Predicting the Chemical Potential and Osmotic Pressure of Polysaccharide Solutions by Molecular Simulations

Differences in the chemical potential of water and the resulting osmotic pressure across semipermeable membranes are of fundamental importance for many biological systems. Here, we calculate the osmotic pressure and the chemical potential of water for polysaccharide solutions by molecular simulations. We set up a method to measure the osmotic pressure in polysaccharide systems at different concentrations and found that for monomers the experimental trend with respect to the solute concentration is reproduced correctly. However, the calculated osmotic pressure values are systematically too low, and two common carbohydrate force fields (FFs) cannot correctly describe the relationship between the osmotic pressure and the degree of polymerization. Therefore, we reparametrized parts of the GLYCAM06 TIP5P FF based on osmotic pressure data. The predictive power of the resulting GLYCAM06_OSMOr14^TIP5P FF is demonstrated for two different sugar molecules over a wide range of concentrations, and additional evaluations for other solution properties show improved agreement with experimental data. Finally, we discuss different methods to obtain the chemical potential of water in solutions