Studies on chitin ix. Specific binding of calcium ions by carboxymethyl-chitin

Abstract

Carboxymethylation of chitin was carried out effectively for preparing a cation exchange resin under basic conditions. The resulting carboxymethyl-chitin (CM-chitin) was found to bind calcium ions specifically among alkali-earth metals even in the presence of monovalent cations such as sodium or potassium. Differential IR absorption spectroscopy suggested that the binding of calcium ion by carboxyl groups was assisted by acetamide groups at C2 and primary hydroxyl groups at C6 or secondary hydroxyl groups at C3 in the N-acetylglucosamine residue. The binding constants were estimated at various ionic strengths and ion concentrations. The selectivity coefficient (KNaCa) of CM-chitin for calcium ions over sodium ions was assumed to be 45.6 at neutral pH and 0.1舒0.2 of ionic strength. The fibrous CM-chitin was prepared to investigate the effects of an increase in the number of surface ionic sites and degree of orientation on the binding capacity. The results indicated a marked enhancement. © 1983 The Society of Polymer Science, Japan.