Fragata M, Bellemare F
Biophys Chem. 1982 May;15(2):111-9. doi: 10.1016/0301-4622(82)80023-9.
A theoretical model for the effect of the dielectric constant (c) of the solvent medium on ferrocytochrome c oxidation by ferricyanide is developed to account for the observed variations of the rate constant (k) of reactions in aqueous binary mixtures with alcohols (less than 5-10 mol% ethanol and propranolol). A correlation between k and c is found if ln k is expressed as a function of the Kirkwood parameter (c-1)(2c+1). The results of calculations indicate that the use of the 'overall dipole moment' of cytochrome c in oxidoreduction studies is likely to be unreliable. Instead, the decrease in k in alcohol/water mixtures is best explained--in conformity with Onsager's theory of the reaction field--by a polarity effect on the dipole moment of the cytochrome c heme upon diffusion of the polar solvent molecules into the low dielectric constant heme crevice.
建立了一个理论模型，用于解释溶剂介质的介电常数（c）对铁氰化物氧化亚铁细胞色素c的影响，以说明在与醇类（乙醇和普萘洛尔含量低于5 - 10摩尔%）的二元水混合物中反应速率常数（k）的观测变化。如果将ln k表示为柯克伍德参数（c - 1）（2c + 1）的函数，则可发现k与c之间存在相关性。计算结果表明，在氧化还原研究中使用细胞色素c的“总偶极矩”可能不可靠。相反，根据翁萨格反应场理论，醇/水混合物中k的降低最好解释为极性溶剂分子扩散到低介电常数的血红素缝隙中时，对细胞色素c血红素偶极矩产生的极性效应。
