Structure and equilibria of Ca(2+)-complexes of glucose and sorbitol from multinuclear ((1)H, (13)C and (43)Ca) NMR measurements supplemented with molecular modelling calculations

Abstract

Ca(2+)-complexation of D-glucose and D-sorbitol have been investigated with the aid of multinuclear ((1)H, (13)C and (43)ca) NMR spectroscopy and ab initio quantum chemical calculations. Formation constants of the forming 1:1 complexes have been estimated from one-dimensional (13)C NMR spectra obtained at constant ionic strength (1 M NaCl). Binding sites were identified from 2D (1)H-(43)Ca NMR spectra. 2D NMR measurements and ab initio calculations indicated that Ca(2+) ions were bound in a tridentate manner via the glycosidic OH, the ethereal oxygen in the ring and the OH on the terminal carbon for the alpha- and beta-anomers of glucose and for sorbitol simultaneous binding of four hydroxide moieties (C1, C2, C4 and C6) was suggested. (C) 2010 Elsevier B.V. All rights reserved