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Article
Electron Transfer Quenching and Photoinduced EPR of Hypericin and the Ciliate Photoreceptor Stentorin
Journal of Physical Chemistry A (1997)
  • Todd A. Wells, University of Nebraska - Lincoln
  • Aba Losi, University of Parma
  • Renke Dai, University of Nebraska - Lincoln
  • Marvin Paul Scott, University of Nebraska - Lincoln
  • Su-Moon Park, University of New Mexico
  • John H. Golbeck, University of Nebraska - Lincoln
  • Pill-Soon Song, University of Nebraska - Lincoln
Abstract
Time-correlated single photon counting was used to observe dynamic quenching of the hypericin and stentorin excited singlet states. The fluorescence quenching data for hypericin and stentorin were interpreted in terms of electron transfer. The observed correlation between free energy change of electron transfer and quenching rate constant suggests that quenching proceeds via electron transfer from hypericin and stentorin to the quenchers. EPR spectra for hypericin, stentorin, and stentorin chromoprotein demonstrated that free radical formation was initiated or enhanced by visible light and that similar radical species were produced in each sample. Furthermore, the EPR signal for stentorin was significantly enhanced by 1,4-benzoquinone, but the overall shape and g-value was unchanged. We suggest that electron transfer in the excited state of these chromophores results in the formation of a cation radical. This electron transfer is a rapid and efficient pathway for deactivation of hypericin and stentorin excited singlet states and should be considered when discussing the photoreactivity of hypericin as a photodynamic agent and of stentorin as the Stentor coeruleus photoreceptor.
Publication Date
January, 1997
DOI
10.1021/jp9612588
Publisher Statement
This article is from Journal of Physical Chemistry A 101 (1997): 366, doi: 10.1021/jp9612588.
Citation Information
Todd A. Wells, Aba Losi, Renke Dai, Marvin Paul Scott, et al.. "Electron Transfer Quenching and Photoinduced EPR of Hypericin and the Ciliate Photoreceptor Stentorin" Journal of Physical Chemistry A Vol. 101 Iss. 4 (1997) p. 366 - 372
Available at: http://works.bepress.com/paul-scott/5/