title: Molecular spectroscopy: complexity of excited-state dynamics in DNA.
abstract: Absorption of ultraviolet light by DNA is known to lead to carcinogenic mutations, but the processes between photon absorption and the photochemical reactions are poorly understood. In their study of the excited-stated dynamics of model DNA helices using femtosecond transient absorption spectroscopy, Crespo-Hernández et al. observe that the picosecond component of the transient signals recorded for the adenine-thymine oligonucleotide (dA)18.(dT)18 is close to that for (dA)18, but quite different from that for (dAdT)9.(dAdT)9; from this observation, they conclude that excimer formation limits excitation energy to one strand at a time. Here we use time-resolved fluorescence spectroscopy to probe the excited-state dynamics, which reveals the complexity of these systems and indicates that the interpretation of Crespo-Hernández et al. is an oversimplification. We also comment on the pertinence of separating base stacking and base pairing in excited-state dynamics of double helices and question the authors' assignment of the long-lived signal component found for (dA)18.(dT)18 to adenine excimers.
authors.affiliation: Laboratoire Francis Perrin, CEA/DSM/DRECAM/SPAM-CNRS URA 2453, CEA Saclay, 91191 Gif-sur-Yvette, France. dimitra.markovitsi@cea.fr
authors.forename: Dimitra
authors.initials: D
authors.lastname: Markovitsi
authors.forename: Francis
authors.initials: F
authors.lastname: Talbot
authors.forename: Thomas
authors.initials: T
authors.lastname: Gustavsson
authors.forename: Delphine
authors.initials: D
authors.lastname: Onidas
authors.forename: Elodie
authors.initials: E
authors.lastname: Lazzarotto
authors.forename: Sylvie
authors.initials: S
authors.lastname: Marguet
mesh_terms: D000225:Adenine / Q000737:chemistry / Q000378:metabolism; D020029:Base Pairing; D004247:DNA / Q000737:chemistry* / Q000378:metabolism*; D005453:Fluorescence; D007700:Kinetics; D009838:Oligodeoxyribonucleotides / Q000737:chemistry / Q000378:metabolism; D017785:Photons; D013050:Spectrometry, Fluorescence; D013941:Thymine / Q000737:chemistry / Q000378:metabolism
chemical_list: D009838:Oligodeoxyribonucleotides; D004247:DNA; D000225:Adenine; D013941:Thymine