Density functional theory investigations on the structure and dissolution mechanisms for cellobiose and xylan in an ionic liquid: gas phase and cluster calculations.

Density functional theory (DFT) calculations have been carried out for cellobiose and xylan chosen as models for cellulose and hemicellulose, respectively, in gas phase, implicit and explicit solvent (water, methanol, and the ionic liquid, 1,3-dimethylimidazolium acetate) media using plane wave and atom centered basis set approaches in order to find out lowest energy conformers and configurations. Geometry, vibrational properties, and 1H and 13C NMR chemical shift values have been discussed under all three conditions. Calculations predict that inter- and intramolecular hydrogen bonding play an important role in the dissolution processes. In the gas phase and in implicit solvent, the anti–anti conformer of cellobiose and the anti–syn conformer of xylan are the most stable due to the formation of a large number of intramolecular hydrogen bonds. However, in the cluster calculations containing ion pairs of the ionic liquid (IL) surrounding the cellulosic units, the anti–syn conformer of cellobiose is more sta...