UV-induced DNA Damage: The Role of Electronic Excited States

International audienceThe knowledge of the fundamental processes induced by the direct absorption of UV radiation by DNA allows extrapolatingconclusions drawn from in vitro studies to the in-vivo DNA photoreactivity. In this respect, the characterization ofthe DNA electronic excited states plays a key role. For a long time, the mechanisms of DNA lesion formation were discussedin terms of generic “singlet” and “triplet” excited state reactivity. However, since the beginning of the 21st century,both experimental and theoretical studies revealed the existence of “collective” excited states, i.e. excited states delocalizedover at least two bases. Two limiting cases are distinguished: Frenkel excitons (delocalized pp* states) andcharge-transfer states in which positive and negative charges are located on different bases. The importance of collectiveexcited states in photon absorption (in particular in the UVA spectral domain), the redistribution of the excitation energywithin DNA, and the formation of dimeric pyrimidine photoproducts is discussed. The dependence of the behavior of thecollective excited states on conformational motions of the nucleic acids is highlighted