, [H+] = 0.0001,0.05 M, I = 0.15 M, and T = 25°C in the presence of cationic surfactant, cetyl pyridium chloride (CPC), and anionic surfactant, sodium dodecyl sulfate (SDS),in aqueous acidic medium. The oxygen atom transfer reaction from O = CrV to nitrite ion is influenced by the ionic nature of the micelle. The redox reaction is accelerated in presence of CPC and slowed down by 40 times in presence of SDS. The mechanism of the reaction involves an inner-sphere process involving the formation of an intermediate followed by oxo transfer process. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 79,86 2004 [source] A novel rate-accelerating additive for atom transfer radical polymerization of styreneJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2007Zhuang Jiaming Abstract The polymerization of styrene was mediated by copper (I) bromide/pentramethldiethyltriamine (PMDETA) using ethyl 2-bromopropionate (EBP) as initiator and a catalytic amount of malononitrile (MN) as a novel rate-accelerating additive. The optimal molar ratios of MN/EBP under which the polymerization of styrene can proceed fastest was 4:1. The rate-enhancement-efficiency had a dependence on temperature and the apparent rate constant of polymerization improved by a factor of 2.67 at 85 °C. Polymerization resulted in a conversion as high as 87% in 4.3 h in the presence of MN, while a conversion of 79.7% was gained even in 10 h without MN at 85 °C. The polymerizations of styrene in the presence of MN proceeded in a living fashion indicated by the first-order kinetic plots, with the increase of Mn with respect to conversion and the relatively narrow polydispersity. The possible rate enhancing mechanism is that the addition of MN weakens the coordination between the copper center and ligand and facilitates the atom transfer process. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4082,4090, 2007 [source] Comparative 1H NMR studies of saturation transfer in copolymer gels and mouse lensesNMR IN BIOMEDICINE, Issue 6 2010Koji Nakamura Abstract Saturation transfer in cross-linked copolymer gels and excised intact and perforating trauma-induced cataract mouse lenses (4- or 8-week-old) were studied using intermolecular cross-relaxation rates (1/TIS(H2O); 1/TIS), monitored with f2 -irradiation at ,8.79, ,4.00, and 7.13,ppm (,H2/2,,,,69,Hz). [1] The 1/TIS(7.13,ppm) vs dry weight [W (%)] profiles for hydrophilic copolymer gels were far steeper than those for hydrophobic copolymer gels, indicating the participation of an amount of bound water and a number of copolymer hydroxyl groups in the saturation transfer process. In contrast, the 1/TIS(,8.79,ppm) vs W (%) profiles exhibited little difference between the hydrophilic and hydrophobic copolymer gels, indicating the major participation of molecular rigidity, i.e. W (%) in the saturation transfer process. [2] The 1/TIS(7.13,ppm) values for cataractous mouse lenses were larger than those for intact lenses, indicating the formation of large, immobile lens protein associates or aggregates containing a sufficient amount of bound water for the saturation transfer. [3] The 1/TIS(7.13,ppm) vs W (%) profiles for the hydrophilic copolymer gels exhibited similar characteristics to the intact and cataractous mouse lenses with regard to the saturation transfer process. Copyright © 2010 John Wiley & Sons, Ltd. [source] | ||||||||||