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991.
Camden JP Bechtel HA Ankeny Brown DJ Martin MR Zare RN Hu W Lendvay G Troya D Schatz GC 《Journal of the American Chemical Society》2005,127(34):11898-11899
A comparison between theory and experiment for the benchmark H + CD4 --> HD + CD3 abstraction reaction yields a reinterpretation of the reaction mechanism and highlights the unexpected contribution of a stripping mechanism. Whereas the best analytic surface fails to reproduce experiment, a first-principles direct-dynamics (on the fly) treatment is in good agreement, showing that the H + CD4 reaction exhibits extreme sensitivity to modest differences in the potential energy surface. We find that bent H-D-C transition state geometries play an important role in the dynamics. A simple model that relates the scattering angle impact parameter and cone of acceptance accounts well for the overall reaction dynamics. 相似文献
992.
Solid dispersions of silymarin were prepared by the fusion method with the intention of improving the dissolution properties of silymarin. Polyethylene glycol 6000 (PEG 6000) was used as the inert hydrophilic matrix. The dissolution studies of the solid dispersions were performed in vitro. And the results obtained showed that the dissolution rate of silymarin was considerably improved when formulated in solid dispersions with PEG 6000 as compared to original drug, and the increased dissolution rate might be favorable for further oral absorption. 相似文献
993.
Dr. Qingzhen Yu Le'an Hu Yue Wang Shasha Zheng Prof. Dr. Jianhui Huang 《Angewandte Chemie (International ed. in English)》2015,54(50):15284-15288
A Ru‐catalyzed direct C? H activation/meta‐bromination of arenes bearing pyridyl, pyrimidyl, and pyrazolyl directing groups has been developed. A series of bromo aryl pyridines and pyrimidines have been synthesized, and further coupling reactions have also been demonstrated for a number of representative functionalized arenes. Preliminary mechanistic studies have revealed that this reaction may proceed through radical‐mediated bromination when NBS is utilized as the bromine source. This type of transformation has opened up a new direction for the radical non‐ipso functionalization of metal with regard to future C? H activation development that would allow the remote functionalization of aromatic systems. 相似文献
994.
The direct preparation of a kind of fluorinating reagent 1 [F‐TEDA‐N(SO2Ph)2] was realized in high yield via the complexation of N‐fluorobenzenesulfonimide (NFSI) with 1‐(chloromethyl)‐1,4‐diazabicyclo[2.2.2]octan‐1‐ium N′,N′‐bis‐(benzenesulfonylimide) salt. In its fluorination to oxindoles, the fluorinating products 6 were afforded in moderate to high yields. 相似文献
995.
996.
硼离子对铕掺杂SiO2干凝胶发光性能的影响 总被引:3,自引:0,他引:3
采用溶胶-凝胶法制备了Al单掺和B,Al共掺的Eu掺杂SiO2干凝胶。利用荧光光谱、IR,XRD,DSC,TG/DTG等技术研究了硼离子、退火温度对样品发光性质的影响。经500℃以上退火处理用248nm激发的样品,产生Eu^3+离子^5D0→^7FJ的特征发射,^5D0→^7F1的跃迁分裂为两个峰。比较615nm处的发光强度,掺硼酸样品的发光强度是不加硼酸发光强度的3.3倍。这是因为B离子的加入,在材料中形成了Si—O—B键,破坏了网络的对称性,加强了Eu^3+的红光发射。当退火温度上升到850℃用350nm激发时,样品有很强的Eu^2+蓝光发射。Al单掺的发射中心在437nm处,发射半峰宽约为70nm,而B,Al共掺样品的发光中心蓝移到425nm处,单掺样品的蓝光强度几乎是共掺样品强度的2倍。这是由于硼酸的加入改变了基质的网络结构,从而导致单掺和共掺样品发射峰位和强度的改变。 相似文献
997.
悬浮液进样流动注射在线微波消解-冷蒸气原子荧光光谱法测定生物和环境样品中的汞 总被引:12,自引:0,他引:12
建立了悬浮液进样流动注射在线微波消解-冷蒸气原子荧光光谱法测定生物和环境样品中Hg的方法。样品分散在50%(V/V)王水中,通过磁力搅拌保证样品溶液的均一性与稳定性。方法的检出限为O.06μ/L。方法简单快速,灵敏度高,样品损失少,而且没有样品交叉污染。应用此方法测定了5种标准参考物质以及5个实际样品中的Hg含量,并与传统的高压焖罐强酸消解方法进行了比较,两种方法所得结果一致,标准参考物质的测定值与标准值很好地吻合。 相似文献
998.
Recently, there has been increasing concern about perfluorinated surfactants, especially perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) due to their persistence and chronic toxicity in the aquatic environment. Solid phase extraction (SPE) followed by liquid chromatography coupled with tandem mass spectrometry (LC-MS-MS) are widely applied to quantitatively identify PFOS and PFOA. However, the application of this powerful analytical technique is limited by matrix susceptibility. The co-eluting matrix components in the SPE extracts affect the ionization efficiency and lead to erroneous results. An efficient sample clean-up method was developed in this study to significantly remove co-eluting matrix components by applying the SPE extracts onto a silica cartridge. It was shown that matrix effect (ME%) increased to >70% for both PFOS and PFOA in the analysis of raw sewage. Internal standardization was used to further compensate for the matrix effect, which also proved to improve the signal reproducibility. The clean-up method described in this study was applied to different water samples (surface water and wastewater) to evaluate the efficiency of silica clean-up and the influence of sample origin on the matrix effect. ME% and recovery efficiency (RE%) were in the range of 91.9–98.3% and 89.2–98.0%, respectively. Results showed that the developed method is robust and can be applied to analyze PFOS and PFOA in different environmental matrices. 相似文献
999.
In this study, 3,4-dimethylbenzaldehyde was obtained in 82.3% total yield by oxidation of 3,4-dimethylbenzyl chloride with NaNO3/AcOH catalyzed by PEG-600 in aqueous media. The starting material 3,4-dimethylbenzyl chloride was prepared by chloromethylation of o-xylene in CTAB micellar catalytic system. Compared with other synthetic methods, this method not only enhanced the yield, but also afforded an efficient work-up procedure. The structures of the products were confirmed by Elemental analysis, 1H NMR and 13C NMR or compared with authentic samples. 相似文献
1000.
Shumin Han Yuan Li Zhong Zhang Xilin Zhu Jinhua Li Lin Hu 《Frontiers of Chemistry in China》2009,4(1):48-51
The Ml-Mg-Ni-based (Ml = La-rich mixed lanthanide) hydrogen storage alloy Ml0.88Mg0.12Ni3.0-Mn0.10Co0.55Al0.10 was prepared by inductive melting. The micro-structure was analyzed by XRD and SEM. The alloy consists mainly of CaCu5-type phase, Ce2Ni7-type phase and Pr5Co19-type phase. The electrochemical measurements show that the maximum discharge capacity is 386 mAh/g, 16.3% higher than that
of the commercial AB5-type alloy (332 mAh/g). At discharge current density of 1 100 mA/g, high rate dischargeability is 62%, while that of the
AB5-type alloy is only 45%. The discharge capacity decreases to 315 mAh/g after 300 charge/ discharge cycles, 81.5% of the
maximum discharge capacity.
__________
Translated from Journal of Xi’an Jiao Tong University, 2008, 42(3) (in Chinese) 相似文献