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21.
The dissociation of water adsorbed on the surface of NiO was investigated by using the semi-empirical SCF MO method MSINDO.
Simulations were based on embedded cluster models representing the (100) surface, with and without a monatomic step. The angle
formed between the metal adsorption site and the O–H bond associated with water has been found to be critical to the energetics
of the dissociation process. Based on this criterion, it was shown that water dissociation is favorable on the stepped surface,
but highly unlikely on the planar surface. In addition, the activation energy required for water dissociation in a monatomic
NiO step was considerably lower than for dissociation at the planar surface. The high activation energy associated with water
dissociation on the planar surface is attributed to the rigidity of the NiO lattice.
Dedicated to Prof. K. Jug in honor of his 65th birthday 相似文献
22.
William T. Simpson 《Theoretical chemistry accounts》1972,23(4):295-308
For a particular model with two electronic states, each with two vibrations, the dipole correlation function governing electronic absorption is e ?iωOt cosγt with spectrum ω 0±γ. The function starts as e ?iωOt (γ?ω 0), with Fourier transform peaking around ω 0 instead of ω 0±γ, and this is associated with vertical excitation. After a time t~2/γ the spectrum goes over into the normal one. As a generalization, a procedure is outlined for characterizing the state reached first after interaction with light is initiated. Finally it is suggested that one can understand aspects of internal conversion by analogy with the case of vertical excitation. 相似文献
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25.
Cooper SM Laosripaiboon W Rahman AS Hothersall J El-Sayed AK Winfield C Crosby J Cox RJ Simpson TJ Thomas CM 《Chemistry & biology》2005,12(7):825-833
Mupirocin, a polyketide-derived antibiotic from Pseudomonas fluorescens NCIMB10586, is a mixture of pseudomonic acids (PA) that target isoleucyl-tRNA synthase. The mup gene cluster encodes both type I polyketide synthases and monofunctional enzymes that should play a role during the conversion of the product of the polyketide synthase into the active antibiotic (tailoring). By in-frame deletion analysis of selected tailoring open-reading frames we show that mupQ, mupS, mupT, and mupW are essential for mupirocin production, whereas mupO, mupU, mupV, and macpE are essential for production of PA-A but not PA-B. Therefore, PA-B is not simply produced by hydroxylation of PA-A but is either a precursor of PA-A or a shunt product. In the mupW mutant, a new metabolite lacking the tetrahydropyran ring is produced, implicating mupW in oxidation of the 16-methyl group. 相似文献
26.
用自制的带甲基侧基的环氧树脂(TMBP)作为界面增容剂, 从拉伸性能、键合胶含量、动态性能、扫描电镜和流变性能等方面, 研究了TMBP对炭黑在丁苯橡胶中分散度的影响, 并与市售通用双酚A型环氧树脂(E-51)和橡胶工业常用软化剂邻苯二甲酸二辛酯(DOP)进行了比较. 结果表明, 带甲基侧基的环氧树脂TMBP在提高炭黑分散性方面的效果远比E-51好, 其作用模式具有典型的增容特性. 相似文献
27.
Very recently, we[1] found that L-proline amides and dipeptides acted as efficient catalysts for the asymmetric direct aldol reaction. We report here that L-proline-based peptides 1~5 can catalyze the aldol reactions of hydroxyacetone with aldehydes 6 in aqueous media, to give 1,4-diols (7), the disfavored products with either aldolase or L-proline. Both peptides 3 and 4 give good results. 相似文献
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Eggshell-like carbon materials with high yields have been synthesized by a solvothermal route in a stainless steel autoclave using metallic zinc and absolute ethanol as starting materials. The products were characterized by X-ray powder diffractometry (XRD), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy and scanning electron microscopy (SEM). The eggshell-like carbon spheres had diameters ranging from 500 nm to 1 μm. The optimal reaction conditions to obtain eggshell-like carbon materials were 600 ℃ and 12 h. 相似文献
30.
Eric A. Gregory Mark R. Buckingham Dawn Z. Clayton Freda J. Wolfenden C.J.S.M. Simpson 《Chemical physics letters》1984,104(4):393-397
Rate constants for the vibrational deactivation of CD4 by the collision partners CD4, He, Ne, Ar, Kr, D2 and O2 have been measured using a laser-fluorescence technique. The results are compared with those for the deactivation of CH4 by the same collision partners and with a modified SSH type theoretical treatment. 相似文献