GROMOS 53A6GLYC, an Improved GROMOS Force Field for Hexopyranose-Based Carbohydrates.

An improved parameter set for explicit-solvent simulations of carbohydrates (referred to as GROMOS 53A6GLYC) is presented, allowing proper description of the most stable conformation of all 16 possible aldohexopyranose-based monosaccharides. This set includes refinement of torsional potential parameters associated with the determination of hexopyranose rings conformation by fitting to their corresponding quantum-mechanical profiles. Other parameters, as the rules for third and excluded neighbors, are taken directly from the GROMOS 53A6 force field. Comparisons of the herein presented parameter set to our previous version (GROMOS 45A4), the GLYCAM06 force field, and available NMR data are presented in terms of ring puckering free energies, conformational distribution of the hydroxymethyl group, and glycosidic linkage geometries for 16 selected monosaccharides and eight disaccharides. The proposed parameter modifications have shown a significant improvement for the above-mentioned quantities over the two tested force fields, while retaining full compatibility with the GROMOS 53A6 and 54A7 parameter sets for other classes of biomolecules.