Mechanisms of photoreactivity in hydrogen-bonded adenine-H2O complexes

Xiuxiu Wu, Johannes Ehrmaier, Andrzej L. Sobolewski, Tolga N.V. Karsili, Wolfgang Domcke

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

The mechanisms of photoinduced reactions of adenine with water molecules in hydrogen-bonded adenine-water complexes were investigated with ab initio wave-function-based electronic-structure calculations. Two excited-state electron/proton transfer reaction mechanisms have been characterized: H-atom abstraction from water by photoexcited adenine as well as H-atom transfer from photoexcited adenine or the (adenine+H) radical to water. In the water-to-adenine H-atom transfer reaction, an electron from one of the p orbitals of the water molecule fills the hole in the n (π) orbital of the nπ∗ (ππ∗) excited state of adenine, resulting in a charge-separated electronic state. The electronic charge separation is neutralized by the transfer of a proton from the water molecule to adenine, resulting in the (adenine+H)⋯OH biradical in the electronic ground state. In the adenine-to-water H-atom transfer reaction, πσ∗ states localized at the acidic sites of adenine provide the mechanism for the photoejection of an electron from adenine, which is followed by proton transfer to the hydrogen-bonded water molecule, resulting in the (adenine-H)⋯H3O biradical. The energy profiles of the photoreactions have been computed as relaxed scans with the ADC(2) electronic-structure method. These reactions, which involve the reactivity of adenine with hydrogen-bonded water molecules, compete with the well-established intrinsic excited-state deactivation mechanisms of adenine via ring-puckering or ring-opening conical intersections. By providing additional decay channels, the electron/proton exchange reactions with water can account for the observed significantly shortened excited-state lifetime of adenine in aqueous environments. These findings indicate that adenine possibly was not only a photostabilizer at the beginning of life, but also a primordial photocatalyst for water splitting.

Original languageEnglish
Pages (from-to)14238-14249
Number of pages12
JournalPhysical Chemistry Chemical Physics
Volume21
Issue number26
DOIs
StatePublished - 2019

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