Ab initio calculations on large molecules using molecular fragments. Characterization of the zwitterion of glycine

The ab initio molecular fragment approach is applied to a characterization study of the ground state of the zwitterion of glycine. Included among the properties studied are the — conformational energy surface, the electronic structure, and the magnitude and direction of the dipole moment. The results of the present study are compared to the results of other theoretical and experimental studies.This work was supported in part by the National Science Foundation, the University of Kansas, and the Upjohn Company, Kalamazoo, Michigan 49001.NSF Trainee (1969-1972).Alfred P. Sloan Research Fellow (1971–1973).     

α—甲基苯乙烯离子聚合体分子量分布

聚α-甲基苯乙烯-丁二烯-α-甲基苯乙烯嵌段共聚物是一种性能优异的热塑性弹性体。常温下,α-甲基苯乙烯的聚合是在极性添加剂存在下进行的,添加剂的种类,用量及聚合温度不仅影响聚合动力学,尚且影响聚合物分子量及其分布,控制α-甲基苯乙烯聚合速率、     

液体和非晶态Ni64B36合金结构的从头算分子动力学模拟

运用从头算分子动力学模拟了液体以及猝冷后形成的非晶态Ni₆₄B₃₆合金体系, 得到了它们的对相关函数、结构因子、键对分析方面的结构信息, 与实验结果相当一致; 结果表明, 猝冷得到的合金性质与液体合金性质相似, 为非晶态结构. B原子多数以B—B双原子成键形式分散于Ni原子构成的骨架中. 电子态密度分析表明, Ni 3d电子最活泼, 因此在合金中Ni为活性位. 轨道电荷分析从电子结构角度揭示了在NiB 催化剂中B作为修饰剂的机理.     

SAPO-11分子筛的合成及其晶貌

以二异丙胺或二正丙胺为模板剂用水热合成法合成SAPO-11分子筛,发现pH值及模板剂的种类对所生成的SAPO-11晶体形貌有着明显的影响,通常观察到的球形晶貌实属长形柱体的聚集体。     

几种改进的CoMFA方法比较研究血小板活化因子拮抗剂

由于传统的比较分子场分析(CoMFA)方法本身存在一些缺陷，使得分子的叠合 规则以及叠合分子的空间取向和空间位置等因素对q~2的影响很大，因此相继提出 了几种改进的CoMFA方法。为了优化CoMFA结果，应用传统的CoMFA方法和交叉验证 的R~2引导的区域选择法(q~2-GRS)、全取向搜索法（AOS）、全空间搜索法（APS） 以及比较分子相似性指数(CoMSIA)等四种改进的CoMFA方法，对18个pinusolide类 衍生物这类新发现的血小板活化因子（PAF）拮抗剂进行了比较研究。结果表明四 种改进的CoMFA方法得到的q~2值均比传统CoMFA的高。q~2-GRS方法得到的q~2值有 所提高，但综合结果并不理想，AOS与APS得到的q~2较为理想，而在CoMSIA中， q~2几乎不受空间取向或空间位置的影响。同时我们引人基于样本的偏最小二乘法 （SAMPLS）取代原AOS／APS程序中的传统PLS进行统计分析，明显提高了其运行速 度。最后，根据q~2最高的CoMFA模型和CoMSIA模型设计了几个预测活性更高的 pinusolide类似物。     

Interaction of 4-Isopropoxalyl-1,5-diphenyl-2,3-dihydro-2,3-pyrroledione with Thiosemicarbazide: Synthesis and Crystal and Molecular Structure of (3aS*)(4R*)(6aR*)-4,6a-dihydroxy-4-isopropoxycarbonyl-1-thiocarbamoyl-3,5-diphenyl-1,3a,4,5,6,6a-hexahydropyrrolo[3,4-d]pyrazol-6-one

4-Isopropoxalyl-1,5-diphenyl-2,3-dihydro-2,3-pyrroledione reacts with thiosemicarbazide to form (3aS*)(4R*)(6aR*)-4,6a-dihydroxy-4-isopropoxycarbonyl-1-thiocarbamoyl-3,5-diphenyl-1,3a,4,5,6,6a-hexahydropyrrolo[3,4-d]pyrazol-6-one. The molecular and crystal structure of the latter was studied by single crystal X-ray diffraction.     

Synthesis of molecular sieve AlPO4-12

A member of the novel family of crystalline microporous aluminophosphates, AlPO₄-12, was synthesized by hydrothermal crystallization using different aluminum-containing compounds. Three new crystalline phases were obtained by varying the composition of the reaction mixture. The effect of the synthesis conditions on the hudrothermal process and the kinetics of crystallization are discussed. The apparent activation energies obtained for AlPO₄-12 are 20.9 and 14.6 kcal/mol for nucleation and crystallization, respectively. The adsorption isotherms of one AlPO₄-12 product were measured.     

Comparison of localization and delocalization indices obtained with Hartree-Fock and conventional correlated methods: effect of Coulomb correlation

Atomic populations and localization [lambda(A)] and delocalization [delta(A,B)] indices (LIs and DIs) are calculated for a large set of molecules at the Hartree-Fock (HF), MP2, MP4(SDQ), CISD, and QCISD levels with the 6-311++G(2d,2p) basis set. The HF method and the conventional correlation methods [MP2, MP4(SDQ), CISD, and QCISD] yield distinct sets of LIs and DIs. Yet, within the four conventional correlation methods the differences in atomic populations and LIs and DIs are small. Relative to HF, the conventional correlation methods [MP2, MP4(SDQ), CISD, QCISD] yield virtually the same LIs and DIs for molecules with large charge separations while LIs and DIs that differ significantly from the HF values--the LIs are increased and DIs decreased--are obtained for bonds with no or small charge separations. Such is the case in the archetypal homopolar molecules HC(triple bond)CH, H2C=CH2, CH3-CH3, and "protonated cyclopropane" C(3)H(7) (+), in which case the bonding may be atypical. Relative to HF, the typical effect of the conventional correlation methods is to decrease the DI between atoms.     

FT IR ATR Study of Molecular Interactions in the Urea/Dimethyl Sulfoxide and Urea/Diethyl Sulfoxide Binary Systems

FT IR ATR spectra of urea/dimethyl sulfoxide and urea/diethyl sulfoxide mixtures in the S=O and N—H stretching vibration regions at different molar ratios have been measured. On the basis of the band deconvolution data, various types of intermolecular associated forms, including dimers and hydrogen-bonded urea–sulfoxide complexes, have been revealed. The latter has been confirmed also by ab initio calculations.     

聚电解质溶液中2.6-ANS探针的荧光谱研究

本文合成了2.6—ANS荧光探针分子,并在含有不同外加盐的NaPSS溶液中测定了探针的荧光发射光谱。结果表明:探针的荧光强度随Cs增大而增大,而探针光谱的最大发射波长和半波宽度随Cs增大而减小。当Cs达到一定值时,荧光谱参数与Cs关系曲线出现转折点,此时聚离了链以“类胶束”状态存在。