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Ohne Zusammenfassung 相似文献
304.
The perpendicular band of the E1u vibration ν14 of C6H6, with band origin at 1038.2670 cm?1, was measured on a Bomem high-resolution Fourier transform spectrometer with a 246-cm optical path difference. The spectrum was deconvolved to an effective linewidth of ~0.002 cm?1. A total of 135 subbands have been assigned in the ν14 band. The band was found to be remarkably free of perturbations by other states. A Hamiltonian matrix of order 2, including merely the rotational l-type resonances between the ν14+(J, K) and ν14?(J, K ? 2) levels, was used for the treatment of the upper states of this band. A set of accurate spectroscopic constants was obtained, which reproduces a total of 3258 measured lines with an over-all standard deviation of 0.0006 cm?1. 相似文献
305.
Johns M Landon P Alderson T Hutchings GJ 《Chemical communications (Cambridge, England)》2001,(23):2454-2455
A composite catalyst comprising a physical mixture of a zeolite and a cobalt/manganese oxide Fischer-Tropsch catalyst decreases the formation of methane in the hydrogenation of carbon monoxide without significantly affecting conversion. 相似文献
306.
Thabano JR Breadmore MC Hutchinson JP Johns C Haddad PR 《Journal of chromatography. A》2007,1175(1):117-126
A novel approach for in-line solid-phase extraction capillary electrophoresis (SPE-CE) for basic analytes was developed. The method is based on the use of a weak cation-exchange monolith synthesised in situ in the front end of the CE capillary via photoinitiated polymerization to form poly(methacrylic acid-co-ethylene glycol dimethacrylate), which was used to create the SPE phase in-line with the CE separation capillary. The monolithic SPE material exhibited a surface area of 23.1 m2/g and a capacity of 403 nM for dopamine. Adsorption of the analytes as protonated, cationic species onto the SPE phase was achieved using an electrolyte of 6 mM phosphate and 12 mM sodium ion, buffered at pH 7.0, which is above the pKa of the monolith but below the pKa of the analytes. Elution of the analytes from the SPE phase was achieved using an electrolyte with a pH below that of the pKa of the monolith, namely 12 mM phosphate and 12 mM sodium ion, buffered at pH 3.0. Due to the discontinuous electrolyte combination, analytes were simultaneously eluted and focused as the electrophoretically mobilised pH step boundary moved through the SPE monolith, after which the analytes were separated by conventional CZE in the remainder of the capillary. Quantitative extraction from a solution of 0.5 microg/ml dopamine and epinephrine was achieved when flushing up to 15 column volumes of sample through the capillary. The limits of detection (S/N=3) for dopamine and epinephrine were 3.7 and 4.3 ng/ml, and this method provided a sensitivity enhancement for dopamine of 462 times compared to CZE using hydrodynamic injection. The developed method was used to preconcentrate a test mixture of neurotransmitters comprising dopamine, epinephrine, 5-hydroxytryptamine, metanephrine and also histamine. The applicability of this approach to real life samples was demonstrated by using a urine sample from a healthy person to detect dopamine at sub-ppm levels. 相似文献
307.
Adam J. Gaudry Rosanne M. Guijt Mirek Macka Joseph P. Hutchinson Cameron Johns Emily F. Hilder Greg W. Dicinoski Pavel N. Nesterenko Paul R. Haddad Michael C. Breadmore 《Analytica chimica acta》2013
A novel capillary electrophoresis (CE) approach has been developed for the simultaneous rapid separation and identification of common environmental inorganic anions and cations from a single sample injection. The method utilised a sequential injection-capillary electrophoresis instrument (SI-CE) with capacitively-coupled contactless conductivity detection (C4D) constructed in-house from commercial-off-the-shelf components. Oppositely charged analytes from a single sample plug were simultaneously injected electrokinetically onto two separate capillaries for independent separation and detection. Injection was automated and may occur from a syringe or be directly coupled to an external source in a continuous manner. Software control enabled high sample throughput (17 runs per hour for the target analyte set) and the inclusion of an isolation valve allowed the separation capillaries to be flushed, increasing throughput by removing slow migrating species as well as improving repeatability. Various environmental and industrial samples (subjected only to filtering) were analysed in the laboratory with a 3 min analysis time which allowed the separation of 23 inorganic and small organic anions and cations. Finally, the system was applied to an extended automated analysis of Hobart Southern Water tap water for a period of 48 h. The overall repeatability of the migration times of a 14 analyte standard sample was less than 0.74% under laboratory conditions. LODs ranged from 5 to 61 μg L−1. The combination of automation, high confidence of peak identification, and low limits of detection make this a useful system for the simultaneous identification of a range of common inorganic anions and cations for discrete or continuous monitoring applications. 相似文献
308.
Jose Castro-Perez Thomas P. Roddy Nico M. M. Nibbering Vinit Shah David G. McLaren Stephen Previs Athula B. Attygalle Kithsiri Herath Zhu Chen Sheng-Ping Wang Lyndon Mitnaul Brian K. Hubbard Rob J. Vreeken Douglas G. Johns Thomas Hankemeier 《Journal of the American Society for Mass Spectrometry》2011,22(9):1568-1569
309.
Andrew J. Devine Dr. Alice E. Parnell Dr. Catherine R. Back Dr. Nicholas R. Lees Dr. Samuel T. Johns Ainul Z. Zulkepli Rob Barringer Dr. Katja Zorn Dr. James E. M. Stach Prof. Matthew P. Crump Prof. Martin A. Hayes Dr. Marc W. van der Kamp Prof. Paul R. Race Prof. Christine L. Willis 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(3):e202213053
Abyssomicin C and its atropisomer are potent inhibitors of bacterial folate metabolism. They possess complex polycyclic structures, and their biosynthesis has been shown to involve several unusual enzymatic transformations. Using a combination of synthesis and in vitro assays we reveal that AbyV, a cytochrome P450 enzyme from the aby gene cluster, catalyses a key late-stage epoxidation required for the installation of the characteristic ether-bridged core of abyssomicin C. The X-ray crystal structure of AbyV has been determined, which in combination with molecular dynamics simulations provides a structural framework for our functional data. This work demonstrates the power of combining selective carbon-13 labelling with NMR spectroscopy as a sensitive tool to interrogate enzyme-catalysed reactions in vitro with no need for purification. 相似文献