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Theoretical insights into the mechanism of acetylcholinesterase-catalyzed acylation of acetylcholine
Acylation of acetylcholine (ACh) catalyzed by acetylcholinesterase (AChE) has been studied using high-level theoretical calculations on a model system that mimics the reaction center of the enzyme, and compared with uncatalyzed acylation reaction. The geometries of all the intermediates and transition states, activation energies, and solvent effects have been calculated. The calculations predict simultaneous formation of two short-strong hydrogen bonds (SSHB) in the rate-determining transition state structures [the first SSHB involves the hydrogen atom of Ser-200 (H(s)) and another involves the hydrogen atom of His-440 (H(h))]. In the intermediate states, the H-bond corresponding to H(h) involves SSHB, whereas the one corresponding to H(s) does not. 相似文献
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Several potentially experimentally accessible lithiated heterocyclic and heteroatom compounds with planar tetracoordinate carbons (ptC) have been predicted computationally. These utilize the strong electron-donating ability and the bridging proclivity of lithium to achieve the ptC preferences. As the p orbitals on the central carbons are only partially occupied, their electronic structures are similar to those of the related carbenes, e.g. imidazole-2-ylidene, rather than to the other ptC compounds such as dilithiocyclopropane. 相似文献
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Manojkumar TK Suh SB Oh KS Cho SJ Cui C Zhang X Kim KS 《The Journal of organic chemistry》2005,70(7):2651-2659
[reaction: see text] We present an ab initio study of the acid-promoted hydrolysis reaction mechanism of N-formylaziridine in comparison with formamide. Since the rate of amide hydrolysis reactions depends on the formation of the tetrahedral intermediate, we focused our attention mainly on the reactant complex, the tetrahedral intermediate, and the transition state connecting these two stationary points. Geometries were optimized using the density functional theory, and the energetics were refined using ab initio theory including electron correlation. Solvent effects were investigated by using polarizable continuum method calculations. The proton-transfer reaction between the O-protonated and N-protonated amides was investigated. In acidic media, despite that the N-protonated species is more stable than the O-protonated one, it is predicted that both N-protonated and O-protonated pathways compete in the hydrolysis reaction of N-formylaziridine. 相似文献
4.
C. Yohannan Panicker Hema Tresa Varghese K. Madhusoodanan Pillai Y. Sheena Mary K. Raju T.K. Manojkumar Anna Bielenica Christian Van Alsenoy 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2010,75(5):1559-1565
Fourier-transform-Raman and infrared spectrum of 4-azatricyclo [5.2.2.02,6] undecane-3,5,8-trione were recorded and analyzed. The vibrational wavenumbers were examined theoretically using the Gaussian03 set of quantum chemistry codes, and the normal modes were assigned by potential energy distribution (PED) calculations. The first hyperpolarizability, predicted infrared intensities and Raman activities are reported. The calculated first hyperpolarizability is comparable with reported values of similar structures which makes this compound an attractive object for future studies of nonlinear optics. Optimized geometrical parameters of the compound are in agreement with similar reported structures. The red shift of the NH stretching wavenumber in the infrared spectrum from the computational wavenumber indicates the weakening of NH bond. 相似文献
5.
Avinash Bhardwaj David Richter Manojkumar Chellamuthu Jonathan P. Rothstein 《Rheologica Acta》2007,46(6):861-875
The effect of initial microstructural deformation, alignment, and morphology on the response of wormlike micelle solutions
in transient uniaxial extensional flows is investigated using a pre-shear device attached to a filament stretching rheometer.
In filament stretching experiments, increasing the strength and the duration of the pre-shear just before stretch is found
to delay the onset of strain hardening. In these experiments, the wormlike micelle solution filaments fail through a rupture
near the axial midplane. The value of the elastic tensile stress at rupture is found to decrease with increasing pre-shear
rate and duration. The most dramatic effects are observed at shear rates for which shear banding has been independently observed.
The reduction in the strain hardening suggests that pre-shear before filament stretching might break down the wormlike micelles
reducing their size before stretch. Strain hardening is also observed in capillary breakup rheometry experiments; however,
the pre-sheared wormlike micelle solutions strain harden faster, achieve larger steady-state extensional viscosities and an
increase in the extensional relaxation time with increasing shear rate and duration. The difference between the response of
the wormlike micelles in filament stretching and capillary breakup experiments demonstrates the sensitivity of these self-assembling
micelle networks to pre-conditioning. 相似文献
6.
An exploration of imidazolylpropargyl amides as linchpin synthons for the construction of a diverse array of heterocyclic frameworks, many of which are related to those found in the oroidin derived alkaloids, is described. One such intermediate has been used in a formal total synthesis of cyclooroidin. 相似文献
7.
A simple protocol for the efficient synthesis of 3(2H)-furanones by cycloisomerization of allenic hydroxyketones is described. This transformation is achieved in water and in the absence of any expensive metal catalysts. 相似文献
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M. J. Kamat R. Kaimal T. R. Saranathan 《Fresenius' Journal of Analytical Chemistry》1981,307(1):19-20
Summary A d. c. arc Spectrographic method employing the carrier distillation technique has been developed for the determination of the non-rare earth impurities Bi, Cu, Fe, Mg, Mn, Ni, Pb and Sn in Dy2O3 in the range of 1–100 ppm. The sample is ground with 5% AgCl containing 1000 ppm of Ge as internal standard. The average precision of the method in terms of the coefficient of variation of the concentration is 12–15% for the different impurities.
Bestimmung von Verunreinigungen (außer Seltenen Erden) in gereinigtem Dysprosiumoxid — Ein spektrographisches Verfahren mit Hilfe der Trägerdestillation
Zusammenfassung Die Verunreinigungen Bi, Cu, Fe, Mg, Mn, Ni, Pb und Sn werden im Bereich von 1 bis 100 ppm mit Hilfe der Gleichstrombogenanregung bestimmt. Die Dy2O3-Probe wird mit 5 % eines Trägergemisches vermahlen, das aus AgCl mit 1000 ppm Ge (als innerem Standard) besteht. Die durchschnittliche Genauigkeit der Bestimmungen liegt bei 12–15%.相似文献