DIRECT EFFECTS OF GAMMA-RADIATION ON 2'-DEOXYCYTIDINE IN FROZEN AQUEOUS-SOLUTION

The isolation and characterization of the main stable diamagnetic prod ucts formed upon exposure of frozen aqueous solutions of 2'-deoxycytid ine at 196K to Co-60 gamma-rays are described. The initial formation o f the radical pi-anion of 2'-deoxycytidine is strongly indicated by th e formation of 5,6-dihydro-2'-deoxyuridine and 5,6-dihydrouracil. The formation of radical centres within the sugar moiety is clearly implie d. As reported previously, the observed formation of 5',6-cyclo-5,6-di hydro-2'-deoxyuridine indicates hydrogen atom abstraction at the C5' p osition. 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 f rom direct hydrogen abstraction at this position. In general, the stru ctures of the final products correlate well with those of the primary radicals identified from ESR studies by other workers.