Many biologically-active compounds such as drugs, agrochemicals or food additives, have chiral structures and their physiological properties usually depend on this chirality. Hence, chiral resolution by High Performance Liquid Chromatography (HPLC) has significantly been developed and a variety of chiral columns packed with polysaccharides immobilized on silica gels are commercialized. Cellulose and amylose derivatives, such as phenyl carbamates and esters, are known as chiral selectors when immobilized on silica gels, so-called chiral stationary phases (CSPs), that are packed in columns for chiral HPLC. However, apart from its high enantioseparation performance for a wide variety of racemic mixtures, the HPLC method presents the disadvantage of being typically discontinuous and analytically small-scale. Thus, it is urgent to develop novel strategies that enable large-scale chiral resolutions. Among various techniques, membrane filtration is regarded as economically competitive and, most importantly, it can be operated continuously under mild conditions. Enantioenrichment via permeation of a racemic mixture through enantioselective membranes is one of the promising strategies toward large-scale chiral resolutions. Enantioselective membranes preferentially allow one of the enantiomers to adsorb to or diffuse into the membranes thanks to their chiral recognition sites (e.g., chiral polymer backbones or side chains) incorporated into the membranes. Considering that most of the membranes reported so far are porous membranes cast as polymeric films, they have structural disadvantages (e.g., small specific surface area (SSA), poor liquid transport property, and fragility) for efficient permeation. Thus, the development of optimal structures for enantioselective membranes is the key to efficient chiral resolution. The challenge is to realize large SSA while ensuring mechanical stability of the membrane and its liquid transport properties. We tackled this challenging objective by electrospinning, for the first time, cellulosic CSPs. In this presentation, (i) the electrospinning of the cellulosic CSPs to fabricate self-standing nanofibrous textiles that constitute enantioselective membrane systems and (ii) enantioselective membrane filtrations of racemic compounds will be discussed.

Electrospun cellulosic textiles for chiral resolutions via enantioselective membrane filtration

ACS Spring 2022

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