Direct effects of gamma-radiation on 2'-deoxycytidine in frozen aqueous solution

The isolation and characterization of the main stable diamagnetic products formed upon exposure of frozen aqueous solutions of 2'-deoxycytidine at 196 K to 60 Co gamma-rays are described. The initial formation of the radical pi-anion of 2'-deoxycytidine is strongly indicated by the formation of 5,6-dihydro-2'-deoxyuridine and 5,6-dihydrouracil. The formation of radical centres within the sugar moiety is clearly implied. As reported previously, the observed formation of 5',6-cyclo-5,6-dihydro-2'-deoxyuridine indicates hydrogen atom abstraction at the C5' position. The release of cytosine, and 2-deoxy-D-ribono-1,4-lactone may result from deprotonation of a pristine radical pi-cation at C1' or from direct hydrogen abstraction at this position. In general, the structures of the final products correlate well with those of the primary radicals identified from ESR studies by other workers.