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991.
O. P. Charkin N. M. Klimenko T. P. Nguyen D. O. Charkin Y. -S. Wang H. -C. Chang S. H. Lin 《Russian Journal of Inorganic Chemistry》2006,51(10):1613-1622
The electronic and geometric structures, energy stability, normal mode frequencies, and spin density distribution have been calculated by the density functional theory B3LYP method with the Gen = 6-31+G*(Fe) + 6-31G(C,H,N,O), 6-31G*, and 6-311++G** basis sets for the deep fragmentation products of the free hemin ion with successive removal of methyl and vinyl groups in the electronic states with different multiplicities. The computation results are compared with the available experimental data and previous computation results for the fragmentation products of the isolated heme molecule and hemin ion with removal of carboxymethyl groups. The trends in the behavior of these properties are analyzed as a function of multiplicity, external charge, and the number of peripheral substituents at the porphyrin core. 相似文献
992.
Guoyi Bai Chenfang Zhang Yuecheng Zhang Haijun Yu Fei He Huisen Ning Ligong Chen 《Reaction Kinetics and Catalysis Letters》2007,90(2):373-380
The racemization of R-(-)-2-amino-1-butanol in a reaction using Co/γ-Al2O3 catalysts and catalysts modified by Mg or Ca was investigated in this paper. Complete racemization was achieved with a yield
of over 83% at using the Mg modified Co/γ-Al2O3 catalyst under optimized reaction conditions of 170°C and 2.5 MPa of H2. The catalysts were thoroughly characterized by XRD, XPS, TPR, SEM and TEM. The addition of Mg and Ca may be advantageous
for dispersing and stabilizing the active species of the Co/γ-Al2O3 catalyst, protecting from sintering, significantly improving its catalytic activity and stability. 相似文献
993.
Methylmaleic (citraconic, CTA) acid and methylfumaric (measaconic, MSA) acid in aqueous sulfuric acid solution undergo bromine-catalyzed reversible cis-trans isomerization in the presence of ceric and bromide ions. The positional isomerization of CTA or MSA to itaconic acid (ITA) is not observed. The method of high performance liquid chromatography (HPLC) was applied to study the kinetics of this catalyzed isomerization. The major catalytic species is best expressed as the Br?2 · radical anion. Under suitable catalytic conditions, there is a tendency for the [MSA]/[CTA] ratio to reach an equilibrium value of 4.10 at 25° for the CTA+Br?2 · ? MSA+Br?2 · reaction. Chloromaleic (CMA) and chlorofumaric (CFA) acids undergo similar isomerization with an equilibrium [CFA]/[CMA] ratio of 10.3 at 25°. The isomerization of maleic acid (MA) to fumaric acid (FA) is essentially irreversible with 50 as the lower limit of the equilibrium [FA]/[MA] ratio. The substituent has an important effect on the reversibility of this catalyzed isomerization of butenedicarboxylic acids. The thermodynamic parameters ΔH° and ΔS° at 25° for the CTA+Br?2 · ? MSA+Br?2 · reaction were found to be ?5.1±0.7 kj/mol and ?6.0±3.3 J/mol K, respectively. The present method gives a plausible way to measure the differences in enthalpy and entropy between the trans- and cis-isomers of butenedicarboxylic acids (CRCO2H=CR'CO2H) in aqueous solution. 相似文献
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