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

Tailored Chiral Copper Selenide Nanochannels for Ultrasensitive Enantioselective Recognition and Detection

We constructed a tailorable membrane channel system consisting of penicillamine molecules intercalated in copper selenide nanoparticles (Cu_2-x Se NPs), which exhibited circular dichroism (CD) bands in the near infrared region (CD, 800-1600 nm) with a maximum intensity of 164.5 mdeg at 1440 nm. The chiral ligand hybridized to the surface of achiral Cu_2-x Se NPs by breaking the intrinsic symmetry of Cu_2-x Se NPs and further large-scale assembly induced strong optical activity. The fabricated multilayer chiral membrane achieved an increased rectification ratio (RR) up to 114. The integration of penicillamine allowed for high enantioselective recognition against naproxen,which displayed high sensitivity with a limit of detection (LOD) as low as 0.027 nM.

Enantioselective Gel Phase Synthesis of Metal-Organic Materials

We report the asymmetric synthesis of homochiral metal-organic materials (MOMs) in chiral gels from achiral components. The enantioselectivity of MOMs depends on the chirality of the gel, whereas the synthesis performed in solution phase and achiral gels resulted in conglomerates.

Triptycene-based Chiral Porous Polyimides for Enantioselective Membrane Separation

Enantiomers of 2, 6-diaminotriptycene (R, R-1 and S, S-1) are split by chiral-phase HPLC and their absolute configurations are identified by single-crystal X-ray diffraction technology. Using the enantiomers as monomers, a couple of chiral porous polyimides (R-FTPI and S-FTPI) are prepared by polycondensation reactions and display good heat stability, high BET surface area and good solubility in organic solvents. Moreover, both of R-FTPI and S-FTPI can be cast into robust, free-standing films suitable for enantioselective separation with symmetrical chiral selectivity.

Enantioselective Mixed Matrix Membranes for Chiral Resolution

Most pharmaceuticals are stereoisomers that each enantiomer shows dramatically different biological activity. Therefore, the production of optically pure chemicals through sustainable and energy-efficient technology is one of the main objectives in the pharmaceutical industry. Membrane-based separation is a continuous process performed on a large scale that uses far less energy than the conventional thermal separation process. Enantioselective polymer membranes have been developed for chiral resolution of pharmaceuticals; however, it is difficult to generate sufficient enantiomeric excess (ee) with conventional polymers. This article describes a chiral resolution strategy using a composite structure of mixed matrix membrane that employs chiral fillers. We discuss several enantioselective fillers, including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), zeolites, porous organic cages (POCs), and their potential use as chiral fillers in mixed matrix membranes. State-of-the-art enantioselective mixed matrix membranes (MMMs) and the future design consideration for highly efficient enantioselective MMMs are discussed.

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

Crystalline particles of a microporous, robust, and chiral metal-organic framework (MOF) were synthesized and their enantiomer excess (ee) was visualized for each microparticle by CD imaging. Labtb, a thermally and chemically robust MOF, was employed in this study because it shows a chiral space group. Although Labtb has been obtained as a racemic conglomerate, enantioselective synthesis of Labtb was achieved via a chiral precursor complex consisting of lanthanum and homochiral phenylalanine. Methyl orange (MO) was introduced into the micropores of chiral Labtb, which showed a strong induced CD signal for the absorption band of MO chromophores. High ee of the chiral Labtb was revealed by microscopic CD observation at the particle-level. This result provides a facile way to obtain a robust MOF that has chiral nanospace.

Selective Separation of Isomeric Dicarboxylic Acid by the Preferable Crystallization of Metal-Organic Frameworks

Simple and effective separation of isomeric organic molecules is an important but challenging task. Herein, we successfully developed a selective crystallization strategy to separate the mixtures of isomeric dicarboxylic acids (DCAs) for the first time. The target DCAs could be preferably combined with crystallization inducer of Zr⁴⁺ ions to form a pre-designed metal-organic frameworks (MOFs) crystal structure whereas the entry of non-target isomeric DACs into the MOFs lattice could be exclusively inhibited. Several isomeric pairs were exemplified to verify the extensibility and validity of the developed strategy.