Reduction Potentials and Thermodynamics

In the introductory chapter we stated that the formation of chemical compounds with the metal ion in a variety of formal oxidation states is a characteristic of transition metals. We also saw in Chapter 8 how we may quantify the thermodynamic stability of a coordination compound in terms of the stability constant K. It is convenient to be able to assess the relative ease by which a metal is transformed from one oxidation state to another, and you will recall that the standard electrode potential, E , is a convenient measure of this. Remember that the standard free energy change for a reaction, AG , is related both to the equilibrium constant (Eq. 9.1) 

We can thus use E values to gauge the effects that various ligands have upon the stability of one given oxidation state with respect to any other. 

---

A variety of physical methods has been used to ascertain whether or not surface ruthenation alters the structure of a protein. UV/vis, CD, EPR, and resonance Raman spectroscopies have demonstrated that myoglobin (30, 89), cytochrome c (74, 164, 193, 194), and azurin (113) are not perturbed structurally by the attachment of a ruthenium complex to a surface histidine. The reduction potential of the metal redox center of a protein and its temperature dependence are indicators of protein structure as well. Cyclic voltammetry (113, 193), differential pulse polarography (30, 31, 140), and spectroelectrochemistry (30, 31,194) are commonly used for the determination of the ruthenium and protein redox center potentials in modified proteins. The reduction potential and thermodynamic parameters... 

---