CARBOHYDRATE COMPLEXES WITH ALKALINE-EARTH METAL-IONS - INTERACTION OF D-GLUCONO-1,5-LACTONE WITH THE MG(II), CA(II), SR(II), AND BA(II) CATIONS IN THE CRYSTALLINE SOLID AND AQUEOUS-SOLUTION

The interaction of alkaline earth metal ions with D-glucono-1,5-lactone has been investigated, in aqueous solution at neutral pH, and compounds of the type Mg(D-gluconate)2·2H2O, Ca(D-gluconate)2, Sr(D-gluconate)2 and Ba(D-gluconate)2 have been isolated. These metal-sugar salts are characterized by elemental analysis, 13C-NMR, FTIR spectroscopy, and x-ray powder diffraction measurements. Spectroscopic and x-ray powder diffraction measurements showed isomeric patterns between Mg(D-gluconate)2·2H2O and the structurally identified Mn(D-gluconate)2·2H2O, where the Mn(II) ion is six-coordinate, binding to two sugar anions through the carboxylate 0-1 and an OH group of each sugar anions, as well as to two H2O molecules. The Ca(II)-, Sr(II)-, and Ba(II)-D-gluconate salts are similar, but rather different from that of Mg(II)- and Mn(II)-sugar compounds. Therefore, the eight-coordination around these metal cations could be completed by the coordination of the two D-gluconate anions tridentately via carboxylate O-1, O(2)-H, and O(3)-H and the binding of the two other sugar anions unidentately, through a carboxylate oxygen atom. The alkaline earth metal D-gluconate salts are polymerized through bridging carboxylate groups with acid anions having bent-chain conformation. © 1990.