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81.
A reversed-phase liquid chromatographic column-switching system was used for the determination of phenol, benzoic acid and cresol (PBC) in the presence of toluene in ground water microcosm. A precolumn was connected in series with an analytical column via a column-switching valve. After the injection, as soon as PBC were eluted from the precolumn to the analytical column, the valve was switched so that the precolumn was between the analytical column and the UV detector. Toluene and other non-polar compounds were eluted from the precolumn in a very short time and detected along with the solvent front. Subsequently, PBC were separated on the analytical column and passed through the precolumn one more time before being detected by the UV detector. The total analysis time was 15 min. This technique facilitated the study of the basic mechanism and path way of anaerobic degradation of toluene in ground water aquifer. 相似文献
82.
A rapid method for the simultaneous quantification of non-volatile and volatile fatty acids in aqueous sample by ion-exclusion chromatography is described. The sample is directly injected into the column and detected by a chemically suppressed conductivity detector, connected in tandem with an UV detector at 210 nm. The method allows detection of fatty acid as low as 1 ppm with a linear dynamic range up to 1000 ppm. At least 13 fatty acids can be determined within 50 min. This technique has been used to monitor the common fermentation products (lactate, acetate, propionate and butyrate) of the reductive dehalogenation of tetrachloroethene by anaerobic bacteria. 相似文献
83.
Methods are described for the extraction and qualitative gas-liquid chromatography of a series of microbial transformation systems in which various Streptomycetes and fungi were screened for N-dealkylation activity against a variety of drug molecules. The possibility that microbial transformation products could react under extraction conditions to form gem-diamines was investigated. Rapid on-column acetylation permitted the resolution of N-dealkylated products from starting substrate. Incomplete acetylation under the conditions used ensured that each N-dealkylated transformation product formed at least two species with characteristic retention times; with careful standardization, this increased confidence in the identifications. 相似文献
84.
Kaluzna IA Matsuda T Sewell AK Stewart JD 《Journal of the American Chemical Society》2004,126(40):12827-12832
Eighteen key reductases from baker's yeast (Saccharomyces cerevisiae) have been overproduced in Escherichia coli as glutathione S-transferase fusion proteins. A representative set of alpha- and beta-keto esters was tested as substrates (11 total) for each purified fusion protein. The stereoselectivities of beta-keto ester reductions depended both on the identity of the enzyme and the substrate structure, and some reductases yielded both L- and D-alcohols with high stereoselectivities. While alpha-keto esters were generally reduced with lower enantioselectivities, it was possible in all but one case to identify pairs of yeast reductases that delivered both alcohol antipodes in optically pure form. Taken together, the results demonstrate not only that individual yeast reductases can be used to supply important chiral building blocks, but that GST-fusion proteins allow rapid identification of synthetically useful biocatalysts (along with their corresponding genes). 相似文献
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86.
Frank Podebrad Martin Heil Saandra Leib Bernhard Geier Thomas Beck Armin Mosandl Adrian C. Sewell Hans Bhles 《Journal of separation science》1997,20(7):355-362
Maple Syrup Urine disease (USUD) is an autosomal recessive inherited metabolic disorder of branched-chain amino acid (L-valin, L-leucine, and L-isoleucine metabolism named after the characteristic smell of affected patients urine. MSUD is caused by a deficiency of the branched-chain α-keto acid dehydrogenase compex resulting in an accumulation of branched-chain aamino acids and the corresponding α-keto-and α-hydroxy acids in blood, urine and cerebrospinal fluid causing neurological damage and mental retardation. The enantioselective analysis of chiral MSUD metabolites and analysis of achiral compounds as corresponding N,O-methoxycarbonyl methyl esters by derivatization with methyl chloroformate (MCF) has been achieved simultaneusly by enantioselective multidimensional gas chromatography-mass spectrometry using heptakis (2,3-di-O-methyl-6-O-tert-butyl-dimethyl-silyl)-β-cyclodextrin as chiral stationary phase. Derivatization with MCF allows the analysis of the structurally different metabolitetes such as branched-chain-carboxylic-, α-oxo-, α-hydroxy- and α-amino acids in a single chromaatographic run. Mass selective detection immensely improves the unequivocaaal identification of metabolites even when they occur as trace compound. The described method allows a reliable screening of MSUD metabolites in patients' urine without time consuming sample preparation and is also suitable for label enrichment analysis without any methodical changes. During this investigation urine sample from three MSUD paatients were analyzed. 相似文献
87.
The spectroscopic and photophysical properties of zeolite-Y-entrapped [Ru(bpy)3]2+ co-doped with either [Fe(bpy)3]2+ or [Fe(tpy)2]2+ over a range of iron complex loadings are presented. In solution, [Ru(bpy)3]2+ undergoes efficient bimolecular energy transfer to [Fe(bpy)3]2+, whereas only radiative or trivial energy transfer occurs between [Ru(bpy)3]2+ and [Fe(tpy)2]2+. In sharp contrast, within zeolite Y, both [Fe(bpy)3]2+ and [Fe(tpy)2]2+ were found to effectively quench the donor emission. Fitting the Perrin model to the photophysical data yields an effective quenching radius of 32 and 27 A, respectively, for [Fe(bpy)3]2+ and [Fe(tpy)2]2+. The long-range nature of the quenching suggests F?rster energy transfer. Detailed spectroscopic investigations indicate that [Fe(tpy)2]2+ bound within zeolite Y undergoes significant distortion from octahedral geometry. This distortion results in increased oscillator strength and enhanced spectral overlap, between the [Ru(bpy)3]2+ (3)d pi-pi* donor emission and the co-incident acceptor (1)T2-(1)A1 ligand field absorption compared with solution. This turns on an efficient energy transfer to [Fe(tpy)2]2+ within the confinement of the zeolite Y supercage. Overall, this is an interesting example of the ability of the zeolite environment to provoke new photophysical processes not possible in solution. 相似文献
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90.
The multistage Rh-catalyzed dehydrocoupling of the secondary amine-borane H(3)B·NMe(2)H, to give the cyclic amino-borane [H(2)BNMe(2)](2), has been explored using catalysts based upon cationic [Rh(PCy(3))(2)](+) (Cy = cyclo-C(6)H(11)). These were systematically investigated (NMR/MS), under both stoichiometric and catalytic regimes, with the resulting mechanistic proposals for parallel catalysis and autocatalysis evaluated by kinetic simulation. These studies demonstrate a rich and complex mechanistic landscape that involves dehydrogenation of H(3)B·NMe(2)H to give the amino-borane H(2)B═NMe(2), dimerization of this to give the final product, formation of the linear diborazane H(3)B·NMe(2)BH(2)·NMe(2)H as an intermediate, and its consumption by both B-N bond cleavage and dehydrocyclization. Subtleties of the system include the following: the product [H(2)BNMe(2)](2) is a modifier in catalysis and acts in an autocatalytic role; there is a parallel, neutral catalyst present in low but constant concentration, suggested to be Rh(PCy(3))(2)H(2)Cl; the dimerization of H(2)B═NMe(2) can be accelerated by MeCN; and complementary nonclassical BH···HN interactions are likely to play a role in lowering barriers to many of the processes occurring at the metal center. These observations lead to a generic mechanistic scheme that can be readily tailored for application to many of the transition-metal and main-group systems that catalyze the dehydrocoupling of H(3)B·NMe(2)H. 相似文献