Chelation of chitosan derivatives with zinc ions. II. Association complexes of Zn2+ onto O,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