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Excited‐State Deactivation of Adenine by Electron‐Driven Proton‐Transfer Reactions in Adenine–Water Clusters: A Computational Study
Author(s) -
Wu Xiuxiu,
Karsili Tolga N. V.,
Domcke Wolfgang
Publication year - 2016
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201501154
Subject(s) - conical intersection , chemistry , excited state , electron transfer , proton coupled electron transfer , photochemistry , proton , molecule , computational chemistry , atomic physics , physics , organic chemistry , quantum mechanics
Abstract The reactivity of photoexcited 9 H ‐adenine with hydrogen‐bonded water molecules in the 9 H ‐adenine–(H 2 O) 5 cluster is investigated by using ab initio electronic structure methods, focusing on the photoreactivity of the three basic sites of 9 H ‐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 S 1 –S 0 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 9 H ‐adenine in water. Depending on the branching ratio of the nonadiabatic dynamics at the S 1 –S 0 conical intersection, the electron/proton transfer process can enhance the photostability of 9 H ‐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.