Radicals formed by electron transfer from cytosine and 1-methylcytosine tothe triplet state of anthraquinone-2,6-disulfonic acid. A Fourier-transform EPR study

Radicals generated by electron transfer from cytosine and 1-methylcytosine to the laser-induced triplet state of anthraquinone-2,6-disulfonic acid wer e studied by time-resolved Fourier-transform (FT) EPR in H2O and D2O at 10 degrees C. The main products observed on the nanosecond timescale were succ essors of the base radical cations. Their hyperfine couplings were determin ed by computer simulation of the experimental spectra. Assignment of the ra dical structures was supported by density functional theory (DFT) quantum m echanical calculations. The experiments with cytosine deprotonation at N1 r esulted in the cytosin-1-yl radical 1 with high spin density at N1 and C5 w hereas, for 1-methylcytosine, deprotonation at the exocyclic amino group yi elded the aminyl radical 2. For both parent compounds, cytosine and 1-methy lcytosine, two additional long-lived radicals (3 and 4) with unknown struct ure were detected on the nanosecond to microsecond timescale. Their spectra l parameters were independent of the N1 substituent.