Spectroscopic investigation of the molecular structure of hypericin and its salts

Based on the interpretation of UV/Vis, IR, and NMR spectra of hypericin as well as of its salts: and the products of total O-methylation, it was concl uded that hypericin transfers from solid state to low or moderate polar org anic media as its 1,6-dioxo-tautomer, thereby conserving the molecular stru cture characteristic for the crystalline state of the material. In concentr ated hypericin solutions, the 1,6-dioxo isomer converts slowly into the 7,1 4-dioxo isomer. Dilution of the solution or addition of pyridine DMSO, or o ther polar compounds accelerates the reaction. The metastable hypericin 1,6 -dioxo-tautomer is stabilized in the solid phase and concentrated solutions by intermolecular hydrogen bonds. Salts of hypericin with alkali metals re tain the structure of the 7,14-dioxo-tautomer both in solutions and crystal line state.