MOLECULAR-DYNAMICS STUDY OF CONFORMATIONAL AND ANOMERIC EQUILIBRIA IN AQUEOUS D-GLUCOSE

The free energy differences between six conformations of D-glucose (alpha/beta; GG/GT/TG) were calculated from molecular dynamics simulations using the GROMOS force field. Four different computational approaches were used to this end; the ''adaptive umbrella sampling'' method was found to be the best. The final result is G(beta)-G(alpha) = -0.86 +/- 0.15 kcal mol(-1) (exptl -0.34). About equal percentages of GT and GG forms are calculated, in agreement with observations, but the TG percentage is overestimated which calls for enhancement of the gauche effect in the force field. Some calculations for the free molecule were also performed. Although the results have to be interpreted with caution, they disagree with the view that solvation favors the beta anomer.