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101.
Jian‐Hua Zhao Hsuan‐Liang Liu Hsin‐Yi Lin Chih‐Hung Huang Hsu‐Wei Fang Shau‐Wei Tsai 《中国化学会会志》2007,54(4):835-842
In this study, we present the results from the semiempirical molecular orbital calculations for the acylation step in the lipase‐catalyzed ester hydrolysis. The results reveal that the lowest energy path for the formation of the tetrahedral intermediate is for the serine residue of the catalytic triad to attack the substrate, followed by coupling heavy atom movement and proton transfer. The calculations of four active site models show that the cooperation of the aspartate group and the oxyanion hole is capable of lowering the activation energy by about 16 kcalmol?1. Our results further suggest that the lipase‐catalyzed ester hydrolysis adopts the single proton transfer mechanism. 相似文献
102.
103.
The electrophoretic behavior of concentrated monodispersed, positively charged mercury drops is investigated theoretically. The present study extends previous analyses by considering arbitrary surface potentials, double-layer polarization, and the interaction between adjacent double layers. The coupled equations describing the spatial variations in the flow field, the electric field, and the concentration field are solved by a pseudo-spectral method. For a low surface potential phi(r), the mobility increases monotonically with kappaalpha; kappa and alpha are respectively the reciprocal Debye length and the radius of a mercury drop. For medium and high phi(r), the mobility curve has a reflection point, which arises from the interaction of adjacent double layers, for kappaalpha. Also, if phi(r) is high, the mobility curve may exhibit a local minimum as kappaalpha varies. This phenomenon is pronounced if the concentration of the dispersed phase is high. If the double layer is thick, the mobility increases with phi(r), and the reverse is true if it is thin. We show that the higher the concentration of the dispersed phase the smaller the mobility, and as kappaalpha becomes large the mobility approaches a constant value, which is independent of the concentration of the dispersed phase. The mobility of mercury drops is larger than that of the corresponding rigid particles. 相似文献
104.
S. Hatta R. V. Kasowski W. Y. Hsu 《Applied Physics A: Materials Science & Processing》1992,55(6):508-513
The electronic band structures of CaCuO2 with various planar structures have been computed with the spin polarized, full potential pseudofunction method. The perfect tetragonal structure has metallic bands. If the CuO plane is puckered as proposed on the basis of pulsed neutron experiments, a semi-metallic-like behavior is found. When some of the oxygen atoms are moved from the basal plane into interplanar sites that are coplanar with Ca, an insulating ground state is obtained with antiferromagnetic moments of 0.21
B
. Around this interplanar oxygen defect site, the charge and magnetic moment distributions resemble those of a CuO chain structure with strong coupling to Cu atoms from different basal planes. Small displacements of defect oxygens at interplanar sites along the CaO planar directions produces large changes in band shape near E
F
, suggesting strong electron-lattice coupling. The coupling is much weaker for displacements of O atoms within the CuO basal plane. Such interplanar defects could occur in superconducting cuprates and thus create small insulating regions for the pinning of magnetic flux lines. 相似文献
105.
106.
107.
Duffy DJ Quenneville J Baumbaugh TM Kitchener SA McCormick RK Dormady CN Croce TA Navabi A Stidham HD Hsu SL Guirgis GA Deng S Durig JR 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(3):659-671
Ab initio calculations are reported for three of four possible conformers of 1,3-dichloropropane. The fourth conformer, with Cs symmetry, has a predicted enthalpy difference of more than 1500 cm(-1) from the most stable conformer from each calculation regardless of the basis set used, so there is little chance of observing it. Thus, there is no evidence in the infrared or Raman spectrum of the presence of a fourth conformer. The order of stability given by the ab initio calculations is C2(GG)>C1(AG)>C2v(AA)>Cs(GG'), where A indicates the anti form for one of the CH2Cl groups and G indicates the gauche conformation for the other CH2Cl group relative to the plane of the carbon atoms. Almost every band observed can be confidently assigned to one or another of the conformers. Many observed bands proved to be of a composite nature, with several nearly coincident vibrations of different conformers contributing to the band contour. Nonetheless, a complete assignment of fundamentals is possible for the most stable C2 conformer, and 5 of the fundamentals of the C2v conformer and 13 those of the C1 conformer can be confidently assigned. 相似文献
108.
109.
Chou HC Hsu CH Cheng YM Cheng CC Liu HW Pu SC Chou PT 《Journal of the American Chemical Society》2004,126(6):1650-1651
A molecular recognition concept exploiting multiple-hydrogen-bond fine-tuned excited-state proton-transfer (ESPT) was conveyed using 3,4,5,6-tetrahydrobis(pyrido[3,2-g]indolo)[2,3-a:3',2'-j]acridine (1a). The catalytic type 1a/carboxylic acids hydrogen-bonding (HB) complexes undergo ultrafast ESPT, resulting in an anomalously large Stokes shifted tautomer emission (lambdamax approximately 600 nm). Albeit forming a quadruple HB complex, ESPT is prohibited in the noncatalytic-type 1a/urea complexes (lambdamax approximately 430 nm). The HB configuration tuning ESPT properties lead to a feasible design for sensing multiple-HB-site analytes of biological interest. 相似文献