Site specific binding of calcium ions to anionic chitin derivatives

Abstract

6- O-carboxymethylated chitin (6- O-CM-chitin) and N-succinylated chitosan (Suc-chitosan) are shown to have a high affinity for calcium ions on a 10 5 mol −1 dm 3 order of adsorption constants. It is suggested that 6- O-CM-chitin especially forms a tight complex with calcium ions, which is restricted even in acidic media. The Scatchard plot of 6- O-CM-chitin shows linear behavior, suggesting that each adsorption site is independent for calcium adsorption, while that of 3,6- O-CM-chitin indicates negative cooperativity suggesting a slight interaction among adsorption sites. Thus 6- O-CM-chitin may form more stable complexes with calcium ions than 3,6- O-CM-chitin. These results revealed that a secondary hydroxyl group of an N-acetylglucosamine (GlcNAc) residue at the C-3 position contributed significantly to calcium chelation for 6- O-CM-chitin.