Chiral Metal-organic Frameworks Research Articles

Two-dimensional chiral metal-organic framework nanosheets L-hyp-Ni/Fe@SiO2 composite for HPLC separation

In this study, we have synthesised a chiral L-hyp-Ni/Fe@SiO2 composite as a chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC) for the first time. This was achieved by coating two-dimensional (2D) chiral metal-organic framework nanosheets (MONs) L-hyp-Ni/Fe onto the surface of activated SiO2 microspheres using the “wrapped in net” method. The separation efficiency of the L-hyp-Ni/Fe chromatographic column was systematically evaluated in normal-phase HPLC (NP-HPLC) and reversed-phase HPLC (RP-HPLC) configurations, employing various racemates as analytes. The findings revealed that 16 chiral compounds were separated using NP-HPLC, and five were separated using RP-HPLC, encompassing alcohols, amines, ketones, esters, alkanes, ethers, amino acids and sulfoxides. Notably, the resolution (Rs) of nine chiral compounds exceeded 1.5, indicating baseline separation. Furthermore, the resolution performance of the L-hyp-Ni/Fe@SiO2-packed column was compared with that of Chiralpak AD-H. It was observed that certain enantiomers, which either could not be resolved or were inadequately separated on the Chiralpak AD-H column, attained separation on the 2D chiral MONs column. These findings suggest a complementary relationship between the two columns in racemate separation, with their combined application facilitating the resolution of a broader spectrum of chiral compounds. In addition, baseline separation was achieved for five positional isomers on the L-hyp-Ni/Fe@SiO2-packed column. The effects of the analyte mass and column temperature on the resolution were also examined. Moreover, during HPLC analysis, the L-hyp-Ni/Fe columns demonstrated commendable repeatability, stability and reproducibility in enantiomer separation. This research not only advances the utilisation of 2D chiral MONs as CSPs but also expands their applications in the separation sciences.

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

Chiral metal-organic framework (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 is widely used in chemistry, biology, medicine and materials science because of its ordered and adjustable pores, multi-dimensional network structure, large specific surface area and excellent adsorption properties. In this paper, the synthesis strategies and preparation methods of chiral metal-organic frameworks are reviewed. In addition, the applications of chiral metal-organic framework materials in enantiomer recognition and separation, circularly polarized luminescence and asymmetric catalysis are systematically summarized. Finally, the challenges and prospects of the development of chiral metal-organic frame materials are analyzed in detail.

Photo-Curable 3D Printing of Circularly Polarized Afterglow Metal-Organic Framework Monoliths.

Developing coordination complexes (such as metal-organic frameworks, MOFs) with circularly polarized luminescence (CPL) is currently attracting tremendous attention and remains a significant challenge in achieving MOF with circularly polarized afterglow. Herein, MOFs-based circularly polarized afterglow is first reported by combining the chiral induction approach and tuning the afterglow times by using the auxiliary ligands regulation strategy. The obtained chiral R/S-ZnIDC, R/S-ZnIDC(bpy), and R/S-ZnIDC(bpe)(IDC = 1H-Imidazole-4,5-dicarboxylate, bpy = 4,4'-Bipyridine, bpe = trans-1,2-Bis(4-pyridyl) ethylene) containing a similar structure unit display different afterglow times with 3, 1, and <0.1s respectively which attribute to that the longer auxiliary ligand hinders the energy transfer through the hydrogen bonding. The obtained chiral complexes reveal a strong chiral signal, obvious photoluminescence afterglow feature, and strong CPL performance (glum up to 3.7×10-2). Furthermore, the photo-curing 3D printing method is first proposed to prepare various chiral MOFs based monoliths from 2D patterns to 3D scaffolds for anti-counterfeiting and information encryption applications. This work not only develops chiral complexes monoliths by photo-curing 3D printing technique but opens a new strategy to achieve tunable CPL afterglow in optical applications.

Chiral Metal-Organic Frameworks with Spectroscopic Methods: Towards Chemical Sensor Devices.

Chiral Metal-Organic Frameworks (CMOFs) are a rapidly growing field reflecting their potential as selective and sensitive chemical sensors for chiral analytes. The highly tuneable nature of CMOFs enables the size, shape, and non-covalent interactions to be optimised towards specific analytes to engender strong intermolecular interactions and sensing responses. While CMOFs as chiral chemical sensor devices have been explored with electrochemical methods including differential pulse voltammetry (DPV), bipolar and chemiresistive sensing techniques, the CMOFs as chiral chemical sensors using spectroscopic methods has received significantly less attention. This review examines the synthesis of CMOFs for chemical sensors with spectroscopic methods such as photoluminescence, circular dichroism, and solid-state nuclear magnetic resonance with a view towards their incorporation into chemical sensor devices. Future directions of the field are highlighted for the generation of functional devices.

Layer‐By‐Layer Chiral Induction of Fluorene‐Based Metal–Organic Framework Films for Circularly Polarized Luminescence Sensing of Enantiomers

AbstractDeveloping films of chiral metal–organic frameworks (MOFs) with high circular polarization luminescence (CPL) is facing a great challenge for chiral sensing applications. Herein, a layer‐by‐layer chiral induction method is first reported to prepare enantiopure MOF films for CPL sensing. By layer‐by‐layer induction with the chiral inductor camphorsulfonic acid, fluorene‐based chiral MOF D/L‐ZnHF‐SO2 film (HF‐SO2 = 3,7‐Dibenzothiophenedicarboxylate, 5,5‐dioxide) with preferential growth orientation and homogeneous surface are prepared, which shows strong chiral feature and CPL with higher asymmetry factor of ±0.073. In addition, by mixed ligand approach, the isostructural fluorene ligand 9‐fluororenone‐2,7‐dicarboxylate is chosen to replace part of HF‐SO2 for preparing a series of chiral MOF films with tunable CPL emission. Furthermore, the prepared chiral MOF films with strong CPL performance are further utilized for enantiomers sensing. The CPL changes consisted with enantioselective adsorption results showed that D/L‐ZnHF‐SO2 film has good discrimination against chiral R/S‐phenylethylamine enantiomers, first reporting chiral MOF‐based candidates for the application in CPL sensing of enantiomers. This work provides a facile and effective approach for preparing chiral MOF films materials with high and tunable CPL performance, and also gives a new way to achieve CPL sensing of chiral enantiomers.

Enhancing Electrochemical Signal for Efficient Chiral Recognition by Encapsulating C60 Fullerene into Chiral Lanthanum-Based MOFs.

Chiral metal-organic frameworks (MOFs) have attracted much attention due to their highly tunable regular microporous structures. However, chiral electrochemical recognition based on chiral MOFs is often limited by poor charge separation and slow charge transfer kinetics. In this case, C60 can be encapsulated into the cavity of [La(BTB)]n by virtue of host-guest interactions through π-π stacking to synthesize the chiral composite C60@[La(BTB)]n and amplify electrochemically controlled enantioselective interactions with the target enantiomers. A large electrostatic potential difference is generated in chiral C60@[La(BTB)]n due to the host-guest interaction and the inhomogeneity of the charge distribution, leading to the generation of a strong built-in electric field and thus an overall enhancement of the conductivity of the chiral material. Their enantioselective detection of tryptophan enantiomers was demonstrated by electrochemical measurement. The results showed that chiral MOF materials can be used for enantiomeric recognition. It is worth noting that this new material derived from the concept of host-guest interaction to enhance charge separation opens up unprecedented possibilities for future enantioselective recognition and separation.

Enantiomeric analysis of chiral phenyl aromatic compounds by coated capillary electrochromatography based on aMOF-on-MOF stationary phase.

Chiral phenyl aromatic compounds (CPACs) are widely used in drug development, food/cosmetic production, and other organic synthesis processes, and their different enantiomers have distinct physiological activities and application differences. A double-layer metal-organic framework composite (MOF-on-MOF) was obtained by in situ synthesis of chiral metal-organic framework (CMOM-3S) on the surface of an iron-based metal-organic framework (NH2-MIL-101(Fe)). According to ourinvestigation, MOF-on-MOF composite was for the first time applied tothe stationary phase of capillary electrochromatography (CEC), and enantioseparations of eight CPACs were accomplished. Compared with single CMOM-3S, the enantioseparation performance of the coated capillary columns based on NH2-MIL-101(Fe)@CMOM-3S was improved by 34.07 ~ 720.0%. The R-/S-mandelic acid in actual sample (apricot leaves) was detected by the newly CEC system to be 0.0118mgmL-1 and 0.0523mgmL-1, respectively. The spike recoveries were 96.60 ~ 104.7%, indicating its good stability and accuracy. In addition, the selective adsorption capacity of MOF-on-MOF composites was verified by adsorption experiments.

PH-Tuned Enantioselectivity Reversal in a Defective Chiral Metal Organic Framework.

The introduction of chirality into easy-scalable metal-organic frameworks (MOFs) gives rise to the development of advanced electrochemical sensors. However, integrating chirality by directly connecting metal ions and chiral ligands is unpredictable. Postmodification synthesis is a common method for synthesizing chiral MOFs, but it reduces the size of chiral channels and poses obstacles to the approach of chiral guest molecules. In this work, missing connection defects were introduced into the chiral MOFs through defect engineering strategies, which enhance the recognition of the target enantiomers. pH can tune enantioselectivity reversal in defective chiral MOFs. The chiral MOFs show enantioselectivity for d-Trp at pH = 5 and l-Trp at pH = 8. From the results of zeta potential, regardless of pH 5 or 8, the chiral MOF has a positive potential. The chiral MOFs are positively charged, while tryptophan is negatively charged when pH = 8. The difference in the positive and negative charge interactions between the two amino acids and chiral MOFs leads to chiral recognition. However, the difference in π-π interaction between chiral MOF and Trp enantiomers mainly drives chiral recognition under pH = 5. This study paves a pathway for the synthesis of defective chiral MOFs and highlights the pH-tuned enantioselectivity reversal.

Induced Absolute Configuration of Achiral Tetradentate Ligands in Metal–Organic Frameworks for Circularly Polarized Luminescence

Comprehensive SummaryThe crystallization of chiral molecules is of great significance to understand the origin and evolution of hierarchical chirality and reveal the relationships between structural chirality and circularly polarized luminescence (CPL) activity. Here, we report two pairs of chiral metal–organic frameworks (MOFs) (DCF‐17/LCF‐17, DCF‐18/LCF‐18) by utilizing tetradentate ligands tetra(3‐imidazoylphenyl)ethylene (TIPE) and 4,4'‐[4',5'‐bis[4‐(4‐pyridinyl)phenyl][1,1':2',1”‐terphenyl]‐4,4”‐diyl]bis[pyridine] (TPPP) as linkers. It can be observed that the spontaneous resolution of the achiral ligands is converted into the induced resolution, and the ligands form the absolute configuration by using enantiopure camphoric acid (cam) as chiral induced reagent (CIR). As a result, the racemate MOFs can be driven to generate absolute homochiral crystallization. Another two achiral MOFs [Cd(D‐cam)(TPPP)0.5] (AF‐1, AF = achiral framework) and [Cd(L‐cam)(TPPP)0.5] (AF‐2) were prepared. The position disorder of D/L‐cam skeleton causes the generation of nonchiralization, further leading to disappearance of symmetry breaking of TPPP. For the perspective of structure, this is the first report which reveals the chiral transfer and nonchiralization between chiral induced agents and tetradentate ligands. Besides, DCF‐17 and LCF‐17 show CPL with luminescence dissymmetry factor (glum) of –1.0 × 10‐2 and +9.2 × 10–3, respectively. This work provides the useful evidences to reveal the induced chiral crystallization and the construction of CPL‐active crystalline materials.

Water-Resistant, Scalable, and Inexpensive Chiral Metal–Organic Framework Featuring Global Negative Electrostatic Potentials for Efficient Acetylene Separation

Water-Resistant, Scalable, and Inexpensive Chiral Metal–Organic Framework Featuring Global Negative Electrostatic Potentials for Efficient Acetylene Separation

[Research progress of stationary phase of gas chromatography based on chiral organic frameworks].

Enantiomers typically show different pharmacological, toxicological, and physiological properties. Thus, the preparation of enantiopure compounds is of great significance for human health and sustainable development. Compared with asymmetric catalysis, enantiomeric separation is simpler, faster, and more efficient; as such, it has become the preferred method for obtaining pure enantiomers. At present, enantiomeric separation methods mainly include chromatography, nanochannel membrane separation, selective adsorption, and recrystallization. In particular, gas chromatography (GC) plays an important role in enantioseparation because of its high sensitivity, excellent reproducibility, and outstanding processing capacity for various enantiomers. The stationary phase is key to the separation efficiency of GC, and more efficient, stable, and cost-effective materials that could serve as stationary phases are constantly being explored. Organic frameworks, such as covalent organic frameworks (COFs), metal-organic frameworks (MOFs), porous organic cages (POCs), metal-organic cages (MOCs), and hydrogen-bonded organic frameworks (HOFs), possess large specific surface areas, high porosities, tunable pore sizes, and easy functionalization, rendering them promising candidates for the separation of mixed analytes. Research has shown that the use of organic frameworks as stationary phases for GC results in excellent column efficiency and high resolution for various analytes, including n-alkanes, n-alcohols, polycyclic aromatic hydrocarbons, positional isomers, and organic fluorides. Furthermore, organic frameworks can be prepared as chiral stationary phases for GC by the intelligent introduction of a chiral moiety, thereby enabling the efficient separation of enantiomers. Synthetic strategies for chiral organic frameworks are primarily categorized as post-synthesis or bottom-up approaches. In general, the post-synthesis strategy can introduce various chiral sites to the framework; however, the distribution of chiral sites may not be uniform, and the ordered framework may be destroyed during the post-synthesis process. The bottom-up strategy allows for the uniform and precise distribution of chiral sites in the framework, but the synthesis of chiral monomers and the constraint between asymmetry and crystallinity limit its development. Chiral induction has been proposed as an alternative strategy for synthesizing chiral organic frameworks. The use of this strategy has led to the successful preparation of organic frameworks with abundant chiral sites and excellent crystallinity. Dynamic coating and in situ growth are the main approaches used to transform the as-prepared chiral organic frameworks into stationary phases. Notably, the in situ growth approach can yield chiral COF/MOF-coated capillary columns that provide high resolution for the separation of enantiomers with excellent repeatability and reproducibility. Nevertheless, owing to the slightly complex pretreatment process and the difficulty of synthesizing chiral organic frameworks, the in situ growth approach has not yet been widely applied. Owing to their excellent solvent processing performance, POCs, MOCs, and HOFs can be easily coated on the inner walls of columns to form membranes via dynamic or static coating. A series of enantiomers have been successfully separated and analyzed by immobilizing chiral COFs, MOFs, POCs, MOCs, and HOFs on GC capillary columns, demonstrating the great potential of chiral organic frameworks for enantiomeric separation. In general, the mechanisms by which chiral organic frameworks recognize enantiomers could be mainly categorized as van der Waals interactions, hydrogen bonding, π-π interactions, and size-exclusion effects. While molecular simulations can offer some insights into these recognition mechanisms, clarifying these mechanisms based on effective characterization remains challenging. In summary, organic frameworks show outstanding advantages for enantiomer separation. Given breakthroughs in synthetic strategies for chiral organic frameworks and the in-depth study of chiral recognition mechanisms, chiral organic frameworks may be expected to become an important aspect in the field of chiral materials, further realizing the large-scale analysis and production of chiral analytes. A total of 64 references, most of which are from the American Chemical Society, Springer Nature, Wiley Online Library, and Elsevier databases, are cited in this review.

Obtaining giant Rashba-Dresselhaus spin splitting in two-dimensional chiral metal-organic frameworks.

Two-dimensional (2D) nonmagnetic semiconductors with large Rashba-Dresselhaus (R-D) spin splitting at valence or conduction bands are attractive for magnetic-field-free spintronic applications. However, so far, the number of 2D R-D inorganic semiconductors has been quite limited, and the factors that determine R-D spin splitting as well as rational design of giant spin splitting, remain unclear. For this purpose, by exploiting 2D chiral metal-organic frameworks (CMOFs) as a platform, we theoretically develop a three-step screening method to obtain a series of candidate 2D R-D semiconductors with valence band spin splitting up to 97.2 meV and corresponding R-D coupling constants up to 1.37 eV Å. Interestingly, the valence band spin texture is reversible by flipping the chirality of CMOFs. Furthermore, five keys for obtaining giant R-D spin splitting in 2D CMOFs are successfully identified: (i) chirality, (ii) large spin-orbit coupling, (iii) narrow band gap, (iv) valence and conduction bands having the same symmetry at the Γ point, and (v) strong ligand field.

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.

Hierarchical Chiral MOFs with the Induced Chirality of AIE Ligands Exhibiting the Non-reciprocal CPL

Two pairs of chiral MOFs DCF-15/LCF-15 and DCF-16/LCF-16 were constructed through assembly of the achiral aggregation-induced emission (AIE)-type multidentate linkers (TPPE and TPA) and chiral camphoric acid (D/L-cam). Benefiting from...

Enantioselective enrichment of chiral 1-phenylethanol in the camphor-based chiral metal–organic framework CFA-22

The novel enantioselective CFA-22 metal–organic frameworks were successfully developed and investigated for chiral adsorption separation of e.g. racemic 1-phenylethanol.

Nanoscale and Chiral Metal–Organic Framework for Asymmetric Reactions in Water: Bridging Lewis Acid Catalysis to Biological Systems

Nanoscale and Chiral Metal–Organic Framework for Asymmetric Reactions in Water: Bridging Lewis Acid Catalysis to Biological Systems

Isostructural chiral metal–organic frameworks with metal-regulated performances for electrochemical enantiomeric recognition of tyrosine and tryptophan

Two isostructural homochiral MOFs exhibit significantly different enantioselective recognition performances closely associated with the different coordination habits of the metal centers in the MOFs.

Correction: Constructing chiral MOFs by functionalizing 4,2′:6′,4′′-terpyridine with long-chain alkoxy domains: examples of dia nets

Correction for ‘Constructing chiral MOFs by functionalizing 4,2′:6′,4′′-terpyridine with long-chain alkoxy domains: examples of dia nets’ by Y. Maximilian Klein et al., CrystEngComm, 2016, 18, 4704–4707, https://doi.org/10.1039/C6CE00939E.

Chiral metal-organic frameworks incorporating nanozymes as neuroinflammation inhibitors for managing Parkinson’s disease

Nanomedicine-based anti-neuroinflammation strategy has become a promising dawn of Parkinson’s disease (PD) treatment. However, there are significant gaps in our understanding of the therapeutic mechanisms of antioxidant nanomedicines concerning the pathways traversing the blood-brain barrier (BBB) and subsequent inflammation mitigation. Here, we report nanozyme-integrated metal-organic frameworks with excellent antioxidant activity and chiral-dependent BBB transendocytosis as anti-neuroinflammatory agents for the treatment of PD. These chiral nanozymes are synthesized by embedding ultra-small platinum nanozymes (Ptzymes) into L-chiral and D-chiral imidazolate zeolite frameworks (Ptzyme@L-ZIF and Ptzyme@D-ZIF). Compared to Ptzyme@L-ZIF, Ptzyme@D-ZIF shows higher accumulation in the brains of male PD mouse models due to longer plasma residence time and more pathways to traverse BBB, including clathrin-mediated and caveolae-mediated endocytosis. These factors contribute to the superior therapeutic efficacy of Ptzyme@D-ZIF in reducing behavioral disorders and pathological changes. Bioinformatics and biochemical analyses suggest that Ptzyme@D-ZIF inhibits neuroinflammation-induced apoptosis and ferroptosis in damaged neurons. The research uncovers the biodistribution, metabolic variances, and therapeutic outcomes of nanozymes-integrated chiral ZIF platforms, providing possibilities for devising anti-PD drugs.

Amplified circularly polarized luminescence of chiral metal-organic frameworks via post-synthetic installing pillars

Post-synthetic installation strategy is an effective approach to improve the functions of metal-organic frameworks (MOFs). Herein, a pair of chiral MOFs is successfully constructed through solvothermal subcomponent self-assembly and exhibit circularly polarized luminescence (CPL). These MOFs contain coordinatively unsaturated Zn sites and channels, which allow the installation of pyridyl-terminated pillars into the original structure. Such a post-synthetic installation process reinforces the MOFs’ rigidity and increases the photoluminescence quantum yields (PLQYs). Furthermore, the luminescence dissymmetry factors (glum) of these post-modified MOFs are amplified after installing the pillars. This work provides an appealing strategy for boosting the CPL performance of chiral MOFs.