THE DIRECT EFFECT OF HEAVY-IONS AND ELECTRONS ON THYMIDINE IN THE SOLID-STATE

Purpose: To study the direct effect of heavy ions and electrons on thy midine. Materials and methods: The thymidine samples in the solid stat e were exposed to a beam of O7+ heavy ions with an energy of 10.6 MeV/ u (LET similar to 500 keV/mu m) and to electrons of 2 MeV (LET similar to 0.18 keV/mu m). The major decomposition products of thymidine were purified by high performance liquid chromatography (HPLC) and identif ied by extensive spectrometric measurements (UV, mass spectroscopy, H- 1 and C-13 NMR). Results: The main degradation products of thymidine w ere isolated and characterized. Reaction mechanisms, involving transie nt radical species, are proposed to explain the heavy ion-mediated for mation of the modified products. Furthermore, a semi-quantitative comp arison of the modifications induced within thymidine by the two types of radiations was performed. Conclusion: Several new radiation-induced thymidine decomposition products have been isolated and characterized . The comparison of the effects induced by heavy ions and electrons on thymidine in the solid state clearly indicates several significant di fferences in the mechanisms of action. A relative increase in the exte nt of the modifications of the sugar moiety with respect to those of t he base is observed with the heavy ions by comparison with electrons.