A Plausible Mechanism of Uracil Photohydration Involves an Unusual Intermediate
It is well-known that photolysis of pyrimidine nucleobases, such as uracil, in an aqueous environment results in the formation of hydrate as one of the main products. Although several hypotheses regarding photohydration have been proposed in the past, e.g., the zwitterionic and "hot" ground-state mechanisms, its detailed mechanism remains elusive. Here, theoretical nonadiabatic simulations of the uracil photodynamics reveal the formation of a highly energetic but kinetically stable intermediate that features a half-chair puckered pyrimidine ring and a strongly twisted intracyclic double bond. The existence and the kinetic stability of the intermediate are confirmed by a variety of computational chemistry methods. According to the simulations, the unusual intermediate is mainly formed almost immediately (∼50–200 fs) upon photoabsorption and survives long enough to engage in a hydration reaction with a neighboring water. A plausible mechanism of uracil photohydration is proposed on the basis of the modeling of nucleophilic insertion of water into the twisted double bond of the intermediate.
© 2022 The Authors. Published by American Chemical Society. Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). Received 4 June 2022. Accepted 11 July 2022. Published online 28 July 2022. The support by Samsung Science and Technology Foundations Grant SSTF-BA1701-12 and Grants 2020R1A2C2008246 and 2020R1A5A1019141 funded by the Ministry of Science and ICT is acknowledged. This work was also supported by the Korea Polar Research Institute (KOPRI, PE21120). The authors declare no competing financial interest.
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