The Role of πσ* Excited States in Electron-Induced DNA Strand Break Formation: A Time-Dependent Density Functional Theory Study

Mechanisms of low-energy electron attachment to the DNA and subsequent single-strand break (SSB) formation are of crucial importance to understand the DNA damage. In the present study, we used time-dependent density functional theory (TD-BH&HLYP/6-31G*) to explore the mechanism of SSB, in detail, by calculating the lowest excited states of 5‘-dTMPH radical anion considered as a model of DNA. The C 5 ‘ −O 5 ‘ bond dissociation of 5‘-dTMPH radical anion was considered as the reaction coordinate along the potential energy surface of 5‘-dTMPH. The dissociative σ* state, mainly localized on the phosphate of the 5‘-dTMPH radical anion, is considered responsible for the SSB formation in DNA. Our work predicts that in this DNA model system there are available π* and σ* excited states, near 2 eV, which can couple vibronically and lead to a DNA single strand break via the dissociative σ* surface.