Redox thermodynamics of cytochrome c adsorbed on mercaptoundecanol monolayer electrodes

The redox potentials E-0´ of bovine cytochrome c adsorbed on an 11-mercapto-1-undecanol/Au self-assembled monolayer electrode were studied through direct electrochemistry as a function of the temperature in non-isothermal experiments carried out in the presence of different anions and changes of the ionic strength. The thermodynamic parameters for protein reduction (DeltaH(rc)(0´) and DeltaS(rc)(0´)) re were determined for adsorbed and solution cytochrome and the differences in E-0´ discussed in terms of the enthalpic and entropic contributions. The adsorption process seems to remove the ability of perchlorate anion to bind to the protein surface, while a certain direct interaction is still retained in the case of chloride and phosphate. A moderate increase in E-0´ of adsorbed cytochrome was measured at increasing ionic strength and discussed in the light of the opposite effect observed for solution protein.