title: Ultraviolet Absorption Induces Hydrogen-Atom Transfer in G⋅C Watson-Crick DNA Base Pairs in Solution.
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.
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS (UK).|Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel, Olshausenstrasse 40, 24098 Kiel (Germany).
authors.forename: Katharina
authors.initials: K
authors.lastname: Röttger
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS (UK).
authors.forename: Hugo J B
authors.initials: HJ
authors.lastname: Marroux
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS (UK).
authors.forename: Michael P
authors.initials: MP
authors.lastname: Grubb
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS (UK).
authors.forename: Philip M
authors.initials: PM
authors.lastname: Coulter
authors.affiliation: Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel, Olshausenstrasse 40, 24098 Kiel (Germany).
authors.forename: Hendrik
authors.initials: H
authors.lastname: Böhnke
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS (UK).
authors.forename: Alexander S
authors.initials: AS
authors.lastname: Henderson
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS (UK).
authors.forename: M Carmen
authors.initials: MC
authors.lastname: Galan
authors.affiliation: Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel, Olshausenstrasse 40, 24098 Kiel (Germany). temps@phc.uni-kiel.de.
authors.forename: Friedrich
authors.initials: F
authors.lastname: Temps
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS (UK). a.orr-ewing@bristol.ac.uk.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Orr-Ewing
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS (UK). g.m.roberts@bristol.ac.uk.
authors.forename: Gareth M
authors.initials: GM
authors.lastname: Roberts
mesh_terms: D065966:Absorption, Physicochemical / Q000528:radiation effects*; D020029:Base Pairing / Q000528:radiation effects*; D004247:DNA / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D012996:Solutions; D014466:Ultraviolet Rays
chemical_list: D012996:Solutions; D006859:Hydrogen; D004247:DNA
keywords: DNA; biophysics; photochemistry; proton transfer; ultrafast spectroscopy