Submitted to: Cellulose
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2011
Publication Date: 4/16/2011
Citation: Schnupf, U., Momany, F.A. 2011. Rapidly calculated density functional theory (DFT) relaxed Iso-potential Phi Si Maps: Beta-cellobiose. Cellulose. 18(1):859-887. Interpretive Summary: Cellobiose is the structural building block of cellulose and its favored structural states, both in vacuo and in solvent, are of importance in understanding how cellulose forms. The flexibility and structural organization of cellobiose are properties studied by mapping out many conformations using high level electronic structure calculations. Using software shortcuts, in this research we have reduced the time for energy calculations by a factor of ten or more. This modification reduces the times required for studies such as these by months of computer time. These studies are important to industries developing new methods for alcohol conversion, and for finding new methods for digesting cellulosic materials into useful chemicals.
Technical Abstract: New cellobiose Phi-H/Si-H maps are rapidly generated using a mixed basis set DFT method, found to achieve a high level of confidence while reducing computer resources dramatically. Relaxed iso-potential maps are made 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 Phi-H and Si-H 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 Phi-H/Si-H 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.