Entropy and enthalpy contributions to the kinetics of proton coupled electron transfer to the Mn sub(4)O sub(4)(O sub(2) PPh sub(2)) sub(6) cubane

The dependence of rate, entropy of activation, and ( super(1)H/ super(2)H) kinetic isotope effect for H-atom transfer from a series of p-substituted phenols to cubane Mn sub(4)O sub(4)L sub(6) (L = O sub(2)PPh sub(2)) (1) reveals the activation energy to form the transition state is proportional to the phenolic O-H bond dissociation energy. New implications for water oxidation and charge recombination in photosystem II are described.