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971.
6-Diazopenicillanates react with allylic sulphides, selenides and bromides, to give 6,6-disubstituted penicillanates [2,3]-sigmatropic rearrangements. 相似文献
972.
R. A. Alieva S. Z. Gamidov F. M. Chyragov A. A Azizov 《Journal of Analytical Chemistry》2005,60(12):1114-1117
A method is developed for cadmium and zinc preconcentration on a minicolumn packed with a new chelating polymer sorbent. The effects of the test solution pH and volume, the sample matrix composition, the eluent volume, and the sample and eluent flow rates are studied. Zinc and cadmium in the eluate are determined by flame atomic absorption spectrometry. Under optimal conditions, the determined ion recovery is more than 95%. The detection limits (3σ, n = 20) are found to be 15.0 (Cd) and 17.2 (Zn) ng/mL. The developed method is employed for cadmium and zinc determination in samples of seawater and water obtained after oil pumping. 相似文献
973.
An amperometric detector with a small thin mercury film electrode is described. The device demonstrates advantageous operational
characteristics such as small dispersion (D<2) and “memory effect” (me<0.6%), extensive maximum sample frequency (msf −200
samples/h), and high sensitivity. It has been proven useful in flow-injection analysis at a constant potential under hydrodynamic
conditions. 相似文献
974.
In the course of investigations on equestrian supplemental products for the presence of doping substances, two products were found to contain forbidden substances. As reported earlier a plant extract (Mexican cactus extract) named “Energy 5” contained the anabolic androgenic steroids (AAS) stanozolol, 17β-hydroxy-17α-methyl-5α-androstane-3β-ol (3β,5α-THMT) as well as mestanolone not declared on the label. In the present study, a product called “Super Kalm Paste” was tested. Analysis by gas chromatography - mass spectrometry (GC-MS) revealed that the preparation contained the class I anti-arrhythmics quinine (trade names KinidinTM, Durules) and cinchonine. The samples were prepared according to a sample preparation procedure established for anabolic steroids in nutritional supplements for humans. The sample treatment comprised the extraction and purification of the analytes as well as the chemical conversion with N-methyl-N-trimethylsilyl-trifluoracetamide (MSTFA) to yield the trimethylsilyl (TMS)-derivatives. To verify whether the administration of such products could lead to positive doping tests, a pilot excretion study on “Energy 5” was conducted with two geldings, and urine samples were collected. Gas chromatography - high resolution mass spectrometry (GC-HRMS) after solid phase extraction and mixed derivatisation has demonstrated the presence of the stanozolol metabolite 16β-hydroxy-stanozolol in urine samples after “Energy 5” application. 相似文献
975.
Massue J Bellec N Chopin S Levillain E Roisnel T Clérac R Lorcy D 《Inorganic chemistry》2005,44(24):8740-8748
The reaction of tris(alkylthio)tetrathiafulvalene thiolates with 3-chloro-2,4-pentanedione affords tetrathiafulvalene (TTF) moieties substituted by the acetylacetone function (TTFSacacH), precursors of novel redox-active ligands: the acetylacetonate ions (TTFSacac). These TTFSacacHs have been characterized by X-ray diffraction analyses, and similar trends have been observed, such as a TTF core almost planar and the acetylacetone substituent located in a plane almost perpendicular to the plane formed by the TTF core. Their chelating ability has been demonstrated by the formation of the corresponding M(TTFSacac)2(pyridine)2 complexes in the presence of M(II)(OAc)2.H2O (M = Ni2+, Zn2+). These complexes with TTFSacac moieties, Ni(TTFSacac)2(pyridine)2, 6b, and Zn(TTFSacac)2(pyridine)2, 7b, have been characterized by X-ray diffraction analyses, showing in all structures the metal(II) center chelated by two TTFacac units in the equatorial plane and the octahedral coordination geometry around the metal completed by two axial pyridine ligands. Cyclic voltammetry and UV-visible-near infrared spectroscopic measurements have evidenced a sizable interaction between the two electroactive ligands and the stabilization of a mixed-valence state in the one-electron oxidized complexes. 相似文献
976.
Dusanka Ž. Obadović Anikó Vajda Maya Garić A. Bubnov Vera Hamplová M. Kašpar Katalin Fodor-Csorba 《Journal of Thermal Analysis and Calorimetry》2005,80(2):519-523
Summary Thermal properties of a homologous series of ferroelectric liquid crystals S-(-)-[4-(2-n-alkoxy-propionyloxy)]biphenyl-4'-[n-alkoxy-(3,5-dimethyl)]benzoate have been investigated by polarizing optical microscopy and differential scanning calorimetry.
The mesophases were identified and confirmed by X-ray too. Three binary mixtures were prepared from the individual homologues.
In one of the mixtures (Mix1), the ferroelectric SmC* phase has broadened and became enantiotropic. This mesophase remained
monotropic in the other two mixtures (Mix2, Mix3). The chiral nematic N* phase did not appear in Mix1, but remained monotropic
for the other two mixtures. Two molecular parameters, the layer spacing and the average intermolecular distance have been
calculated from the X-ray results for the homologues and their mixtures. An intercalated tail-to-tail packing of molecules
was found both in the single compounds and their mixtures resulting in the layer spacing about half of the molecular length
of the single compounds. 相似文献
977.
Miniaturizing all dimensions of apparatus, such as electronics and computers, is the current trend followed by scientists
in various fields. The idea of Lab-on-a-Chip has significantly expanded and found its broad applications in analytical chemistry.
Microplasmas can act as a sample excitation source and are the miniaturized versions of full-sized plasmas. These can be created
in various forms, such as direct current, microwave induced, capacitively coupled and inductively coupled plasmas. Scaling
down the size would reduce the amount of gases, liquids and consumables required, as well as the sample analysis time, which
in turn would decrease the operating costs. Therefore, several research groups are involved in the development of microplasmas
for utilisation in analytical instruments. 相似文献
978.
979.
Shandong Yuan Sharifah Bee Derouane-Abd Hamid Yongxue Li Pinliang Ying Qin Xin Eric G Derouane Can Li 《Journal of molecular catalysis. A, Chemical》2002,180(1-2):245-258
The conversion of n-C4H10 was undertaken on MoO3/HZSM-5 catalyst at 773–973 K and the phases of molybdenum species were detected by XRD. The XRD results show that bulk MoO3 on HZSM-5 can be readily reduced by n-C4H10 to MoO2 at 773 K and MoO2 can be gradually carburized to molybdenum carbide above 813 K. The molybdenum carbide formed from the carburization of MoO2 with n-C4H10 below 893 K is -MoC1−x with fcc-structure, while hcp-molybdenum carbide formed above 933 K. During the evolution of MoO3 to MoO2 (>773 K) or the carburization of MoO2 to molybdenum carbide (>813 K), deep oxidation, cracking and coke deposition are serious, in particular at higher reaction temperatures, these lead to the poor selectivity to aromatics. Aromatization of n-C4H10 can proceed catalytically on both Mo2C/HZSM-5 and MoO2/HZSM-5, the distribution of the products for the two catalysts is similar below 813 K, but the activity for Mo2C/HZSM-5 is much higher than that for MoO2/HZSM-5. 相似文献
980.