Molecular Structures and Stability Constants of Gossypol and Its Aza-Derivative Complexes with Silver(I) Cations Studied by Potentiometric, ESI MS, NMR, and AM1d Semiempirical Methods

Abstract

Stability constants of complexes formed by gossypol and by ten of its Schiff bases with Ag (+) cations were determined by the potentiometric method. The potentiometric and ESI MS experiments indicate the formation of AgL (+) and Ag 2L (2+) complexes between the Schiff bases G1-G7 and Ag (+) cations as well as the formation of AgL (+), Ag 2L (2+), AgL 2 (+) and Ag 3L 2 (3+) complexes between the Schiff bases G8-G10 and Ag (+) cations. The highest stability constant was found for the AgL (+) complex of G8 Schiff base and the lowest one for the AgL (+) complex of G molecule. The (13)C NMR spectra of mixtures between G and AgClO 4 as well as G1-G10 and AgClO 4 indicate that the complexation of the Ag (+) cations is exclusively realized by the aldehyde-aldehyde tautomer of gossypol and by the enamine-enamine form of gossypol Schiff bases, respectively. We show that the main coordination sites for the Ag (+) metal cations are either the oxygen or the nitrogen atoms of the amine parts of the Schiff bases of gossypol. The energetically most favorable structures of the Ag (+) complexes with gossypol (G) or with the gossypol Schiff bases (G1-G10) were calculated and visualized by the AM1d method at an semiempirical level of theory.

Synthesis, crystal structures and antibacterial activity studies of aza-derivatives of phytoalexin from cotton plant – gossypol

“…Further important information about the tautomeric forms of gossypol aza-derivatives can be obtained from the position of the C-7 carbon atom signals in the 13 C NMR spectra. In the spectrum of GOS the signal of C(7) carbon atom was found at 155.6 ppm in CDCl 3 [54] and at 151.4 ppm in CD 3 CN [55], whereas the signal of C(7) carbon atom in the spectra of 19-27 was in the range 150.1-157.3 ppm ( Table 5). The chemical shift of the C(7) signals of gossypol hydrazones (19)(20)(21)(22)(23)(24)(25)(26)(27), similar to those of GOS, are in the range characteristic of the C-OH carbon atoms of phenols [46,[56][57][58][59].…”

The influence of protonation on molecular structure and physico-chemical properties of gossypol Schiff bases

“…Gossypol Schiff base with 3-morpholinopropylamine (S2) was obtained by the procedure given in Ref. 21. Gossypol Schiff base with allylamine (S1) was synthesised by the procedure given in Ref.…”

“…Recently, we have shown that conversion of gossypol into its Schiff bases and hydrazones generally improved biological properties and resulted in increased affinity toward metal cations. [19][20][21] In view of potential applications of these compounds in medicine and agriculture there is a need to learn more about their acid-base properties and molecular structures to help structure-activity studies. Although a vast number of gossypol derivatives have been synthesised, only a few have their crystal structures reported.…”

Interaction between (1,1′‐Binaphthalene)‐2,2′‐diol and Lecithin Liposome

“…11 For example, gossypol with a binaphthyl structural unit is applied to the fields of male contraception and anti-tumor. 12 However, it is difficult to understand the functional mechanism between drugs and biological membrane due to complicated structures of these drugs. Therefore, it is important to use drug intermediate for researching the interaction of drugs with biological membrane.…”