On the Deactivation Mechanisms of Adenine-Thymine Base Pair

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.

FAPESP

FAPESP

CAPES

CAPES

European Research Council under the European Community

European Research Council under the European Community [255363]

Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)

CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico)

Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)

FAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo)

services and computer time at the Laboratorio de Computacao Cientifica Avancada (LCCA) of the Universidade de Sao Paulo

services and computer time at the Laboratorio de Computacao Cientifica Avancada (LCCA) of the Universidade de Sao Paulo