title: On the deactivation mechanisms of adenine-thymine base pair.
abstract: 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.
authors.affiliation: Instituto de Química, Universidade de São Paulo, São Paulo, Brazil. jpgobbo@iq.usp.br
authors.forename: João Paulo
authors.initials: JP
authors.lastname: Gobbo
authors.forename: Vicenta
authors.initials: V
authors.lastname: Saurí
authors.forename: Daniel
authors.initials: D
authors.lastname: Roca-Sanjuán
authors.forename: Luis
authors.initials: L
authors.lastname: Serrano-Andrés
authors.forename: Manuela
authors.initials: M
authors.lastname: Merchán
authors.forename: Antonio Carlos
authors.initials: AC
authors.lastname: Borin
mesh_terms: D000225:Adenine / Q000737:chemistry*; D020029:Base Pairing; D006859:Hydrogen / Q000737:chemistry; D011522:Protons; D013941:Thymine / Q000737:chemistry*; D014466:Ultraviolet Rays
chemical_list: D011522:Protons; D006859:Hydrogen; D000225:Adenine; D013941:Thymine