Excited state deactivation mechanisms in nucleic acids are critical for understanding the origins of biological photodamage. Femtosecond transient absorption studies have shown that UV excited states of nucleic acid oligomers and polymers have characteristic lifetimes of between 5 and 200 ps even though excited states of single nucleotides decay nonradiatively in hundreds of femtoseconds. The reasons behind the long-lived excited states in DNA and RNA base multimers are uncertain and the subject of on-going experimental and theoretical efforts. Experiments have now detected long-lived excited states in a wide variety of DNA and RNA model systems ranging from simple dinucleosides to single and multi-strands with significant base-sequence disorder and different helix conformations. In order to better understand how conformation influences electronic energy relaxation, we studied a series of compounds in which two adenosines are joined by flexible linkers of different types and lengths. Long-lived excited states are observed for the various diadenosines in aqueous solution, but these states are absent when the solvent is 80:20 (v/v) methanol-water. The long-lived excited states decay identically in all systems, yet circular dichroism spectra differ greatly, indicating very different folded structures. These results together with temperature-dependent measurements provide new insights into the stacking-unstacking transition in nucleic acids.Funding from the National Science Foundation is gratefully acknowledged ( CHE-1112560) .

Base stacking and electronic energy relaxation in DNA: Insights from diadenosines joined by flexible linkers

244th National Meeting (2012)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.