Chiral separations using ultrafiltration with a stereoselective binding agent

Recent studies have demonstrated the feasibility of using ultrafiltration w ith a stereospecific binding agent in free solution to separate chiral mole cules. The objective of this study was to develop an improved understanding of the key factors that determine the effectiveness of this type of chiral separation. Experiments were performed using a model system of bovine seru m albumin as a stereospecific binding agent for the amino acid tryptophan. Batch ultrafiltration data showed strong stereospecific binding of L-trypto phan with a selectivity of 11 at low amino acid concentrations. Actual sepa rations were performed using a constant volume diafiltration system to wash the less strongly bound isomer through the membrane. The diafiltration pro cess avoids problems associated with the accumulation of retained species d uring filtration and makes it possible to achieve higher purification facto rs. The L-tryptophan was recovered in the retentate with final purity great er than 90% at 60% yield. Model calculations performed using the equilibriu m binding constants for the two stereoisomers were in good agreement with t he data. Simulations were used to examine the performance of this membrane system for chiral separations.