Ionic base radicals in gamma-irradiated oriented non-deuterated and fully deuterated DNA.

The free radicals induced by gamma-irradiation at 77 K in non-deuterated and fully deuterated oriented samples of moist algal DNA have been studied by electron paramagnetic resonance (e.p.r.). The e.p.r. spectra from the non-deuterated sample were found to be similar to those from calf-thymus DNA studied previously. Numerical spectra simulations were performed based on the previously proposed interpretation of the DNA spectra at 77 K in terms of a mixture of two spectral components arising from anionic and cationic base radicals (probably on thymine and guanine, respectively). The simulations were found to account satisfactorily for the main characteristics of the e.p.r. spectra from both the non-deuterated and the fully deuterated algal DNA sample.