AN EXTENSION OF THE GROMOS FORCE-FIELD FOR CARBOHYDRATES, RESULTING IN IMPROVEMENT OF THE CRYSTAL-STRUCTURE DETERMINATION OF ALPHA-D-GALACTOSE

For carbohydrates the GROMOS force field has been extended to a more r ealistic all-atom model, with the use of parameters from the force fie ld proposed by Ha, Giammona, Field & Brady [Carbohydr. Res. (1988), 18 0, 207-221]. This extended and modified GROMOS force field has been us ed to simulate the crystal structures of seven monosaccharides. The re sults, compared with the experimental data, are satisfactory, and an o verall improvement over those obtained with the comparable Ha force fi eld. The experimentally determined positions of the H atoms should be used with caution in this comparison, and the thermal parameters can o nly be used as indicators for the preservation of the symmetry during the simulation. The simulations gave rise to suspicion about the hydro xyl H-atom positions in two of the sugars. These two structures were r edetermined by X-ray diffraction at low temperature. For beta-D-glucos e essentially the same structure was found as in the original publicat ion. In the case of alpha-D-galactose, the new structure confirmed the results from the simulation, in contrast to earlier experimental dete rminations.