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991.
Jin‐Tang Cheng Juan He Xing‐Yao Li Xing‐De Wu Li‐Dong Shao Liao‐Bin Dong Xu Deng Xiu Gao Li‐Yan Peng Xiao Cheng Yan Li Qin‐Shi Zhao 《Helvetica chimica acta》2012,95(7):1158-1163
Three new monosubstituted sucrose fatty acid esters, 1 – 3 , were isolated from Equisetum hiemale L., together with nine known compounds, 4 – 12 . Their structures were elucidated by spectroscopic analyses. Compounds 5, 6 , and 10 – 12 were isolated from the title plant for the first time. All these compounds were evaluated for their cytotoxic activity. However, none of them was cytotoxic. 相似文献
992.
Shao Z Li H Zhang S Li J Dai Z Mo Y Bae YJ Kim MS 《The Journal of chemical physics》2012,136(6):064308
The energy levels of CH(3)Cl(+)X?(2)E showing strong spin-vibronic coupling effect (Jahn-Teller effect) have been measured up to 3500 cm(-1) above the ground vibrational state using one-photon zero-kinetic energy photoelectron and mass-analyzed threshold ionization spectroscopic method. Theoretical calculations have been also performed to calculate the spin-vibronic energy levels using a diabatic model and ab initio adiabatic potential energy surfaces (PESs). In the theoretical calculations the diabatic potential energy surfaces are expanded by the Taylor expansions up to the fourth-order including the multimode vibronic interactions. The calculated spin-orbit energy splitting (224.6 cm(-1)) for the ground vibrational state is in good agreement with the experimental data (219 ± 3 cm(-1)), which indicates that the Jahn-Teller and the spin-orbit coupling have been properly described in the theoretical model near the zero-point energy level. Based on the assignments predicted by the theoretical calculations, the experimentally measured energy levels were fitted to those from the diabatic model by optimizing the main spectroscopic parameters. The PESs from the ab initio calculations at the level of CASPT2/vq(t)z were thus compared with those calculated from the experimentally determined spectroscopic parameters. The theoretical diagonal elements in the diabatic potential matrix are in good agreement with those determined using the experimental data, however, the theoretical off-diagonal elements appreciably deviate from those determined using the experimental data for geometric points far away from the conical intersections. It is also concluded that the JT effect in CH(3)Cl(+) mainly arises from the linear coupling and the mode coupling between the CH(3) deform (υ(5)) and CH(3) rock (υ(6)) vibrations. The mode couplings between the symmetric C-Cl stretching vibration υ(3) with υ(5) and υ(6) are also important to understand the spin-vibronic structure of the molecule. 相似文献
993.
A rapid and highly sensitive high-performance liquid chromatograpy method with fluorescence detection has been developed for determination of glutathione (GSH) in human plasma. A simple pre-column derivatization procedure with 7-flouro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-F) reagent was employed. The separation of the derivatized glutathione was performed using a mobile phase consisting of phosphate buffer (0.02 mol/L, pH 6.0)-acetonitrile (77:23, v/v) at a flow rate of 1.0 mL/min with the column temperature 2°C. The eluted derivatives were fluorometrically detected at an excitation wavelength 470 nm and an emission wavelength 530 nm. Under the optimum chromatographic conditions, the calibration curve was linear over the range of 0.1 μmol/L to 10.0 μmol/L with the correlation coefficient of 0.9988. The precision of the method was satisfactory with the intra- and inter-day coefficient of variation being 6.3%, 6.9%, respectively. This method has been used to determine glutathione concentrations in plasma samples from healthy individuals. 相似文献
994.
G.K. Surya Prakash Nan Shao Zhe Zhang Chuanfa Ni Fang Wang Ralf Haiges George A. Olah 《Journal of fluorine chemistry》2012
α-Fluoromethyl phenyl sulfone derivatives have been extensively employed in various reactions as versatile fluoromethylating reagents. While nucleophilic monofluoromethylations of aldehydes have been achieved using fluoromethyl phenyl sulfone or fluorobis(sulfonyl)methanes, a facile protocol under mild reaction conditions remains an ardently sought goal. We now report a feasible synthetic approach toward β-monofluorinated alcohols using α-trimethylsilyl-α-fluorobis(phenylsulfonyl)methane [TMSCF(SO2Ph)2, TFBSM] as a novel monofluoromethylating reagent. Initiated by a catalytic amount of fluoride, the reagent can be readily added to a variety of aldehydes providing the desired products in high yields. Computational and kinetic studies have revealed the exceptional lability of the Si–C bond in TFBSM compared with other fluoromethylsilane counterparts. 相似文献
995.
A new tetranuclear manganese complex [Mn2IIMn2III(bhmcpH)2(hmp)4Cl2(MeOH)2] ( 1 ) [bhmcpH3 = 2, 6‐bis(hydroxymethyl)‐4‐chlorophenol, hmpH = 2‐(hydroxymethyl)pyridine] was synthesized and characterized. X‐ray diffraction analyses reveal that complex 1 crystallizes in the monoclinic space group P21/c. It has a mixed‐valence tetranuclear dicubane unit, which comprises two MnII and two MnIII ions. The temperature dependence of the magnetic susceptibilities of 1 indicates ferromagnetic interactions between the manganese ions. 相似文献
996.
Cheng Shao Hong-Jie Yu Chen-Guo Feng Rui Wang Guo-Qiang Lin 《Tetrahedron letters》2012,53(22):2733-2735
A variety of novel C1-symmetric chiral diene ligands based on the dicyclopentadiene (DCP) skeleton were easily prepared from commercially available DCP. The application of these diene ligands in the rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids to α,β-unsaturated carbonyl compounds has been examined and excellent enantioselectivities (up to 97% ee) as well as good yields were achieved under mild reaction conditions. 相似文献
997.
A novel technique in controlling the size of SiO2 nano‐particles in the preparation of Nafion/SiO2 composite membranes via in situ sol–gel method, as well as the effects of nano‐particle size on membrane properties and cell performance, is reported in this paper. Nafion/SiO2 composite membranes containing SiO2 nano‐particles with four different diameters (5 ± 0.5, 7 ± 0.5, 10 ± 1, and 15 ± 2 nm) are fabricated by altering the reactant concentrations during in situ sol–gel reaction. Sequentially, size effects of SiO2 nano‐particles on membrane properties and cell performance are investigated by SEM/EDAX, TEM, TGA, mechanical tensile, and single cell tests, etc. The results suggest that 10 nm is a critical diameter for SiO2 incorporated into Nafion matrix, exhibiting desirable physico‐chemical properties for operation at elevated temperature and low humidity. At 110°C and 59% RH, the output voltage of the cell equipped with Nafion/SiO2 (10 nm) obtains an output voltage of 0.625 V at 600 mA/cm2, which is 50 mV higher than that of unmodified Nafion. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
998.
In a recent letter [E. Proynov, Y. Shao, and J. Kong, Chem. Phys. Lett. 493, 381 (2010)], Becke's B05 model of nondynamic electron correlation in density functional theory was implemented self-consistently with computational efficiency (the "SCF-RI-B05" scheme). Important modifications of the algorithm were done in order to make the self-consistency feasible. In the present work, we give a complete account of the SCF-RI-B05 algorithm, including all the formulae for the analytical representation of the B05 functional and for its self-consistent field (SCF) potential. The average performance of the SCF-RI-B05 method reported in the above letter was somewhat less accurate, compared to the original B05 implementation, mainly because the parameters of the original B05 model were optimized with post-local-spin-density calculations. In this work, we report improved atomization energies with SCF-RI-B05, based on a SCF re-optimization of its four linear parameters. The re-optimized SCF-RI-B05 scheme is validated also on reaction barriers, and on the subtle energetics of NO dimer, an exemplary system of strong nondynamic correlation. It yields both the binding energy and the singlet-triplet splitting of the NO dimer correctly, and close to the benchmarks reported in the literature. 相似文献
999.
Modelling of spall damage in ductile materials and its application to the simulation of the plate impact on copper 下载免费PDF全文
A statistical model of dynamic spall damage due to void nucleation and growth is proposed for ductile materials under intense loading, which takes into account inertia, the elastic-plastic effect, and initial void size. To some extent, void interaction could be accounted for in this approach. Based on this model, the simulation of spall experiments for copper is performed by using the Lagrangian finite element method. The simulation results are in good agreement with experimental data for the free surface velocity profile, stress record behind copper target, final porosity, and void concentrations across the target. The influence of elastic-plastic effect upon the damage evolution is explored. The correlation between the damage evolution and the history of the stress near the spall plane is also analyzed. 相似文献
1000.
A density-functional theory investigation on desorption of O2 on Sn(111) and its comparison with initial oxidation on the X(111) (X=Si,Ge, Sn,Pb) surfaces 下载免费PDF全文
<正>The first-principles calculations are performed to investigate the adsorption of O2 molecules on an Sn(111) 2×2 surface.The chemisorbed adsorption precursor states for O2 are identified to be along the parallel and vertical channels, and the surface reconstructions of Sn(lll) induced by oxygen adsorption are studied.Based on this,the adsorption behaviours of O2 on X(111)(X=Si,Ge,Sn,Pb) surfaces are analysed,and the most stable adsorption channels of O2 on X(111)(X=Si,Ge,Sn,Pb) are identified.The surface reconstructions and electron distributions along the most stable adsorption channels are discussed and compared.The results show that the O2 adsorption ability declines gradually and the amount of charge transferred decreases with the enhancement of metallicity. 相似文献