The kinetics and thermodynamics of quinone–semiquinone–hydroquinone systems under physiological conditions
作者:Vitaly A. Roginsky、Leonid M. Pisarenko、Wolf Bors、Christa Michel
DOI:10.1039/a807650b
日期:——
The steady-state concentration of semiquinones (QËâ) 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 + QH2âQËâ + QËâ + 2H+ (k1; 2kâ1; K1 = k1/2kâ1). The rate constants for comproportionation between Q and QH2, k1, were calculated from the combination of K1 determined in this work and 2kâ1 reported previously. The Nernst equation was applied to calculate the change in one-electron reduction potential ÎE1 = E(Q/QËâ) â E(QËâ/QH2) in equilibrium (1). The E(QËâ/QH2) values were calculated from ÎE1 and the values of E(Q/QËâ) known from the literature. The correlations between E(QËâ/QH2) and E(Q/QËâ) as well as between ÎE1 (k1) and E(Q/QËâ) are discussed. The values of ÎE1 and k1 are suggested to be the key factors governing the autoxidation of QH2.
在pH 7.40的水性缓冲液中,通过电子顺磁共振(EPR)测定的十一种烷基、甲氧基和氯取代的1,4-苯醌和1,4-萘醌(Q)与相应的氢醌(QH2)混合物中的稳态亚醌浓度(QËâ)被用于计算平衡常数 (1) Q + QH2âQËâ + QËâ + 2H+(k1;2kâ1;K1 = k1/2kâ1)。Q与QH2之间的等比例反应速率常数k1是通过结合本研究中确定的K1与之前报道的2kâ1计算得出的。应用能斯特方程计算平衡 (1) 中单电子还原电位的变化ÎE1 = E(Q/QËâ) - E(QËâ/QH2)。E(QËâ/QH2)值是从ÎE1和文献中已知的E(Q/QËâ)值计算得出的。探讨了E(QËâ/QH2)与E(Q/QËâ)之间的关系,及ÎE1 (k1)与E(Q/QËâ)之间的关系。提出ÎE1和k1的值是决定QH2自氧化的关键因素。