Chelation of chitosan derivatives with zinc ions. II. Association complexes of Zn2+ ontoO,N-carboxymethyl chitosan

The chelation of zinc ions onto O,N-carboxymethyl chitosan (ONCMCh) was characterized using a Fourier transform infrared (FTIR) spectrophotometer and a scanning electron microscope (SEM). From the FTIR spectra, little change in the absorption intensities and frequencies at 3300–3600 cm−1 of Zn2+ONCMCh chelated specimens suggested that OH and NH2 groups were not participating in the chelation reaction. The absence of absorption bands at 1755–1700 cm−1 suggested that the carboxyl group CO was not ionized, and the ionized CO bands were observed at 1400–1600 cm−1 for chelated specimens. Thus, the chelation sites took place at the carboxyl group rather than at the OH and NH2 groups. It also confirmed that water-insoluble chelates, which were formed through the ZnO and ZnN bonds, presented a tetrahedral structure. The water-soluble complexes where zinc ions connected with oxygen of CO and water molecules were only due to electron attraction. Formation of different microstructures on the surfaces, as revealed by SEM, provided evidence to distinguish different chelating mechanisms between water-soluble and water-insoluble complexes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1476–1485, 2001