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In this contribution, the multiconfigurational second-order perturbation theory method based on a complete active space reference wave function (CASSCF/CASPT2) is applied to study all possible single and double proton/hydrogen transfers between the nucleobases in the adenine-thymine (AT) base pair, analyzing the role of excited states with different nature [localized (LE) and charge transfer (CT)], and considering concerted as well as step-wise mechanisms. According to the findings, once the lowest excited states, localized in adenine, are populated during UV irradiation of the Watson-Crick base pair, the proton transfer in the N-O bridge does not require high energy in order to populate a CT state. The latter state will immediately relax toward a crossing with the ground state, which will funnel the system to either the canonical structure or the imino-enol tautomer. The base pair is also capable of repairing itself easily since the imino-enol species is unstable to thermal conversion.


João Paulo Gobbo, Vicenta Saurí, Daniel Roca-Sanjuán, Luis Serrano-Andrés, Manuela Merchán, Antonio Carlos Borin. On the deactivation mechanisms of adenine-thymine base pair. The journal of physical chemistry. B. 2012 Apr 5;116(13):4089-97

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PMID: 22414119

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