| Abstract
| - Time-correlated single photon counting was used to observe dynamicquenching of the hypericin and stentorinexcited singlet states. The fluorescence quenching data forhypericin and stentorin were interpreted in termsof electron transfer. The observed correlation between free energychange of electron transfer and quenchingrate constant suggests that quenching proceeds via electron transferfrom hypericin and stentorin to thequenchers. EPR spectra for hypericin, stentorin, and stentorinchromoprotein demonstrated that free radicalformation was initiated or enhanced by visible light and that similarradical species were produced in eachsample. Furthermore, the EPR signal for stentorin wassignificantly enhanced by 1,4-benzoquinone, but theoverall shape and g-value was unchanged. We suggestthat electron transfer in the excited state of thesechromophores results in the formation of a cation radical. Thiselectron transfer is a rapid and efficientpathway for deactivation of hypericin and stentorin excited singletstates and should be considered whendiscussing the photoreactivity of hypericin as a photodynamic agent andof stentorin as the Stentor coeruleusphotoreceptor.
|
