Radicals derived from adenine: Prediction of large electron affinities with a considerable spread

The electron affinities of five radicals of adenine minus a hydrogen atom are predicted using carefully calibrated (Chem. Rev. 2002, 102, 231) computational methods. Density functional theory (DFT) and hybrid DFT/ Hartree-Fock functionals were used with double-xi quality basis sets augmented with polarization and diffuse functions, DZP++. Vibrational frequency analyses were performed to compute zero-point energy corrections and to determine the nature of the stationary points. The energetic spacing of the five adenine-related radicals and five anions is predicted and found to be quite different between the radicals and anions. The electron affinities are found to be large, ranging from 0.9 to 3.2 eV. In all anions, the "last" electron displays little diffuse character. Breaking a N-H bond leads (experimentally corresponding to deprotonating the electron-oxidized adenine radical) to the most stable radical, which in turn has the highest electron affinity. Radicals and anions which are created at carbon centers are less stable with respect to those generated at nitrogen centers in the adenine framework.