Hydrogen Atom Loss in Pyrimidine DNA Bases Induced by Low-Energy Electrons: Energetics Predicted by Theory

Abstract

In addition to inducing DNA strand breaks, low-energy electrons (LEEs) also have been shown to induce fragmentation of pyrimidine bases (uracil, thymine, and cytosine) in the gas and condensed phases. Loss of a hydrogen atom from a DNA base−electron adduct initiates chemical modification of the base, which can cause permanent damage to the base as well as to DNA. Thus, the energetics of hydrogen atom loss reactions from anionic bases is crucial to understanding the mechanism of LEE-induced damage to DNA and its component bases. Following our previous report on LEE interactions with uracil [J. Phys. Chem. B 2004, 108, 5472−5476], in this work we investigate LEE interactions with thymine and cytosine. The adiabatic potential energy surface along each N−H or C−H bond is explored up to 3 A at the DFT level. The changes in energy, enthalpy, and free energy (ΔE, ΔH, and ΔG) for a complete separation of an H atom or a methyl (amino) group from the anionic base as well as bond dissociation energies of neutral bas...