Oxidation of nucleic acid bases by hexavalent manganese in aqueous alkaline medium: a kinetic study

Oxidation of uracil or thymine by Mn^VI in aqueous alkali shows first order dependence on MnO ₄ ²⁻ ] and fractional order dependence on uracil] or thymine]. The effect of ionic strength is negligible on the rate of oxidation. The product of oxidation is the 5,6-dihydroxy compound. A mechanism is proposed involving the formation of a 5-membered cyclic complex between the substrate and manganate in a fast step, which subsequently disproportionates to give the final products. The large negative values of the entropy of activation suggest the formation of an intermediate complex. The formation constants of the latter and the rate of its disproportionation have been calculated from the derived rate law. The rate of oxidation of thymine is faster than that of uracil.