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91.
Zhenshan Jia Xiang Zhang Gaihong Zhang Shaohua Huang Hao Fang Xiangqing Hu Yuliang Li Prof. Liangbing Gan Prof. Shiwei Zhang Prof. Daoben Zhu Prof. 《化学:亚洲杂志》2007,2(2):290-300
The Cs‐symmetric fullerene chlorohydrin C60(Cl)(OH)(OOtBu)4 reacts with 4‐dimethylaminopyridine (DMAP) and 1,4‐diazabicyclo[2.2.2]octane (DABCO) to yield two isomers with the formula C60(O)(OOtBu)4 in good yields. These isomers differ with respect to the location of the epoxy functionality. The one from DMAP is Cs symmetric, whereas that from DABCO is C1 symmetric with the epoxy group on the central pentagon. Two different mechanisms are proposed to explain the chemoselectivity of these reactions. The reaction with DMAP involves single‐electron transfer as the key step; DMAP acts as the electron donor. A combination of an oxygen‐atom shift and SN2′′ processes (boomerang substitution) are responsible for the formation of isomer with DACBO. Various related reactions support the proposed mechanisms. The structures of new fullerene derivatives were determined by spectroscopy, single‐crystal X‐ray analysis, and chemical correlation experiments. 相似文献
92.
Yi‐Zhen Tang Hao Sun Ya‐Ru Pan Xiu‐Mei Pan Rong‐Shun Wang 《International journal of quantum chemistry》2007,107(6):1495-1501
The mechanisms for the reaction of CH3S with NO2 are investigated at the QCISD(T)/6‐311++G(d,p)//B3LYP/6‐311++G(d,p) on both single and triple potential energy surfaces (PESs). The geometries, vibrational frequencies, and zero‐point energy (ZPE) correction of all stationary points involved in the title reaction are calculated at the B3LYP/6‐311++G(d,p) level. More accurate energies are obtained at the QCISD(T)/6‐311++G(d,p). The results show that 5 intermediates and 14 transition states are found. The reaction is more predominant on the single PES, while it is negligible on the triple PES. Without any barrier height for the whole process, the main channel of the reaction is to form CH3SONO and then dissociate to CH3SO+NO. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
93.
94.
Libera JA Cheng H Olvera de la Cruz M Bedzyk MJ 《The journal of physical chemistry. B》2005,109(48):23001-23007
We show an experimental approach for directly observing the condensation of polynucleotides and their electrolyte counterions at a liquid/solid interface. X-ray standing waves (XSW) generated by Bragg diffraction from a d = 20 nm Si/Mo multilayer substrate are used to measure the distinct distribution profiles of the polyanions and simple cations along the surface normal direction with subnanometer resolution. The 1D spatial sensitivity of this approach is enhanced by observing the XSW induced fluorescence modulations over multiple orders of Bragg peaks. We study the interesting divalent cation driven adsorption of anionic polynucleotides to anionic surfaces by exposing a hydroxyl-terminated silica surface to an aqueous solution with ZnCl2 and mercurated poly-uridylic acid (a synthetic RNA molecule). The in situ long-period XSW measurements are used to follow the evolution of both the Zn and Hg distribution profiles during the adsorption process. The conditions and physical mechanisms that govern the observed divalent cation adsorption and subsequent polynucleotide adsorption to an anionic surface are explained by a thermodynamic model that incorporates nonlinear electrostatic effects. 相似文献
95.
Highly porous nanocomposites of zirconium dioxide and silicate are synthesised in an aqueous system from an inorganic salt of zirconium; the nanacomposites, with tailorable pore structures, exhibit superior performance as catalyst supports. 相似文献
96.
The graft copolymers of chitosan with polycaprolactone (PCL) were prepared through a protection-graft-deprotection route using phthaloylchitosan as intermediate. PCL macromonomers terminated with isocyanate groups reacted with hydroxyl groups of phthaloyl-protected chitosan regioselectively, and then phthaloyl groups were deprotected to give the free amino groups. The graft reaction was carried out in homogeneous system and yielded copolymers with high grafting content due to solubilization. FTIR, NMR and XRD were detected to characterize the resultant chitosan-graft-PCL copolymers. 相似文献
97.
Chen H Li G Zhang FF Sun L Chen HL Zhang SY 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(12):2767-2774
Time resolved photoacoustic calorimetry (PAC) was applied to a study of the photolysis of a coenzyme B(12) analog 2',5'-dideoxyadenosylcobalamin, which lacks an -OH group at the 2' position of ribofuranose ring. In aqueous solution, we report for the first time the quantum yield Phi(d) (0.25+/-0.02), Co-C bond dissociation energy (BDE; 31.8+/-2.5 kcal mol(-1)) and reaction volume change deltaV(R) (6.5+/-0.5 ml mol(-1)) due to conformation changes of the corrin ring and its side chains accompanying the cleavage of the Co-C bond. These values for the analog are very similar to those for the natural cofactor. Based our results and previous studies, a possible explanation for the similarity in their structure and properties versus the large difference in their enzymatic activity is discussed. 相似文献
98.
99.
TEOS-MTES基SiO2溶胶微结构的SAXS研究 总被引:3,自引:0,他引:3
正硅酸乙酯(TEOS)为前驱体,在碱性条件下制备含有无定形SiO2颗粒的溶胶,以甲基三乙氧基硅烷(MTES)在酸性条件下获得聚甲基硅氧链,二者混合后应用同步辐射X射线进行混合溶胶的SAXS散射强度测定,计算了溶胶的平均回转半径、平均粒径、两相界面层厚度、散射体体积分数、两相间比表面积等参数,辅以光子相关光谱法(PCS)和透射电子显微镜(TEM)观测溶胶粒度,证实SiO2颗粒被MTES混合物连接成族团.实验发现所测混合溶胶样品均表现出对Porod定理的负偏离,说明溶胶中颗粒与溶剂之间存在很明显的两相间界面层. 相似文献
100.
X. Li Y. Zhao X. Jing F. Liu F. Hao 《International journal of quantum chemistry》2006,106(5):1086-1092
The equilibrium geometries, vibrational frequencies, and dissociation energies of rare gas iodine clusters Rg2I?(Rg = Ar, Kr, Xe) were calculated at the Hartree–Fock (HF), second‐order Møller–Plesset (MP2), the coupled cluster method with single and double excitation and a noniterative correction for triple excitations method [CCSD(T)] levels. The title species have bent C2v structure of about 60° angle. The electron correlation effects and relativistic effects on the geometry and stability were investigated at CCSD(T) level. Both effects stabilize title species. The calculated electron affinities are in good agreement with the experimental results available. The effect of high angular momentum functions (g and h) was studied. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献