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Unstable Intermediate (unstable + intermediate)
Selected AbstractsA novel coupled enzyme assay reveals an enzyme responsible for the deamination of a chemically unstable intermediate in the metabolic pathway of 4-amino-3-hydroxybenzoic acid in Bordetella sp. strain 10dFEBS JOURNAL, Issue 15 2004Chika Orii 2-Amino-5-carboxymuconic 6-semialdehyde is an unstable intermediate in the meta -cleavage pathway of 4-amino-3-hydroxybenzoic acid in Bordetella sp. strain 10d. In vitro, this compound is nonenzymatically converted to 2,5-pyridinedicarboxylic acid. Crude extracts of strain 10d grown on 4-amino-3-hydroxybenzoic acid converted 2-amino-5-carboxymuconic 6-semialdehyde formed from 4-amino-3-hydroxybenzoic acid by the first enzyme in the pathway, 4-amino-3-hydroxybenzoate 2,3-dioxygenase, to a yellow compound (,max = 375 nm). The enzyme in the crude extract carrying out the next step was purified to homogeneity. The yellow compound formed from 4-amino-3-hydroxybenzoic acid by this purified enzyme and purified 4-amino-3-hydroxybenzoate 2,3-dioxygenase in a coupled assay was identified as 2-hydroxymuconic 6-semialdehyde by GC-MS analysis. A mechanism for the formation of 2-hydroxymuconic 6-semialdehyde via enzymatic deamination and nonenzymatic decarboxylation is proposed based on results of spectrophotometric analyses. The purified enzyme, designated 2-amino-5-carboxymuconic 6-semialdehyde deaminase, is a new type of deaminase that differs from the 2-aminomuconate deaminases reported previously in that it primarily and specifically attacks 2-amino-5-carboxymuconic 6-semialdehyde. The deamination step in the proposed pathway differs from that in the pathways for 2-aminophenol and its derivatives. [source] Oxidative behavior and relative reactivities of some unsaturated compounds towards hexachloroiridate(IV) in perchloric acid mediumINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 7 2002Kalyan K. Sen Gupta The kinetics of the oxidation of styrene, cinnamic acid, and some of their substituted derivatives by hexachloroiridate(IV) in dimethyl formamide,water mixtures and in the presence of perchloric acid have been investigated. The reactions appear to proceed via the formation of an unstable intermediate 1:1 complex between iridium(IV) and the substrate, followed by the decomposition of the complex in the rate-determining step. Correlation with , yielded , values of ,4.0 and ,3.5 which suggests the formation of a cationic intermediate in the rate-determining step of the reaction. Subsequent cleavage of the carbon,carbon bond yielded the product aldehydes. Thermodynamic and activation parameters associated with the equilibrium and the rate-determining steps were also evaluated. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 411,417, 2002 [source] The mechanisms of the homogeneous, unimolecular, elimination kinetics of several , -substituted diethyl acetals in the gas-phaseJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 9 2010José R. Mora Abstract The rates of gas-phase elimination of several , -substituted diethyl acetals have been determined in a static system and seasoned with allyl bromide. The reactions, inhibited with toluene, are homogeneous, unimolecular, and follow first-order law kinetics. These elimination processes involve two parallel reactions. The first parallel reaction yields ethanol and the corresponding ethyl vinyl ether. The latter product is an unstable intermediate and further decomposes to ethylene and the corresponding substituted aldehyde. The second parallel reaction gives ethane and the corresponding ethyl ester. The kinetics has been measured over the temperature range of 370,441,°C and pressure range of 23,160,torr. The rate coefficients are given by the following Arrhenius equations: The differences in the rates of ethanol formation may be attributed to electronic transmission of the , -substituent. The comparative kinetic and thermodynamic parameters of the parallel reactions suggest two different concerted polar four-membered cyclic transition state types of mechanisms. Copyright © 2010 John Wiley & Sons, Ltd. [source] Direct observation of the unstable intermediates in radical addition reaction by using an interfacing microchip combined with an NMRMAGNETIC RESONANCE IN CHEMISTRY, Issue 11 2007Masamichi Nakakoshi Abstract Direct observation of the unstable intermediate in the radical addition reaction of the oxime ether 1 mediated by triethylborane (Et3B) is described using 1H and 11B micro channeled cell for synthesis monitoring (MICCS), which was recently developed as an interfacing microchip for NMR. It was possible that the signal of the intermediate was observed as a result of using MICCS technique with a standard NMR instrument. This result supports the structure of the intermediate analyzed by diffusion-ordered spectroscopy (DOSY) NMR method in a previous paper. The procedure of micro channeled cell for synthesis monitoring-nuclear magnetic resonance (MICCS-NMR) was much easier than that of DOSY method. It was proven that it could be applied to the reaction in an anhydrous condition. Copyright © 2007 John Wiley & Sons, Ltd. [source] | ||||||||||