Affiliation:
1. Laboratory for Computational Modeling of Functional Materials Namur Institute of Structured Matter Université de Namur Rue de Bruxelles, 61 5000 Namur Belgium
2. Case Western Reserve University Cleveland 44106 Ohio United States
3. Department of Fundamental Chemistry Institute of Chemistry University of São Paulo Av. Prof. Lineu Prestes 748 05508-000 São Paulo SP Brazil
Abstract
AbstractThe (6–4) photolesion is a key photodamage that occurs when two adjacent pyrimidine bases in a DNA strand bond together. To better understand how the absorption of UVB and UVA radiation by the 2‐pyrimidinone moiety in a (6–4) lesion can damage DNA, it is important to study the electronic deactivation mechanism of its 2‐pyrimidinone chromophore. This study employs theoretical (MS‐CASPT2/cc‐pVDZ level) and experimental (steady state and femtosecond broadband spectroscopic) methods to elucidate the photochemical relaxation mechanisms of 2‐(1H)‐pyrimidinone and 1‐methyl‐2‐(1H)‐pyrimidinone in aqueous solution (pH 7.4). In short, excitation at 320 nm leads to the population of the S1 1(ππ*) state with excess vibrational energy, which relaxes to the S1 1(ππ*) minimum in one picosecond or less. A trifurcation event in the S1 1(ππ*) minimum ensued, leading to radiative and nonradiative decay of the population to the ground state or the population of the long‐lived and reactive T1 3(ππ*) state in hundreds of picoseconds. Collectively, the theoretical and experimental results support the idea that in DNA and RNA, the T1 3(ππ*) state of the 2‐pyrimidinone moiety in the (6–4) lesion can further participate in photosensitized chemical reactions increasing DNA and RNA damage.
Funder
National Science Foundation
Conselho Nacional de Desenvolvimento Científico e Tecnológico