DFTMD studies of β-cellobiose: conformational preference using implicit solvent.

Previous DFT in vacuo studies on the conformational preferences for cellobiose showed that upon optimization the φ(H)-anti conformations were of lower energy than the syn forms. Upon optimization using an implicit solvation method, COSMO, the syn or observed form was still not predicted to be of lower energy than the φ(H)-anti form, even though optimization after addition of several explicit water molecules did show a relative energy difference favoring the syn form. In order to examine the predictive ability of COSMO on this carbohydrate, constant energy dynamics, DFTMD, simulations were carried out on low energy syn and φ(H)-anti conformations with and without COSMO included during the dynamics. The resulting analysis confirmed that when COSMO is included in the dynamics, the syn conformations become energetically favored over the φ(H)-anti forms suggesting that both solvent and entropy play roles in dictating the solution conformation of cellobiose. Analysis of the dynamic runs includes distributions of selected dihedral angles versus time, conformational transitions, and populations of some quasi-planar, boat, skew forms during the simulations.