Optimization of the enantiomeric separation of tryptophan analogs by membrane processes

The separation of racemic tryptophan analogs has been performed by two ways: ultrafiltration in a solution system using bovine serum albumin (BSA) as a free chiral selector and dialysis using BSA grafted nylon membrane. A complexation mechanism based on competitive binding of both d- and l-tryptophan zwitter-ionic form on the same unprotonated protein site has been used to predict recovery and purity of both d- and l-tryptophan in the retentate and permeate. The corresponding model gave correct prediction for a large set of experimental conditions (pH from 7 to 11, [BSA]0 from 1.5×10−5 to 10−3 M, [l]0=[d]0 from 10−4 to 5×10−4 M). The operational parameters which can be used to optimize production criteria such as purity, recovery and production rate have been discussed. For enantiomeric separations using BSA chiral selector (solution system or enantioselective membrane), a specific attention has to be taken to both filtration and complexation parameters.