CHARMM additive all-atom force field for acyclic carbohydrates and inositol

The CHARMM carbohydrate force field parameters developed previously for hexopyranose monosaccharides are extended to linear sugar alcohols (alditols) having carbon backbone lengths ranging from n = 3 to n = 6 as well as to linear aldoses and ketoses and six-membered cyclic polyols. Dihedral parameters are developed for the linear carbon backbone, as required to reproduce conformational energies at the MP2/cc-pVTZ//MP2/6-31 G(d) level of theory, and both bonded and nonbonded parameters are developed for the ketose carbonyl group, while the remaining parameters are transferred directly from prior work. Solute-water hydrogen bonding interaction energies and distances show good agreement with quantum mechanical values that have been scaled appropriately for use as target data for a condensed-phase force field. Computed densities for aqueous solutions of a variety of alditols, including a ternary mannitol+sorbitol+water mixture and ranging in concentration from 0.07 molal to 6 molal, are all within 1.5% of experimental values. Additionally, both the heat of vaporization and molecular volume of neat liquid glycerol (n = 3) are within 2% of the experimental values. Taken together, these results show that the parameters as used for hexopyranose monosaccharides, including the aliphatic and hydroxyl nonbonded Lennard-Jones and partial charge parameters, are transferable to sugar alcohols. In line with previous aqueous hexopyranose monosaccharide data, analysis of the computed radial distribution functions and number integrals of aqueous alditol solutions shows the local microstructure of water to remain unperturbed despite the presence of the alditols. The new parameter set enables the modeling of the linear forms of monosaccharides such as glucose and fructose as well as the alditols that are the products of their reduction.