UV-Induced Adenine Radicals Induced in DNA A-Tracts: Spectral and Dynamical Characterization

Adenyl radicals generated in DNA single and double strands, (dA)(20) and (dA)(20)center dot(dT)(20), by one- and two-photon ionization by 266 nm laser pulses decay at 600 nm with half-times of 1.0 +/- 0.1 and 4 +/- 1 ms, respectively. Though ionization initially forms the cation radical, the radicals detected for (dA)(20) are quantitatively identified as N6-deprotonated adenyl radicals by their absorption spectrum, which is computed quantum mechanically employing TD-DFT. Theoretical calculations show that deprotonation of the cation radical induces only weak spectral changes, in line with the spectra of the adenyl radical cation and the deprotonated radical trapped in low temperature glasses.