Covalent Anion of the Canonical Adenine−Thymine Base Pair. Ab Initio Study

Abstract

Theoretical ab initio calculations have been performed to determine the stability of the covalent anions of adenine and the adenine−thymine (AT) Watson−Crick base pair. The conclusions of this work are as follows: (i) the covalent anion of adenine is predicted to be a stable system with respect to a vertical electron detachment, but unstable with respect to adiabatic detachment; (ii) the covalent anion of the adenine−thymine dimer (A−T-) has similar properties, although in this system the presence of the second base provides an additional stabilization to the excess electron; (iii) in A−T- the excess electron is localized at the thymine molecule, and this molecule's ring is puckered; (iv) no valence A−T anion was found in the calculations with the excess electron located at the adenine molecule; and (v) in view of the above results, we predict that the AT base pair is not an effective trap of excess electrons.