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

Preparation of gold nanoparticles decorated UiO-66-NH2 incorporated epichlorohydrin and cyclodextrin as novel efficient catalyst in cross coupling and carbonylative reactions

This study presents a new, highly effective, and reusable catalyst: UiO-66-NH2@Epichlorohydrin@Cyclodextrin@Au-NPs. This innovative catalyst starts with the Zr-based UiO-66 material, which is functionalized with amino groups (-NH2). We enhanced its surface compatibility by modifying it with epichlorohydrin and cyclodextrin via a post-synthesis modification method. Gold nanoparticles were then stabilized on this modified composite, resulting in the UiO-66-NH2@Epichlorohydrin@Cyclodextrin@Au-NPs complex. We used this catalyst for C-C coupling and Carbonylative Sonogashira reactions in mild conditions. Its effectiveness was underscored by various analytical techniques, including XRD, EDS, SEM, FT-IR, TEM, BET, ICP, TGA, and elemental mapping. The catalyst exhibited exceptional performance in Sonogashira, Heck, Suzuki coupling, and Carbonylative reactions, achieving good to excellent yields. It proved to be highly recyclable, maintaining its catalytic activity for up to nine cycles with minimal loss.

UiO-67-Typed Zr-MOFs Modified with Chiral Amine Alcohol Pendants for Adsorption Separation of Chiral Aromatic Alcohol Enantiomers

Robust UiO-67-typed Zr-HMOFs 1 and 2 (HMOFs = homochiral metal-organic frameworks) functionalized with isomeric chiral amine alcohol pendants, which have the same topology, but the relative positions between hydrogen-bonding sites and chiral carbons are different, were synthesized as adsorption platforms for the enantioseparation of 1-phenylethanol, 1-phenyl-2-propanol, and 2-phenyl-1-propanol. Both materials exhibited effective enantioseparation performance for the aforementioned alcohols. Particularly, 2 achieved an enantiomeric excess (ee) value of 96.4% for 1-phenylethanol, while 1 exhibited an exceptionally high ee value of 99.6% for 2-phenyl-1-propanol, ranking among the highest ee values reported for HMOFs. Based on the experimental results and host-guest structure analysis, it can be inferred that the higher the similarity of groups directly bonded to the chiral carbon in Zr-HMOFs and substrate, the better the performance of enantioseparation. Replacing the chiral ligand in material 1 with an achiral ligand with the same skeleton, four 1@x % (x % being the molar percentage of chiral ligand used during synthesis) materials were synthesized to explore the impact of the framework's pore size and chiral active site concentration on enantiomeric separation performance. The results showed that 1@50% had the highest adsorption capacity and ee value for 1-phenylethanol, which were 47.7 mg g-1 and 98.6%, respectively.

Mechanisms for translating chiral enantiomers separation research into macroscopic visualization

Chirality is a common phenomenon in nature, including the dominance preference of small biomolecules, the special spatial conformation of biomolecules, and the biological and physiological processes triggered by chirality. The selective chiral recognition of molecules in nature from up-bottom or bottom-up is of great significance for living organisms. Such as the transcription of DNA, the recognition of membrane proteins, and the catalysis of enzymes all involve chiral recognition processes. The selective recognition between these macromolecules is mainly achieved through non covalent interactions such as hydrophobic interactions, ammonia bonding, electrostatic interactions, metal coordination, van der Waals forces, and π-π stacking. Researchers have been committed to studying how to convert this weak non covalent interaction into macroscopic visualization, which has further understood of the interactions between chiral molecules and is of great significance for simulating the interactions between molecules in living organisms. This article reviews several models of chiral recognition mechanisms, the interaction forces involved in the chiral recognition process, and the research progress of chiral recognition mechanisms. The outlook in this review points out that studying chiral recognition interactions provides an important bridge between chiral materials and the life sciences, providing an ideal platform for studying chiral phenomena in biological systems.

From individuals to families: design and application of self-similar chiral nanomaterials

Establishing an intimate relationship between similar individuals is the beginning of self-extension. Various self-similar chiral nanomaterials can be designed using an individual-to-family approach, accomplishing self-extension. This self-similarity facilitates chiral communication, transmission, and amplification of synthons. We focus on describing the marriage of discrete cages to develop self-similar extended frameworks. The advantages of utilizing cage-based frameworks for chiral recognition, enantioseparation, chiral catalysis and sensing are highlighted. To further promote self-extension, fractal chiral nanomaterials with self-similar and iterated architectures have attracted tremendous attention. The beauty of a fractal family tree lies in its ability to capture the complexity and interconnectedness of a family's lineage. As a type of fractal material, nanoflowers possess an overarching importance in chiral amplification due to their large surface-to-volume ratio. This review summarizes the design and application of state-of-the-art self-similar chiral nanomaterials including cage-based extended frameworks, fractal nanomaterials, and nanoflowers. We hope this formation process from individuals to families will inherit and broaden this great chirality.

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

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

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.

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.

High-Enantioselectivity Adsorption Separation of Racemic Mandelic Acid and Methyl Mandelate by Robust Chiral UiO-68-Type Zr-MOFs

Mandelic acid and its analogues are highly valuable medical intermediates and play an important role in the pharmaceutical industry, biochemistry, and life sciences. Therefore, effective enantioselective recognition and separation of mandelic acid are of great significance. In this study, two of our recently reported chiral amine-alcohol-functionalized UiO-68-type Zr-HMOFs 1 and 3 with high chemical stability, abundant binding sites, and large chiral pores were selected as chiral selectors for the enantioselective separation of mandelic acid (MA), methyl mandelate (MM), and other chiral molecules containing only one phenyl. Materials 1 and 3 exhibited excellent enantioselective separation performance for MA and MM. Especially for the separation of racemate MA, the enantiomeric excess values reached 97.3 and 98.9%, which are the highest reported values so far. Experimental and density functional theory (DFT) computational results demonstrated that the introduction of additional phenyls on the chiral amine alcohol pendants in 3 had somewhat impact on the enantioselective adsorption and separation of MA or MM compared with 1, but it was not significant. Further research on the enantioselective separation of those chiral adsorbates containing only one phenyl by material 1 indicated the crucial role of the groups directly bonded to the chiral carbons of the adsorbates in the selective separation of enantiomers, especially showing higher enantioselectivity for the adsorbates with two hydrogen-bonding groups directly bonded to its chiral carbon.

Strategies for chiral separation: from racemate to enantiomer

Chiral separation has become a crucial topic for effectively utilizing superfluous racemates synthesized by chemical means and satisfying the growing requirements for producing enantiopure chiral compounds. However, the remarkably close physical and chemical properties of enantiomers present significant obstacles, making it necessary to develop novel enantioseparation methods. This review comprehensively summaries the latest developments in the main enantioseparation methods, including preparative-scale chromatography, enantioselective liquid-liquid extraction, crystallization-based methods for chiral separation, deracemization process coupling racemization and crystallization, porous material method and membrane resolution method, focusing on significant cases involving crystallization, deracemization and membranes. Notably, potential trends and future directions are suggested based on the state-of-art "coupling" strategy, which may greatly reinvigorate the existing individual methods and facilitate the emergence of cross-cutting ideas among researchers from different enantioseparation domains.