Carbon-13 NMR Spectra of Sodium D-Gluco- and D-Galacto-pyranuronates in the Presence of Lanthanide Ions

Abstract

Carbon-13 NMR spectra of sodium D-gluco- and D-galactopyranuronates were measured in the presence of lanthanum, europium, praseodymium, or neodymium ions in deuterium oxide. The lanthanide-induced shifts of all the carbon signals were divided into three components based on complex-formation, contact, and pseudocontact effects. The last effects on C-1 in the α-anomers were exceedingly greater than those in the corresponding β-anomers. Carbon-13 spin-lattice relaxation times and their reduction induced by gadolinium ion were also measured and the binding sites of the ion were estimated, which showed marked differences between the two anomers and suggested the formation of bidentate complexes, involving linkages to both the ring and the carboxyl oxygen only between the a-anomers and the lanthanide ions.