Chitin and Chitosan Binding to the α-Chitin Crystal: A Molecular Dynamics Study.

Understanding the binding of chitosan oligomers to the surface of a chitin nanocrystal is important for improving the enzymatic deacetylation of chitin and for the design of chitin/chitosan composite films. Here, we study the binding of several chito-oligomers to the (100) surface of an α-chitin crystal using molecular dynamics (MD), steered MD, and umbrella sampling. The convergence of the free energy was carefully considered and yielded a binding energies of -12.5 and -2 kcal mol for 6-monomer-long chitin and uncharged chitosan oligomers, respectively. We also found that the results for the umbrella sampling were consistent with the force profile from the steered MD and with classical MD simulations of the adsorption process. Our results give insight into the molecular-scale interactions, which can be helpful for the design of new chitin composite films. Furthermore, the free energy curves we present can be used to validate coarse-grained models for chitin and chitosan, which are necessary to study the self-assembly of chitin crystals due to the long time scale of the process.