Novel PEFC Application for Deuterium Isotope Separation.
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ABSTRACT:
SUBMITTER: Matsushima H
PROVIDER: S-EPMC5503345 | biostudies-other | 2017 Mar
REPOSITORIES: biostudies-other
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Project description:The kinetic V/K isotope effect upon peroxidation of (1R)-[1-2H1]ethanol by liver catalase was studied by using a radiochemical assay with both 3H ad 14C as tracers. The value of 1.9 found is in agreement with the value of 2.52 for peroxidation of (1R)-[1-3H1]ethanol according to the 'Swain equation' [Swain, Stivers, Ruver & Schaad (1958) J. Am. Chem. Soc. 80, 5885-5893]. There was no isotope effect on V, the catalase haem up to 500 min-1. Even at rates 20-fold higher the isotope effect on V may not be different from 1. A detailed description of the synthesis of the 2H- and 3H-substituted ethanol compounds and the analysis of these has been deposited as Supplementary Publication SUP 50110 (5 pages) at the British Library Lending Division, Boston Spa, Wetherby, W. Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1978) 169,5.
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Project description:Isotope effects on the excited-state dynamics of single- and double-stranded GC-containing DNAs were studied by femtosecond transient absorption spectroscopy. A pronounced deuterium isotope effect was observed in alternating d(GC)(9).d(GC)(9), but none was seen in the nonalternating or single-stranded variations investigated. These findings demonstrate that an interstrand process involving proton-coupled electron transfer contributes to the excited-state dynamics in DNAs having an appropriate base sequence.
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Project description:The biosynthetic pathways to isoprenoid compounds involve transfer of the prenyl moiety in allylic diphosphates to electron-rich (nucleophilic) acceptors. The acceptors can be many types of nucleophiles, while the allylic diphosphates only differ in the number of isoprene units and stereochemistry of the double bonds in the hydrocarbon moieties. Because of the wide range of nucleophilicities of naturally occurring acceptors, the mechanism for prenyltransfer reactions may be dissociative or associative with early to late transition states. We have measured ?-secondary kinetic isotope effects operating through four bonds for substitution reactions with dimethylallyl derivatives bearing deuterated methyl groups at the distal (C3) carbon atom in the double bond under dissociative and associative conditions. Computational studies with density functional theory indicate that the magnitudes of the isotope effects correlate with the extent of bond formation between the allylic moiety and the electron-rich acceptor in the transition state for alkylation and provide insights into the structures of the transition states for associative and dissociative alkylation reactions.
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Project description:A solvent deuterium isotope effect on the catalytic affinity (km) and catalytic constant (kcat) of tyrosinase in its action on different monophenols and o-diphenols was observed. The catalytic constant decreased in all substrates as the molar fraction of deuterated water in the medium increased, while the catalytic affinity only decreased for the o-diphenols with an R group in C-1 [-H, -CH3 and -CH(CH3)2]. In a proton inventory study of the oxidation of o-diphenols, the representation of kcat fn/kcat f0 against n (atom fractions of deuterium), where kcat fn is the catalytic constant for a molar fraction of deuterium (n) and kcat f0 is the corresponding kinetic parameter in a water solution, was linear for all substrates, indicating that only one of the four protons transferred from the hydroxy groups of the two molecules of substrate, which are oxidized in one turnover, is responsible for the isotope effects, the proton transferred from the hydroxy group of C-4 to the peroxide of the oxytyrosinase form (Eox). However, in the representation of Km fn/Km f0 against n, where Km fn represents the catalytic affinity for a molar fraction of deuterium (n) and Km f0 is the corresponding kinetic parameter in a water solution, a linear decrease was observed as n increased in the case of o-diphenols with the R group [-H, -CH3 and -CH(CH3)2], and a parabolic increase with other R groups, indicating that more than one proton is responsible for the isotope effects on substrate binding. In the case of monophenols with six protons transferred in the catalytic cycle, the isotope effect occurs in the same way as for o-diphenols. In the present paper, the fractionation factors of different monophenols and o-diphenols are described and possible mechanistic implications are discussed.
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