Structural and semiempirical investigation of hydrazone of gossypol and its protonated species

Hydrazone of gossypol with hydrazine (GH) has been synthesised and its structure has been studied by 1H NMR, 13C NMR, 13C CP-MAS, 15N CP-MAS, FT-IR and PM5 semiempirical methods. The results have shown that the simplest hydrazone of gossypol exists both in solution and in solid in the N-imine–N-imine tautomeric form, stabilized by several intramolecular hydrogen bonds among which the O7H···N16 intramolecular one is the strongest. The structure of GH is visualized by the PM5 semiempirical calculations. The ESI-MS studies have shown that the GH molecule can be present in the mono- and di-protonated forms. It is demonstrated that the protonation occurs at the amino groups of GH molecule and has no influence on the intramolecular hydrogen bonds within the N-imine–N-imine tautomeric form.