The Adenine−Thymine Base Pair Radical Anion: Adding an Electron Results in a Major Structural Change

Abstract

The adiabatic electron affinity (AEA) for the Watson−Crick adenine−thymine (AT) DNA base pair is predicted and contrasted to that of guanine−cytosine (GC) with a range of density functional methods with double- and triple-ζ plus polarization plus diffuse (DZP++ and TZ2P++) basis sets. An estimate of the true AEA is provided using a bracketing method that has been calibrated against a comprehensive tabulation of experimental electron affinities [Rienstra-Kiracofe, J. C.; Tschumper, G. S.; Schaefer, H. F.; Nandi, S.; Ellison, G. B. Chem. Rev. 2002, 102, 10163]. Optimized structures for AT and the AT anion are compared to the neutral and anionic forms of the individual bases as well as Rich's 1976 X-ray structure for the related sodium adenylyl-3‘,5‘-uridine hexahydrate, ApU·6H2O. In contrast to the angular distortions (to nonplanarity) occurring in GC upon anion formation, the angular distortions for the AT anion are slight. However, in an analogous fashion to the GC anion, major changes in the AT anion hyd...