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91.
利用Bridgman-Stockbarger方法在氩气气氛下生长出KZnF3:Eu^3+单晶,测定了晶体的激发光谱、荧光发射光谱和ESR谱,讨论了Eu离子的取代格位。 相似文献
92.
Conformational statistics of polymer chain terminally attached to wall (Ⅲ)——NRW model loop chain 总被引:1,自引:0,他引:1
When the two end groups of a linear polymer chain are absorbed on a solid surface,the polymer chain forms the "loop" conformation.Investigation has been made on the conformational statistics of a model loop chain by the normal landom walk (NRW) on a lattice confined in the half-infinite space.Based on the conformational distribution function of the NRW model tail chain,it is easy to deduce an analytical formula expressing the conforma-tional number of the model loop chain.It was found that the ratio of the conformational number of the model loop chain to that of the free chain varies with the power function N-2/3 when the chain length N→∞ The same result was obtained by means of the recursion equation.The ratio of the mean square end-to-end distance h2 for the model loop chain to its mean square bond length I2 is 2N/3 Compared with the free chain with the same length N,the mean square end-to-end distance of the model loop chain contracts to a certain extent.The basic relationships deduced were support 相似文献
93.
The ring opening of the oxadiaziridine by cleavage of the N-N bond has been theoretically investigated by SCF calculations improved with limited CI. The possible competition of this reaction with the better known ones (N-O bond cleavage, inversion of the N atom) is discussed. The chemical implications of the formation of a new type of 1,3-dipole are examined. 相似文献
94.
95.
Lämmerhofer M 《Journal of chromatography. A》2005,1068(1):3-30
Enantiomer separations by CE employing nonaqueous conditions are reviewed. The general focus of this article is directed towards solvent effects on chiral recognition and the separation mechanism. After a general discussion of solvent effects on the individual processes involved in CE enantiomer separation, specifics for various selector classes are discussed together with a few applications of enantioselective nonaqueous CE. 相似文献
96.
利用羧基取代法, 通过化合物Pt4(OCOCH3)8与过量的丙烯酸作用合成了配合物Pt4(OCOCH3)4(OCOCH=CH2)4. 晶体结构研究结果表明, 化合物Pt4(OCOCH3)8中的4个乙羧基能够被烯丙羧基有规律地选择性替换, 从而形成一个含双键的对称铂配合物. 利用Si—H与不饱和键的加成性质将该配合物嫁接到氢化n型单晶硅(111)表面, 发现配合物Pt4(OCOCH3)4(OCOCH=CH2)4除了能嫁接到单晶硅表面外, 还能在n型单晶硅表面进行自组装而形成许多岛状纳米粒子, 这种组装体系具有良好的热稳定性和一定的抗酸性. 相似文献
97.
A sequential injection system based on the ABTS (2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulphonic-acid) methodology was developed. The proposed method, incorporating a mixing chamber in the side port of the selection valve, was evaluated to measure the total antioxidant activity of several beverages and foods.The ABTS+ is generated by oxidation of ABTS with potassium persulfate and is reduced in presence of hydrogen-donating antioxidants converting into a colourless product. The applicability of the developed method was tested by measurement of the antioxidant activity of pure compounds as well as by analysing complex food and beverage samples. The antioxidant activity was presented as l(+) ascorbic acid equivalence. The values obtained by this methodology were not significantly different from the results obtained by the original spectrophotometric ABTS assay. For most of the studied antioxidants, antioxidant activity varied with pH and dilution. The proposed SIA system is suitable for screening direct or diluted total antioxidant activity of pure compounds or food samples. 相似文献
98.
The force fields, in-plane vibrations, and relative intensities of Raman spectra have been calculated and analyzed for the N1H and N3H tautomers of imidazole, imidazolium cation, and their model structures. The results obtained for the isolated state of imidazole correspond to the intramolecular mechanism of proton transfer. 相似文献
99.
With regard to the ideal network it is shown that the concept ofN non-interacting polymer chains can be transformed in a problem of non interacting excitations (called conformons) for rubber elasticity. Modelling the interaction on permanent crosslinks as a scattering problem and taking the finite chain length into account, an interpretation of the second Mooney coefficient can be given. There is some evidence that the junctions move by constrained self diffusion.Dedicated to Prof. Dr. W. Ruland on the occasion of his 60th birthday. 相似文献
100.
Ian Dance Prof. 《化学:亚洲杂志》2007,2(8):936-946
How does the enzyme nitrogenase reduce the inert molecule N2 to NH3 under ambient conditions that are so different from the energy‐expensive conditions of the best industrial practices? This review focuses on recent theoretical investigations of the catalytic site, the iron–molybdenum cofactor FeMo‐co, and the way in which it is hydrogenated by protons and electrons and then binds N2. Density functional calculations provide reaction profiles and activation energies for possible mechanistic steps. This establishes a conceptual framework and the principles for the coordination chemistry of FeMo‐co that are essential to the chemical mechanism of catalysis. The model advanced herein explains relevant experimental data. 相似文献