Simulação computacional da interação de nanopartículas de quitosana com íons metálicos

Abstract

Chitosan is one of the most important chitin derivative, which is a second most abundant natural biopolymer after cellulose. Among the various chitosan properties, its ability to interact with environmental contaminants, such as metal ions, makes this polymer an attractive bioremediation agent. In particular, water contamination by Cu2+ and Cd2+ has hazardous effects to human health. Chitosan has been shown to be very efficient for the removal of these ions in aqueous solution. The mechanisms involved in this adsorption process are not yet fully understood, and the experimental techniques used cannot completely explain certain phenomena related to adsorption. Theoretical methods can contribute significantly in the investigations of these interactions. This study aimed to describe the intermolecular interactions between chitosan and divalent copper and cadmium ions through molecular dynamics simulations. The interactions were analyzed between ions and chitosan in different systems, which were composed of either a single chitosan s chain or an aggregate. Each system was evaluated as a function of degree of acetylation (0, 20 and 40%) and at different pH values (3, 5.9 and 6.5). The results showed that the intermolecular interactions were specific to each cation. The Cu2+ ions showed ion-dipole interactions between an amino group and a hydroxyl group, while the Cd2+ ions interact preferentially with hydroxyl groups. The degree of acetylation and pH significantly influenced the adsorption of each ion. The increase of acetylation degree contributed to better adsorption of Cd2+ ions. The adsorption of Cu2+ was better observed at an acetylation degree of 20% and circumneutral pH. The pH effect on the interaction of Cd2+ did not show a trend. Several factors contributed to the stabilization of the interactions, such as electrostatic attraction, solvation entropy and chitosan flexibility.