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Xiaojun Guo,Chongpin Huang,Yingxia Li 한국화학공학회 2008 Korean Journal of Chemical Engineering Vol.25 No.4
Keggin-type heteropoly compounds (HPCs) H3.2−xCsxCu0.25As0.1PMo11VO40 (x, 0-2.5) were used as catalysts for coupling reaction of methylmethacrylate (MMA) from methacrolein (MAL) in this study. And the catalytic performance of the HPCs was investigated in the oxidation-esterification coupling reaction. Moreover, the HPCs were characterized by NH3-TPD, TG-pyridine-adsorption/desorption, N2-adsorption/desorption, ICP, TG-DSC, FT-IR, XRD and TPR. These reactive results have been correlated to the acidity, surface area and reducibility. With the increasing of Cs content, surface area of the HPCs increased, while the acidity and reducibility decreased. Difference of the quantity of acid sites originated from the hydration protons being substituted by Cs+. Effects of Cs+ content on the reducibility of the HPCs indicated that Cs+ changed the structural stability of V as coordinating atoms and the proportion of the different reducible states of Mo6+.
Shizhen Wang,Jing Wang,Xiaofen Zhou,Yingxia Guo,Baishan Fang 한국생물공학회 2013 Biotechnology and Bioprocess Engineering Vol.18 No.4
The substitution of the catalytic zinc ion of glycerol dehydrogenase (GDH) from Klebsiella pneumonia sp. by divalent metal ions, Mn2+ and Mg2+, enabled improvements of activity, substrate promiscuity and stability. The activity of Mn-GDH and Mg-GDH improved several folds in comparison to the native GDH. The activity of substituted GDH towards non-natural substrates, 4-chloroacetoacetate,3-chloroacetylpyridine, p-chloroacetophenone, and acetophenone was 30 folds higher than native GDH. Manganese substitution increased the half-life of GDH by 6 folds at 60and 70oC. The two-fraction first order inactivation models fitted the nonlinear thermal inactivation curves well. Combined with the kinetic and thermodynamic analysis,further mechanistic insights to the metal ion roles in thermostability enhancements were studied. The thermodynamic parameters of inactivation, enthalpy, entropy and the Gibbs free energy indicated that Mn-GDH was stabilized entropically and elucidated the mechanisms of enzyme inactivation.