A theoretical study of 5-halouracils: electron affinities, ionization potentials and dissociation of the related anions

The gas phase and solution electron affinities and ionization potentials of uracil, thymine and a series of 5-halouracils (5XU, X=F, Cl, Br) are investigated with B3LYP. Halogen substitution has a smaller effect on the IP than the EA of U. The EAs are calculated to increase according to T<U<5FU<5ClU<5BrU. The calculated barriers for the dissociation of the resulting 5XU anions to X− plus uracil-centered radicals decrease along the series 5FU−>5ClU−>5BrU−. The calculated trends are consistent with suggestions that 5XUs enhance the sensitivity of deoxyribonucleic acid, DNA (ribonucleic acid, RNA) to ionizing radiation and that 5BrU leads to the greatest enhancement.