Jul 24, 2008

UV excitation of single DNA and RNA strands produces high yields of exciplex states between two stacked bases

Proceedings of the National Academy of Sciences of the United States of America
Tomohisa TakayaB Kohler


Excited electronic states created by UV excitation of the diribonucleoside monophosphates ApA, ApG, ApC, ApU, and CpG were studied by the femtosecond transient-absorption technique. Bleach recovery signals recorded at 252 nm show that long-lived excited states are formed in all five dinucleosides. The lifetimes of these states exceed those measured in equimolar mixtures of the constituent mononucleotides by one to two orders of magnitude, indicating that electronic coupling between proximal nucleobases dramatically slows the relaxation of excess electronic energy. The decay rates of the long-lived states decrease with increasing energy of the charge-transfer state produced by transferring an electron from one base to another. The charge-transfer character of the long-lived states revealed by this analysis supports their assignment to excimer or exciplex states. Identical bleach recovery signals were seen for ApA, (A)(4), and poly(A) at delay times >10 ps after photoexcitation. This indicates that excited states localized on a stack of just two bases are the common trap states independent of the number of stacked nucleotides. The fraction of initial excitations that decay to long-lived exciplex states is approximately equal to t...Continue Reading

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Mentioned in this Paper

Biochemical Pathway
RNA Conformation
Base Pairing
Genotoxic Stress
Genetic Techniques
Hydrogen-Ion Concentration
Disintegration (Morphologic Abnormality)
Molecular Genetics (Discipline)

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