USE OF UMBRELLA SAMPLING IN THE CALCULATION OF THE POTENTIAL OF MEAN FORCE FOR MALTOSE IN VACUUM FROM MOLECULAR-DYNAMICS SIMULATIONS

Molecular dynamics simulations have been used to calculate the potential of mean force for conformational transitions in Ramachandran space for the disaccharide beta-maltose in vacuum. The negative of the adiabatic energy map for maltose in vacuum was used as an umbrella potential in this calculation to increase sampling in high-energy regions. The calculated potential of mean force was not identical to the vacuum adiabatic surface. Entropic effects were found to lower the barrier between two of the wells on the vacuum surface, leading to facile transitions between these conformations, as has been observed in standard molecular dynamics simulations of this molecule, and resulting in an increased probability for that region of the Ramachandran map, in accord with experimental evidence.