Gerson, Fabian and Gescheidt, Georg and Haering, Pascal and Mazur, Yehuda and Freeman, Dalia and Spreitzer, Hubert and Daub, Jörg (1995) Electron-Acceptor Properties of Hypericin and Its Salts: An ESR/ENDOR and Electrochemical Study. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 117 (48). pp. 11861-11866. ISSN 0002-7863, 1520-5126
Full text not available from this repository.Abstract
Hypericin (HyH) and its conjugate base Hy(-) (existing as salts Hy(-)X(+), where X = Na, Cs, Et(3)NH, lysineH) undergo one-electron reduction to yield the radical anion [HyH](.-) and the radical dianion Hy(.2-), respectively, which have been investigated by ESR, ENDOR, and TRIPLE-resonance spectroscopy. Whereas Hy(.2-) can be generated from Hy(-) by electrolysis or by several reducing agents in a variety of solvents and is stable for weeks even at room temperature, the spectra of [HyH](.-), produced from HyH with zinc in anhydrous N,N-dimethylformamide or with potassium in tetrahydrofuran, are replaced within a few minutes by those of Hy(.2-). The hyperfine data for [HyH](.-) and Hy(.2-) are consistent with a helically twisted carbon framework of C-2 symmetry. A prominent hyperfine feature of Hy(.2-) is a relatively large coupling constant of +0.167 mT due to a single proton situated on the 2-fold axis in a symmetric C(3)-O-delta-... H ...O-delta--C(4) bridge. This value is missing for [HyH](.-) which does not possess such a bridge but has two non-dissociated OH groups in the 3,4-positions. Cyclic voltammograms of hypericin salts (Hy(-)X(+)) exhibit up to three reversible reduction waves in the region -1.0 to -2.2 V (vs Ag/AgCl). They are attributed to the consecutive redox steps Hy(-)/Hy(.2-), Hy(.2-)/Hy(3-), and (presumably) Hy(3-)/Hy(.4-). Analogous electrochemical studies of free hypericin (HyH) require the use of strictly anhydrous solvents, in which HyH is sufficiently soluble and the facile deprotonation to Hy(-) can be avoided. Under these conditions, a wave attributed to reduction of a proton is observed at a less negative potential than that of Hy(-) to Hy(.2-), while the subsequent waves correspond to those of Hy(-)X(+).
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | HUMAN-IMMUNODEFICIENCY-VIRUS; 5 REDOX STAGES; PHOTODYNAMIC-ACTION; UV/VISIBLE/NEAR-IR; RESONANCE-SPECTRA; SINGLET OXYGEN; SPIN RESONANCE; FREE-RADICALS; ROSE-BENGAL; INHIBITION |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Organische Chemie > Alumni or Retired Professors > Prof. Dr. Jörg Daub |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 15 Nov 2023 10:41 |
| Last Modified: | 15 Nov 2023 10:41 |
| URI: | https://pred.uni-regensburg.de/id/eprint/52166 |
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