Revelation of the Electrochemical Chiral Recognition of l-Proline-Tuned Zr-MOFs

Reticular Synthesis of a Highly Stable Homochiral Cr3+-Based Metal-Organic Framework for Enantioselective Separation

Homochiral porous metal-organic frameworks (HMOFs) are highly promising as enantioselective adsorbents. However, reports on HMOFs, especially those with high stability, are still scarce, restricting their applications in enantioseparation, particularly in the resolution of highly reactive amines with important pharmaceutical value, which can potentially dissociate MOF structures. Synthesizing new and stable chiral MOFs remains an urgent and important task for the current MOF development. In this study, a new robust chiral Cr-MOF, Cr-SXU-5, has been constructed using S-1,1-bi-2-naphthol (BINOL) as the chirality source by converting corresponding Fe-MOFs, Fe-SXU-5, through a solvent-assisted metal metathesis under mild conditions. In contrast to the vulnerable Fe-SXU-5, Cr-SXU-5 exhibited high stability under various conditions, including exposure to 3 M HCl and pH = 12 NaOH aqueous solutions. The results demonstrated that Cr-SXU-5 not only exhibits good adsorption selectivity for CO2/N2 (15/85) and C2H2/CO2 (50/50) but also can effectively separate several chiral amines, particularly 3-methylbutan-2-amine, achieving an enantiomeric excess (ee) value of over 99.3%, which is the highest among reported HMOFs. Furthermore, Cr-SXU-5 also showed excellent recyclability, maintaining its separation efficiency and structural integrity over multiple cycles.

Engineering Chiral Confinement Environment in Polyoxometalate Intercalated Graphene Oxide Sensor for Electrochemical Enantioselective Recognition

The electrochemistry recognition of enantiomeric chiral molecules holds great significance for the pharmaceutical industry and scientific research. However, enhancing sensitivity and selectivity simultaneously, and elucidating chiral recognition mechanism, are two primary challenges. Here, an electrochemical chiral sensor L-C4-PMoV/GO is developed by confining chiral imidazole cations (L-C4) and [PMo10V2]5- (PMoV) signal anions within the interlayer of graphene oxide (GO). The L-C4-PMoV/GO is highly sensitive to recognition towards the chiral drug Levodopa (L-DOPA), which exhibits 16 times higher than the L-C4/GO. In addition, the enantioselectivity of ΔS = 19.92 is achieved. Mechanism studies suggest that the chiral confinement effect plays a crucial role in the synergism between the signal site PMoV and the enantioselectivity L-C4. In the chiral-confined microenvironment, the chiral induction from L-C4 to PMoV is facilitated, which results in the distortion of Mo (V)─O bonds. The hydrogen-bonding networks among the L-C4, Mo (V)─O, and DOPA generate the adsorption energy difference between the L/D-DOPA, as revealed by the in situ Raman spectroscopy and theoretical calculation. Compared to the conventional techniques, the electrochemical sensor shows comparable enantiomer excess (ee) value determination, low limits of detection (LOD) (6.7 nm for L-DOPA, 50.6 nm for D-DOPA), and portability, enabling practical chiral recognition.

Recent advance for enantiorecognition of chiral drugs sensing: Electrochemical, electrochemiluminescent and photoelectrochemical application

Chiral isomers show different behaviours and properties in physiological activities. It is of great significance to find productive approach to realize the recognition of enantiomers, which is a key issue in biochemical and pharmaceutical fields. Nowadays, chiral identification can be successfully achieved according to the discrepancies of special signals correlated with different enantiomers of multiple electrode structures. Electrochemical technologies have attracted wide interest in enantioselective analysis because of its unique merits, such as the economic and miniaturized instruments, simplified and environmental-friendly sample preparations. This review summarizes the development trends of electrochemical sensing in the enantiospecific analysis of chiral drugs, expounds the enantiospecific recognition mechanism between chiral selector and target enantiomers based on general electrochemical, electrochemiluminescent and photoelectrochemical sensors, respectively. In addition, this review attempts to predict the future application of electrochemical, electrochemiluminescent and photoelectrochemical-based technologies in the enantioselective recognition and detection.

Tailoring Chirality and Optimizing Enantioselective Recognition in Strategic Defect Engineering of Chiral Metal-Organic Frameworks

Introducing chiral molecules into metal-organic frameworks (MOFs) to obtain chiral MOFs (CMOFs), the tunability of their structures makes them a highly anticipated class of chiral materials for electrochemical sensing. However, the structure of CMOFs is often limited by synthesis challenges, and introducing chiral molecules into MOFs often leads to a decrease in their internal space. This study introduces a defect engineering strategy into the synthesis of CMOFs to obtain CMOFs with defects, which is an efficient synthesis method. The two CMOFs constructed with different structures not only have more chiral recognition sites but also greatly increase the substrate capacity due to the defects, making them have a wide range of substrates and enhancing the enantioselective recognition effect of the two defective CMOFs. In addition, using MOF as a chiral carrier greatly overcomes the problem of low conductivity of chiral molecules. Based on the advantages of defective CMOFs, we have designed a novel chiral electrochemical sensor with an excellent enantiomer recognition performance. This study provides a simple and scalable synthetic method for constructing CMOFs with defects and high stability.

Recent progress of chiral metal-organic frameworks in enantioselective separation and detection

Chiral compounds are abundantly distributed in both the natural world and biological systems. It is crucial to identify and detect chiral compounds in living systems or to separate and determine them in the natural environment. Many researchers have developed a range of chiral materials with different functionalizations to separate and detect chiral substances. Chiral metal-organic frameworks (CMOFs) have the potential to be used in enantioselective separation and detection due to their large surface areas, regulated framework topologies, particular substrate interactions, and accessible chiral sites. CMOFs contribute significantly to the development of enantiomer separation and detection in medicine, agriculture, food, environment, and other fields. This review focuses on four synthesis methods of CMOFs and their applications in chiral separation and chiral sensing in the past five years, mainly including chromatographic separation, membrane separation, optical sensing, electrochemical sensing, and other sensing methods. Finally, the challenges and potential growth direction of CMOFs in enantiomer separation and detection are discussed and prospected.

Defect-engineered chiral metal-organic frameworks

Chirality has an important impact on chemical and biological research, as most active substances are chiral. In recent decades, metal-organic frameworks (MOFs), which are assembled from metal ions or clusters and organic linkers via metal-ligand bonding, have attracted considerable scientific interest due to their high crystallinity, exceptional porosity and tunable pore sizes, high modularity, and diverse functionalities. Since the discovery of the first functional chiral metal-organic frameworks (CMOFs), CMOFs have been involved in a variety of disciplines such as chemistry, physics, optics, medicine, and pharmacology. The introduction of defect engineering theory into CMOFs allows the construction of a class of defective CMOFs with high hydrothermal stability and multi-stage pore structure. The introduction of defects not only increases the active sites but also enlarges the pore sizes of the materials, which improves chiral recognition, separation, and catalytic reactions, and has been widely investigated in various fields. This review describes the design and synthesis of various defective CMOFs, their characterization, and applications. Finally, the development of the materials is summarized, and an outlook is given. This review should provide researchers with an insight into the design and study of complex defective CMOFs.

Synthesis Strategies, Preparation Methods, and Applications of Chiral Metal-Organic Frameworks

Chiral Metal-Organic Frameworks (CMOFs) is a kind of material with great application value in recent years. Formed by the coordination of metal ions or metal clusters with organic ligands. It has ordered and adjustable pores, multi-dimensional network structure, large specific surface area and excellent adsorption properties. This material structure combines the properties of metal-organic frameworks (MOFs) with the chiral properties of chiral molecules. It has great advantages in catalysis, adsorption, separation and other fields. Therefore, it has a wide range of applications in chemistry, biology, medicine and materials science. In this paper, various synthesis strategies and preparation methods of chiral metal-organic frameworks are reviewed from different perspectives, and the advantages of each method are analyzed. In addition, the applications of chiral metal-organic framework materials in enantiomer recognition and separation, circular polarization luminescence and asymmetric catalysis are systematically summarized, and the corresponding mechanisms are discussed. Finally, the challenges and prospects of the development of chiral metal-organic frame materials are analyzed in detail.

Hydrogen Bonding-Induced Aggregation of Chiral Functionalized AuNS@Ag NPs for Photothermal Enantioanalysis

Toward the challenges of signaling transduction amplified in enantioselective recognition, we herein devised an innovative strategy for highly selective recognition of amino acids and their derivatives, leveraging photothermal effects. In this approach, bifunctional l-ascorbic acid is employed to reduce silver ions in situ on Au nanostars. Simultaneously, its oxidate (l-dehydroascorbic acid) is bonded to the silver shell as a chiral selector to prepare chiral nanoparticles (C-AuNS@Ag NPs) with the ability to recognize stereoisomers and sensitively modulate the photothermal effect. l-Dehydroascorbic acid can selectively capture one of the enantiomers of the two forms through hydrogen bonding and drive aggregation of the nanoparticles, which sharply enhances the photothermal effect. Consequently, the two forms of the system exhibit a significant temperature difference, which enables the discrimination and quantification of enantiomers. Our strategy verifies that six chiral amino acids and their derivatives can be discriminated with enantioselective response values of up to 79. Additionally, the chiral recognition mechanism was revealed through density functional theory (DFT) calculations, providing a paradigm shift in the development of enantiomeric recognition strategies.

A chiral metal-organic framework/cyclodextrin sensing interface for the chiral discrimination of tryptophan enantiomers

A chiral metal-organic framework (CMOF) was synthesized by introducing L-histidine (L-His) to zeolitic imidazolate framework-8 (ZIF-8) and then grafting with carboxymethyl-β-cyclodextrin (CM-β-CD). Compared with L-His-ZIF-8, the CM-β-CD-functionalized L-His-ZIF-8 (L-His-ZIF-8-CD) showed significantly enhanced discrimination ability for the tryptophan (Trp) enantiomers owing to the inherent chirality of CM-β-CD. The specificity of the chiral interface was also studied, and the results indicated that the discrimination ability for Trp enantiomers is significantly stronger than that for the enantiomers of cysteine (Cys) and tyrosine (Tyr), which might be due to the better matching between the indole ring of Trp and the chiral cavity of CM-β-CD.