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Photoinduced damage of DNA is a well-known but still far from fully understood phenomenon. Electronic structure methods are here employed to investigate potential roles of πσ∗ states in initiating photodamage, and ways in which πσ∗-state driven photochemistry might evolve with increasing molecular complexity. The study starts with the bare 9H-adenine molecule and progresses through to a model double-helix DNA duplex in aqueous solution. Relative to the gas phase, aqueous solvation is predicted to stabilize the 1πσ∗ states of these systems when exciting at the respective ground state equilibrium geometries, but to have relatively little effect on the asymptotic NH bond strengths. But the study also re-emphasises the potential importance of rival σ∗ ← π excitations, wherein a solute π electron is promoted to a σ∗ orbital localized on an OH bond of a complexing H2O molecule, as a route to forming parent radical cations – as have recently been observed following near UV photoexcitation of double-helix adenine-thymine duplexes in water (Banyasz et al., 2018). The subsequent deprotonation of such radical cations offers a rival low energy route to NH bond fission and radical formation in such duplexes.
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- 1 Finished
8/01/14 → 31/12/19