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排序方式: 共有1024条查询结果,搜索用时 8 毫秒
31.
Gianfranco Denti Mauro Ghedini Jon A. McCleverty Harry Adams Neil A. Bailey 《Transition Metal Chemistry》1982,7(4):222-224
Summary Treatment of [Mo{HB(3,5-Me2C3HN2)3}(NO)I2] with one or two moles of AgPF6 in acetonitrile afforded the paramagnetic (one unpaired electron) complex [Mo{HB(3,5-Me2C3NH2)3}(NO)(NCMe)2][PF6]. The structure of this complex was determined crystallographically, and the six-coordinate geometry of the complex cation confirmed. 相似文献
32.
E Bailey A G Brooks R Purchase M Meakings M Davies D G Walters 《Journal of chromatography. A》1987,421(1):21-31
An improved method has been developed for the determination of the major neutral steroids (cholesterol and 5 beta-cholestan-3 beta-ol) and unconjugated bile acids (deoxycholic acid and lithocholic acid) in human faeces, using capillary gas chromatography with flame ionization detection. The freeze-dried faecal sample was subjected to a two-stage Soxhlet extraction followed by an aqueous alkali-organic solvent partition step to separate neutral steroids from bile acids. The neutral steroids were analysed as their trimethylsilyl ether derivatives on an OV-1 capillary column. The bile acids were further purified on a Sep-Pak C18 cartridge and then fractionated on a Sep-Pak SIL cartridge. Unconjugated bile acids were analysed as their methyl ester-trimethylsilyl ether derivatives also on an OV-1 capillary column. Quantitation of neutral steroids and unconjugated bile acids was achieved by reference to appropriate internal standards, added to the faecal extract immediately after the Soxhlet extraction stage. The method is being used in a study of the effect of diet on the metabolic activity of human gut flora. 相似文献
33.
A rapid method is presented for the gravimetric determination of molybdenum (as the oxinate) in ferromolybdenum and molybdenum additives. The sample is fused with a mixed flux of sodium peroxide and sodium carbonate in a zirconium crucible for complete decomposition. Leaching the cooled fusion cake with water provides instantaneous separation of molybdenum as sodium molybdate from iron(III) and other hydrous oxides. After filtration, the molybdenum is precipitated with oxine after addition of EDTA and oxalate to obviate interference from other metal oxinates, and determined gravimetrically. The precision and accuracy are comparable to those of referee methods. 相似文献
34.
P. M. Henrichs J. M. Hewitt L. J. Schwartz D. B. Bailey 《Journal of polymer science. Part A, Polymer chemistry》1982,20(3):775-782
Spin-lattice relaxation times and nuclear Overhauser enhancements (NOE) for 13C nuclei in copolymers of acrylonitrile and vinylidene chloride were measured at 20.1 and 67.9 MHz. In the ? CCl2? region of the spectrum T1 and NOE values of the various resonances are equal within experimental error and are invariant to changes in composition. The T1 and NOE values of the ? CCl2? region, however, are not equal to those of the ? CH? or ? CN region. As a result compositions cannot be calculated by direct comparison of the areas in the ? CCl2? region and either the ? CH? or the ? CN region. Discrepancies can be corrected for the ? CH? resonances by multiplication of the area by an empirical constant. A similar constant for the ? CN region is composition-dependent at 20.1 and 67.9 MHz. A chemical shift anisotropy mechanism is postulated as important for relaxation of the ? CN resonances. The overall influence of variable T1 and NOE values on quantitative determination of polymer composition is considered. 相似文献
35.
Measuring the metabolome: current analytical technologies 总被引:44,自引:0,他引:44
The post-genomics era has brought with it ever increasing demands to observe and characterise variation within biological systems. This variation has been studied at the genomic (gene function), proteomic (protein regulation) and the metabolomic (small molecular weight metabolite) levels. Whilst genomics and proteomics are generally studied using microarrays (genomics) and 2D-gels or mass spectrometry (proteomics), the technique of choice is less obvious in the area of metabolomics. Much work has been published employing mass spectrometry, NMR spectroscopy and vibrational spectroscopic techniques, amongst others, for the study of variations within the metabolome in many animal, plant and microbial systems. This review discusses the advantages and disadvantages of each technique, putting the current status of the field of metabolomics in context, and providing examples of applications for each technique employed. 相似文献
36.
Petrie RJ Bailey T Gorman CB Genzer J 《Langmuir : the ACS journal of surfaces and colloids》2004,20(23):9893-9896
In this Letter, we report on the motion of water droplets on surfaces decorated with molecular gradients comprising semifluorinated (SF) organosilanes. SF molecular gradients deposited on flat silica substrates facilitate faster motion of water droplets relative to the specimens covered with an analogous hydrocarbon gradient. Further increase in the drop speed is achieved by advancing it along porous substrates coated with the SF wettability gradients. The results of our experiments are in quantitative agreement with a simple scaling theory that describes the faster liquid motion in terms of reduced friction at the liquid/substrate interface. 相似文献
37.
Wenzel TJ Freeman BE Sek DC Zopf JJ Nakamura T Yongzhu J Hirose K Tobe Y 《Analytical and bioanalytical chemistry》2004,378(6):1536-1547
Chiral crown ethers 1 and 5 are useful enantiomeric discriminating agents in 1H NMR spectroscopy for neutral and protonated primary amines, amino acids, and amino alcohols. The presence of the carboxylic acid groups in 1 and 5 provide sites at which ytterbium(III) can bind. Adding ytterbium(III) nitrate to crown–substrate mixtures in methanol-d4 causes shifts in the spectra of substrates and often enhances the chiral discrimination in the 1H NMR spectrum. The enhancement in enantiomeric discrimination that occurs in the presence of ytterbium(III) allows lower concentrations of the crown ether to be used in chiral recognition studies. Several amide derivatives of 1 were prepared and evaluated as chiral NMR discriminating agents, although except for 1e, these were less effective than 1. 相似文献
38.
Latent low-coordinate titanium imides supported by a sterically encumbering beta-diketiminate ligand
Basuli F Clark RL Bailey BC Brown D Huffman JC Mindiola DJ 《Chemical communications (Cambridge, England)》2005,(17):2250-2252
Addition of an equal molar quantity of R- (R = Me, SiMe3) to complex (Nacnac)Ti=NAr(OTf) (Nacnac- =[ArNC(tBu)]2CH, Ar = 2,6-iPr2C6H3) forms the imido alkyl (Nacnac)Ti=NAr(R), which can be readily protonated to afford [(Nacnac)Ti=NAr(L)]+ (L = THF, Et2O, eta1-C6H5NMe2), or treated with B(C6F5)3 to afford the zwitterion (Nacnac)Ti=NAr(micro-CH3)B(C6F5)3. 相似文献
39.
Cecil D. Bailey 《Foundations of Physics》1981,11(3-4):279-296
It has been recognized in the literature of the calculus of variations that the classical statement of the principle of least action (Hamilton's principle for conservative systems) is not strictly correct. Recently, mathematical proofs have been offered for what is claimed to be a more precise statement of Hamilton's principle for conservative systems. According to a widely publicized version of this more precise statement, the action integral for conservative systems is a minimum for discrete systems for small time intervals only and is never minimum for continuous systems. In this paper, two contradictions to this more precise statement are demonstrated, one for a discrete system and one for a continuous system. 相似文献
40.
Harry Adams Neil A. Bailey David E. Fenton Choki Fukuhara Masatoshi Kanesato 《Supramolecular chemistry》2013,25(4):325-330
Abstract The synthesis and crystal structure of the diprotonated cryptand derived from the reaction of tren and 2,6-diacetyl pyridine is reported. The imino nitrogens of the Schiff base linkages are directed so that the dicarbimine functions are in trans, trans geometry relative to the pyridine C-N bond. This configuration has not previously been reported in related pyridine-derived Schiff base macrocycles. 相似文献