Binding of metal ions to polysaccharides. V. Potentiometric, spectroscopic, and viscosimetric studies of the binding of cations to chondroitin sulfate and chondroitin in neutral and acidic aqueous media.

Binding of cations to chondroitin sulfate A and C, chondroitin, and D-glucuronate was investigated in neutral and acidic aqueous media using H+, Cu2+, and Na+ ion-specific electrodes, viscometry, electron spin resonance (esr), and ligand-field spectroscopy. Site binding to the carboxylate group and only electrostatic interaction with the sulfate group could describe the results well. The nitrogen atom of the N-acetyl group appeared not to be involved in bonding of cations to chondroitin(sulfate) systems. The interaction of the divalent metal ions follows the Irving-Williams series. The value of the electrostatic potential at the carboxylate group of chondroitin(sulfate), as experienced by a cation, was determined in dependence of cation bonding. It proved to be difficult to establish the composition of a complex of a metal ion with a polyion by means of a molar ratio curve.

A 13C-n.m.r. study of the binding of ytterbium(III) to chondroitin sulphate and chondroitin.

13C-N.m.r. spectra of chondroitin 4- and 6-sulphates, chondroitin, beta-D-glucuronate, and beta-D-glucose 6-sulphate were measured in the presence of ytterbium(III) in deuterium oxide. The structure of the ytterbium-polysaccharide compounds in solution was found to be similar to that reported for calcium chondroitin 4-sulphate in a stretched film. In the glucuronate complex, Yb(III) coordinates to the carboxylate group. For beta-D-glucose 6-sulphate, the ytterbium-induced shifts are too small to allow the structure to be determined.