Enantioselective Membranes

Abstract

The enantioseparation (optical resolution or chiral separation) of one specific enantiomer from others is in demand in the pharmaceutical production industry because most pharmaceuticals are stereoisomers, with each enantiomer possessing different biological activity. There is considerable demand for separation techniques appropriate for the large‐scale resolution of chiral molecules. Enantioseparation of racemic mixtures of pharmaceuticals through enantioselective (chiral) or achiral polymeric membranes with or without a chiral selector is a desirable system for future commercial application(s). This article describes several polymeric materials for the enantioselective (chiral) separation of pharmaceuticals. Enantioselective membranes were prepared from chiral polymers from which enantioselectivity was generated from chiral carbons in the main chain. However, it is rather difficult to generate enantioselective membranes with high selectivity from chiral polymers alone because the racemic penetrants interact with the flexible side chains of the membranes. Therefore, enantioseparation membranes were prepared using polymers with a chiral branch. The chiral branch, which possesses the ability to specifically interact with drugs, was immobilized in enantioseparation membranes. Cyclodextrins (CDs), crown ether derivatives, albumin, and DNA have all been typically selected as stereoselective ligands in enantioseparation membranes. Nanofiber membranes, electrospun from enantioselective polymers, have also been developed for use in enantioselective membranes that were prepared using recent developments in nanotechnology and should be useful for efficient enantioseparation because of high flux and high enantioselectivity. A molecularly imprinted polymeric membrane, formed by interactions with a “template” chiral molecule, has also been reported to serve as an enantioselective membrane, although the polymer composing the enantioselective membrane did not contain any chiral molecules. There are two basic methods of preparing molecularly imprinted membranes: covalent and noncovalent molecular imprinting. In both methods, the template molecules are selected for their interactions with the functional group of the imprinted polymeric membranes, and the templates are subsequently removed from the membranes. Finally, this article discusses future trends in polymeric materials for enantioselective membranes.

Bio-Mimetic Sensors Based on Molecularly Imprinted Membranes

“…Most common prepared MIMs have flat-sheet configurations and are used for recognition of a wide range of compounds like pesticides [ 153 ], flavonoids [ 48 , 146 , 154 ], biomolecules like uric acid [ 13 ], vitamins [ 155 ] optical isomers [ 156 – 159 ] drugs [ 160 ] proteins [ 161 ] and much other. For example, Trotta et al developed MIMs for the recognition of the antibiotic tetracycline hydrochloride.…”

Molecularly Imprinted Nanofiber Membranes: Localization of Molecular Recognition Sites on the Surface of Nanofiber

“…The enhancement of amount of molecular recognition site, which theoretically leads to enhancement of concentration of incorporated permeant into membrane. This can be attained by molecularly imprinted nanofiber membrane, which is shown in Figure 1c, since a surface area of nanofiber membrane is a few hundred magnitudes larger than that of usual cast membrane [10]. Even though a total concentration of molecular recognition site for molecularly imprinted nanofiber membrane is high, the molecular recognition sites, located in the central area of the nanofiber, are difficult to be accessed by permeant.…”

“…From this, introduction of molecular recognition site into membrane is indispensable so that membrane performance can be improved. To this end, alternative molecular imprinting [5][6][7][8][9][10] and conventional molecular imprinting [7,9,[11][12][13] have been applied to membrane preparation to enhance permselectivity. However, a trade-off relationship is often observed in membrane separation.…”

Enantioseparation with liquid membranes

“…The need for enantiopure products has increased tremendously in the last few decades, due to the increased awareness of the differences in the bioactivity of enantiomers. In addition to the pharmaceutical industries, the agrochemical, flavor, polymer and fragrances industries increasingly rely on enantiopure products . Many new biologically active substances have a strictly defined stereostructure .…”