Effect of iron (III) ions on the radiosensitivity of uracil

Aqueous solutions of uracil(U) in the presence of iron(III) were irradiated with 60Co gamma-rays both in the presence and in the absence of dissolved oxygen. The products of radiolysis (uracil dimer, cis- and trans-uracil glycol, hydroxy-dihydrouracil and isobarbituric acid) were separated by means of paper chromatography using n-butanol: water (86:14) as the solvent. Radiolytic reduction of Fe(III) and the formation of Fe(II) were followed spectrophotometrically. In the absence of any additive, G(-U) is approximately 1.3, but with Fe(III) added G(-U) approaches a limiting value of 3.3 and the yield of cis-glycol increases. Radiosensitization by Fe(III) is found to be different from that of oxygen, which results in the yield of cis glycol decreasing and the yields of trans glycol and isobarbituric acid increasing. The mechanisms involved are discussed.