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601.
The nature and number of species in Yb(III)-daunomycin solutions have been investigated by graphical and computational methods both of which are based on matrix rank analyses. Determination of the rank of an absorbance matrix, which is the largest non-zero determinant of the matrix, permits the determination of the number of species in solution. The multiple regression analyses performed on the Yb(III)-daunomycin system enabled the determination of the nature of a species that exists at different metal to ligand ratios: ML2 at ratios less than 1.5, M2L at ratios greater than 15, and probably predominantly ML in between the two ratios. The matrix rank analyses approach is suited, it was found, to bracket the range of concentration ratios where a particular species predominates. While this is true by and large, it appears that the adequacy of the methods depends on the degree of complexity of the system. 相似文献
602.
Summary As the transition state for the solvolysis of [Co(NH3)5Cl]2+ ions is known to have Cl- ions in a situation closely similar to that in the bulk solvent, the kinetics of this solvolysis have been investigated for comparison in H2O with added cosolvents of low and high hydrophobicities. A linear variation of log(rate constant) with the reciprocal of the dielectric constant is found with the former, but not with the latter cosolvent. Maxima in the enthalpies and entropies of activation found using the more hydrophobic cosolvent appear at solvent compositions where extrema occur in the physical properties influenced by structural changes in the solvent. The application of a free energy cycle to the solvolysis in H2O and in the mixtures shows that the emergent solvated cobalt(III) ion in the transition state is more stabilised in the latter than [Co(NH3)5Cl]2+ with both cosolvents. The application of such a cycle to cases where the initial state is destabilised in the mixture is discussed. 相似文献
603.
Matthew J. Cuthbertson Darryl W. Hawker Peter R. Wells 《Journal of organometallic chemistry》1985,287(1):7-23
Product and kinetic studies on the reactions of hydrogen chloride in methanol solution with the substrates (CH3)3SnM(CH3)3 (M = Sn; Ge and Si) show that both SnM and SnCH3 cleavage reactions occur, at similar rates, and are followed by other reactions giving complex but explicable mixtures of products. Similar behaviour is observed for trifluoroacetolysis in carbon tetrachloride solution, and some intermediates are observable. Trifluoroacetolysis of (CH3)3SnC(CH3)3 results in exclusive SnCH3 cleavage. The very slow apparent solvolysis in acetic acid solution is thought to involve reaction with dissolved oxygen. 相似文献
604.
Wells JM Chrisman PA McLuckey SA 《Journal of the American Society for Mass Spectrometry》2002,13(6):614-622
Novel instrumentation has been developed which allows for the sequential injection and subsequent reaction of oppositely-charged ions generated via electrospray ionization (ESI) in a quadrupole ion trap mass spectrometer. The instrument uses a DC turning quadrupole to sequentially direct the two ion polarities into the ion trap from ESI sources which are situated 90 degrees from the axial (z) dimension of the trap, and 180 degrees from one another. This arrangement significantly expands the range of ionic reactants amenable to study over previously-used instrumentation. For example, ion/ion reactions of multiply-charged positive ions with multiply-charged negative ions can be studied. Also, reactions of multiply-charged ions with singly-charged ions of opposite polarity that could not be generated by previously used ionization methods, or that could not be efficiently injected through the ion trap ring electrode, can be studied with the new instrument. This capability allows, for example, the charge state manipulation of negatively-charged precursor and product ions derived from proteins and oligonucleotides via proton transfer reactions with singly-charged cations generated by ESI. 相似文献
605.
606.
Miller KA Bartolin JM O'Neill RM Sweeder RD Owens TM Kampf JW Banaszak Holl MM Wells NJ 《Journal of the American Chemical Society》2003,125(30):8986-8987
Regioselective, room-temperature C-H activation of alkanes and ethers by stable germylenes and aryl halides is reported. Germylenes, Ge[CH(SiMe3)2]2 and Ge[N(SiMe3)2]2, and aryl halides, PhI, PhBr, and PhCl, have been employed. High yields of C-H activation products can be obtained through the use of high-dilution techniques. 相似文献
607.
Louis G. M. Th. Tuinstra Arie H. Roos Dave E. Wells Ben Griepink 《Mikrochimica acta》1989,97(1-2):1-7
A comparison is made between interlaboratory studies in which individual chlorobiphenyls (CBs) are measured in fish and sludge samples. The target coefficient of variation (CV(R)) between laboratories at CB levels of 0.01–1.0 mg/kg should be in the order of 20–30%. An improvement in the CV(R) is clearly shown in studies in which a learning program, paying attention to the optimization of gas Chromatographic operating conditions, is included. For standard solutions, where no interference problems of the matrix occur, excellent CV(R)s are obtained in the order of 6%. In fish oil CV(R)s of 10–30% and in sludge CV(R)s of 20–30% are reached. 相似文献
608.
The dissociation constants of (CH3)3PbCl at 26°C in water and in methanol have been determined to be 0.51 mol/l and 4.65 x 10 -4 mol/l, respectively, from the variations of Pb NMR chemical shifts (by INDOR) with concentration. Chemical shifts to (CH3)4Pb have been obtained for (CH3)3PbCl, for solvated (CH3)3Pb+, and for a possible dimer [(CH3)3PbCl]2 formed in methanol. 相似文献
609.
The formation constants for CH3HgCl2? at 26°C (0.31 l/mole), and for CH3HgBr2? at 26°C (0.94 l/mole) and at 60°C (0.70 l/mole) in ethanol solution have been determined from the variation of Hg NMR chemical shift (by INDOR) with composition of methylmercuric halide-lithium halide solutions. These data have been employed in a reexamination of the “one-anion” and “two-anion” catalysed reactions of mercuric bromide with alkylmercuric bromides. 相似文献
610.
Jemal M Ouyang Z Zhao W Zhu M Wu WW 《Rapid communications in mass spectrometry : RCM》2003,17(24):2732-2740
Using a single platform of a triple-quadrupole mass spectrometer equipped with enhanced resolution and accurate mass capabilities, a strategy for metabolite identification of a drug in a biological matrix has been demonstrated. The strategy is based on first screening for metabolites via neutral loss and precursor ion scan schemes, devised as the result of the product ion spectrum of a matrix-free standard of the drug. The accurate masses of the precursor ions identified via the two scan schemes plus the precursor ions of structurally likely metabolites are then determined by enhanced resolution, accurate mass (AM) selected ion monitoring (SIM). The identities of the metabolites are further established by determining the accurate masses of the product ions via enhanced resolution AM selected reaction monitoring (SRM). The feasibility of the strategy was demonstrated using a liver microsome incubation sample of nefazodone, an antidepressant drug. The neutral loss and precursor ion screening runs were able to identify most of the metabolites of nefazodone. The subsequent SIM and SRM experiments gave mass accuracy of better than +/-0.003 u for the masses of the precursor and product ions of nefazodone and all the metabolites. The ability to perform metabolite screening by using the scan features followed by accurate mass determinations on the same instrument is an attractive feature of using a triple-quadrupole mass spectrometer with enhanced resolution and accurate mass capability. 相似文献