Homochiral metal-organic frameworks for enantioseparation

A Novel Cerium(IV)-Based Metal-Organic Framework for CO2 Chemical Fixation and Photocatalytic Overall Water Splitting

Cerium (IV)-based metal-organic frameworks (MOFs) are highly desirable due to their unique potential in fields such as redox catalysis and photocatalysis. However, due to the high reduction potential of Ce^IV species in solution, it is still a great challenge to synthesize Ce^IV -MOFs with novel structures, which are extremely dominated by the hexanuclear Ce-O cluster inorganic building units (IBUs). Herein, a Ce-O IBU chain containing Ce^IV -MOF, CSUST-3 (CSUST: Changsha University of Science and Technology), was successfully prepared using the kinetic stabilization study of UiO-66(Ce)-NDC (H₂ NDC=2,6-naphthalenedicarboxylic acid). Furthermore, owing to the superior redox activity, Lewis acidity and semiconductor-like behavior owing to Ce⁴⁺ , activated CSUST-3 was demonstrated to be an excellent catalyst for CO₂ chemical fixation. One-pot synthesis of styrene carbonate from styrene and CO₂ was achieved under mild conditions (1 atm CO₂ , 80 °C, and solvent free). Moreover, activated CSUST-3 was shown to be a remarkable co-catalyst-free photocatalyst for overall water splitting (OWS), rendering 59 μmol g^-1  h^-1 of H₂ and 22 μmol g^-1  h^-1 of O₂ under simulated sunlight irradiation (Na₂ S-Na₂ SO₃ as sacrificial agent).

A biomimetic metal–organic framework with cuboid inner cavities for enantioselective separation

A biomimetic metal–organic framework with cuboid inner cavities and multiple recognition sites was constructed from a phenylalanine-derived ligand. It can enantioselectively separate various racemic alcohols, diols and epoxides with ee up to 99.5%.

Enantioselective chiral sorption of 1-phenylethanol by homochiral 1D coordination polymers

Enantiomeric selectivity is shown within the pores of a 1D coordination polymer, dependent on the nature of the pore space.

Homochiral porous coordination polymer of EuIII for metal ion sensing and enantioselective adsorption

A novel multifunctional homochiral porous metal–organic framework was obtained by combining the luminescent component Eu(iii) with an enantiopure triangular polycarboxylic ligand.

Syntheses of New Zeolitic Imidazolate Frameworks in Dimethyl Sulfoxide

Presented here are the syntheses of ZIFs in dimethyl sulfoxide (DMSO). A series of new ZIFs with various topologies such as ACO, coi, zni, ANA, GIS, even new topology can...

Stepwise synthesis of Zr-based metal–organic frameworks: incorporating a trinuclear zirconocene-based metallo-pyridine ligand

Based on a presynthesized Zr3 precursor, two isostructural 2D heterometallic ZrMOFs have been synthesized by a step synthesis strategy.

Synthesis of a novel chiral DA-TD covalent organic framework for open-tubular capillary electrochromatography enantioseparation

Herein, a novel chiral covalent organic framework, DA-TD COF, with good chemical/thermal stability was synthesized and used as a chiral stationary phase for open-tubular capillary electrochromatography enantioseparation. The DA-TD COF coated capillary exhibited excellent enantioseparation efficiency and its separation efficiency did not show an obvious decrease over 200 runs. Furthermore, the enantioseparation mechanism was studied.

A new two-dimensional folding sheet-like coordination polymer assembled from cadmium(II) and (S)-2-(benzylamino)succinic acid: synthesis, structure and properties

A new two-dimensional (2D) coordination polymer, namely, poly[[diaqua[μ₃-(S)-2-(benzylamino)succinato-κ⁴N,O¹:O^1':O⁴]cadmium(II)] monohydrate], {[Cd(C₁₁H₁₁NO₄)(H₂O)₂]·H₂O}_n, has been synthesized by the solvothermal reaction of Cd(CH₃COO)₂·2H₂O with the synthesized ligand (S)-2-(benzylamino)succinic acid (H₂L). The title compound has been structurally characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction analysis. In the crystal structure, each Cd^II cation binds to three carboxylate groups from three symmetry-related L^2- dianions. The tetradentate L^2- ligand links three symmetry-related Cd^II cations into a 2D folding sheet, which can be simplified as a uninodal (3,3)-connected hcb net with the point symbol (6³). In the lattice, all the folding sheets are arranged in an interdigitated fashion and aggregate into zipper-like arrays through interlayer π-π interactions. The large and nonpolar side chain may play an important role in the formation and aggregation of the 2D sheet. The thermal stability and photoluminescence properties of the title compound were investigated, and it exhibits a blue emission with a quantum yield of 8%.

Artificial Metal-Peptide Assemblies: Bioinspired Assembly of Peptides and Metals through Space and across Length Scales

The exploration of chiral crystalline porous materials, such as metal-organic complexes (MOCs) or metal-organic frameworks (MOFs), has been one of the most exciting recent developments in materials science owing to their widespread applications in enantiospecific processes. However, achieving specific tight-affinity binding and remarkable enantioselectivity toward important biomolecules is still challenging. Perhaps most critically, the lack of adaptability, compatibility, and processability in these materials severely impedes practical applications in chemical engineering and biological technology. In this Perspective, artificial metal-peptide assemblies (MPAs), which are achieved by the assembly of peptides and metals with nanometer-sized cavities or pores, is a new development that could address the current bottlenecks of chiral porous materials. Bioinspired assembly of pore-forming MPAs is not foreign to biological systems and has granted scientists an unprecedented level of control over the chiral recognition sites, conformational flexibility, cavity sizes, and hydrophilic segments through ultrafine-tuning of peptide-derived linkers. We will specifically discuss exemplary MPAs including structurally well-defined metal-peptide complexes and highly crystalline metal-peptide frameworks. With insights from these structures, the peptide assembly and folding by the closer cooperation of metal coordination and noncovalent interactions can create adaptable protein-like nanocavities undergoing a myriad of conformational variations that is reminiscent of enzymatic pockets. We also consider challenges to advancing the field, where the deployment of side-chain groups and manipulation of amino acid sequences are more likely to access the programmable, genetically encodable peptide-mediated porous materials, thus contributing to the enhanced enantioselective recognition as well as enabling key biochemical processes in next-generation versatile biomimetic materials.

The Synthesis and Properties of TIPA-Dominated Porous Metal-Organic Frameworks

Metal-Organic Frameworks (MOFs) as a class of crystalline materials are constructed using metal nodes and organic spacers. Polydentate N-donor ligands play a mainstay-type role in the construction of metal-organic frameworks, especially cationic MOFs. Highly stable cationic MOFs with high porosity and open channels exhibit distinct advantages, they can act as a powerful ion exchange platform for the capture of toxic heavy-metal oxoanions through a Single-Crystal to Single-Crystal (SC-SC) pattern. Porous luminescent MOFs can act as nano-sized containers to encapsulate guest emitters and construct multi-emitter materials for chemical sensing. This feature article reviews the synthesis and application of porous Metal-Organic Frameworks based on tridentate ligand tris (4-(1H-imidazol-1-yl) phenyl) amine (TIPA) and focuses on design strategies for the synthesis of TIPA-dominated Metal-Organic Frameworks with high porosity and stability. The design strategies are integrated into four types: small organic molecule as auxiliaries, inorganic oxyanion as auxiliaries, small organic molecule as secondary linkers, and metal clusters as nodes. The applications of ratiometric sensing, the adsorption of oxyanions contaminants from water, and small molecule gas storage are summarized. We hope to provide experience and inspiration in the design and construction of highly porous MOFs base on polydentate N-donor ligands.

Porphyrin Based 2D-MOF Structures as Dual-Kinetic Sorafenib Nanocarriers for Hepatoma Treatment

The existing clinical protocols of hepatoma treatment require improvement of drug efficacy that can be achieved by harnessing nanomedicine. Porphyrin-based, paddle-wheel framework (PPF) structures were obtained and tested as dual-kinetic Sorafenib (SOR) nanocarriers against hepatoma. We experimentally proved that sloughing of PPF structures combined with gradual dissolving are effective mechanisms for releasing the drug from the nanocarrier. By controlling the PPF degradation and size of adsorbed SOR deposits, we were able to augment SOR anticancer effects, both in vitro and in vivo, due to the dual kinetic behavior of SOR@PPF. Obtained drug delivery systems with slow and fast release of SOR influenced effectively, although in a different way, the cancer cells proliferation (reflected with EC50 and ERK 1/2 phosphorylation level). The in vivo studies proved that fast-released SOR@PPF reduces the tumor size considerably, while the slow-released SOR@PPF much better prevents from lymph nodes involvement and distant metastases.

Two Isostructural Titanium Metal-Organic Frameworks for Light Hydrocarbon Separation

Presented here is the light hydrocarbon separation of titanium metal-organic frameworks (Ti-MOFs). Compared with the cyclic Ti-oxo cluster (Ti₈O₈(CO₂)₁₆, Ti₈Ph), porous structures of FIR-125 and FIR-126 (FIR = Fujian Institute Research) can effectively improve the adsorption amounts of light hydrocarbons. The introduction of different functional groups and Ti-oxo clusters with small window sizes enables them to exhibit the highly selective separation of C₂ and C₃ hydrocarbons versus methane in an ambient atmosphere. The results show that Ti-MOFs are potential porous adsorbents for the separation of light hydrocarbons.

Fabrication of Homochiral Metal-Organic Frameworks in TiO2 Nanochannels for In Situ Identification of 3,4-Dihydroxyphenylalanine Enantiomers

Enantioselective identification of chiral molecules is important for biomedical and pharmaceutical research. However, owing to identical molecular formulas and chemical properties of enantiomers, signal transduction and amplification are still the two major challenges in chiral sensing. In this study, we developed an enantioselective membrane by integrating homochiral metal-organic frameworks (MOFs) with nanochannels for the sensitive identification and quantification of chiral compounds. The membrane was designed using a TiO₂ nanochannel membrane (TiNM) as the metal ion precursor of MOFs (using MIL-125(Ti)) and incorporating l-glutamine (l-Glu) into the framework of MIL-125(Ti). Using 3,4-dihydroxyphenylalanine (DOPA) as the model analyte, the as-prepared homochiral l-Glu/MIL-125(Ti)/TiNM exhibits a remarkable chiral recognition to d-DOPA than l-DOPA. More importantly, benefiting from the highly enlarged surface area and confinement effect provided by the MOFs-in-nanochannel architecture, the discrimination for chiral recognition is largely amplified through the chelation interaction of Fenton-like activity of Fe³⁺ onto DOPA. Using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) as the substrate, the positively charged ABTS^•+ product via Fenton-like reaction induces significant ionic transport changes in nanochannels, which in turn provides information about chiral recognition. This innovative signal amplification strategy on homochiral nanochannels might pave a new way for sensitive monitoring and chiral recognition.

Factors Affecting Hydrogen Adsorption in Metal-Organic Frameworks: A Short Review

Metal–organic frameworks (MOFs) have significant potential for hydrogen storage. The main benefit of MOFs is their reversible and high-rate hydrogen adsorption process, whereas their biggest disadvantage is related to their operation at very low temperatures. In this study, we describe selected examples of MOF structures studied for hydrogen adsorption and different factors affecting hydrogen adsorption in MOFs. Approaches to improving hydrogen uptake are reviewed, including surface area and pore volume, in addition to the value of isosteric enthalpy of hydrogen adsorption. Nanoconfinement of metal hydrides inside MOFs is proposed as a new approach to hydrogen storage. Conclusions regarding MOFs with incorporated metal nanoparticles, which may be used as nanoscaffolds and/or H₂ sorbents, are summarized as prospects for the near future.