Charge separation and charge delocalization identified in long-living states of photoexcited DNA

Dominik B. Bucher, Bert M. Pilles, Thomas Carell, Wolfgang Zinth

Research output: Contribution to journalArticlepeer-review

113 Scopus citations

Abstract

Base stacking in DNA is related to long-living excited states whose molecular nature is still under debate. To elucidate the molecular background we study well-defined oligonucleotides with natural bases, which allow selective UV excitation of one single base in the strand. IR probing in the picosecond regime enables us to dissect the contribution of different single bases to the excited state. All investigated oligonucleotides show long-living states on the 100-ps time scale, which are not observable in a mixture of single bases. The fraction of these states is well correlated with the stacking probabilities and reaches values up to 0.4. The long-living states show characteristic absorbance bands that can be assigned to charge-transfer states by comparing them to marker bands of radical cation and anion spectra. The charge separation is directed by the redox potential of the involved bases and thus controlled by the sequence. The spatial dimension of this charge separation was investigated in longer oligonucleotides, where bridging sequences separate the excited base from a sensor base with a characteristic marker band. After excitation we observe a bleach of all involved bases. The contribution of the sensor base is observable even if the bridge is composed of several bases. This result can be explained by a charge delocalization along a well-stacked domain in the strand. The presence of charged radicals in DNA strands after light absorption may cause reactions - oxidative or reductive damage - currently not considered in DNA photochemistry.

Original languageEnglish
Pages (from-to)4369-4374
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume111
Issue number12
DOIs
StatePublished - 25 Mar 2014
Externally publishedYes

Keywords

  • DNA damage
  • DNA electron transfer
  • DNA photophysics
  • Ultrafast vibrational spectroscopy

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