Predicting chemical potential and osmotic pressure of polysaccharide solutions by molecular simulations

Differences in the chemical potential of water and the resulting osmotic pressure across semi-permeable membranes are of fundamental importance for many biological systems. Here, we calculate the osmotic pressure and the chemical potential of water for polysaccharide solutions in molecular simulations. We set up a method to measure the osmotic pressure in polysaccharide systems at different concentrations and find 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 cannot correctly describe the relation between the osmotic pressure and the degree of polymerization. Therefore, we re-parametrize parts of the GLYCAM06 TIP5P force field based on osmotic pressure data. The predictive power of the resulting GLYCAM06OSMOr14TIP5P force field is demonstrated for two different sugar molecules over a wide range of concentrations and additional evaluation for other solution properties show improved agreement with experimental data. Finally we discuss different methods to obtain the chemical potential of water in the solutions