Reactions of some free radicals derived from uracil with nickel(II) compounds

Abstract

Reactions of Ni^II compounds with the transient adducts of uracil, viz. U^– and UOH, have been studied in the steady-state radiolysis of uracil in the presence of different Ni^II species, e.g. NiSO₄, Ni^IIEDTA, Ni^IINTA, Ni^IIIDA and Ni^II(IDA)₂. The U^– radicals formed by the reaction of uracil with e^–_aq transfer an electron to the Ni^II species. The redox behaviour of UOH radicals has been investigated by following the ligand-degradation products of the Ni^II complexes and the degradation of the base. The ligand-degradation products, e.g. formaldehyde and glyoxalic acid, arise from the degradation of the metal complex through its oxidation to Ni^III by C₆–UOH radical species. Unlike Cu^II or Fe^III ions, Ni^II ions have very little effect on the radiosensitivity of uracil. The radiosensitising ability of the metal ions, which is dependent on electron transfer from UOH to the metal ion, is correlated with the redox potential of the metal ion couple Mⁿ⁺/M^(n–1)+.