Theoretical study of damage to DNA by 0.2-1.5 eV electrons attached to cytosine

We extended our earlier study on single strand break (SSB) formation in DNA induced by low-energy electrons that attach to DNA bases' pi*-orbitals. In particular, we examined a range of electron energies (E) representative of the Heisenberg width of the lowest pi*-resonance state of cytosine, and we considered how the SSB rates depend on E and on the solvation environment. Moreover, we evaluated the adiabatic through-bond electron transfer rate with which the attached electron moves from the base, through the deoxyribose, and onto the phosphate unit. Our findings show that the SSB rate depends significantly on the electron energy E and upon the solvation environment near the DNA base. For example, in solvation characterized by a dielectric constant of 4.9, the rates range from 10(0) to 10(7) s(-1) as the electrons' kinetic energy varies from 0.2 to 1.5 eV. We also find that the rate of through-bond electron transfer is not the factor that limits SSB formation; rather, it is the rate at which a barrier is surmounted on the anion's energy surface and it is this barrier that depends on E and on solvation.