title: Photoinduced formation mechanism of the thymine-thymine (6-4) adduct.
abstract: The photoinduced mechanism leading to the formation of the thymine-thymine (6-4) photolesion has been studied by using the CASPT2//CASSCF approach over a dinucleotide model in vacuo. Following light absorption, localization of the excitation on a single thymine leads to fast singlet-triplet crossing that populates the triplet (3)(nπ*) state of thymine. This state, displaying an elongated C(4)═O bond, triggers (6-4) dimer formation by reaction with the C(5)═C(6) double bond of the adjacent thymine, followed by a second intersystem crossing, which acts as a gate between the excited state of the reactant and the ground state of the photoproduct. The requirement of localized excitation on just one thymine, whose main decay channel (by radiationless repopulation of its ground state) is nonphotochemical, can rationalize the experimentally observed low quantum yield of formation for the thymine-thymine (6-4) adduct.
authors: Instituto de Ciencia Molecular, Universitat de València, Apartado 22085, ES-46071 Valencia, Spain. Angelo.Giussani@uv.es
authors: Angelo
authors: A
authors: Giussani
authors: Luis
authors: L
authors: Serrano-Andrés
authors: Manuela
authors: M
authors: Merchán
authors: Daniel
authors: D
authors: Roca-Sanjuán
authors: Marco
authors: M
authors: Garavelli
mesh_terms: D018736:DNA Adducts / Q000737:chemistry*; D008958:Models, Molecular; D011740:Pyrimidine Dimers / Q000737:chemistry*; D011789:Quantum Theory; D014466:Ultraviolet Rays
chemical_list: D018736:DNA Adducts; D011740:Pyrimidine Dimers