Spin trapping of reactive uracilyl radicals produced by ionizing radiation in aqueous solutions

The DNA base analogue 5-bromouracil (BU) reacts with hydrated electrons to produce a highly reactive uracil-5-yl (uracilyl) radical. The uracilyl radical was spin trapped by 5,5-dimethylpyrroline-1-oxide (DMPO) and t-nitrosobutane (tNB). DMPO solutions (0.01 M at pH = 7, N2 or N2O saturated) without BU were irradiated with 60Co gamma-rays and the resulting spin adducts produced by e-aq, H., and OH. were identified. The irradiation of alkaline (pH 12, N2 saturated) solutions of DMPO alone simplified the e.p.r. spectrum of spin adducts in that only the H. adduct was observed. Irradiated DMPO solutions (pH 12, N2 saturated) containing BU yielded a composite of two six-line e.p.r. spectra, attributed to uracilyl spin adducts that have two distinct steric configurations, and a background spectrum of H.-DMPO adducts which was removed by computer-subtraction. Uracilyl-tNB spin adducts were detected by first trapping uracilyl radicals in irradiated photobleached 10 M NaOH glasses at 77 K and then dissolving these glasses in pH-adjusted tNB solutions.