Ultraviolet Absorption Induces Hydrogen‐Atom Transfer in G⋅C Watson–Crick DNA Base Pairs in Solution |
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Authors: | Dr Katharina Röttger Hugo J B Marroux Dr Michael P Grubb Philip M Coulter Hendrik Böhnke Dr Alexander S Henderson Dr M Carmen Galan Prof Friedrich Temps Prof Andrew J Orr‐Ewing Dr Gareth M Roberts |
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Institution: | 1. School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS (UK);2. Institut für Physikalische Chemie, Christian‐Albrechts‐Universit?t zu Kiel, Olshausenstrasse 40, 24098 Kiel (Germany) |
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Abstract: | Ultrafast deactivation pathways bestow photostability on nucleobases and hence preserve the structural integrity of DNA following absorption of ultraviolet (UV) radiation. One controversial recovery mechanism proposed to account for this photostability involves electron‐driven proton transfer (EDPT) in Watson–Crick base pairs. The first direct observation is reported of the EDPT process after UV excitation of individual guanine–cytosine (G?C) Watson–Crick base pairs by ultrafast time‐resolved UV/visible and mid‐infrared spectroscopy. The formation of an intermediate biradical species (G?H]?C+H]) with a lifetime of 2.9 ps was tracked. The majority of these biradicals return to the original G?C Watson–Crick pairs, but up to 10 % of the initially excited molecules instead form a stable photoproduct G*?C* that has undergone double hydrogen‐atom transfer. The observation of these sequential EDPT mechanisms across intermolecular hydrogen bonds confirms an important and long debated pathway for the deactivation of photoexcited base pairs, with possible implications for the UV photochemistry of DNA. |
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Keywords: | biophysics DNA photochemistry proton transfer ultrafast spectroscopy |
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