title: Excited-State Deactivation of Adenine by Electron-Driven Proton-Transfer Reactions in Adenine-Water Clusters: A Computational Study.
abstract: The reactivity of photoexcited 9H-adenine with hydrogen-bonded water molecules in the 9H-adenine-(H2 O)5 cluster is investigated by using ab initio electronic structure methods, focusing on the photoreactivity of the three basic sites of 9H-adenine. The energy profiles of excited-state reaction paths for electron/proton transfer from water to adenine are computed. For two of the three sites, a barrierless or nearly barrierless reaction path towards a low-lying S1 -S0 conical intersection is found. This reaction mechanism, which is specific for adenine in an aqueous environment, can explain the substantially shortened excited-state lifetime of 9H-adenine in water. Depending on the branching ratio of the nonadiabatic dynamics at the S1 -S0 conical intersection, the electron/proton transfer process can enhance the photostability of 9H-adenine in water or can lead to the generation of adenine-H(⋅) and OH(⋅) free radicals. Although the branching ratio is yet unknown, these findings indicate that adenine might have served as a catalyst for energy harvesting by water splitting in the early stages of the evolution of life.
authors.affiliation: Department of Chemistry, Technische Universität München, 85747, Garching, Germany.
authors.forename: Xiuxiu
authors.initials: X
authors.lastname: Wu
authors.affiliation: Department of Chemistry, Technische Universität München, 85747, Garching, Germany. Tolga.Karsili@tum.de.
authors.forename: Tolga N V
authors.initials: TN
authors.lastname: Karsili
authors.affiliation: Department of Chemistry, Technische Universität München, 85747, Garching, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Domcke
mesh_terms: D000225:Adenine / Q000737:chemistry*; D003198:Computer Simulation; D004583:Electrons; D011522:Protons; D014867:Water / Q000737:chemistry
chemical_list: D011522:Protons; D014867:Water; D000225:Adenine
keywords: ab initio calculations; adenine; electron transfer; photochemistry; proton transfer