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991.
992.
皂甙的三维定量构效关系研究 总被引:7,自引:0,他引:7
针对目标分子柔性大的特点,在比较分子场分析(CoMFA)方法中采用交叉验证相关系数平方R^2引导的构象选择法。对12个皂甙分子的生物活性进行了三维定量构效关系研究。探讨了几种探针对构效关系结果的影响,并选择了一种较合理的“复合”探针方案。应用该复合探针构建CoMFA模型,发现影响药效的立体场与静电场的贡献分别为40%和40%,其它能量项的贡献为20%。该模型交叉验证的相关系数平方R^2为0.653,非交叉验证的R^2为0.991,方差比F(4,7)值130.195(即置信度99%以上),活性预计的标准偏差与极差比(s/△γ)为4.2%,表明模型具有较好的预测能力。根据该模型,预计在指定位置添加位阻较大的基团活性值提高将会比较明显。 相似文献
993.
994.
A new fluorinated polystyrene bearing a p-sulbstiuted perfluoro[1-(2-fluorosulfonylethoxy)]ethyl group was synthesized via one-electron oxidation of polystyrene by perfluoro[2-(2-fluorosulfonylethoxy)]propionyl peroxide at different peroxide to polystyrene molar ratios.The yield of perfluoroalkylation decreases with the increase of the reactant molar ratio.The modified polymer has been characterized by various techniques:the ring pefluoro[1-(2-fluorosulfonylethoxy)]ethylation has been proved by FT-IR and ^19FNMR;the X-ray photoelectron spectra(XPS) show the maximum binding energy of F18,O18,C18(two kinds of carbon atoms,namely C-H and C-F)and S2p,respectively; desulfonylation of the fluorinated polystyrene appearing at 217℃ has been found by its thermogravimetric analysis (TGA).The determinations of contact angle,refractive index and glass transition temperature of the modified polymer have disclosed that when the contact angle increases with the increase of the molar ratio,the refractive index and glass transition temperature decrease.The polydispersity values indicate that the degradation of the polymer chains did not occur during the reaction. 相似文献
995.
Fe2O3/Al2O3催化氧化苯偶姻制备苯偶酰 总被引:13,自引:1,他引:13
考察了几种常用载体负载金属氧化物催化分子氧氧化苯偶姻制备苯偶酰的性能 ,发现氧化铁、三氧化二铝催化活性较高,稳定性较好。以吡啶为溶剂,用483K下 活化的含铁14.8%的氧化铁/三氧化二铝作催化剂,当其用量为苯偶姻用量20% (质量分数),253K下反应1h,苯偶酰平均产率98.1%。用IR,MS,和^1H NMR光 谱对其结构进行了表征。 相似文献
996.
Guo-dong Liang Jun-ting Xu Zhi-qiang Fan 《高分子科学》2006,(4):341-344
Thin film morphology of a symmetric semicrystalline oxyethylene/oxybutylene diblock copolymer (E76B38) on silicon was investigated by tapping mode atomic force microscopy (AFM). It is found that the nascent thin film is composed of multiple polymer layers having mixed thicknesses of L ≈ L0 and L ≈ L0/2 (L0 is the long period of the block copolymer in bulk) besides the first layer near the substrate. This shows that the crystalline domain in the block copolymer consists of double poly(oxyethylene) layers. Annealing leads to disappearance of the polymer layers with thickness L ≈L0/2, indicating that such polymer layers are metastable. 相似文献
997.
Assembly of [Ag(CN)2]^- units with M(Ⅱ)-diamine complex cations [Cu(LN-N)2]^2+, where LN-N represents L2-diaminopropane (pn) and ethylenediamine (en), afforded two complexes, [Cu(pn)2][Ag2(CN)4] (1) and [Cu(en)2][Ag3(CN)5] (2), which were characterized by elemental analysis, IR, UV-Vis and ESR spectra. Single crystal X-ray analyses show that these complexes have 2D and 3D architectures through silver-silver interactions and other weak interactions. The luminescence behaviors of the two complexes were also studied by means of emission spectra. 相似文献
998.
Synthesis and Structural Characterization of [Mn(sapn)(H2O)2]Br 总被引:1,自引:0,他引:1
1 INTRODUCTION Many of the recent advances in the coordination chemistry of manganese have been driven by the involvement of the manganese in several biological redox-active systems[1,2], of which the most important is the oxygen-evolving complex (EOC) of photosystem II (PS II) in green plants [3]. Since the preparations and structural characterizations of the complexes containing N,O-donor ligands have been studied extensively as simple active-site models for the photosystem II[4,5]… 相似文献
999.
1000.
Lophenol, cholest-4α-methyl-7-en-3β-ol (1), obtained from Dracaena cochinchinensis (Lour.) S. C. Chen, was structurally modified. It was acetylated to protect 3β-hydroxyl group, and then oxidised by selenium dioxide in acetic acid to give cholest-4a-methyl-8-en-3β, Ta-diol diacetate (3). This compound 3 is unstable in chloroform solution or when heated and easily converted to a diene compound, cholest-4a-methyl-7,14-dien-3β-ol acetate (4). The structures of 3 and 4 were elucidated by means of IR, ^1H NMR, ^13C NMR and MS, and the absolute configuration of 3 was established by X-ray crystallography. The property of 3 was also discussed in this paper. Both 3 and 4 are new compounds and were reported for the first time. 相似文献