Vibrational spectra, structure and antioxidant activity of gossypol imine derivatives

The structures and tautomeric equilibria of natural polyphenol gossypol and four its imine derivatives were studied by FT-IR-, NMR-spectroscopy and quantum chemistry methods. It was shown that gossypol Schiff bases exist in solution as enamine–enamine tautomer and hydrazones as imine–imine tautomer. Infrared absorption spectra of studied compounds were simulated using the PM3 method. The fundamental vibrational frequencies were evaluated using various scale factors which yield a good agreement between observed and calculated frequencies. Free radical scavenging activity of gossypol and its imine derivatives was evaluated using DPPH method. Antioxidant activity of studied compounds was characterized. Gossypol hydrazones were shown to be more efficient, while Schiff base to be less efficient as antioxidants in comparison with gossypol itself.

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► Tautomeric equilibria of gossypol and its imine derivatives.
► Calculated and experimental IR spectra of studied compounds.
► Free radical scavenging activity of polyphenols toward DPPH
► New characteristic of antioxidant activity – AE (antioxidant efficiency) parameter.