Abstract
AMBER/GLYCAM and CHARMM are popular force fields for simulations of amino acids and sugars. Here we report excessively attractive amino acid-sugar interactions in both force fields, and corrections to nonbonded interactions that match experimental osmotic pressures of mixed aqueous solutions of diglycine and sucrose. The modified parameters also improve the ΔG(trans) of diglycine from water to aqueous sucrose and, with AMBERff99SB/GLYCAM06, eliminate a caging effect seen in previous simulations of the protein ubiquitin with glucose.