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Roginsky, V.* ; Michel, C. ; Bors, W.

Reactivity of Semiquinones with Ascorbate and the Ascorbate Radical as Studied by Pulse Radiolysis.

Arch. Biochem. Biophys. 384, 74-80 (2000)
DOI
Open Access Green möglich sobald Postprint bei der ZB eingereicht worden ist.
Free-radical interactions between hydroquinones (QH2) and ascorbate (AscH−) have a profound impact in many biological situations. Despite the obvious biological significance, not much is known about the kinetics of reactions of QH2 and AscH− with their corresponding free radicals, i.e., semiquinones, Q•−, and the ascorbate radical, Asc•−. Furthermore, a general approach to reliably measure rate constants for the above reactions is fraught with complications. In this work, the kinetic behavior of Q•− and Asc•−, after pulse radiolytic oxidation of mixtures of a series of alkyl- and methoxy-substituted hydroquinones and ascorbate by azide radicals in aqueous buffer, pH 7.40, was monitored in submillisecond range by time-resolved UV spectroscopy. Rate constants for reactions of Q•− with AscH− (reaction [1]) and Asc•− (reaction [2]) were directly determined by using new kinetic procedures which distinguished between reactions [1] and [2]. The results show that the rate constants for reaction [2] vary only within a narrow range from 1.2 × 108 to 2.5 × 108 M−1 s−1 and do not display any pronounced correlation with Q•− structures. In contrast, the value of k1 for nonsubstituted Q•− was found to be (1.8 ± 0.2) × 105 M−1 s−1 and decreases with the number of alkyl and methoxy substituents as well as with the decrease of the one-electron reduction potential E(Q•−/QH2).
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Publikationstyp Artikel: Journalartikel
Dokumenttyp Wissenschaftlicher Artikel
Korrespondenzautor
Schlagwörter semiquinones hydroquinones ascorbate ascorbate radical pulse radiolysis kinetic spectroscopy rate constants redox potentials
ISSN (print) / ISBN 0003-9861
e-ISSN 1096-0384
Zeitschrift Archives of Biochemistry and Biophysics
Quellenangaben Band: 384, Heft: 1, Seiten: 74-80 Artikelnummer: , Supplement: ,
Verlag Elsevier
Nichtpatentliteratur Publikationen
Begutachtungsstatus Peer reviewed
Institut(e) Institute of Radiation Biology (ISB)