Spectroscopic and semiempirical studies of gossypol complexes with Fe2+ and Fe3+ cations

The complexes of gossypol with Fe2+ and Fe3+ cations were studied in acetonitrile by UV–Vis and FT-IR spectroscopy. Very complex equilibria and structural changes were observed for various ratios of gossypol–iron cation mixtures. With the formation of complexes, the ketol–ketol tautomer form of gossypol was favored. With increasing concentration of iron cation in the mixture, the deprotonation of hydroxyl groups was indicated. The semiempirical studies show that the most stable complexes of gossypol with iron cations are 1:4, 1:1 and 2:1. The structures of these complexes are discussed.