The Structure of Hypericin in Solution. Searching for Hypericin's 1,6 Tautomer

Hypericin in organic solvents displays two types of electronic spectra: one type which shows a distinct solvatochromic effect, the stable form, and the other, the unstable form, which lacks this property. The latter type is formed in dry nonprotic solvents (e.g. tetrahydrofuran, EtOAc) and can be co...

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Bibliographic Details
Published in:Photochemistry and photobiology 2001-08, Vol.74 (2), p.206-210
Main Authors: Freeman, Dalia, Konstantinovskii, Leonid, Mazur, Yehuda
Format: Article
Language:English
Subjects:
Isomerism
Magnetic Resonance Spectroscopy
Perylene - analogs & derivatives
Perylene - chemistry
Photosensitizing Agents - chemistry
Solutions
Spectrophotometry
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Summary:Hypericin in organic solvents displays two types of electronic spectra: one type which shows a distinct solvatochromic effect, the stable form, and the other, the unstable form, which lacks this property. The latter type is formed in dry nonprotic solvents (e.g. tetrahydrofuran, EtOAc) and can be converted to the stable form on addition of protic solvents. In order to establish the tautomeric structure of the unstable form we applied conventional nuclear magnetic resonance techniques as well as two-dimensional gradient-enhanced heteronuclear multiple-quantum correlation, gradient-enhanced ROESY and one-dimensional nuclear Overhauser effect difference experiments. All these techniques pointed to the fact that the unstable form has the 7,14-diketo tautomeric structure, like the stable form, and not the 1,6-diketo structure. Electronic spectroscopy indicated that the unstable form has acidic properties and therefore possesses two free OH groups at C3 and C4 at the bay region of the molecule.
ISSN:0031-8655
1751-1097
DOI:10.1562/0031-8655(2001)074<0206:TSOHIS>2.0.CO;2