Rapidly calculated DFT relaxed iso-potential ϕ/ψ maps: β-cellobiose

Abstract

New cellobiose ϕH/ψH maps are generated using a mixed basis set DFTr method, found to achieve a high level of confidence while reducing computer resources dramatically. Relaxed iso-potential maps are created for different conformational states of cellobiose, showing how glycosidic bond dihedral angles vary as different sets of hydroxymethyl rotamers and hydroxyl directions are examined. These maps are generated, fixing the dihedral ϕH and ψH values at ten degree intervals and energy optimizing the remaining geometry using the B3LYP/6-31+G* functional for all atoms except carbon atoms, where the functional B3LYP was used with the mixed basis set, 4-31G. Mapping results are compared between in vacuo structures using the mixed basis set, in vacuo using the full basis set, and those in which the implicit solvent method, COSMO, is included with the mixed basis set. Results show significant changes in position of energy minima with variation in hydroxyl rotamers and with application of solvent. Unique to this study is the mapping of the hydration energy at each ϕH/ψH point on the map using the energy derived at each point by applying COSMO. Using hydration gradients as a guide one observes directional solvent driven changes in the minimum energy positions. Interesting internal coordinate variances are described.