The Schiff base of gossypol with 2-(aminomethyl)-15-crown-5 complexes with monovalent cations studied by MS,1H NMR, FT-IR and PM5 semiempirical methods

Abstract

A new Schiff base of gossypol with 2-(aminomethyl)-15-crown-5 [GSCB] was shown to be capable of complexation of monovalent cations. This process of complex formation was studied by electrospray ionization (ESI) mass spectrometry, 1H NMR and FT-IR spectroscopy, as well as by PM5 semiempirical method. It was found that the gossypol Schiff base can form 1 ∶ 1 and 1 ∶ 2 complexes with monovalent cations. With H+, Li+ or Na+ cations the Schiff base preferentially forms 1 ∶ 2 complexes. In the complex with protons they are localised on the N atoms of the Schiff base and the molecule exists in the imine–imine tautomeric form. The 1 ∶ 2 complexes of the Schiff base with Li+ and Na+ cations occur only in the enamine–enamine tautomeric form and the cations are coordinated only by the oxygen atoms of the crowns. The complexes of the Schiff base with K+, Rb+ or Cs+ cations are of 1 ∶ 1 and 1 ∶ 2 type with the oxygen atoms of the crowns, as well as O1H and O1′H groups coordinating the cations. The structures of the complexes are calculated by PM5 semiempirical method and disscussed.