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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)

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Open Access Green as soon as Postprint is submitted to ZB.

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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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Publication type Article: Journal article

Document type Scientific Article

Corresponding Author

Keywords semiquinones hydroquinones ascorbate ascorbate radical pulse radiolysis kinetic spectroscopy rate constants redox potentials

ISSN (print) / ISBN 0003-9861

e-ISSN 1096-0384

Journal Archives of Biochemistry and Biophysics

Quellenangaben Volume: 384, Issue: 1, Pages: 74-80

Publisher Elsevier

Non-patent literature Publications

Reviewing status Peer reviewed

Institute(s) Institute of Radiation Biology (ISB)