title: Excited-State Dynamics of DNA Duplexes with Different H-Bonding Motifs.
abstract: The excited-state dynamics of three distinct forms of the d(GC)9·d(GC)9 DNA duplex were studied by combined time-resolved infrared experiments and quantum mechanical calculations. In the B- and Z-forms, bases on opposite strands form Watson-Crick (WC) base pairs but stack differently because of salt-induced changes in backbone conformation. At low pH, the two strands associate by Hoogsteen (HG) base pairing. Ultraviolet-induced intrastrand electron transfer (ET) triggers interstrand proton transfer (PT) in the B- and Z-forms, but the PT pathway is blocked in the HG duplex. Despite the different decay mechanisms, a common excited-state lifetime of ∼ 30 ps is observed in all three duplex forms. The ET-PT pathway in the WC duplexes and the solely intrastrand ET pathway in the HG duplex yield the same pair of π-stacked radicals on one strand. Back ET between these radicals is proposed to be the rate-limiting step behind excited-state deactivation in all three duplexes.
authors.affiliation: Department of Chemistry and Biochemistry, Montana State University , Bozeman, Montana 59717, United States.
authors.forename: Yuyuan
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Physics, United States Air Force Academy , USAF Academy, Colorado 80840, United States.
authors.forename: Kimberly
authors.initials: K
authors.lastname: de La Harpe
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: Consiglio Nationale delle Ricerche, Istituto di Biostrutture e Bioimmagini , 80136 Naples, Italy.
authors.forename: Lara
authors.initials: L
authors.lastname: Martínez-Fernández
authors.affiliation: Consiglio Nationale delle Ricerche, Istituto di Biostrutture e Bioimmagini , 80136 Naples, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Improta
authors.affiliation: Department of Chemistry and Biochemistry, Montana State University , Bozeman, Montana 59717, United States.
authors.forename: Bern
authors.initials: B
authors.lastname: Kohler
mesh_terms: D020029:Base Pairing; D059371:DNA, B-Form / Q000737:chemistry* / Q000528:radiation effects; D043542:DNA, Z-Form / Q000737:chemistry* / Q000528:radiation effects; D006860:Hydrogen Bonding; D007700:Kinetics; D008956:Models, Chemical; D013055:Spectrophotometry, Infrared; D014466:Ultraviolet Rays
chemical_list: D059371:DNA, B-Form; D043542:DNA, Z-Form