Electron affinities of the radicals derived from cytosine

Abstract

Theoretical studies have been carried out to investigate the electron affinities (EAs) of five radicals derived from cytosine by removing a hydrogen atom (C_−H*), using carefully calibrated computational methods. Significant structural differences are predicted between cytosine, its five radicals and the five corresponding anions. The largest bond distance differences between the radical and its analogous anion are 0.05 Å. The theoretical EAs (predicted using carefully calibrated methods) for the five cytosine radicals range from 2.22 eV to 3.00 eV. Among these the N-centred radical 2 has the largest adiabatic electron affinity (EA_ad = 3.00 eV), and the carbon-centred radical 8 has the smallest (2.22 eV). These values are much larger than EA_ad for the neutral closed-shell cytosine molecule. The largest EA_ad value predicted for the cytosine radical isomers (C_−H*) is comparable to those for radicals related to other nucleoside bases. The ordering for the four DNA bases is EA(T_−H*) = 3.46 > EA(A_−H*) = 3.26 > EA(C_−H*) = 3.00 > EA(G_−H*) = 2.99 eV.