Structure and equilibria of Ca2+-complexes of glucose and sorbitol from multinuclear (1H, 13C and 43Ca) NMR measurements supplemented with molecular modelling calculations

Ca2+-complexation of D-glucose and D-sorbitol have been investigated with the aid of multinuclear (H-1, C-13 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 C-13 NMR spectra obtained at constant ionic strength (1 M NaCl). Binding sites were identified from 2D H-1-Ca-43 NMR spectra. 2D NMR measurements and ab initio calculations indicated that Ca2+ 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.