Pulse Radiolytic Study of the Interaction of SO⁻·₄ with Deoxynucleosides. Possible Implications for Direct Energy Deposition

Summary

Using the technique of pulse radiolysis it has been demonstrated that the interaction of SO⁻·₄ with deoxynucleosides (k ∼ < 2 × 10⁸–2·3 × 10⁹ dm³ mol⁻¹ s⁻¹) in aqueous solution at pH 7·0 results in the formation of the corresponding one-electron oxidized radicals which either deprotonate or hydrate to yield OH adducts. Based upon the ease of oxidation of the deoxynucleosides, dG, dA, dC, dT, by SO⁻·₄, the apparent redox potentials are in the order dG ≫ dA ≈ dC > dT. With the exception of deoxyuridine, the deoxynucleoside radicals produced on interaction with SO⁻·₄ have been shown to have oxidizing properties based upon the interactions with tetranitromethane and the nitroxyls, TMPN and NPPN. The deoxynucleoside radicals (dG, dA and dC) do not interact with oxygen (k < 10⁶ dm³ mol⁻¹ s⁻¹) in contrast to the interaction observed with the thymidine radical (k = 2·5 × 10⁷ dm³ mol⁻¹ s⁻¹). The implications of these findings are presented in terms of the properties of the discussed radicals as relating to those of potential DNA base radicals (positive centres) produced by direct energy deposition within DNA. The use of SO⁻·₄ to mimic, to some extent, the effects of direct energy deposition in DNA may assist in our understanding of the resulting molecular processes relevant to radiobiological studies.