The Effect of Chloride Ions on the γ-radiation-induced Destruction of DNA, Nucleosides and Nucleotides in Aqueous Solution

Summary

DNA in oxygenated aqueous solution is protected from the effects of ionizing radiation by chloride ions, as measured by chromophore destruction. The mechanism of this protection is probably a change in the mode of decay of the DNA-OH radicals and not a change in the primary attacking species. Chloride ions have no effect on the radiation-induced destruction of nucleosides and nucleotides in neutral solution. The chloride effects observed for these compounds in acid solution can be attributed to conversion of OH radicals to Cl₂⁻ ion radicals, and differences in the reaction of the latter species with solutes. There is no observable chloride effect on thymine or adenine compounds. The reaction of Cl₂⁻ with pyrimidine nucleosides and nucleotides results in destruction of the glycosidic bond and the release of undamaged base. This effect is not observed with the purine compounds or with the deoxyribose compounds. The radical which results from the reaction of Cl₂⁻ with guanine compounds reacts efficiently to reform the parent compound.