Radiation-induced fluorescence changes of 2'-deoxycytidine and cytidilyl-cytidine in aqueous solution

We have reported previously on the radiation-induced formation of highly fluorescent products from thymine, cytosine, adenine, 2'-deoxyadenosine, and 2'-deoxyguanosine. For comparison with these substances, 2'-deoxycytidine (5.0 x 10-4 mol/dm3) and cytidilyl-cytidine (2.5 x 10-4 mol/dm3) in buffered aqueous solution (pH 7.0) were irradiated with 60Co gamma-rays under various atmospheric conditions. Fluorescence yield increased markedly with increase of radiation dose under O2, N2 and N2O but not under t-butanol-N2, indicating that OH radical is the predominant participant in the formation of highly fluorescent products and that O2 does not suppress the yield. These behaviors are very similar to those for cytosine. However, the fluorescent products from 2'-deoxycytidine and cytidilyl-cytidine were radiolytically more stable than those from cytosine. To summarize the formation of highly fluorescent products from various kinds of nucleobase derivatives by radiation, the order for fluorescence yield can be arranged as follows: C > A > G > T under O2, A > G > C > T under N2O, and G >> A >> C > T under t-butanol-N2, excepting the complex yield under N2. (author)