Separation of racemic compound by nanofibrous composite membranes with chiral selector

A series of unique composite membranes formed from a nanoµ fibrous material with different amounts of a chiral selector was used for separation of chiral drugs. The membrane performances were demonstrated through sorption tests, wherein they were soaked in an aqueous solution of racemic D, L-tryptophan (a model chiral drug). The changes in concentration of both enantiomers over time were monitored by HPLC analysis. During 100 days, a blank membrane (without the chiral selector) exhibited no sorption activity. The membranes containing the selector had no influence on the amount of D-enantiomer, while the L-enantiomer was preferentially adsorbed on each membrane. The intensity of the sorption was found to be a direct function of the amount of the selector contained in a particular membrane. The separation of the same model chiral compound was further studied in diffusion cells by pertraction. The preferential sorption of L-tryptophan in the feed underlined the crucial importance of the selector in an active layer in view of chiral recognition of enantiomers. Due to the exclusive membrane material, the retention of L-tryptophan in the membrane materials did not block the passage of D-enantiomer into the permeate at any point during the experiment. Moreover, the nanomaterial in the active layer assured the distribution of the selector to the point that only 50% of (S, S)-1,2-diaminocyclohexane in one part of the active layer was sufficient to achieve 99% of enantioselectivity. The membranes – fresh and used – were analysed by Fourier-transform infrared (FTIR) spectroscopy and characterized by scanning electron microscopy (SEM) confirming the stability of the tested membranes. To complete the study, the role of the polyamide active layer in chiral recognition of tryptophan enantiomers was proposed.