Preparation of cross-linked chitosan/glyoxal molecularly imprinted resin for efficient chiral resolution of aspartic acid isomers

An enantioselective l-aspartic acid imprinted chitosan (LAIC) was prepared by cross-linking of chitosan by glyoxal cross-linker, in the presence of l-aspartic acid as an imprinted template molecule and 1% acetic acid solution as a solvent. Non-imprinted cross-linked chitosan (NIC) as control was also prepared by the same procedure in the absence of template molecules. The surface morphology of both LAIC and NIC was examined by scanning electron microscope (SEM). LAIC particles were applied to determine the optimum operational condition for l-aspartic acid separation from dilute aqueous solution. In adsorption step, optimum pH and retention time were 5 and 90 min, while corresponding values in extraction step were 2 and 50 min, respectively. Also, the adsorption isotherms indicated that the maximum adsorption capacities of l- and d-aspartic acid on LAIC were 48 ± 0.7 and 27 ± 1 mg g−1, respectively, while in the case of NIC, both l- and d-aspartic acid present the same maximum adsorption capacity 9 ± 0.8 mg g−1, which confirms that the molecular imprinting technique creates an enantioselectivity of LAIC toward l-aspartic acid. In addition, chiral resolution of l,d-aspartic acid racemic mixture was carried out using column of LAIC.