The interaction of Co 2+ ions and sodium deoxycholate micelles

Abstract

To mimic the interaction between divalent metal ions and bile slats in vivo, two groups of coordination complex compounds, crystalline and gel-like, were synthesized in vitro by mixing the aqueous solutions of CoCl 2 with sodium deoxycholate (NaDC) at various concentrations. Structures and compositions of the compounds were investigated using FT-IR, EXAFS, XRD as well as elemental and ICP analysis, respectively. Then the interaction of Co 2+ with deoxycholate in solution was observed by laser light scattering (LLS), Transmission electronic microscope techniques and ICP analysis. Conclusions are (1) the crystalline complexes, Co (DC) 2·3H 2O were obtained by reaction of Co 2+ with mono-molecules of NaDC, and the gel-like complexes, Na n Co m (DC) n+2 m formed by reaction of Co 2+ with NaDC micelles. The gel-like complexes exhibit the non-stoichiometric character; (2) the coordination structures of carboxyl groups with Co 2+ were different between the crystalline and gel-like complexes. In Co(DC) 2·3H 2O complex, the carboxyl groups of deoxycholate coordinated with Co 2+ in chelating and pseudo-chelating modes, but that in bridge mode in the case of Na n Co m (DC) n+2 m complexes. The non-stoichiometric complexes of Na n Co m (DC) n+2 m are formed with a macromolecular structure through the Co 2+ bridges; (3) NaDC can increase the solubility of Co(DC) 2·3H 2O in aqueous solution, and larger micelles (30–80 nm diameter) formed in the supernate. It is a mixed micelle formed by Co 2+ ions bridges connecting with NaDC simple micelles. So these micelles are a new kind of micelle containing two kinds of metal ions; (4) these results are in agreement with those formed under physiological conditions in that the different states such as gel, precipitate, micelles of various structures are present in bile of gallbladder. An ideal model of the interaction between Co 2+ and bile salts in vivo has been proposed.