title: Antioxidant reactions of dihydrolipoic acid and lipoamide with triplet duroquinone.
abstract: The oxidation of the antioxidants dihydrolipoate and lipoamide by triplet duroquinone (3DQ) has been studied by laser flash photolysis and time-resolved resonance Raman (TR3) spectroscopy. Reaction of 3DQ with lipoamide by electron transfer [k(H2O)/k(D2O approximately 1] was more rapid than with dihydrolipoate, in which a proton is also involved [k(H2O)/k(D2O approximately 2]. For dihydrolipoate at neutral pH the undeprotonated form was the major reactive species with k approximately 10(9) dm3 mol-1 s-1. At higher pH values the reaction of ionised (thiolate) forms was observed with k > or = 4 x 10(9) dm3 mol-1 s-1. The electron transfer mechanism of reaction between 3DQ and lipoamide was confirmed by TR3 spectra in which formation of the durosemiquinone radical anion and lipoamide disulfide radical cation (RSS+.) was observed.
authors.affiliation: Department of Biological Sciences, University of Salford, United Kingdom.
authors.forename: R H
authors.initials: RH
authors.lastname: Bisby
authors.forename: A W
authors.initials: AW
authors.lastname: Parker
mesh_terms: D000975:Antioxidants / Q000378:metabolism*; D016227:Benzoquinones / Q000378:metabolism*; D005609:Free Radicals / Q000378:metabolism; D007700:Kinetics; D007834:Lasers; D010782:Photolysis; D013059:Spectrum Analysis, Raman; D008063:Thioctic Acid / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D000975:Antioxidants; D016227:Benzoquinones; D005609:Free Radicals; D008063:Thioctic Acid; C015144:dihydrolipoic acid; C013091:lipoamide; C034257:duroquinone