Initial state versus transition state solvation effects on the kinetics of oxidation of nickel(II) dioxocyclam by peroxodisulfate

The kinetics of oxidation of 1,4,8,11-tetraazacyclotetradecane-5,7-diamidonickel(II) ('nickel dioxocyclam') by peroxodisulfate have been measured in a range of binary aqueous solvent mixtures. Reaction rates are retarded by the presence of organic co-solvents, indicative of destabilization of the transition state (TS) relative to the initial state (IS) in the binary aqueous mixtures. Thus the TS is more hydrophilic than the IS. From solubility measurements of the nickel(II) macrocycle, the transfer chemical potential of the IS of the reaction has been estimated and compared with that of the TS. The transfer potential of the IS is dominated by the solvation of the peroxodisulfate ion.