Double proton transfer dynamics of model DNA base pairs in the condensed phase.

  • Kwon O
  • Zewail A
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The dynamics of excited-state double proton transfer of model DNA
base pairs, 7-azaindole dimers, is reported using femtosecond fluorescence
spectroscopy. To elucidate the nature of the transfer in the condensed
phase, here we examine variation of solvent polarity and viscosity,
solute concentration, and isotopic fractionation. The rate of proton
transfer is found to be significantly dependent on polarity and on
the isotopic composition in the pair. Consistent with a stepwise
mechanism, the results support the presence of an ionic intermediate
species which forms on the femtosecond time scale and decays to the
final tautomeric form on the picosecond time scale. We discuss the
results in relation to the molecular motions involved and comment
on recent claims of concerted transfer in the condensed phase. The
nonconcerted mechanism is in agreement with previous isolated-molecule
femtosecond dynamics and is also consistent with the most-recent
high-level theoretical study on the same pair.

Author-supplied keywords

  • Base Pairing; DNA; Protons; Spectrum Analysis; Tim

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  • Oh-Hoon Kwon

  • Ahmed H Zewail

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