INTERACTION OF ZINC(II) ION WITH D-ALDONIC ACIDS IN THE CRYSTALLINE SOLID AND AQUEOUS-SOLUTION

The interaction of zinc(II) ion with D-glucoheptonic acid, D-gluconic acid, D-gulonic acid, D-galactonic acid and D-ribonic acid has been investigated and compounds of the type Zn(D-glucoheptonate)2 . 3H2O. Zn(D-gluconate)2 . 3H2O, Zn(D-gulonate)2 . 3H2O, Zn(D-galactonate)2 . 3H2O and Zn(D-ribonate)2 . H2O, have been isolated. These metal-sugar salts were characterized by elemental analysis, FT IR spectroscopy, thermogravimetric analysis and C-13-NMR. Spectroscopic measurements showed similar patterns between these complexes and the structurally identified Mn(D-gluconate)2 . 2H2O. The zinc(II) ion is binding to two ligand molecules through the carboxylate and OH groups of each sugar, as well as to water molecules. The potentiometric measurements in aqueous solutions for the systems formed by the sugar acids investigated and the zinc(II) ion at different metal-ligand ratios showed the 1 : 1 complexes formation. On the basis of the C-13 NMR, the participation of C-1 and C-2 in this complex formation was verified. Due to the hydroxide precipitation, quantitative evaluation of the stability constants was not performed.