Enantiomeric Separation of Racemic Mixtures Using Chiral-Selective and Organic-Solvent-Resistant Thin-Film Composite Membranes

Abstract

Membrane-based chiral separation has emerged as a promising method for the efficient separation of chiral molecules. Ideally, the membranes should be able to achieve good enantioselectivity, while maintaining high stability in harsh solvents. However, engineering membranes for chiral molecular separation in harsh organic solvent environments is still a big challenge. In this study, we fabricated a novel thin-film composite nanofiltration membrane composed of (2-hydroxypropyl)-beta-cyclodextrin (HP-β-CD) as the chiral selector for the enantiomeric separation of racemic 1-phenylethanol chiral compounds in organic solvents. The fabricated membrane achieved 60–80% enantioselectivity of R-phenylethanol over S-phenylethanol in nonpolar n-hexane. It was found that HP-β-CD played a critical role in the enantioselective performance, as the membrane without HP-β-CD showed no chiral selectivity. Molecular docking calculations substantiate the experiments by showing that the average free binding energy of S-phenylethanol with HP-β-CD is stronger than that of R-phenylethanol, indicating that the complex of S-phenylethanol with HP-β-CD has a higher thermodynamic stability and greater interaction. Furthermore, the crosslinked network between HP-β-CD and the polyamide layer conferred the membrane with solvent stability in nonpolar solvents. Moreover, this new membrane exhibited good solvent permeance and a molecular weight cutoff of around 650 g mol–1.

Recent Advances in Separation and Analysis of Chiral Compounds

“…Several other materials, including MIPs, , hollow fibers, and the composite of multiple materials, − were also applied for chiral membrane separation. The chiral membrane separation has been rapidly improved in its scale as well as purity toward large-scale industrial use.…”

Organic Solvent Nanofiltration in Pharmaceutical Applications

“…Ong et al have fabricated a TFC chiral separation membrane using (2-hydroxypropyl)-beta-cyclodextrin (HP-β-CD) as the chiral selector for enantiomeric separation of racemic 1-phenylethanol chiral compounds. The obtained membrane achieved 60–80% enantioselectivity of R-phenylethanol over S-phenylethanol . Zhu et al have prepared a mixed matrix membrane using cellulose acetate as membrane polymer matrix, graphene oxide as the modifier and mono­(6-ethylenediamine-6-deoxy)-β-cyclodextrin (EDA-β-CD) as chiral selector.…”

Enantioseparation Membranes: Research Status, Challenges, and Trends

“…Interfacial polymerization technology is effective and easy to scale and is the most widely used chemical modification method for preparing composite membranes. [ 102–105 ] Some chiral molecules serve as selection sites and are chemically modified to form thin and dense highly selective membranes on the surface of the supporting layer. Ji's research group [ 106,107 ] prepared chiral composite membranes by interfacial polymerization method and studied the effects of interfacial polymerization modification conditions (such as reaction temperature, concentration of crosslinker, and number of IP reaction cycles) on the separation performance of the membranes.…”