Ultraviolet Absorption Induces Hydrogen-Atom Transfer in G⋅C Watson-Crick DNA Base Pairs in Solution

• Published in: Angewandte Chemie Vol. 127; no. 49; pp. 14932 - 14935
• Main Authors: Röttger, Katharina, Marroux, Hugo J. B., Grubb, Michael P., Coulter, Philip M., Böhnke, Hendrik, Henderson, Alexander S., Galan, M. Carmen, Temps, Friedrich, Orr-Ewing, Andrew J., Roberts, Gareth M.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.12.2015; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Absorption; Base pairs; Bases (nucleic acids); Biophysik; Chemistry; Cytosine; Deactivation; Deoxyribonucleic acid; DNA; Guanine; Hydrogen; Hydrogen bonding; Hydrogen bonds; Infrared spectroscopy; Photochemie; Photochemistry; Protonentransfer; Structural integrity; Ultraschnelle Spektroskopie; Ultraviolet absorption; Ultraviolet radiation
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.201506940

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. Aufgrund ultraschneller Energiedissipationsprozesse nach UV‐Absorption ist DNA intrinsisch photostabil. Einer der meist diskutierten Mechanismen in einzelnen Guanin‐Cytosin‐Basenpaaren wurde jetzt bestätigt: Eine Kette von Wasserstofftransfers über die H‐Bindungen im Dimer führt zur effizienten Relaxation des Basenpaares zur ursprünglichen Struktur, allerdings bilden bis zu 10 % der angeregten Moleküle stattdessen möglicherweise mutagene Tautomere.