Chiral Recognition and Separation by Chirality‐Enriched Metal–Organic Frameworks

Abstract

Endowed with chiral channels and pores, chiral metal-organic frameworks (MOFs) are highly useful; however, their synthesis remains a challenge given that most chiral building blocks are expensive. Although MOFs with induced chirality have been reported to avoid this shortcoming, no study providing evidence for the ee value of such MOFs has yet been reported. We herein describe the first study on the efficiency of chiral induction in MOFs using inexpensive achiral building blocks and fully recoverable chiral dopants to control the handedness of racemic MOFs. This method yielded chirality-enriched MOFs with accessible pores. The ability of the materials to form host-guest complexes was probed with enantiomers of varying size and coordination and in solvents with varying polarity. Furthermore, mixed-matrix membranes (MMMs) composed of chirality-enriched MOF particles dispersed in a polymer matrix demonstrated a new route for chiral separation.

Covalent Organic Frameworks with Chirality Enriched by Biomolecules for Efficient Chiral Separation

“…[1] Theseparation of racemic compounds has long been of great significance,especially for pharmaceutical and medicinal applications, [2,3] which has spurred continuous interest in the exploration of new materials/approaches for efficient separation of enantiomers. [4][5][6][7] To achieve efficient separation of enantiomers,i tis essential the material possess both strong chiral environment and preferable binding ability through some specific interactions (for example,h ydrogen bonding,v an der Waals interactions,and electrostatic interactions). [8][9][10] Biomolecules such as enzymes that are created by nature, [11] can well discriminate enantiomers owing to their natural conformations composed of chiral subunits (that is,amino acids) as well as amphiphilic and zwitterionic features capable of providing specific interactions.T his makes them appealing for chiral separation particularly as chiral stationary phases (CSPs) in chromatography if they can be immobilized on some solidstate materials.H erein, we contribute ag eneral approach to immobilize biomolecules into an ew class of solid-state materials,c ovalent organic frameworks (COFs), and the afforded biomolecules&COFs can serve as versatile and highly efficient CSPs towards various racemates in both normal-phase and reverse-phase high-performance liquid chromatography.Emerging as an ew class of crystalline solid-state materials,COFs feature high surface area, low mass density,tunable pore size,high stability,and easily tailored functionality, [12][13][14] which means they hold promise for applications in many fields such as gas storage, [15] photoelectricity, [16] catalysis, [17][18][19] environmental remediation, [20] drug delivery, [21] and functional devices.…”

Homochiral MOF–Polymer Mixed Matrix Membranes for Efficient Separation of Chiral Molecules

“…Several synthetic approaches have been developed for fabricating homochiral MOFs, including:( i) direct synthesis method by using enantiopure ligands or by forming SBUsw ith chiral linkers; [5] (ii)p ostsynthetic modification of parent achiral MOFs with homochiral molecules; [6] and (iii)s elf-assembly of achiral building units into an enantiopure morphology by the influence of the chiral environment. [7] Compared to the latter two methods, the preparation of self-assembled chiral ligands has been widely investigated;however, it is acomplex synthesis process and very expensive,w hich limits the broad practical applications of homochiral MOFs for chiral resolution.…”

Synthesis of Chiral Labtb and Visualization of Its Enantiomeric Excess by Induced Circular Dichroism Imaging

“…One group consists of homochiral organic ligandso rl inkers complexed to metal ions. [2] These approaches use simple amino acids, [16,21] chiral amine, [22] alkaloids, [19] or nucleotides [20] as ac hiral source, instead of homochiral ligands, which require many synthetic efforts. [9] Lin and co-workersr eported ab ridging ligand containing axial chirality to synthesize porousc hiral MOF that could be used as an enantioselective catalyst.…”

“…[14][15][16][19][20][21][22][23] Su, Wang and co-workersr eported a Cd(bpdc) 1.5 framework consisting of octuple helices and chiral pores, and inductiono ft he chirality was achieved by the addition of l-leucine in the reactionm ixture. To inducec hiral molecular arrangementi nt he coordination networks, chiral molecules are employeda ss tructure-directing reagents.…”

“…[14,6] Morris and coworkersr eported an enantiopure [Ni 3 (Hbtc) 4 ]( H 3 btc = trimesic acid) framework synthesized by using ac hiral ionic liquid containinga spartate. [2] These approaches use simple amino acids, [16,21] chiral amine, [22] alkaloids, [19] or nucleotides [20] as ac hiral source, instead of homochiral ligands, which require many synthetic efforts. [16] Yaghi and co-workers pickedu pas ingle crystal of MOF-520 from its racemic conglomerate and determined the structure of the guest by XRD analysis.…”