212 - The Effect of Bulk Solvent Structure on the Temperature Dependence of the Reduction Potential of Cytochrome c

The reduction potential of horse heart cytochrome c in various sodium halide solutions in H2O and D2O has been measured over the temperature range of 25 to 50 °C. In aqueous chloride solutions the temperature dependence was biphasic with the intersection point at 42 °C. This biphasic behavior is interpreted in terms of chloride-induced bulk destructuring of water at 42 °C. All samples in D2O and samples in H2O not containing chloride ion gave a linear temperature dependence. The decrease in reduction potential with increasing temperature for solutions containing F−, Cl−, Br− and I − correlates with the extent of anion binding to the oxidized form of cytochrome c.