Direct evidence for 1-methylthymine radical cations and their transformation to successor radicals by Fourier transform electron paramagnetic resonance in the nanosecond time scale

Using Fourier transform electron paramagnetic resonance (FT EPR), the radic als generated by the oxidation of 1-methylthymine were detected in the nano second time scale. The radicals were generated via triplet-sensitized elect ron transfer to anthraquinone-2,6-disulfonic acid in aqueous solution with laser photolysis at 308 nm. Both radicals show strong chemically induced dy namic electron polarization (CIDEP) by the triplet mechanism. This strong e nhancement of the FT EPR intensity enabled the radical cation of 1-methylth ymine to be detected in the nanosecond time scale at a low pH. The transfor mation of the radical cation to the N3-deprotonated successor radical was d irectly observed in the microsecond time scale. After a few microseconds, a dditional successor radicals of the primary radical cation were measured de pending on the pH, and the radicals formed by the addition of OH- and/or PO 43- at C6 of the radical cation were detected.