Amphiphilic polymer conetworks as chiral separation membranes

There is an urgent need for enantiopure chemicals, e.g., as basic compounds for pharmaceuticals. Although great progress has been made to obtain these compound using chiral catalysts, enzymes or even whole cells, it is often not possible or at least not economic to obtain enantiopure compounds. Thus enantioseparation is still required. Besides the elaborate and expensive chromatography and crystallization techniques, chiral membranes have been found to be effective in enantioseparation. Generally such membranes have to be developed specifically for a certain compound in a suited solvent. This is an elaborate development, because little is known about the complex transport process through a chiral membrane. In order to get better insights in the function of such membranes, we have designed a new class of chiral separating membranes that are applicable for nearly every solvent and therefore potentially many substrates. The conetworks are based on nanophasic, amphiphilic polymer conetworks (APCN) featuring a chiral phase of poly((R),(S)-N-(1-hydroxy-butan-2-yl)acrylamide) (P-(R),(S)-HBA) and a non-chiral polydimethylsiloxane (PDMS) phase. This APCN allows to directly exploring interactions between a chiral membrane and an enantiopure compound in dependence on a broad range of solvents varying from n-heptane to water by simply measuring the permeabilities of the compounds. Besides the numerous insights in the solvent-dependent interactions between membrane and five model substrates, we demonstrate that the APCNs are excellent chiral separation membranes. Further, it could be shown that the superior selectivity of these materials is based on the structure of their nanophases.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (176 K)Download as PowerPoint slideHighlights► Amphiphilic polymer conetworks are a new class of chiral separating membranes. ► The described membranes consist of chiral nanophase and nonchiral nanophase. ► The solvent directs selective diffusion of substrates through the respective swollen nanophase. ► Diffusion through the non-chiral phase affords the highest enantioselectivity. ► The nature of the solvent controls the transport mechanisms within the membrane. ► The selectivity of the membrane is influenced by the structure of the nanophases.