Density functional study toward understanding dehydrogenation of the adenine-thymine base pair and its anion.

The dehydrogenated radicals and anions of Watson-Crick adenine-thymine (A-T) base pair have been investigated by the B3LYP/DZP++ approach. Calculations show that the dehydrogenated radicals and anions have relatively high stabilities compared with the single base adenine and thymine. The electron attachment to the A-T base pair and its derivatives significantly modifies the hydrogen bond interactions and results in remarkable structural changes. As for the dehydrogenated A-T radicals, they have relatively high electron affinities and different dehydrogenation properties with respect to their constituent elements. The relatively low-cost hydrogen eliminations correspond to the (N9)-H (adenine) and (N1)-H (thymine) bonds cleavage. Both dehydrogenation processes have Gibbs free energies of reaction DeltaG degrees of 13.4 and 17.2 kcal mol-1, respectively. The solvent water exhibits significant effect on electron attachment and dehydrogenation properties of the A-T base pair and its derivatives. In the dehydrogenating process, the anionic A-T fragment gradually changes its electronic configuration from pi* to sigma* state, like the single bases adenine and thymine.