Separation of chiral molecules using polypeptide-modified poly(vinylidene fluoride) membranes

A membrane-based chiral separation system was developed by the modification of poly(vinylidene fluoride) (PVDF) ultrafiltration membranes with polyglutamate derivatives. Both physisorbed and chemisorbed poly(γ-benzyl-l-glutamates) (PBLG) were vapor-deposited on the membranes, and the resulting poly(amino acids) were modified through debenzylation or ester exchange reaction to produce poly(l-glutamic acid) (PLGA) and polyglutamates with triethylene glycol monomethyl ether side chains (PLTEG). The enantioselectivities for chiral α-amino acids (tryptophan (Trp), phenylalanine (Phe), and tyrosine (Tyr)) and chiral drugs (propranolol, atenolol, and ibuprofen) were determined by performing permeation cell experiments, with enantioselectivities ranging from 1.04 to 1.47. The selectivity of PLGA increased as its helical content increased, which occurred at high ethanol concentrations and at low pH. In addition, an increase in enantioselectivity was observed for chemically grafted polymers compared to physisorbed polypeptides. This may be attributed to an increase in molecular weight (MW) and density of the polymer chains, which may enhance the interaction between the chiral compounds and the surface-bound polypeptides.