Chiral resolution by polysulfone-based membranes prepared via mussel-inspired chemistry

Reported herein is a chiral resolution polysulfone membrane prepared via mussel-inspired chemistry. Polysulfone membranes were modified with dopamine, which underwent in situ polymerization on the membrane substrate, and beta-cyclodextrin was used as a chiral selector. The preparation conditions were optimized and the resultant membrane obtained under these conditions showed desirable water permeability (similar to 24.0 L/(m(2).h.bar)) and surface hydrophilicity (contact angle is lower than 37.1 +/- 3.4 degrees). The polydopamine layer exhibited desirable stability in a series of aqueous solutions with pH values ranging from 4.0-6.0 or in isopropanol for less than an hour (detachment ratio was lower than 1.2%). Characterization of the surface morphology and XPS elemental analysis revealed that the membrane surface was fully coated by polydopamine and a beta-cyclodextrin monolayer formed on the surface of the polydopamine coating. The grafting density of beta-cydodextrin calculated from the XPS results was similar to 11.5 mg/m(2). The optimal pH value for the resolution of (D)- or L-tryptophan feed solution was 5.90 and a low concentration of the feed solution provided a high resolution efficiency. The enantiomeric excess (e.e.) value of the membrane for Trp racemic mixture achieved to similar to 3.2% with the feed solution of tryptophan racemic mixture was 5 x 10(-5) mol/L and the operating pressure was 0.1 MPa. After 3 times of isopropanol-washed regeneration processes, the e.e. value was still stable around to similar to 3%. The mussel-inspired chemically modified membrane exhibited the same mechanical properties as the purely polysulfone-based membrane. The methods and results provided in this paper may facilitate the large-scale production of chiral resolution membranes or other chiral separation membranes with higher performance.