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991.
992.
High-performance thin-layer chromatographic analysis of selected organophosphorous pesticide residues in tea 总被引:1,自引:0,他引:1
The separation of 9 organophosphates (monocrotophos, quinalphos, triazophos, parathion-methyl, isofenphos-methyl, temephos, parathion, phoxim-ethyl, and chlorpyrifos) by high-performance thin-layer chromatography (HPTLC) with automated multiple development was studied. The HPTLC method was developed and validated for analysis of residues of phoxim-ethyl and chlorpyrifos in tea. The sample was extracted with acetonitrile and cleaned up by ENVI-CARB solid-phase extraction. The extract was directly applied as bands to glass-backed silica gel 60F254 HPTLC plates. The plates were developed with dichloromethane-hexane (1 + 1, v/v) in a glass twin-trough chamber. Evaluation of the developed HPTLC plates was performed densitometrically. The results indicated that the detection limits of phoxim and chlorpyrifos were 5.0 x 10(-9) and 1.0 x 10(-8) g, respectively. Recoveries of the pesticides from tea by this analytical method were 90.7-105.5%, and relative standard deviations were 7.3-13.5%. The precision and accuracy of the method were generally satisfactory for analysis of pesticide residues in tea. 相似文献
993.
Density functional theory (DFT) and conceptual/chemical DFT studies are carried out in this work for the normal electron demand Diels-Alder reaction between isoprene and acrolein to compare chemical reactivity and regioselectivity of the reactants in the absence and presence of Lewis acid (LA) catalysts. A cyclic coplanar structure of acrolein-LA complex has been observed and the natural bond orbital analysis has been employed to interpret the interaction between acrolein and LAs. Reactivity indices from frontier molecular orbital energies are proved to be adequate and efficient to evaluate the catalytic property of LAs. Linear relationships have been discovered among the bond order, bond length, catalytic activation, and chemical reactivity for the systems concerned. The validity and applicability of maximum hardness principle, minimum polarizability principle, and minimum electrophilicity principle are examined and discussed in the prediction of the major regioselective isomer and the preferred reaction pathway for the reactions in the present study. 相似文献
994.
岳嵘 《数学的实践与认识》2008,38(3):135-141
针对"亚正定阵理论(Ⅱ)"一文的广义Minkowski不等式不成立问题,在已有的修正结果基础上,给出一种完整的修正结果;并更正了"亚正定阵的几个开问题及一些不等式"一文中有关的错误结论;用反例说明"广义正定矩阵的进一步研究"一文中的有关结论是错误的,给出完整的修正结果. 相似文献
995.
Let S be a regular semigroup, S° an inverse subsemigroup of S.S° is called a generalized inverse transversal of S, if V(x)∩S°≠Ф. In this paper, some properties of this kind of semigroups are discussed. In particular, a construction theorem is obtained which contains some recent results in the literature as its special cases. 相似文献
996.
997.
Youwen Rong Dr. Tianfu Liu Jiaqi Sang Dr. Rongtan Li Dr. Pengfei Wei Dr. Hefei Li Dr. Aiyi Dong Prof. Dr. Li Che Prof. Dr. Qiang Fu Prof. Dr. Dunfeng Gao Prof. Dr. Guoxiong Wang 《Angewandte Chemie (International ed. in English)》2023,62(45):e202309893
Electrochemically converting CO2 to valuable chemicals holds great promise for closing the anthropogenic carbon cycle. Owing to complex reaction pathways and shared rate-determining steps, directing the selectivity of CO2/CO electrolysis to a specific multicarbon product is very challenging. We report here a strategy for highly selective production of acetate from CO electrolysis by constructing metal-organic interfaces. We demonstrate that the Cu-organic interfaces constructed by in situ reconstruction of Cu complexes show very impressive acetate selectivity, with a high Faradaic efficiency of 84.2 % and a carbon selectivity of 92.1 % for acetate production, in an alkaline membrane electrode assembly electrolyzer. The maximum acetate partial current density and acetate yield reach as high as 605 mA cm−2 and 63.4 %, respectively. Thorough structural characterizations, control experiments, operando Raman spectroscopy measurements, and density functional theory calculation results indicate that the Cu-organic interface creates a favorable reaction microenvironment that enhances *CO adsorption, lowers the energy barrier for C−C coupling, and facilitates the formation of CH3COOH over other multicarbon products, thus rationalizing the selective acetate production. 相似文献
998.
999.
Dr. Tao Yuan Ziwei Wu Senmao Zhai Rong Wang Shiwen Wu Prof. Jiajia Cheng Prof. Meifang Zheng Prof. Xinchen Wang 《Angewandte Chemie (International ed. in English)》2023,62(27):e202304861
Light-driven fixation of CO2 in organics has emerged as an appealing alternative for the synthesis of value-added fine chemicals. Challenges remain in the transformation of CO2 as well as product selectivity due to its thermodynamic stability and kinetic inertness. Here we develop a boron carbonitride (BCN) with the abundant terminal B/N defects around the mesoporous walls, which essentially enhances surface active sites as well as charge transfer kinetics, boosting the overall rate of CO2 adsorption and activation. In this protocol, anti-Markovnikov hydrocarboxylation of alkenes with CO2 to an extended carbon chain is achieved with good functional group tolerance and specific regioselectivity under visible-light irradiation. The mechanistic studies demonstrate the formation of CO2 radical anion intermediate on defective boron carbonitride, leading to the anti-Markovnikov carboxylation. Gram-scale reaction, late-stage carboxylation of natural products and synthesis of anti-diabetic GPR40 agonists reveal the utility of this method. This study sheds new insight on the design and application of metal-free semiconductors for the conversion of CO2 in an atom-economic and sustainable manner. 相似文献
1000.
Yaqi Jiang Rong Yu Yuelin Bai Zhaoxiong Xie Lansun Zheng 《Transition Metal Chemistry》2008,33(8):1019-1026
Three novel coordination polymers, namely, [Mn(ndc)(bpy)]
n
· n(H2O) (1), [Mn(ndc)(phen)]
n
(2), and [Mn3(ndc)3(bpy)2]
n
(3) (H2ndc = 2,6-naphthalenedicarboxylic acid, bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline) have been hydrothermally synthesized
and characterized by elemental analysis, IR, and single-crystal X-ray diffraction analysis. Complexes 1–3 exhibit three-dimensional metal-organic frameworks (MOFs); 1 and 2 are assemblies of the same secondary building units (SBUs), linear infinite chains {Mn(CO2)2}
n
, forming one-dimensional channel, while complex 3 is constructed by trinuclear clusters {Mn3(CO2)6} SBUs. Magnetic properties of complexes 1 and 3 are also discussed with respect to the bridging mode of the carboxylate groups. 相似文献