Deoxyadenosine-5′-monophosphate (dAMP) was irradiated at 77 K in frozen aqueous solution, and then annealed, step by step, until disappearance of any detectable ESR signal. Computer analysis of the qualitative and quantitative transformations undergone by ESR spectra during this process enabled us to postulate a mechanism accounting for radical reactions involving primary and secondary species and to delineate the corresponding pathways. The following mechanism was postulated as being responsible for the experimental data obtained. At 77 K the free radical population formed on dAMP by the direct effect of radiation is mainly composed of adenine anions and cations. Under heat treatment both such adenine ions react with neighboring water molecules to give respectively H-addition and OH-addition radicals on the adenine base group. Addition of the electron scavenger iodoacetamide to the dAMP solution prior to irradiation inhibits the formation of H-addition radicals selectively, by preventing the formation of their anionic precursors. In addition to the base-located free radicals mentioned, another radical species, located on the deoxyribose moiety of dAMP was also detected. Individual temperature kinetics were described for each radical species.

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