Issue 4, 1999

The kinetics and thermodynamics of quinone–semiquinone–hydroquinone systems under physiological conditions

Abstract

The steady-state concentration of semiquinones (Q˙–) determined by EPR in the mixtures of eleven alkyl-, methoxy- and chloro-substituted 1,4-benzoquinones as well as 1,4-naphthoquinone (Q) with corresponding hydroquinones (QH2) in aqueous buffer, pH 7.40, was used to calculate a constant for equilibrium (1) Q + QH2⇌Q˙– + Q˙– + 2H+ (k1; 2k–1; K1 = k1/2k–1). The rate constants for comproportionation between Q and QH2, k1, were calculated from the combination of K1 determined in this work and 2k–1 reported previously. The Nernst equation was applied to calculate the change in one-electron reduction potential ΔE1 = E(Q/Q˙–) – E(Q˙–/QH2) in equilibrium (1). The E(Q˙–/QH2) values were calculated from ΔE1 and the values of E(Q/Q˙–) known from the literature. The correlations between E(Q˙–/QH2) and E(Q/Q˙–) as well as between ΔE1 (k1) and E(Q/Q˙–) are discussed. The values of ΔE1 and k1 are suggested to be the key factors governing the autoxidation of QH2.

Article information

Article type
Paper

J. Chem. Soc., Perkin Trans. 2, 1999, 871-876

The kinetics and thermodynamics of quinone–semiquinone–hydroquinone systems under physiological conditions

V. A. Roginsky, L. M. Pisarenko, W. Bors and C. Michel, J. Chem. Soc., Perkin Trans. 2, 1999, 871 DOI: 10.1039/A807650B

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