Homochiral metal-organic frameworks for enantioseparation

Crystalline Olefin-Linked Chiral Covalent Organic Frameworks as a Platform for Asymmetric Catalysis

The construction of olefin-linked chiral covalent organic frameworks (COFs) with high crystallinity is highly desirable while remains great challenge due to the poor reversibility of the formation reaction for the olefin linkages during the in situ structural self-healing process. Herein, we successfully synthesized two sets of enantiomeric olefin-linked COFs. The chiral catalytic groups are uniformly distributed on the pore walls of COFs, resulting in the full exposure of catalytic sites to the reactants in asymmetric catalysis. The as-prepared (R)/(S)-CCOF8 exhibits excellent catalytic performance with exceeding 99 % enantiomeric excess in the enantioselective electrophilic amination reaction. Moreover, the heterogeneous chiral catalysts are conveniently recycled and could maintain the performance after ten catalytic cycles. Our findings expand the scope to construct stable and crystalline chiral COFs for the asymmetric catalysis.

Metal-organic framework (MOF)/C-dots and covalent organic framework (COF)/C-dots hybrid nanocomposites: Fabrications and applications in sensing, medical, environmental, and energy sectors

Developing new hybrid materials is critical for addressing the current needs of the world in various fields, such as energy, sensing, health, hygiene, and others. C-dots are a member of the carbon nanomaterial family with numerous applications. Aggregation is one of the barriers to the performance of C-dots, which causes luminescence quenching, surface area decreases, etc. To improve the performance of C-dots, numerous matrices including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and polymers have been composited with C-dots. The porous crystalline structures, which are constituents of metal nodes and organic linkers (MOFs) or covalently attached organic units (COFs) provide privileged features such as high specific surface area, tunable structures, and pore diameters, modifiable surface, high thermal, mechanical, and chemical stabilities. Also, the MOFs and COFs protect the C-dots from the environment. Therefore, MOF/C-dots and COF/C-dots composites combine their features while retaining topological properties and improving performances. In this review, we first compare MOFs with COFs as matrices for C-dots. Then, the recent progress in developing hybrid MOFs/C-dots and COFs/C-dots composites has been discussed and their applications in various fields have been explained briefly.

Robust Homochiral Polycrystalline Metal-Organic Framework Membranes for High-Performance Enantioselective Separation

Homochiral MOF membranes offer a promising route to efficient chiral separation, but their fabrication remains challenging. Here, we report for the first time the design and preparation of homochiral polycrystalline MOF-808 membranes for the first time. The membrane exhibits a high integrity and thin membrane thickness. Achieving homochirality through chiral amino acid postsynthetic modification, MOF-808 membranes demonstrate remarkable solvent stability. Notably, they successfully separated racemic naproxen enantiomers, achieving enantiomeric excess (ee) values of up to ∼95.0%. This work paves the way for turning achiral polycrystalline MOF membranes into high-performance chiral membranes for enantioselective separation.

Endowing Metal-Organic Coordination Materials with Chiroptical Activity by a Chiral Anion Strategy

Recently, chiral metal-organic coordination materials have emerged as promising candidates for a wide range of applications in chiroptoelectronics, chiral catalysis, and information encryption, etc. Notably, the chiroptical effect of coordination chromophores makes them appealing for applications such as photodetectors, OLEDs, 3D displays, and bioimaging. The direct synthesis of chiral coordination materials using chiral organic ligands or complexes with metal-centered chirality is very often tedious and costly. In the case of ionic coordination materials, the combination of chiral anions with cationic, achiral coordination compounds through noncovalent interactions may endow molecular materials with desirable chiroptical properties. The use of such a simple chiral strategy has been proven effective in inducing promising circular dichroism and/or circularly polarized luminescence signals. This concept article mainly delves into the latest advances in exploring the efficacy of such a chiral anion strategy for transforming achiral coordination materials into chromophores with superb photo- or electro-chiroptical properties. In particular, ionic small-molecular metal complexes, metal clusters, coordination supramolecular assemblies, and metal-organic frameworks containing chiral anions are discussed. A perspective on the future opportunities on the preparation of chiroptical materials with the chiral anion strategy is also presented.

Multifunctional Chiral d10-Metal Coordination Polymers: Tunable Photoluminescence and Efficient Second-Harmonic Generation with Circular Dichroic Response

A series of homochiral coordination polymers (HCPs), [M2(SIAP)2(bpy)2] [M(S)] and [M2(RIAP)2(bpy)2] [M(R)] (M = Zn or Cd, SIAP or RIAP = (S,S)- or (R,R)- 2,2'-(isophthaloylbis(azanediyl))di-propionic acid, bpy = 4,4'-bipyridine), is successfully synthesized through solvothermal reactions, self-assembling d10 metal cations, chiral dicarboxylic ligands, and π-conjugated bipyridyl ligands. The HCPs crystallize in the extremely rare triclinic chiral space group, P1, and present 3D framework structures attributed to the strong intermolecular interactions, such as hydrogen bonds and π-π stacking. Due to the unique crystal structures, the title compounds reveal efficient photoluminescence emission across a broad visible range, with significant brightness and color tuning by varying the excitation wavelength. Moreover, they exhibit efficient phase-matched second-harmonic generation (SHG) with very high laser-induced damage thresholds, essential for high-power nonlinear optical (NLO) applications. Intriguingly, the title compounds exhibit a measurable contrast in the SHG response under right- and left-handed circularly polarized excitation, thereby providing a unique case of SHG circular dichroism from the chiral centers of SIAP2- or RIAP2- ligand packed in the noncentrosymmetric environment. These exceptional attributes position these HCPs as promising candidates for multifunctional materials, with potential applications ranging from NLO devices to tailored luminescent systems with polarization control.

Assembly of Homochiral Aluminum Oxo Clusters for Circularly Polarized Luminescence

Chiral aluminum oxo clusters (cAlOCs) are distinguished from other classes of materials on account of their abundance in the earth's crust and their potential for sustainable development. However, the practical synthesis of cAlOCs is rarely known. Herein, we adopt a synergistic coordination strategy by using chiral amino acid ligands as bridges and auxiliary pyridine-2,6-dicarboxylic acid as chelating ligands and successfully isolate an extensive family of cAlOCs. They integrate molecular chirality, absolute helicity, and intrinsic hydrogen-bonded chiral topology. Moreover, they have the structural characteristics of one-dimensional channels and replaceable counteranions, which make them well combined with fluorescent dyes for circularly polarized luminescence (CPL). The absolute luminescence dissymmetry factor (glum) of up to the 10-3 order is comparable to several noble metals, revealing the enormous potential of cAlOCs in low-cost chiral materials. We hope this work will inspire new discoveries in the field of chirality and provide new opportunities for constructing low-cost chiral materials.

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.

Coordination recognition of differential template units of lanthanide chiral chain

Coordination-driven self-assembly processes often produce remarkable structures. In particular, self-assembly processes mediated by chiral template units have provided research ideas for analyzing the formation of chiral macromolecules in living organisms. In this study, by regulating the proportion of reaction raw materials in the "one-pot" synthesis of lanthanide complexes, we constructed chiral template units with different coordination orientations. As a result, lanthanide chiral chains connected to different structures were obtained through the self-assembly process of coordination recognition. In particular, driven by coordination, chiral template units with codirectional coordination points (called cis configuration) coordinate solely with cis template units during the self-assembly process to obtain a one-dimensional (1D) chain R-1/S-1 with an "S"-shaped distribution. Moreover, chiral template units with reversed coordination sites (called trans configuration) and twisted chiral template units are connected solely to templates with the same configuration to form a 1D chain R-2/S-2 with an axial helix. A circular dichroism spectrum shows that R-1/S-1 and R-2/S-2 are two pairs of enantiomers. The controllable construction of these two differential 1D chains is of great significance for studying coordination recognition at the molecular level. To the best of our knowledge, this is the first study to construct a 1D lanthanide chain through the self-assembly process of coordination recognition. The assembly process of nucleotides to form a hierarchical structure is simulated. This work provides a vivid example of the controllable synthesis of lanthanide complexes with precise structures and offers a new perspective on the formation process of chiral macromolecules that simulates natural processes.

A free carboxyl-decorated metal-organic framework with 3D helical chirality for highly enantioselective recognition

With the judicious selection of a designed polycarboxylate derived from L-phenylalanine, (S)-5-(((1-carboxy-2-phenylethyl)amino)methyl)isophthalic acid (H3L), a novel homochiral metal-organic framework decorated with a free carboxyl, {[Cu2(HL)2(bipy)]∙2H2O}n (Cu-MOF), has been designed and synthesized in a solvothermal process. The result of single crystal X-ray diffraction analysis showed that Cu-MOF had the character of a three-dimensional structure with helical chirality. As we expected, in Cu-MOF, one accessible free carboxylic acid group on H3L pointed toward the spiral channels, and the other two -COOH groups were utilized in bonding. The enantioseparation performance of Cu-MOF was thoroughly investigated and the results showed that Cu-MOF can specifically recognize S-1-(1-naphthyl) ethanol (S-NE) with enantiomeric excess (ee) value of 99.35 %, which was much higher than the other three racemates. The appropriate size together with suitable interaction sites played an important role in enantioseparations. Inspired by the excellent chiral recognition effects towards S-NE, the chiral recognition mechanism was experimentally clarified. A fully agreement observed in 13C CP MAS NMR analysis as well as the X-ray photoelectron spectroscopy (XPS) determination revealed that a strong hydrogen bonding interaction forces existed between the hydroxyl of the optical S-NE and the decorated -COOH in the chiral framework. The control experiment further identified the decisive role of the uncoordinated carboxyl group in Cu-MOF. In addition, the strong intermolecular off-set π-π interactions between the phenyl ring involved with the coordinated COO- groups in Cu-MOF and the naphthyl ring of S-NE, was the another important factor for the specifical enantioseparation of S-enantiomer. On the basis of strong intermolecular hydrogen bonding, NE racemates were enantioselective discriminated and enantiomeric purity can be determined by means of Raman scattering spectroscopy.

Metal-organic framework boosts heterogeneous electron donor-acceptor catalysis

Metal-organic framework (MOF) is a class of porous materials providing an excellent platform for engineering heterogeneous catalysis. We herein report the design of MOF Zr-PZDB consisting of Zr6-clusters and PZDB (PZDB = 4,4'-(phenazine-5,10-diyl)dibenzoate) linkers, which served as the heterogeneous donor catalyst for enhanced electron donor-acceptor (EDA) photoactivation. The high local concentration of dihydrophenazine active centers in Zr-PZDB can promote the EDA interaction, therefore resulting in superior catalytic performance over homogeneous counterparts. The crowded environment of Zr-PZDB can protect the dihydrophenazine active center from being attacked by radical species. Zr-PZDB efficiently catalyzes the Minisci-type reaction of N-heterocycles with a series of C-H coupling partners, including ethers, alcohols, non-activated alkanes, amides, and aldehydes. Zr-PZDB also enables the coupling reaction of aryl sulfonium salts with heterocycles. The catalytic activity of Zr-PZDB extends to late-stage functionalization of bioactive and drug molecules, including Nikethamide, Admiral, and Myristyl Nicotinate. Systematical spectroscopy study and analysis support the EDA interaction between Zr-PZDB and pyridinium salt or aryl sulfonium salt, respectively. Photoactivation of the MOF-based EDA adduct triggers an intra-complex single electron transfer from donor to acceptor, giving open-shell radical species for cross-coupling reactions. This research represents the first example of MOF-enabled heterogeneous EDA photoactivation.

Effect of Extra-Framework Anion Substitution on the Properties of a Chiral Crystalline Sponge

Chiral metal-organic materials, CMOMs, are of interest as they can offer selective binding sites for chiral guests. Such binding sites can enable CMOMs to serve as chiral crystalline sponges (CCSs) to determine molecular structure and/or purify enantiomers. We recently reported on the chiral recognition properties of a homochiral cationic diamondoid, dia, network {[Ni(S-IDEC)(bipy)(H2O)][NO3]}n (S-IDEC = S-indoline-2-carboxylicate, bipy = 4,4'-bipyridine), CMOM-5[NO3]. The modularity of CMOM-5[NO3] means there are five feasible approaches to fine-tune structures and properties via substitution of one or more of the following components: metal cation (Ni2+); bridging ligand (S-IDEC); linker (bipy); extra-framework anion (NO3-); and terminal ligand (H2O). Herein, we report the effect of anion substitution on the CCS properties of CMOM-5[NO3] by preparing and characterizing {[Ni(S-IDEC)(bipy)(H2O)][BF4]}n, CMOM-5[BF4]. The chiral channels in CMOM-5[BF4] enabled it to function as a CCS for determination of the absolute crystal structures of both enantiomers of three chiral compounds: 1-phenyl-1-butanol (1P1B); methyl mandelate (MM); ethyl mandelate (EM). Chiral resolution experiments revealed CMOM-5[BF4] to be highly selective toward the S-isomers of MM and EM with enantiomeric excess, ee, values of 82.6 and 78.4%, respectively. The ee measured for S-EM surpasses the 64.3% exhibited by [DyNaL(H2O)4] 6H2O and far exceeds that of CMOM-5[NO3] (6.0%). Structural studies of the binding sites in CMOM-5[BF4] provide insight into their high enantioselectivity.

Enantiomeric filtration separation of supramolecular framework membranes

A two-dimensional supramolecular framework with a tetragonal structure is constructed via host-guest interaction of a pillar[5]arene grafted polyanion with a modified porphyrin. The membrane of the framework with a chiral counterion exhibits enantiomeric selectivity during the filtration of racemic molecules with amino groups, demonstrating broadened potential in chiral separations.

Chiral Materials: Progress, Applications, and Prospects

Chirality is a universal phenomenon in molecular and biological systems, denoting an asymmetric configurational property where an object cannot be superimposed onto its mirror image by any kind of translation or rotation, which is ubiquitous on the scale from neutrinos to spiral galaxies. Chirality plays a very important role in the life system. Many biological molecules in the life body show chirality, such as the "codebook" of the earth's biological diversity-DNA, nucleic acid, etc. Intriguingly, living organisms hierarchically consist of homochiral building blocks, for example, l-amino acids and d-sugars with unknown reason. When molecules with chirality interact with these chiral factors, only one conformation favors the positive development of life, that is, the chiral host environment can only selectively interact with chiral molecules of one of the conformations. The differences in chiral interactions are often manifested by chiral recognition, mutual matching, and interactions with chiral molecules, which means that the stereoselectivity of chiral molecules can produce changes in pharmacodynamics and pathology. Here, the latest investigations are summarized including the construction and applications of chiral materials based on natural small molecules as chiral source, natural biomacromolecules as chiral sources, and the material synthesized by design as a chiral source.

Chiral MOF Derived Wearable Logic Sensor for Intuitive Discrimination of Physiologically Active Enantiomer

Chiral sensors have attracted growing interest due to their application in health monitoring. However, rational design of wearable logic chiral sensors remains a great challenge. In this work, a dual responsive chiral sensor RT@CDMOF is prepared through in situ self-assembly of chiral γ-cyclodextrin metal-organic framework (CDMOF), rhodamine 6G hydrazide (RGH), and tetracyanovinylindane (TCN). The embedded RGH and TCN inherit the chirality of host CDMOF, producing dual changes both in fluorescence and reflectance. RT@CDMOF is explored as a dual channel sensor for chiral discrimination of lactate enantiomers. Comprehensive mechanistic studies reveal the chiral binding process, and carboxylate dissociation is confirmed by impedance and solid-state 1 H nuclear magnetic resonance (NMR). A flexible membrane sensor is successfully fabricated based on RT@CDMOF for wearable health monitoring. Practical evaluation confirms the potential of fabricated membrane sensor in point-of-care health monitoring by indexing the exercise intensity. Based on above, a chiral IMPLICATION logic unit can be successfully achieved, demonstrating the promising potential of RT@CDMOF in design and assembly of novel smart devices. This work may open a new avenue to the rational design of logic chiral sensors for wearable health monitoring applications.

Tetrahedral Imidazolate Frameworks with Auxiliary Ligands (TIF-Ax): Synthetic Strategies and Applications

Zeolitic imidazolate frameworks (ZIFs) are an important subclass of metal-organic frameworks (MOFs). Recently, we reported a new kind of MOF, namely tetrahedral imidazolate frameworks with auxiliary ligands (TIF-Ax), by adding linear ligands (Hint) into the zinc-imidazolate system. Introducing linear ligands into the M2+-imidazolate system overcomes the limitation of imidazole derivatives. Thanks to the synergistic effect of two different types of ligands, a series of new TIF-Ax with interesting topologies and a special pore environment has been reported, and they have attracted extensive attention in gas adsorption, separation, catalysis, heavy metal ion capture, and so on. In this review, we give a comprehensive overview of TIF-Ax, including their synthesis methods, structural diversity, and multi-field applications. Finally, we also discuss the challenges and perspectives of the rational design and syntheses of new TIF-Ax from the aspects of their composition, solvent, and template. This review provides deep insight into TIF-Ax and a reference for scholars with backgrounds of porous materials, gas separation, and catalysis.

Water-Etched Approach to Hierarchically Porous Metal-Organic Frameworks with High Stability

The development of hierarchically porous metal-organic frameworks (MOFs) with high stability is desirable to expand their applications but remains challenging. Herein, an anionic sodalite-type microporous MOF (Yb-TTCA; TTCA3- = triphenylene-2,6,10-tricarboxylate) was synthesized, which shows outstanding catalytic activities for the cycloaddition of CO2 into cyclic carbonates. Moreover, the microporous Yb-TTCA can be transformed into a hierarchical micro- and mesoporous Yb-TTCA by water treatment with the mesopore sizes of 2 to 12 nm. The hierarchically porous Yb-TTCA (HP-Yb-TTCA) not only exhibits a high thermal stability up to 500 °C but also shows a high chemical stability in aqueous solutions with pH values ranging from 2 to 12. In addition, the HP-Yb-TTCA displays enhanced performance for the removal of organic dyes in comparison with microporous Yb-TTCA. This work provides a facile way to construct hierarchically porous MOF materials.

Crystal Engineering of a Chiral Crystalline Sponge That Enables Absolute Structure Determination and Enantiomeric Separation

Chiral metal-organic materials (CMOMs), can offer molecular binding sites that mimic the enantioselectivity exhibited by biomolecules and are amenable to systematic fine-tuning of structure and properties. Herein, we report that the reaction of Ni(NO₃)₂, S-indoline-2-carboxylic acid (S-IDECH), and 4,4'-bipyridine (bipy) afforded a homochiral cationic diamondoid, dia, network, [Ni(S-IDEC)(bipy)(H₂O)][NO₃], CMOM-5. Composed of rod building blocks (RBBs) cross-linked by bipy linkers, the activated form of CMOM-5 adapted its pore structure to bind four guest molecules, 1-phenyl-1-butanol (1P1B), 4-phenyl-2-butanol (4P2B), 1-(4-methoxyphenyl)ethanol (MPE), and methyl mandelate (MM), making it an example of a chiral crystalline sponge (CCS). Chiral resolution experiments revealed enantiomeric excess, ee, values of 36.2-93.5%. The structural adaptability of CMOM-5 enabled eight enantiomer@CMOM-5 crystal structures to be determined. The five ordered crystal structures revealed that host-guest hydrogen-bonding interactions are behind the observed enantioselectivity, three of which represent the first crystal structures determined of the ambient liquids R-4P2B, S-4P2B, and R-MPE.

An Organic Chiroptical Detector Favoring Circularly Polarized Light Detection from Near-Infrared to Ultraviolet and Magnetic-Field-Amplifying Dissymmetry in Detectivity

Circularly polarized light detection has attracted growing attention because of its unique application in security surveillance and quantum optics. Here, through designing a chiral polymer as a donor, a high-performance circularly polarized light detector is fabricated, successfully enabling detection from ultraviolet (300 nm) to near-infrared (1100 nm). The chiroptical detector presents an excellent ability to distinguish right-handed and left-handed circularly polarized light, where dissymmetries in detectivity, responsivity, and electric current are obtained and then optimized. The dissymmetry in electric current can be increased from 0.18 to 0.23 once an external magnetic field is applied. This is a very rare report on the dissymmetry tunability by an external field in chiroptical detectors. Moreover, the chirality-generated orbital angular momentum is one of the key factors determining the performance of the circularly polarized light detection. Overall, the organic chiroptical detector presents excellent stability in detection, which provides great potential for future flexible and compact integrated platforms.

Peptide-derived coordination frameworks for biomimetic and selective separation

Peptide-derived metal-organic frameworks (PMOFs) have emerged as a class of biomimetic materials with attractive performances in analytical and bioanalytical chemistry. The incorporation of biomolecule peptides gives the frameworks conformational flexibility, guest adaptability, built-in chirality, and molecular recognition ability, which greatly accelerate the applications of PMOFs in enantiomeric separation, affinity separation, and the enrichment of bioactive species from complicated samples. This review focuses on the recent advances in the engineering and applications of PMOFs in selective separation. The unique biomimetic size-, enantio-, and affinity-selective performances for separation are discussed along with the chemical structures and functions of MOFs and peptides. Updates of the applications of PMOFs in adaptive separation of small molecules, chiral separation of drug molecules, and affinity isolation of bioactive species are summarized. Finally, the promising future and remaining challenges of PMOFs for selective separation of complex biosamples are discussed.

Design and Electrochemical Chiral Sensing of the Robust Sandwich Chiral Composite d-His-ZIF-8@Au@ZIF-8

In the pursuit of chiral materials with significant chiral recognition effects and stability, various strategies have been explored, among which the integration of metal nanoparticles and chiral metal-organic frameworks (CMOFs) is highly promising. However, metal nanoparticles (MNPs)/CMOFs show high chiral properties but inferior stabilities due to the MNPs being easily detached from the outside layer under certain conditions. Sandwich MOFs@MNPs@CMOF chiral materials can overcome this dilemma because the sandwich structure can maximize the regulation of the chiral interface activity, while the controlled outer layer can stop the MNPs from falling off in the procedure of chiral recognition. Here, a novel sandwich chiral material (d-His-ZIF-8@Au@ZIF-8) was synthesized by a ligand-assisted strategy with a well-defined sandwich morphology and chiral recognition capabilities. The electrochemical chiral recognition showed that d-His-ZIF-8@Au@ZIF-8 was the most efficient for the enantiomer of phenylalanine (Phe). This experiment presents a novel perspective for the fabrication of a chiral electrochemical sensing platform based on a solid sandwich chiral nanocomposite.

Engineering UiO-68-Typed Homochiral Metal-Organic Frameworks for the Enantiomeric Separation of Fmoc-AAs and Mechanism Study

Homochiral metal-organic frameworks (HMOFs) have been widely investigated in the application of enantiomeric separation. Nonetheless, it remains a significant challenge to explore the effect of multiple weak interactions between HMOF adsorbents and chiral adsorbates on enantiomeric separation performance still. In this work, robust chiral amine-alcohol-functionalized UiO-68-typed Zr-HMOFs 1-3 with the same hydrogen-bonding sites but slightly different π-binding sites were prepared for the enantioseparation of amino acid derivatives (Fmoc-AAs) with large π-binding groups. As a consequence of multiple host-guest interactions, these Zr-HMOFs exhibit speedy adsorption and high adsorption capacity for Fmoc-L/D-AAs and dissimilar enantioselectivity for the adsorption of their enantiomers. Materials 1 and 2 exhibit excellent enantioselective separation performance for Fmoc-valine with a single terminal π-binding group, while material 3 displays excellent enantioselective separation performance for Fmoc-phenylalanine and Fmoc-tryptophan with π-binding groups at both ends. As evidently demonstrated by our experimental and density functional theory (DFT) computational results, when the number of π-binding groups preset in the confined chiral space of adsorbents matches the number of π-binding groups of chiral adsorbates, the synergism of π-π or σ-π interactions will increase enantioselectivity; otherwise, the competition interactions from redundant identical binding sites will weaken enantioselectivity. Our case not only provides a tremendously typical system for investigating the collaborative discrimination of multiple weak interactions and exploring the impact of relatively excessive binding sites of HMOF adsorbents or chiral adsorbates on the enantioselective separation performance but also provides guidance for targeted functional modifications of high-performance chiral porous materials.

Enantioseparation Membranes: Research Status, Challenges, and Trends

The purity of enantiomers plays a critical role in human health and safety. Enantioseparation is an effective way and necessary process to obtain pure chiral compounds. Enantiomer membrane separation is a new chiral resolution technique, which has the potential for industrialization. This paper mainly summarizes the research status of enantioseparation membranes including membrane materials, preparation methods, factors affecting membrane properties, and separation mechanisms. In addition, the key problems and challenges to be solved in the research of enantioseparation membranes are analyzed. Last but not least, the future development trend of the chiral membrane is expected.

Chiral metal-organic frameworks and their composites as stationary phases for liquid chromatography chiral separation: A minireview

Chiral metal organic frameworks (CMOFs) are a kind of crystal porous framework material that has attracted increasing attention due to the customizable combination of metal nodes and organic ligands. In particular, the highly ordered crystal structure and rich adjustable chiral structure make it a promising material for developing new chiral separation material systems. In this review, the progress of CMOFs and their different types of composites used as chiral stationary phases (CSPs) in liquid chromatography for enantioseparation are discussed. The characteristics of CMOFs and their composites are summarized, aiming to provide new ideas for the development of CMOFs with better performance and further promote the application of CMOFs materials in enantioselective high-performance liquid chromatography (HPLC).

Stereoselective Assembly of Hydrogen-Bonded Anionic Cages Dictated by Organophosphate-Based Chiral Nodes

Inspired by the signal transduction function of organophosphates in biological systems, bioactive organophosphates were utilized for the first time as chiral nodes to dictate the stereoselective assembly of hydrogen-bonded anionic cages. Phosphonomycin (antibiotics), tenofovir (antivirals), adenosine monophosphate (natural product, AMP) and clindamycin phosphate (antibiotics) were assembled with an achiral bis-monourea ligand, thereby leading to the stereoselective formation of quadruple or triple helicates. The extent of the stereoselectivity could be enhanced by either lowering the temperature or adding stronger-binding cations as templates. With the chiral anionic cages as the host, some enantioselectivity was achieved when binding chiral quaternary ammonium cations.

Two temperature-induced 1D CuII chain enantiomeric pairs showing different magnetic properties and nonlinear optical responses

At different reaction temperatures, using Cu(NO₃)₂·3H₂O to react with enantiomerically pure N-donor ligands (L_S/L_R), respectively, two pairs of chiral one-dimensional (1D) Cu^II chain enantiomers formulated as [Cu(μ₂-NO₃)(NO₃)(L_S)]_n/[Cu(μ₂-NO₃)(NO₃)(L_R)]_n (S-1-Cu/R-1-Cu, formed at 40 °C with an NO₃^- group as a sole bridging ligand) and [Cu(μ₂-L_S)(NO₃)₂]_n/[Cu(μ₂-L_R)(NO₃)₂]_n (S-2-Cu/R-2-Cu, formed at 25 °C with L_S or L_R as a bridging ligand) were prepared, where L_S/L_R = (+)/(-)-4,5-pinenepyridyl-2-pyrazine. Interestingly, such a disparity in bridging ligands leads not only to their distinct structural features but also to their completely different magnetic couplings together with a large difference in their nonlinear optical responses. S-1-Cu with a 1D helical structure shows weak ferromagnetic coupling between Cu^II ions, while S-2-Cu with a 1D stairway-like structure presents weak antiferromagnetic coupling. In particular, they simultaneously possess both second- and third-harmonic generation (SHG and THG) responses in one molecule with large strength differences. More remarkably, S-1-Cu exhibits a very large THG response (162 × α-SiO₂), which is 22.5 times that of S-2-Cu, and the SHG strength of S-1-Cu is more than 3 times that of S-2-Cu. This work demonstrates that reaction temperature has a great impact on the self-assembled structures of coordination polymers and subsequently results in their large performance differences.

Creation and stabilization of carbon dots in silica-confined compartments with high thermal stability

Inspired by the formation procedures and high stability of ambers, we report herein a facile approach for the in situ creation and stabilization of carbon dots (CDs) in confined silica compartments by a solvothermal reaction and subsequent thermal treatment, and the endowed CDs exhibit the initial photoluminescence (PL) properties at 400 °C, which could be used to fabricate highly thermal-stable light-emitting diodes (LEDs) that work well at a current of 600 mA and temperature of 205 °C.

Pore Environment Optimization of Microporous Metal-Organic Frameworks with Huddled Pyrazine Pillars for C2H2/CO2 Separation

Metal-organic frameworks (MOFs) have been proven promising in addressing many critical issues related to gas separation and purification. However, it remains a great challenge to optimize the pore environment of MOFs for purification of specific gas mixtures. Herein, we report the rational construction of three isostructural microporous MOFs with the 4,4',4"-tricarboxyltriphenylamine (H₃TCA) ligand, unusual hexaprismane Ni₆O₆ cluster, and functionalized pyrazine pillars [PYZ-x, x = -H (DZU-10), -NH₂ (DZU-11), and -OH (DZU-12)], where the building blocks of Ni₆O₆ clusters and huddled pyrazine pillars are reported in porous MOFs for the first time. These building blocks have enabled the resulting materials to exhibit good chemical stability and variable pore chemistry, which thus contribute to distinct performances toward C₂H₂/CO₂ separation. Both single-component isotherms and dynamic column breakthrough experiments demonstrate that DZU-11 with the PYZ-NH₂ pillar outperforms its hydrogen and hydroxy analogues. Density functional theory calculations reveal that the higher C₂H₂ affinity of DZU-11 over CO₂ is attributed to multiple electrostatic interactions between C₂H₂ and the framework, including strong C≡C···H-N (2.80 Å) interactions. This work highlights the potential of pore environment optimization to construct smart MOF adsorbents for some challenging gas separations.

Metal-Organic Frameworks@Calcite Composite Crystals

The direct incorporation of guest crystals into another type of host crystals during the formation of the latter is technically challenging due to the large difference in surface energy for different crystalline components. Nevertheless, we herein demonstrate that metal-organic frameworks (MOFs, UiO-66-NH₂ as a model guest crystal) after postsynthetic modification with poly(methacrylic acid) can be efficiently incorporated into calcite single crystals, forming a unique composite structure where the MOF crystals are uniformly distributed throughout the whole calcite host crystals. Remarkably, such MOF@calcite composite crystals exhibit superior performance in fluoride removal compared with the MOF or calcite alone. Moreover, this incorporation strategy is general as it can be extended to other guest particles. In principle, this study opens up a versatile avenue for the rational design and preparation of a wide range of hybrid functional materials with controllable compositions and enhanced physicochemical properties.

ZnO/CeO2 Nanocomposites: Metal-Organic Framework-Mediated Synthesis, Characterization, and Estimation of Cellular Toxicity toward Liver Cancer Cells

The Zinc-doped cerium oxide nanocomposite (ZnO/CeO₂ NC) was synthesized using a metal-organic framework as a precursor through the combustion method. It was characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), field emission electron microscopy (FESEM), energy dispersive analysis (EDX), transmission electron microscopy (TEM), dynamic light scattering (DLS), and ξ-potential. The PXRD demonstrated the successful synthesis of ZnO/CeO₂ NC with a crystallite size of 31.9 nm. FESEM and TEM images displayed hexagonal and spherical morphologies, and the solid-phase size was 65.03 ± 30.86 nm for ZnO/CeO₂ NCs. DLS, TEM, and FESEM showed that the NCs have a high tendency for agglomeration/aggregation in both aqueous media and solid phase. The anticancer attributes of ZnO/CeO₂ NC were investigated against Liver cancer cells (HepG2), which showed inhibition of cancer cell growth on a concentration-dependent gradient. The cell toxicity effects of ZnO/CeO₂ nanocomposites were also studied toward NIH-3T3, in which the data displayed the lower toxicity of NC compared to the HepG2 cell line.

Challenges and opportunities for chiral covalent organic frameworks

As highly versatile crystalline porous materials, covalent organic frameworks (COFs) have emerged as an ideal platform for developing novel functional materials, attributed to their precise tunability of structure and functionality. Introducing chiral functional units into frameworks produces chiral COFs (CCOFs) with chiral superiorities through chirality conservation and conversion processes. This review summarises recent research progress in CCOFs, including synthetic methods, chiroptical characterisations, and their applications in asymmetric catalysis, chiral separation, and enantioselective recognition and sensing. Challenges and limitations are discussed to uncover future opportunities in CCOF research.

The progress on porous organic materials for chiral separation

Chiral compounds have similar structures and properties, but their pharmacological action is very different or even opposite. Therefore, the separation of chiral compounds has great significance in pharmaceutical and agriculture. Porous organic materials are novel crystalline porous materials, which possess high surface area, controllable pore size, and favorable functionalization. Therefore, porous organic materials are considered to be an ideal material for chiral separation. In this review, we summarized the progress of chiral porous organic materials for chiral separation in recent years. Furthermore, the applications of chiral porous organic materials as chiral separation medias (chromatography stationary phases and membrane materials) in enantioseparation were highlighted. Finally, the remaining challenges and future directions for porous organic materials in chiral separation were also briefly outlined further to promote the development of porous organic materials in chiral separation.

Recognition in the Domain of Molecular Chirality: From Noncovalent Interactions to Separation of Enantiomers

It is not a coincidence that both chirality and noncovalent interactions are ubiquitous in nature and synthetic molecular systems. Noncovalent interactivity between chiral molecules underlies enantioselective recognition as a fundamental phenomenon regulating life and human activities. Thus, noncovalent interactions represent the narrative thread of a fascinating story which goes across several disciplines of medical, chemical, physical, biological, and other natural sciences. This review has been conceived with the awareness that a modern attitude toward molecular chirality and its consequences needs to be founded on multidisciplinary approaches to disclose the molecular basis of essential enantioselective phenomena in the domain of chemical, physical, and life sciences. With the primary aim of discussing this topic in an integrated way, a comprehensive pool of rational and systematic multidisciplinary information is provided, which concerns the fundamentals of chirality, a description of noncovalent interactions, and their implications in enantioselective processes occurring in different contexts. A specific focus is devoted to enantioselection in chromatography and electromigration techniques because of their unique feature as "multistep" processes. A second motivation for writing this review is to make a clear statement about the state of the art, the tools we have at our disposal, and what is still missing to fully understand the mechanisms underlying enantioselective recognition.

Bubble-pen lithography: Fundamentals and applications: Nanoscience: Special Issue Dedicated to Professor Paul S. Weiss

Developing on-chip functional devices requires reliable fabrication methods with high resolution for miniaturization, desired components for enhanced performance, and high throughput for fast prototyping and mass production. Recently, laser-based bubble-pen lithography (BPL) has been developed to enable sub-micron linewidths, in situ synthesis of custom materials, and on-demand patterning for various functional components and devices. BPL exploits Marangoni convection induced by a laser-controlled microbubble to attract, accumulate, and immobilize particles, ions, and molecules onto different substrates. Recent years have witnessed tremendous progress in theory, engineering, and application of BPL, which motivated us to write this review. First, an overview of experimental demonstrations and theoretical understandings of BPL is presented. Next, we discuss the advantages of BPL and its diverse applications in quantum dot displays, biological and chemical sensing, clinical diagnosis, nanoalloy synthesis, and microrobotics. We conclude this review with our perspective on the challenges and future directions of BPL.

Hierarchical Porous Nanocellulose Aerogels Loaded with Metal-Organic Framework Particles for the Adsorption Application of Heterocyclic Aromatic Amines

This work overcomes the long-standing challenge of cumbersome pretreatment methods in the detection of heterocyclic aromatic amines (HAAs). A UiO-66/nanocellulose composite aerogel (CMC-CNC-UiO-66) with layered pores and low density prepared by a self-cross-linking method is applied as a simple and rapid adsorbent for capturing 14 HAAs via strong electrostatic interactions, van der Waals force, and the steric effect. The adsorption capacity of CMC-CNC-UiO-66 to 14 HAAs reached 98.00-188.00 nmol/mg at equilibrium within 10 min. The adsorption and desorption abilities of CMC-CNC-UiO-66 were retained with values of 93.36 and 97.34% after two cycles. In the meantime, the kinetics study demonstrated the chemisorption between HAA molecules and CMC-CNC-UiO-66 due to the excellent agreement with the pseudo-second-order adsorption models. The fit with the Freundlich isotherm models suggested a multilayer adsorption mechanism between HAA molecules and materials with heterogeneous surfaces. Moreover, coupled with the ultrahigh-performance liquid chromatography-tandem mass spectrometry detection, the CMC-CNC-UiO-66 extraction process can be completed with a high average recovery ranging from 86.68 to 115.33%, indicating a potential application of CMC-CNC-UiO-66 in HAA adsorption for further quantitative analysis.

Construction of a chiral zinc-camphorate framework for enantioselective separation

A chiral metal-organic framework (CMOF) with open chiral channels and multiple recognition sites is constructed from camphoric acid and a dipyridyl ligand. It can act as an efficient chiral solid adsorbent, capable of separating a variety of racemic alcohols and epoxides with excellent enantioselectivities.

Enantioseparation in Hierarchically Porous Assemblies of Homochiral Cages

Efficient enantioselective separation using porous materials requires tailored and diverse pore environments to interact with chiral substrates; yet, current cage materials usually feature uniform pores. Herein, we report two porous assemblies, PCC-60 and PCC-67, using isostructural octahedral cages with intrinsic microporous cavities of 1.5 nm. The PCC-67 adopts a densely packed mode, while the PCC-60 is a hierarchically porous assembly featuring interconnected 2.4 nm mesopores. Compared with PCC-67, the PCC-60 demonstrates excellent enantioselectivity and recyclability in separating racemic diols and amides. This solid adsorbent PCC-60 is further utilized as a chiral stationary phase for high-performance liquid chromatography (HPLC), enabling the complete separation of six valuable pharmaceutical intermediates. According to quantitative dynamic experiments, the hierarchical pores facilitate the mass transfer within the superstructure, shortening the equilibrium time for adsorbing chiral substrates. Notably, this hierarchically porous material PCC-60 indicates remarkably higher enantiomeric excess (ee) values in separating racemates than PCC-67 with uniform microporous cavities. Control experiments confirm that the presence of mesopores enables the PCC-60 to separate bulky substrates. These results uncover the traditionally underestimated role of hierarchical porosity in porous-superstructure-based enantioseparation.

Pillar-Layer Chiral MOFs as a Crystalline Platform for Circularly Polarized Luminescence and Single-Phase White-Light Emission

The construction of circularly polarized luminescence (CPL) materials with high porosity and high rigidity is still challenging. Herein, we propose a chiral reticular chemistry strategy to prepare the homochiral porous metal-organic frameworks (MOFs) as CPL-active materials. Two pairs of enantiomeric MOFs are synthesized through the self-assembly of chiral D/L-cam (DL-camphorates) and achiral fluorescent ligand TPB (1,2,4,5-tetra(pyridin-4-yl)benzene). The g_lum values of Cd-CMOF-D and Cd-CMOF-L were up to 0.010 and 0.009; the high g_lum values could be compared to those of the partially pure multicomponent self-assembly systems obtained by the complicated process. We further trace the generation and transfer of the hierarchical chirality from chiral molecule to 3D framework, demonstrating that the CPL was dominated by the original molecular chirality rather than the global chirality of the hierarchical structure. Moreover, the single-phase white-light materials with nearly ideal CIE coordinates (0.33, 0.33) were constructed through the introduction of dye emitters into Zn-CMOF (Zn-based chiral MOF). This work provided not only an insightful view of the chirality transfer and disappearance mechanism but also an efficient method for the preparation of the highly porous CPL materials.

Chiral Metal-Organic Frameworks

In the past two decades, metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) assembled from metal ions or clusters and organic linkers via metal-ligand coordination bonds have captivated significant scientific interest on account of their high crystallinity, exceptional porosity, and tunable pore size, high modularity, and diverse functionality. The opportunity to achieve functional porous materials by design with promising properties, unattainable for solid-state materials in general, distinguishes MOFs from other classes of materials, in particular, traditional porous materials such as activated carbon, silica, and zeolites, thereby leading to complementary properties. Scientists have conducted intense research in the production of chiral MOF (CMOF) materials for specific applications including but not limited to chiral recognition, separation, and catalysis since the discovery of the first functional CMOF (i.e., d- or l-POST-1). At present, CMOFs have become interdisciplinary between chirality chemistry, coordination chemistry, and material chemistry, which involve in many subjects including chemistry, physics, optics, medicine, pharmacology, biology, crystal engineering, environmental science, etc. In this review, we will systematically summarize the recent progress of CMOFs regarding design strategies, synthetic approaches, and cutting-edge applications. In particular, we will highlight the successful implementation of CMOFs in asymmetric catalysis, enantioselective separation, enantioselective recognition, and sensing. We envision that this review will provide readers a good understanding of CMOF chemistry and, more importantly, facilitate research endeavors for the rational design of multifunctional CMOFs and their industrial implementation.

A Stable Y(III)-Based Amide-Functionalized Metal-Organic Framework for Propane/Methane Separation and Knoevenagel Condensation

Here, a Y(III)-based metal-organic framework, JLU-MOF112 {[Y₃(μ₃-O)₂(μ₃-OH)(H₂O)₂(BTCTBA)₂]·2[(CH₃)₂NH₂]·5DMF·C₆H₅Cl·4H₂O}, has been successfully synthesized under solvothermal conditions. JLU-MOF112 was constructed with amide-functionalized tricarboxylate ligands and Y(III)-based infinite chains, where the Y₃ repeating units are arranged in a trans order. The overall framework could be viewed as a novel (3,5)-connected net with two types of channels along the [100] and [010] directions. JLU-MOF112 possesses a large BET surface area (1553 m² g^-1), a permanent pore volume (0.67 cm³ g^-1), and outstanding thermal and chemical stability, which give JLU-MOF112 potential for the purification of natural gas, especially the equimolar separation of C₃H₈/CH₄ with a high selectivity of 176. In addition, benefiting from the amide functional groups as Brønsted basic sites and the exposure of open metal sites as Lewis acid sites after activation, JLU-MOF112 can serve as a high-efficiency heterogeneous catalyst for Knoevenagel condensation by the reactions of malononitrile with benzaldehyde (yield of 98%, turnover number of 392, and turnover frequency of 3.27 min^-1) and diverse aldehyde compounds. A rational mechanism was put forward that the Knoevenagel condensation was catalyzed by the synergistic effect of the Lewis acid sites and Brønsted basic sites, engendering the polarization of the carbonyl groups and the deprotonation of the methylene groups for nucleophilic attack.