Electrochemistry of Cytochrome c in Aqueous and Mixed Solvent Solutions:  Thermodynamics, Kinetics, and the Effect of Solvent Dielectric Constant

• Published in: Langmuir 2005-02, Vol.21 (3), p.1009-1014
• Main Authors: O'Reilly, Niall J, Magner, Edmond
• Format: Article
• Language: English
• Subjects: Animals; Chemistry; Cytochromes c - chemistry; Electrochemistry; Electron Transport; Exact sciences and technology; General and physical chemistry; Horses; In Vitro Techniques; Kinetics; Kinetics and mechanism of reactions; Oxidation-Reduction; Solutions; Solvents; Thermodynamics; Water
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la048796t

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°‘), enthalpy, and entropy of reduction. The temperature dependence of the solvent dielectric constant (ε) was also measured. The results show that ε alone cannot regulate the E°‘ 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.