The interaction between chitosan and tannic acid calculated based on the density functional theory

This paper presented a study of the interaction between tannic acid and chitosan in flocculation process at molecular level. Gallic acid (GA) was selected as tannic monomer and dimer chitosan was selected as the chitosan for simulation based on the density functional theory. Molecular electrostatic potential analysis was conducted to clarify the active interaction site and the possible atoms formed hydrogen bond. A series of analysis were performed to reveal the non-covalent interaction between GA and chitosan, including calculation of statistic thermodynamic properties under solvent effect, reduced density gradient (RDG) analysis, independent gradient model (IGM) analysis and symmetry adapted perturbation theory (SAPT) energy decomposition analysis. It was concluded that electrostatic interactions was the main driving energy in the tannic acid flocculation process, its contribution is about 55.5% in total attractive energies. Besides, the dispersion and induction interaction were also crucial for the complex stabilization.