Schiff base of gossypol with 3,6,9‐trioxa‐decylamine complexes with monovalent cations studied by mass spectrometry, 1 H‐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, 1 H‐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 O 1 H or O 1′ H group coordinating the cation. The structures of the complexes are calculated by the PM5 semiempirical method and discussed. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004