Side-chain-induced changes in aminated chitosan: Insights from molecular dynamics simulations

Chitosan is a functional polymer with diverse applications in biomedicine, agriculture, water treatment, and
beyond. Via derivatization of pristine chitosan, its functionality can be tailored to desired applications, e.g.
immobilization of biomolecules. Here, we performed molecular dynamics simulations of three aminated chitosan
polymers, where one, two, and three long-distanced side chains have been incorporated. These polymers have
been previously synthesized and their properties were investigated experimentally, however, the observed de-
pendencies could not be fully explained on the molecular level. Here, we develop a computational protocol for
the simulation of functionalized chitosan polymers and perform advanced analysis of their conformational states,
intramolecular interactions, and water binding. We demonstrate that intra- and intermolecular forces, especially
hydrogen bonds induced by polymer side chain modifications, modulate dihedral angle conformational states of
the polymer backbone and interactions with water. We explain the role of the chemical composition of the
functionalized chitosans in their tendency to collapse and reveal the key role of the protonation of the amino
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group near the polymer backbone on the reduction of polymer collapse. We demonstrate that specific binding of
water molecules, especially the intermediate water, is more pronounced in the polymer exhibiting such an amino
group.