Molecular mode of complexation between carboxymethylchitin and the copper(II) ion in aqueous systems

Complex formation between carboxymethylchitin (CMCh) and copper(II) ions in aqueous solutions has been studied using dynamic viscoelasticity and 13C NMR measurements. The frequency dependence curve of loss modulus shows a marked maximum and the pseudo-equilibrium modulus, GN, can be calculated by integration of the curve. The increment in GN with addition of Cu ions is proportional to the concentration of Cu ions. It is revealed that the complexation between CMCh and Cu ions involves an intermolecular process (i.e. crosslinking) and that ca. 3.4% of Cu ions added to the system act effectively as a crosslinking adduct. The spin–lattice relaxation time shows that the site of complexation is near a carboxyl group. Our new complexation model between CMCh and alkaline-earth-metal ions is also applicable to the complexation between CMCh and Cu ions.