title: Excited State Relaxation of Neutral and Basic 8-Oxoguanine.
abstract: 8-Oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dGuo) is one of the most common forms of DNA oxidative damage. Recent studies have shown that 8-oxo-dGuo can repair cyclobutane pyrimidine dimers in double-stranded DNA when photoexcited, making its excited state dynamics of particular interest. The excited state lifetimes of 8-oxo-dGuo and its anion have been previously probed using transient absorption spectroscopy; however, more information is required to understand the decay mechanisms. In this work, excited state potential energy surfaces for the neutral and deprotonated forms of the free base, 8-oxoguanine (8-oxo-G), are explored theoretically using multireference methods while the nucleoside is experimentally studied using steady-state fluorescence spectroscopy. It is determined that the neutral species exhibits ultrafast radiationless decay via easy access to conical intersections. The relatively long lifetime for the anion can be explained by the existence of sizable barriers between the Franck-Condon region and two S1/S0 minimum energy conical intersections. A Strickler-Berg analysis of the experimentally measured fluorescence quantum yields and lifetimes is consistent with emission from ππ* excited states in line with theoretical predictions.
authors.affiliation: †Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122-6081, United States.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Lu
authors.affiliation: ‡Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States.
authors.forename: Ashley A
authors.initials: AA
authors.lastname: Beckstead
authors.affiliation: ‡Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States.
authors.forename: Bern
authors.initials: B
authors.lastname: Kohler
authors.affiliation: †Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122-6081, United States.
authors.forename: Spiridoula
authors.initials: S
authors.lastname: Matsika
mesh_terms: D000080242:8-Hydroxy-2'-Deoxyguanosine; D003849:Deoxyguanosine / Q000031:analogs & derivatives / Q000737:chemistry; D006147:Guanine / Q000031:analogs & derivatives* / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008956:Models, Chemical; D012997:Solvents; D013050:Spectrometry, Fluorescence
chemical_list: D012997:Solvents; C024829:8-hydroxyguanine; D006147:Guanine; D000080242:8-Hydroxy-2'-Deoxyguanosine; D003849:Deoxyguanosine