Radicals Derived from Guanine: Structures and Energetics

Abstract

The electron affinities (EA) of five radicals derived from guanine by removing a hydrogen atom are predicted by using four carefully calibrated (Chem. Rev. 2002, 102, 231) density functional methods. The most stable guanine radical arises from the removal of the H10b atom (Fig. 1) from the NH2 group. The theoretical adiabatic electron affinities (EAad) for the five possible guanine radicals are substantial, in the range of 2.18-2.99 eV, which is much higher than that for the closed-shell guanine molecule (-0.17 eV). The N9 dehydrogenated radical has the highest EAad (2.99 eV), and its related anion is the lowest energy species among those studied in the present research. The energy difference between the two N10-sited (amino group) radicals is 4.8 kcal/mol, indicating that these two structures are not conventional internal-rotation conformers.