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901.
Determination of trace elements in biological materials using tetramethylammonium hydroxide for sample preparation 总被引:1,自引:0,他引:1
Patrícia Martins Dirce Pozebon Valderi L. Dressler Gisele A. Kemieciki 《Analytica chimica acta》2002,470(2):62-204
A method to prepare milk powder, bovine liver and bovine muscle samples for analysis by electrothermal atomic absorption spectrometry (ETAAS) is proposed. Samples are mixed with a small amount of tetramethylammonium hydroxide (TMAH) and a stable and homogeneous slurry is produced in ca. 2 h with heating at 60–70 °C. After such sample preparation and dilution with water, trace elements are determined in certified reference materials. Pyrolysis and atomisation temperatures are optimised for each element, and several modifiers are investigated. External calibration is used for every analyte. Limits of detection (LODs), precision and accuracy are reported for Cd, Pb, Ni, Cr, Cu and Ag and compared with those obtained after conventional acid digestion. The main advantages of the proposed method are the simplicity of sample preparation and the longer lifetime of the graphite tube. 相似文献
902.
R. M. Zolotar' A. I. Bykhovets S. K. Ananich N. V. Kovganko 《Chemistry of Natural Compounds》2002,38(2):164-166
The toxicity of steroid benzoates 4-10 for Colorado beetle (Leptinotarsa decemlineata Say.) larvae was studied by a contact-intestinal method. The most active growth and development regulator for this insect is 3-benzoyloxy-5-hydroxy-7-6-ketosteroid 9a. 相似文献
903.
Activation of CO2 at Transition Metal Centres: The Route of the CO2 Reduction at Nikel(0) Moieties A competing reaction in the catalytic cyclooligomerization of hex-3-yne and CO2 at the (TMED)Ni(0)-fragment (TMED = N,N,N′,N′-tetramethylethylendiamine) is the formation of carbon monoxide and (TMED)Ni(CO3). So it is possible to explain the generation of II (TMED)Ni(diethylmalicacidanhydride) and III (a nickel trimer with two (TMED)Ni(CO3) units). Both complexes are characterized by X-ray analysis. The reduction of CO2 to CO most likely proceeds via an intermediate in which two molecules of carbon dioxide are coupled head-to-tail to form a metallacycle. An ab initio scf geometry optimization supports the existence of such an intermediate. 相似文献
904.
Fused-sphere surfaces can be used to mimic a molecular boundary associated with a constant value of the electron density. The simplest of such fused-sphere models are constructed by using the atomic radii for the spherical isodensity surfaces of individual atoms. In this work, we discuss the extension of this model to molecules containing atoms beyond the second row. In these many- electron systems, the computation of electron densities is usually simplified by adopting a pseudopotential (or effective-core potential) approach. Here, we discuss the performance of large- and small-core pseudo-potential calculations as a tool to derive atomic radii. Our results provide an optimum set of variable radii that can be used to build fused-sphere surfaces. This continuum of surfaces provides a simple approximation to the low-electron-density regions around molecules with heavy atoms. 相似文献
905.
SAPO—11分子筛用i—Pr2NH导向合成及其酸性研究 总被引:3,自引:0,他引:3
以AlPO4、H3PO4、SiO2等为原料采用单一模板剂iPr2NH合成了SAPO11分子筛,利用Avrami方程等对合成过程进行了定量描述。还利用红外(IR)、程序升温脱附(TPD)、线性丁烯骨架异构反应催化活性测试等手段表征了SAPO11的酸性。结果表明,合成过程随温度有明显变化,晶化阶段的活化能远高于核化阶段的值。可用Avrami方程的参数来表征合成过程的难易程度。分子筛中存在B酸和L酸位,主要在中等强度范围,从而对线性丁烯骨架异构反应有较好的催化活性。提高分子筛中硅含量可明显增大酸位浓度,酸强度也有轻度增强。 相似文献
906.
V. F. Mironov L. M. Burnaeva G. A. Khlopushina I. V. Konovalova M. A. Kurykin A. I. Rakhmatullin 《Russian Chemical Bulletin》1996,45(12):2858-2860
Benzo-1,3,2,dioxaphosphorin-4-ones react with hexafluoroacetone imine to form 2-R-2,5-dioxo-3,3-bis(trifluoromethyl)-6,7-benzo,1,4,2-oxozaphosphepanes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No, 12, pp. 3008–3010, December, 1996. 相似文献
907.
908.
909.
IntroductionInthcsclcctivcoxidationofalkanes.suchas'theoxidativccouplingofmcthanc(0CM)andthcoxidativcdch}'drogenationofcthanc(0DE)t0prcparccth}'lene.bothoxidcionsofthelatticeandtheox}'genspeciesovercataIystsuffocepla}'animportantrole.Althoughcxtcnsivcinvcstigationshavcbeengivcntothecharactcrizationofox}'gcnspccicsandthcreactionofox}'gcnspecicsx`ithalkanes,itisstilldifficulttosayt`hichoncsofox}'gcnspcciesarcthcactivcspecicsinthcactivation0falkancs.bccauscthenaturcofcatal}'stsandthecxperimcntc… 相似文献
910.
5,7,8位取代的喹诺酮类化合物定量构效关系的量子化学研究 总被引:2,自引:0,他引:2
5,7,8位取代的喹诺酮类化合物定量构效关系的量子化学研究俞庆森,朱龙观,林瑞森,蔡国强(浙江大学化学系杭州310027)关键词:氟喹喏酮类,定量构效关系,CNDO/2氟喹诺酮类是一类重要的抗感染化疗药物 ̄[1],近十年对其研究进展神速 ̄[2],结构... 相似文献