Schiff base of gossypol with 3,6,9-trioxa-decylamine complexes with monovalent cations studied by mass spectrometry, 1H-NMR, FTIR, and PM5 semiempirical methods

A new Schiff base of gossypol with 3,6,9-trioxa-decylamine (GSTB) forms stable complexes with monovalent cations. This process of complex formation was studied by electrospray ionization mass spectrometry, 1H-NMR and FTIR spectroscopy, and the PM5 (parametric method 5) semiempirical method. It is found that GSTB forms 1 : 1 and 1 : 2 complexes with Li+ and Na+ and 1 : 1 complexes with K+, Rb+, or Cs+ cations and exists in all these complexes in the enamine-enamine tautomeric form. Moreover, within these complexes only Li+ cations can fluctuate between the oxygen atoms of trioxaalkyl chains. All other cations are strongly localized. In the complex of GSTB with two protons localized on the N atoms of the Schiff base, the imine-imine tautomeric form is realized. The complexes of the Schiff base with K+, Rb+, or Cs+ cations are the 1 : 1 type with the oxygen atoms of the trioxaalkyl chains, as well as the O1H or O1ʹH group coordinating the cation. The structures of the complexes are calculated by the PM5 semiempirical method and discussed.