Structure and dynamics of photogenerated triplet radical ion pairs in DNA hairpin conjugates with anthraquinone end caps

Raanan Carmieli, Amanda L. Smeigh, Sarah M. Mickley Conron, Arun K. Thazhathveetil, Masaaki Fuki, Yasuhiro Kobori, Frederick D. Lewis, Michael R. Wasielewski

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19 Citations (Scopus)

Abstract

A series of DNA hairpins (AqGn) possessing a tethered anthraquinone (Aq) end-capping group were synthesized in which the distance between the Aq and a guanine-cytosine (G-C) base pair was systematically varied by changing the number (n - 1) of adenine-thymine (A-T) base pairs between them. The photophysics and photochemistry of these hairpins were investigated using nanosecond transient absorption and time-resolved electron paramagnetic resonance (TREPR) spectroscopy. Upon photoexcitation, 1*Aq undergoes rapid intersystem crossing to yield 3*Aq, which is capable of oxidizing purine nucleobases resulting in the formation of 3(Aq -•Gn +•). All 3(Aq -•Gn +•) radical ion pairs exhibit asymmetric TREPR spectra with an electron spin polarization phase pattern of absorption and enhanced emission (A/E) due to their different triplet spin sublevel populations, which are derived from the corresponding non-Boltzmann spin sublevel populations of the 3*Aq precursor. The TREPR spectra of the 3(Aq -•Gn +•) radical ion pairs depend strongly on their spin-spin dipolar interaction and weakly on their spin-spin exchange coupling. The anisotropy of 3(Aq -•Gn +•) makes it possible to determine that the π systems of Aq -• and G +• within the radical ion pair are parallel to one another. Charge recombination of the long-lived 3(Aq -•Gn +•) radical ion pair displays an unusual bimodal distance dependence that results from a change in the rate-determining step for charge recombination from radical pair intersystem crossing for n < 4 to coherent superexchange for n > 4.

Original languageEnglish
Pages (from-to)11251-11260
Number of pages10
JournalJournal of the American Chemical Society
Volume134
Issue number27
DOIs
Publication statusPublished - Jul 11 2012

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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    Carmieli, R., Smeigh, A. L., Mickley Conron, S. M., Thazhathveetil, A. K., Fuki, M., Kobori, Y., Lewis, F. D., & Wasielewski, M. R. (2012). Structure and dynamics of photogenerated triplet radical ion pairs in DNA hairpin conjugates with anthraquinone end caps. Journal of the American Chemical Society, 134(27), 11251-11260. https://doi.org/10.1021/ja303721j