Interaction of d-glucose with alkaline-earth metal ions. Synthesis, spectroscopic, and structural characterization of Mg(II)- and Ca(II)- d-glucose adducts and the effect of metal-ion binding on anomeric configuration of the sugar

Abstract

The interaction of d-glucose with the hydrated alkaline-earth metal halides has been studied in solution, and adducts of the type Mg( d-glucose)X 2·4 H 2O, Ca( d-glucose)X 2·4 H 2O, and Ca( d-glucose) 2X 2·4 H 2O, where X = Cl − and Br −, have been isolated, and characterized by means of F.t.-i.r. and 1H-n.m.r. spectroscopy, X-ray powder diffraction, and molar conductivity measurements. Spectroscopic and other evidence suggested that the Mg(II) ion in the Mg( d-glucose)X 2·4 H 2O adducts six-coordinate, binding to a d-glucose molecule (possibly via O-1 and O-2 atoms) and to four H 2O molecules, whereas, in the corresponding 1:1 Ca- d-glucose adduct, the Ca(II) ion is possibly seven-coordinate, binding to a sugar moiety (through the O-1, O-2, and other sugar donor atoms) and to four H 2O molecules. In 1:2 Ca( d-glucose) 2X 2·4 H 2O, the calcium ion may be eight-coordinate, binding to two d-glucose molecules (possibly via the O-1 and O-2 atoms of each sugar moiety) and to four H 2O molecules. The strong, sugar H-bonding network is rearranged upon d-glucose adduct-formation, and the α-anomeric configuration is favored by these metal cation coordinations.