Enantiomeric resolution of tryptophan via stereoselective binding in an ion-exchange membrane partitioned free flow isoelectric focusing system

The optical resolution efficiency of a membrane system that integrates stereoselective affinity dialysis and ion-exchange membrane partitioned free flow isoelectric focusing (FFIEF) is shown to be superior to normal affinity dialysis (AD) and affinity ultrafiltration (AUF) membrane processes under similar experimental conditions, i.e. by using the same sulfonated polyetherketone (SPEK) membranes and identical human serum albumin (HSA) to tryptophan ratio of 0.75. The chiral separation is achieved by isolating the unbound tryptophan, which contains D-tryptophan in excess, and the protein-tryptophan complex into the permeation and feed chambers, respectively, by controlling their migration under an external electric field. The separation factor is increased with increasing protein concentration while the permeation flux can be enhanced by increasing the operating current. The rationale for using HSA instead of BSA as the chiral selector, and the use of four-chamber system rather than two are also discussed.