Chemical equilibrium in the complexation of first transition series divalent cations Cu2+, Mn2+ and Zn2+ with chitosan

This study provided the data for calculating the stability constants formed in the aqueous HCl equilibrium of chitosan and CUI, Mn2+ and Zn2+, and determined the species distribution diagrams to show the influence of pH in the complexation systems based on data obtained from potentiometric and spectrophotometric titrations. The solid complexes further obtained from these aqueous HCI systems, were investigated by infrared spectroscopy. It was verified that chitosan coordinated with the cations CU2+, Mn2+ and Zn2+ at pHs > 4 > 5 and > 2 respectively, in ligand to metal ratio of 1:1. The logarithms of the binding constants for ML species presented the following stability order: CU2+> Zn2+> Mn2+. Some possible complexed structures were suggested having both N and/or O atoms as binding sites with one or two monomers of the biopolymer studied.