A fine match between the stereoselective ligands and membrane pore size for enhanced chiral separation

A D,L-tryptophan separation factor of 12-15 and D-tryptophan yield of >95% have been successfully achieved through using human serum albumin (HSA) as the stereoselective ligand in an affinity ultrafiltration (UF) system. The obtained separation factor in this work is even higher than the intrinsic value of 8.5 of HSA. This synergism may arise from the fact that a fine match between the regular crystalline structure of HSA molecules and suitable pore size of membranes makes some HSA molecules be retained within the membrane cross-section, thus offering a second-stage binding opportunity for L-tryptophan molecules. Therefore, a simultaneous enhancement in separation factor and D-tryptophan yield has been fulfilled in this work. The feasibility of HSA regeneration after D,L-tryptophan separation has also been demonstrated through a series of pH adjustment experiments. This study reveals the applicability of HSA in affinity UF systems for chiral separation due to economization of material costs.