The exploration of the reversed enantioselectivity of a chitosan functionalized cellulose acetate membranes in an electric field driven process

In this study, the optical resolution of tryptophan using a chitosan functionalized cellulose acetate membrane is investigated in three processes with different driving forces. The enantiomeric excesses obtained using the same membrane in concentration gradient, hydraulic pressure and electric field driven processes are 94%, 66% and -19%, respectively. This reverse in the enantioselectivity in the electric driven process is also observed in phenylalanine resolution and is mainly due to the orienting force exerted by the electric field and the tryptophan complexes formed with copper ions generated via electrolysis. The minimized total energies of the copper complexes and the polymer amorphous cells are calculated with the aid of molecular simulation and the membrane surface morphology is observed in Scanning Electron Microscope (SEM) and Atomic Force Microscopy (AFM). Without chitosan and solvent evaporation, the cellulose acetate membrane does not show much enantioselectivity. The necessities of chitosan functionalization and solvent evaporation during membrane preparation, and the effects of operating conditions in chiral resolution tests are also studied in details.