Correction to “A Chiral Hierarchical Helical Covalent Organic Framework for Enantiomeric Separation”

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.

Comprehensive SummaryThe preparation and resolution of chiral molecules hold significant importance in scientific and industrial domains, such as drug development and manufacturing. In recent years, chiral porous frameworks have attracted increasing attention in asymmetric catalysis and enantiomer resolution due to their excellent performance. The metal‐organic frameworks (MOFs), covalent organic frameworks (COFs), porous organic cages (POCs), and porous coordination cages (PCCs) are important representative of the porous framework family. Significantly, chirality can be easily introduced into these framework materials through simple bottom‐up or post‐modification methods, thereby promoting their applications related to chirality. In this review, we systematically summarize the synthesis strategies of four classes of chiral framework materials and their applications in asymmetric catalysis and enantiomeric resolution. Finally, we present some perspectives on the future development in chiral porous frameworks. Key ScientistsSignificant progress has been made in the development of chiral porous frameworks, primarily driven by the application of chiral molecules. This area of research has seen contributions from many distinguished scientists. A particularly important milestone was reached in 2000, when Kimoon Kim reported the first catalytic Chiral Metal‐Organic Framework (CMOF). In 2001, Lin et al. reported a new generation of recyclable CMOF capable of chiral separation and heterogeneous catalysis. Simultaneously, researchers such as Cui and Duan have made substantial contributions, advancing the field considerably. Furthermore, notable developments have been made in the area of Chiral Covalent Organic Frameworks (CCOFs), with pioneering work by researchers like Jiang, Wang, and Cui. Meanwhile, some groups such as Su and Li have made significant strides in the chiral cages. These remarkable accomplishments have drawn considerable interest.

A Gold Quartet Framework with Reversible Anisotropic Structural Transformation Accompanied by Luminescence Response

Chiral nanostructures hold transformative potential across diverse fields, yet their assembly construction remains hindered by the high entropic barrier of dissymmetric building units. Inspired by biological structural dynamics, we construct two chiral copper-based hydrogen-bonded frameworks [D(L)-Cu-crystals] via hydrogen-bonded assembly using chiral metal-organic helical as the building unit. Single-crystal X-ray diffraction elucidates hierarchical chirality evolution from asymmetric coordinations to helical chains and framework packing. Furthermore, disassembling D(L)-Cu-crystals yields corresponding single-unit chiral metal-organic helices [D(L)-Cu-SMOHs], fully exposed active sites and well-preserved helical architectures. Notably, D(L)-Cu-SMOHs inhibit amyloid fibrillization effectively with pronounced chirality discrimination, driven by entropy-favored hydrophobic interaction. Molecular docking reveals that D-Cu-SMOH exhibits enhanced binding to critical amyloidogenic regions relative to the L-enantiomer. This work establishes a dynamic and reversible assembly-disassembly approach applicable for constructions of chiral nanomaterials. Moreover, it provides insights into understanding enantioselective amyloid inhibition, extending applications in asymmetric catalysis, enantioselective separation and chiroptical devices.

Comprehensive SummaryChiral covalent organic frameworks (COFs) have shown promising applications in asymmetric catalysis, enantiomer separation and chiral recognition due to their tunable structures and permanent porosity. Currently, synthesis of chiral COFs mainly relies on direct‐ synthesis method which requires asymmetric monomers to polymerize and crystallize with symmetric monomers and post‐synthesis method which has been greatly limited to having complete reactions with the micro‐/meso‐sized pores of COFs. Recently, the synthesis of two‐dimensional COFs by covalent replacement of chiral competitor has been reported. Herein, we present the synthesis of three types of 3D COFs with tunable chirality using chiral amino acid derivative surfactant as inducer in water under ambient conditions. The hydrogen bonds and electrostatic interactions between amino acid derivative surfactant and monomers as well as their precursors facilitate the transfer of the chirality.

Integrating Superwettability within Covalent Organic Frameworks for Functional Coating

Chiral porous organic frameworks have emerged in the last decade as candidates for heterogeneous asymmetric organocatalysis. This review aims to provide a summary of the synthetic strategies towards the design of chiral organic materials, the characterization techniques used to evaluate their chirality, and their applications in asymmetric organocatalysis. We briefly describe the types of porous organic frameworks, including crystalline (covalent organic frameworks, COFs) and amorphous (conjugated microporous polymers, CMPs; covalent triazine frameworks, CTFs and porous aromatic frameworks, PAFs) materials. Furthermore, the strategies reported to incorporate chirality in porous organic materials are presented. We finally focus on the applications of chiral porous organic frameworks in asymmetric organocatalytic reactions, summarizing and categorizing all the available literature in the field.

Covalent organic frameworks (COFs) are a class of ordered porous organic material formed via the covalent bonding among various organic monomers. Recently, studies of chiral COFs have attracted great attention because chirality plays an important role in medicine, pharmacy and agriculture, and chiral COFs possess many fascinating characteristics like inherent porosity, tunable pore size, structural periodicity, high stability and reusability. Ascribed to the great advantages of chiral COFs, they demonstrate many potential applications in asymmetrical catalysis, asymmetrical separation and so on. One strategy to construct chiral COFs is using multifarious chiral building blocks to directly prepare chiral COFs. Various chiral COFs structures can be designed via choosing different building blocks and adding functional groups to monomers. An alternative strategy to construct chiral COFs is to incorporate metal particles or organic species into COFs via post-synthetic modifications.

Chiral covalent organic framework materials have many excellent properties, which have received much attention in the field of separation. Synthesized the covalent organic framework COF-TpBD (NH2 )2 modified, respectively, by L-valine trifluoroacetyl derivative, L-hydroxyproline, and (1S)-(+)-10-camphorsulfonyl chloride, three capillary columns of chiral covalent organic framework materials were obtained for gas chromatography. Those columns are able to separate some chiral compounds, positional isomers, n-alkanes, n-alcohols, aromatic hydrocarbon mixture, and Grob's reagents. They are complementary to other chiral capillary columns and are possible for potential applications.

Covalent organic frameworks (COFs) represent an emerging class of crystalline porous materials that are constructed by the assembly of organic building blocks linked via covalent bonds. Several strategies have been developed for the construction of new COF structures; however, a facile approach to fabricate hierarchical COF architectures with controlled domain structures remains a significant challenge, and has not yet been achieved. In this study, a dynamic covalent chemistry (DCC)-based postsynthetic approach was employed at the solid-liquid interface to construct such structures. Two-dimensional imine-bonded COFs having different aromatic groups were prepared, and a homogeneously mixed-linker structure and a heterogeneously core-shell hollow structure were fabricated by controlling the reactivity of the postsynthetic reactions. Solid-state nuclear magnetic resonance (NMR) spectroscopy and transmission electron microscopy (TEM) confirmed the structures. COFs prepared by a postsynthetic approach exhibit several functional advantages compared with their parent phases. Their Brunauer-Emmett-Teller (BET) surface areas are 2-fold greater than those of their parent phases because of the higher crystallinity. In addition, the hydrophilicity of the material and the stepwise adsorption isotherms of H2O vapor in the hierarchical frameworks were precisely controlled, which was feasible because of the distribution of various domains of the two COFs by controlling the postsynthetic reaction. The approach opens new routes for constructing COF architectures with functionalities that are not possible in a single phase.

Covalent organic frameworks (COFs) have undergone extensive research as heterogeneous catalysts for a wide range of significant reactions, but they have not yet been investigated in the realm of electrochemical asymmetric catalysis, despite their recognition as an economical and sustainable strategy for producing enantiopure compounds. Here, we report a mixed-linker strategy to design multicomponent two-dimensional (2D) chiral COFs with tunable layer stacking for highly enantioselective electrocatalysis. By crystallizing mixtures of triamines with and without the MacMillan imidazolidinone catalyst or aryl substituent (ethyl and isopropyl) and a dialdehyde derivative of thieno-[3,2-b]thiophene, we synthesized and structurally characterized a series of three-component homochiral 2D COFs featuring either AA or ABC stacking. The stacking modes that can be synthetically controlled through steric tuning using different aryl substituents affect their chemical stability and electrochemical performance. With the MacMillan catalyst periodically appended on their channels, all three COFs with conductive thiophene moieties can be highly enantioselective and recyclable electrocatalysts for the asymmetric α-arylation of aldehydes, affording alkylated anilines with up to 97% enantiomeric excess by an anodic oxidation/organocatalytic protocol. Presumably due to their higher charge transfer ability, the ABC stacking COFs exhibit improved reactivity compared to the AA stacking analogue. This work therefore advances COFs as electrocatalysts for asymmetric catalysis and may facilitate the design of more redox-active crystalline organic polymers for electrochemical enantioselective processes.

Network interpenetration plays a crucial role in functionalizing porous framework materials. However, controlling the degree of interpenetration in covalent organic frameworks (COFs) to influence their pore sizes, shapes, and functionalities still remains a significant challenge. Here, we demonstrate a steric tuning strategy to control the degree of COF interpenetration and modulate their physicochemical properties. By imine condensations of 1,1'-bi-2-naphthol-derived tetraaldehydes bearing different alkyl substituents with the monomer tetra(p-aminophenyl)-methane, we synthesized and characterized a family of two-component and three-component chiral COFs with different interpenetrated dia networks. The alkyl groups are periodically appended on the pore walls, and their types/contents that can be synthetically tuned control the interpenetration degree of COFs by minimizing repulsive interactions between the alkyl groups. Specifically, the COF with -OH groups adopts an interpenetrated dia-c5 topology, those with -OMe/-OEt groups take an interpenetrated dia-c4 topology, whereas those with the bulky -OnPr/-OnBu groups exhibit a noninterpenetrated dia-c1 topology. The multivariate COFs with both -OH and -OnBu groups display either a noninterpenetrated or dia-c5 topology, depending on the proportion of -OnBu groups. The extent of interpenetration in COFs significantly affects their porosity, thermal stability, and chemical stability, resulting in varying selective performances in the adsorption and separation of dyes and asymmetric catalysis. This work highlights the potential of using steric hindrance to tune and control interpenetration, porosity, stability, and functionalities of COFs materials, broadening the range of their applications.

Mercapto-β-cyclodextrin covalent organic frameworks for enantioselective liquid-liquid extraction

A new approach to the preparation of enantioselective porous polymer monolithic columns with incorporated chiral metal-organic framework for nano-liquid chromatography has been developed. While no enantioseparation was achieved with monolithic poly(4-vinylpyridine-co-ethylene dimethacrylate) column, excellent separations of both enantiomers of (±)-methyl phenyl sulfoxide were achieved with its counterpart prepared after admixing metal-organic framework [Zn2 (benzene dicarboxylate)(l-lactic acid)(dmf)], which is synthesized from zinc nitrate, l-lactic acid, and benzene dicarboxylic acid in the polymerization mixture. These novel monolithic columns combined selectivity of the chiral framework with the excellent hydrodynamic properties of polymer monoliths, may provide a great impact on future studies in the field of chiral analysis by liquid chromatography.

Although several studies related with the electrochemiluminescence (ECL) technique have been reported for chiral discrimination, it still has to face some limitations, namely, complex synthetic pathways and a relatively low recognition efficiency. Herein, this study introduces a facile strategy for the synthesis of ECL-active chiral covalent organic frameworks (COFs) employed as a chiral recognition platform. In this artificial structure, ruthenium(II) coordinated with the dipyridyl unit of the COF and enantiopure cyclohexane-1,2-diamine was harnessed as the ECL-active unit, which gave strong ECL emission in the presence of the coreactant reagent (K2S2O8). When the as-prepared COF was used as a chiral ECL-active platform, clear discrimination was observed in the response of the ECL intensity toward l- and d-enantiomers of amino acids, including tryptophan, leucine, methionine, threonine, and histidine. The biggest ratio of the ECL intensity between different configurations was up to 1.75. More importantly, a good linear relationship between the enantiomeric composition and the ECL intensity was established, which was successfully employed to determine the unknown enantiomeric compositions of the real samples. In brief, we believe that the proposed ECL-based chiral platform provides an important reference for the determination of the configuration and enantiomeric compositions.