共查询到20条相似文献,搜索用时 46 毫秒
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The structural stabilities and electronic structures of Ga atomic chains are studied by the first-principles plane wave pseudopotential method based on the density functional theory. The present calculations show that gallium can form planar chains in linear-, zigzag- and ladder-form one-dimensional structures. The most stable one among the studied structures is the zigzag chain with a unit cell rather close to equilateral triangles with four nearest neighbors, and all the other structures are metastable. The relative structural stability, the energy bands and the charge densities are discussed based on the ab initio calculations and the Jahn-Teller effect. 相似文献
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使用第一原理密度泛函理论中的离散变分方法(DFT-DVM)对(S2Mo18O62)4-的电子结构进行了理论计算,并与Keggin结构(SMo12O40)2-的电子结构作了比较分析,结果表明,(S2Mo18O62)中的电子离域地分布在整个阴离子骨架中,但极位和赤道位原子的电荷分布有明显差异。端氧与Mo之间的键均较强,中心氧与Mo之间形成的键最弱。(S2Mo18O62)4-的化学行为的活性中心是赤道位钼Moe、极位端氧Opt、极位共顶桥氧Opea、赤道位端氧Oet和赤道位共边桥氧Oeb。与(SMo12O40)2-相比,(S2Mo18O62)4-的稳定性和氧化性均较弱。但在两种类型的硫钼杂多阴离子中,Mo对其氧化性的产生起了重要的作用。 相似文献
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Polymeric surfactants are amongst the most widespread of all polymers. In nature, proteins and polysaccharidescause self organization as a result of this surfactancy; in industry, polymeric surfactants play key roles in the food, explosivesand surface coatings sectors. The generation of useful nano- and micro-structures in films and emulsions as a result ofpolymer amphiphilicity and the application of mechanical stress is discussed. The use of X-ray and neutron small anglescattering and reflectivity to measure these structures and their dynamic properties will be described. New results on linear and dendritic polymer surfactants are presented. 相似文献
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乙烯与甲基丙烯酸二甲氨基乙酯共聚物序列结构与结晶结构关系的研究*陈群罗会浚杨光(华东师范大学分析测试中心上海200062)徐端夫(中国科学院化学所北京100080)关键词乙烯共聚物,高分辨核磁共振,序列结构,最小可结晶序列长度乙烯与甲基丙烯酸二甲氨基... 相似文献
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H. Scheer E. Gross B. Nitsche E. Cmiel S. Schneider W. Schfer H.-M. Schiebel H.-R. Schulten 《Photochemistry and photobiology》1986,43(5):559-571
Abstract— The methanolic extract of the cyanobacterium (blue-green alga) Spirulina geitleri has been treated with methanolic acid to convert all chlorophyllous pigments to their methylpheophorbides. Fractionation of the latter from methylpheophorbide a by thin layer chromatography and high pressure liquid chromatography yielded methylpheophorbide-RCI. Its structure has been determined as 132S-hydroxy-20-chloro-methylpheophorbide a by 1H-nuclear magnetic resonance, absorption and circular dichroism spectroscopy, mass spectrometry and by partial synthesis from chlorophyll a. The pigment is isolated from Spirulina geitleri irrespective of the use or omission of chlorinated substances during the isolation procedure. 相似文献
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熔融反应加工是聚合物改性和制备聚合物纳米复合材料的重要途径之一.在此过程中,多数加成聚合物由于受到热、剪切或引发剂作用,通常可原位形成大分子自由基反应中间体.我们系统地研究了如何利用这类大分子自由基调控聚合物分子链的拓扑结构和聚合物纳米复合体系的相结构与界面.然而,某些聚合物大分子自由基,如聚丙烯(PP),受其分子链化学结构决定,在熔融反应条件下非常易于发生降解.研究发现,将可控自由基聚合中调控自由基反应活性的方法应用在熔融反应过程中可以显著抑制PP的降解,促进主反应的发生,在制备长链支化聚合物、调控聚合物纳米复合材料的相结构方面发挥了重要作用.本文介绍了本研究组近几年来通过熔体自由基反应调控PP体系的链结构和相结构的相关研究工作,如实现PP的长链支化,制备高熔体强度PP;在制备PP/C60 、PP/碳纳米管(CNTs)纳米复合材料过程中,利用熔体界面区域所发生的自由基反应,提高了纳米粒子与PP的界面相互作用,改善了纳米粒子在PP中的分散状态等. 相似文献
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Plasma-polymerization of octafluorocyclobutane was carried out in a capacitively coupled tubu-lar reactor with external electrodes. The number-average molecular weight, melting temperature,decomposition temperature and solubility in te trafluorodibromoethane of the products was mea-sured and the polymer structure was characterized by ESR. IR and ~(1)9F-NMR methods. The experi-mental results show the absence of the highly crosslinked structure but a fluorine-deficient structurecaused by free-radicals, carbonyl groups. double bonds and multicage-like segments in the polymer. 相似文献
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《结构化学》1985,(2)
<正> Neo-dihydrokoumine(3) was obtained by reduction of BHa-NfCzHs) and hydrakouminol(2) which was yield from koumine(l) via acid-induced rearrangement hydration.The crystal is orthorhombic, space group P2i2i2i, with unit cell parameters a = 12.671(4), b = 13.634(5), c = 9.653(3) A, Z=4. The intensities of 1053 independent observed reflections were recorded on a four-circle dif-fractometer. The structure has been determined by the RANTAN procedure, and the final residual factors is 0.071 after refining the coordinates and the thermal parameters.The crystal structure shows that the rearrengment of the C=N bond results in forming C(2)=C(7) of the indole residue in 3, meanwhile both the C(2)-C(3) and C(7)-C(20) bonds are cleaved, followed by the formation of a new bond C(2)-C(20) in neo-dihydrokoumine(3). The 5-membered pyrrole ring in 3 is approximately perpendicular to the 6-membered piperidine and* tetrahydropyrane rings which are fused together in a cis-fashion through 0(15) and C(16). 相似文献
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本文分析了旋光性分子中的螺旋结构,由此得出结论:螺旋结构是引起旋光性的根本原因。右手螺旋一定为右旋的,左手螺旋一定为左旋的。当分子内存在螺旋结构,而这些螺旋结构的旋光性不能完全相互抵消时,这个分子一定有旋光性。从螺旋方向可以预测旋光方向,知道旋光方向以预测螺旋方向,进而预测化合物的构型。 相似文献