Polyelectrolyte complexation of chitosan and hyaluronic acid: Simulation of the effect of salt addition

The presence of the Hofmeister Series in biomolecular systems impacts coacervation , as observed in this study where the influence of Hofmeister Series on the coacervation of 50 units of chitosan (CHI) and 50 units of hyaluronic acid (HA) is investigated in the presence and absence of various salts, including NaCl, MgCl2, NaNO3, NaOAC, KCl, and CaCl2. 2 coacervation systems are analyzed, the first consisting of 1-chain of CHI and 1-chain of HA, and the second comprising 2-chains of both polymers. Utilizing coarse-grained (CG) Molecular Dynamic (MD) Simulation with the LAMMPS package, the enthalpy values for the CHI-HA coacervate systems are calculated with and without salt addition. The radius of gyration of CHI and HA polymers is individually measured during a 100 ns equilibrium run. It proves that both CHI and HA are in equilibrium after 100 ns run with LAMMPS. Radial distribution functions (RDF) are computed proving the interaction between CHI and HA. Various methods for calculating binding energy are explored, followed by Steered Molecular Dynamic Simulations (SMD) on the coacervates of 1-chain and 2-chain systems under different external forces (50, 75, and 100 (kcal/mol)/Angstrom). The findings predominantly support the notion of salt addition exerting a screening effect on CHI-HA interactions. Specifically, in the 1-chain system, the hydration order of anions (OAc->Cl->NO3-)and in the 2-chain systems, both anions and cations (Mg+2>Ca+2>Na+>K+) is in agreement with literature when the ratio of binding energies approaches zero under an external force of 50 (kcal/mol)/Angstrom in SMD simulations.