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131.
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133.
Ab initio valence bond method is employed to quantitatively study the concepts of ionic resonance energy and ionicity of a chemical bond in the cases of hydrides XH(X=Li,Be,B,C,N,O,F) and fluorides XF(X=Li,Be,B),By establishing the relationship between resonance and stability,and comparing the calculated ionicities with Pauling‘s earlier estimations in the above diatomic molecules,the merits of Pauling‘s classical resonance theory were demonstrated at the ab initio level. 相似文献
134.
Densities have been measured for the electrolyte (NaCl, NaBr and NaI)‐monosaccharide (D ‐mannose and D‐ribose)‐water solutions at 298.15 K. These data have been used to calculate the apparent molar volumes of the saccharides (VΦ,S) and electrolytes (VΦ,E) in the studied solutions. Infinite dilution apparent molar volumes, VΦ,S0 and VΦ,E0, have been evaluated, together with the standard transfer volumes of the saccharides (ΔtVS0) from water to aqueous electrolyte solutions and those of the electrolytes (ΔtVE0) from water to aqueous saccharide solutions. It was shown that both the ΔtVS0 and ΔtVE0 values are positive and increase with increasing molalities of sodium halides and saccharides, respectively. Overall, the ΔtVS0 and ΔtVE0 values have the order of NaCl > NaBr > NaI except for NaI‐ribose and NaI‐ribose. Volumetric interaction parameters for the electrolyte‐monosaccharide pairs in water were obtained and interpreted by the stereochemistry of the monosaccharide molecules and the structural interaction model. 相似文献
135.
中药一枝黄花、黄连、天麻、蛇床子中8种微量元素的测定 总被引:13,自引:2,他引:13
采用原子吸收光谱仪对一枝黄花、黄连、天麻、蛇床子中Fe、Ca、Mg、Mn、Cr、Cu、Zn、Pb八种无机元素的含量进行了测定,为进一步研究其药理和用途提供基础。 相似文献
136.
137.
丙氨酰-谷氨酰胺的简便有效合成 总被引:2,自引:0,他引:2
谷氨酰胺 (Gln)是肠道必需氨基酸 ,是肠粘膜细胞氧化的重要燃料。肠粘膜缺乏Gln将严重损伤肠屏障功能 ,创伤性休克及化疗应激可加重损害 ,导致肠粘膜萎缩 ,肠道细菌移位 ,甚至促发脓毒症和多器官功能不全 (MODS) [1] 。但Gln性质不稳定 ,不能耐高温消毒 ,因此 ,一般氨基酸制剂不含Gln。Ala Gln为Gln代谢前体 ,溶解度高 ,性质较Gln稳定 ,能耐受热灭菌 ,在体内数分钟即分解出Gln ,能部分补偿肠道所需Gln ,减少严重创伤及腹腔注射化疗药物 5 氟尿嘧啶 (5 FU)引发的小肠粘膜形态功能改变 ,细菌移位 ,降低… 相似文献
138.
“软平板印刷”微结构制备技术为微米和亚微米器件的制备提供了一条新的途径 [1] ,已被电子学家和材料学家所应用 ,近年来进入了生物学领域[2 ] .本实验室将这一方法与生物分子电子学相结合 ,提出了用于 DNA芯片在片合成的分子印章法 [3,4 ] .分子印章法的实质是接触压印与组合化学相结合的固相界面反应 .聚二甲氧基硅氧烷 ( PDMS)是一种软印刷的优良材料 [5] ,但是由于其疏水性和较差的机械性能 ,必须对其进行改性才能用来制备 DNA分子印章 [6 ] . 聚氨酯作为一种功能材料 ,由于分子中交替的软、硬链段及其不同的热动力学性能而形成… 相似文献
139.
The cis and trans isomers of [Cd(dmbpy)2](NO3)2] (dmbpy = 4,4′-dimethyl-2,2′-bipyridine) have been synthesized simultaneously via a one-pot reaction of Cd(NO3)2 · 4H2O with the dmbpy ligand in a MeOH/H2O mixture; they can be obtained individually by means of the mechanical separation due to their different growing habit of
the single-crystals. Different π-stacking interactions are observed in the cis and trans isomers forming different one-dimensional networks. The outcome of the DFT calculations agrees well with the experimental
results. 相似文献
140.
This paper develops a quantitative k-nearest neighbors modeling technique. The technique is used to demonstrate that a compound's biological binding activity to a receptor can be calculated from the minimum of the square root of the sum of squared deviations (SSSD) of a structurally assigned chemical shift on a template between the unknown compound to be predicted and a set of known compounds with known activities. When building models of biological activity, nonlinear relationships are built into the input training data. If a model is developed by selecting only compounds with minimum structurally assigned chemical shift deviations from the unknown compound, some of the nonlinear relationships can be removed. The smaller the total chemical shift deviation between a compound with known activity and another compound with unknown activity, the more likely it will have similar biological, chemical, and physical properties. This means that a model can be produced without rigorous statistics or neural networks. This technique is similar to structure-activity relationship (SAR) modeling, but instead of relying on substructure fragments to produce a model, this new model is based on minimum chemical shift differences on those substructure fragments. We refer to this method as minimum deviation of structurally assigned spectra analysis (MiDSASA) modeling. Modeling by the minimum deviation concept can be applied to other chemoinformatic data analyses such as metabolite concentrations in metabolic pathways for metabolomics research. A MiDSASA template model for 30 steroids binding the corticosterone binding globulin based on the activity factors of the two nearest compounds had a correlation of 0.88. A MiDSASA template model for 50 steroids binding the aromatse enzyme based on the average activity of the four nearest compounds had a correlation of 0.71. 相似文献