The Electrochemistry of Cytochrome c in Aqueous and Mixed Solvent Solutions: Thermodynamics, Kinetics and the Effect of Solvent Dielectric Constant: Thermodynamics, kinetics, and the effect of solvent dielectric constant

The solvent dielectric constant is considered an important factor in determining the redox potential of the heme-containing protein cytochrome c in solution. In this study, we investigate the electrochemical response of cytochrome c in aqueous/organic solvent mixtures (100% aqueous buffer, 30% acetonitrile, 40% dimethyl sulfoxide, and 50% methanol), reporting the redox potential (E^o′), enthalpy, and entropy of reduction. The temperature dependence of the solvent dielectric constant () was also measured. The results show that 6 alone cannot regulate the E^o′ of cytochrome c in mixed solvent systems. The implications of the temperature dependence of ε on the validity of the thermodynamic data are also discussed. The effect of solvent and temperature on the electron-transfer rate constant, k_s, was determined in each solvent mixture. A substantial increase in the activation energy for electron transfer was observed in 40% DMSO.