Molecular Dynamics Simulation Study of Chitosan-Zinc Chloride Complex Model

We report molecular dynamics simulation study of chitosan-zinc chloride complex crystal model to predict a hydrated structure and to evaluate the potential of mean force (PMF), namely, the free energy difference, in migration of a guest zinc chloride molecule in the crystal model. The accelerated molecular dynamics method was adopted to predict the hydrate structure of the crystal model, which proposed the crystal model interior involving four to five water molecules per a unit cell. The water molecules were mostly located in the crystal void surrounded by the functional groups of D-glucosamine and zinc chloride molecules, where the water molecules were mostly coordinated to zinc atoms. The PMF profile, obtained by using adaptive steered molecular dynamics method, exhibited continuously increase in the base line accompanied with appreciable minima, each of which corresponded to formations of interactions between the zinc chloride molecule and the polar functional groups, suggesting that the zinc chloride molecule on migration was handed over the C6 hydroxyl and C2 amino groups, while C3 hydroxyl groups were irrelevant to such an interaction. It was suggested that a zinc chloride molecule was more readily accommodated in the void through coordination with a C6 hydroxyl group which was more spatially mobile through C5-C6 bond rotation.