Surface modified polysulfone membranes: Separation of mixed proteins and optical resolution of tryptophan

Ultrafiltration separation experiments on mixed solution of bovine serum albumin and gamma globulin were performed in a stirred batch cell through nonmodified and surface modified polysulfone membranes. Gamma globulin permeated through the surface modified membrane to some extent, but the bovine serum albumin was 100% rejected towards the end of the concentration process at pH 7.2 and 9.0, although the molecular weight of gamma globulin is higher than that of bovine serum albumin. It is suggested that the separation of mixed proteins is caused not by a sieving effect or by charge repulsion between membranes and proteins but by the balance of hydrophilic and hydrophobic segments on the surface of the modified membranes. Ultrafiltration separation experiments on a racemic tryptophan solution were also performed by using the binding site of bovine serum albumin to L-tryptophan. It was found that immobilized bovine serum albumin membranes efficiently demonstrated optical resolution of racemic tryptophan.