Direct Evidence for 1-Methylthymine Radical Cations and Their Transformation to Successor Radicals by Fourier Transform Electron Paramagnetic Resonance in the Nanosecond Time Scale

Abstract

Using Fourier transform electron paramagnetic resonance (FT EPR), the radicals generated by the oxidation of 1-methylthymine were detected in the nanosecond time scale. The radicals were generated via triplet-sensitized electron transfer to anthraquinone-2,6-disulfonic acid in aqueous solution with laser photolysis at 308 nm. Both radicals show strong chemically induced dynamic electron polarization (CIDEP) by the triplet mechanism. This strong enhancement of the FT EPR intensity enabled the radical cation of 1-methylthymine to be detected in the nanosecond time scale at a low pH. The transformation of the radical cation to the N3-deprotonated successor radical was directly observed in the microsecond time scale. After a few microseconds, additional successor radicals of the primary radical cation were measured depending on the pH, and the radicals formed by the addition of OH- and/or PO43- at C6 of the radical cation were detected.