Heterogeneous catalysis with encapsulated haem and other synthetic porphyrins: Harnessing the power of porphyrins for oxidation reactions

Encapsulated metalloporphyrins have been widely studied for their use as efficient heterogeneous catalysts, inspired by the known catalytic activity of porphyrins in haemoproteins. The oxidation of organic substrates by haemoproteins is one of the well-known roles of these proteins, in which the haem (ferriprotoporphyrin IX = FePPIX) cofactor is the centre of reactivity. While these porphyrins are highly efficient catalysts in the protein environment, once removed, they quickly lose their reactivity. It is for this reason that they have garnered much interest in the field of heterogeneous catalysis of oxidation reactions. This review details current research in the field, focusing on the application of encapsulated haem, and other synthetic metalloporphyrins, applied to oxidation reactions.

Sequence-Dependent Peptide Surface Functionalization of Metal-Organic Frameworks

We report a noncovalent surface functionalization technique for water-stable metal-organic frameworks using short peptide sequences identified via phage display. Specific frameworks-binding peptides were identified for crystalline Zn(MeIM)₂ (MeIM: 2-methylimidazole, ZIF-8), semiamorphous Fe-BTC (BTC: 1,3,5-benzene-tricarboxylate), and Al(OH)(C₄H₂O₄) (MIL-53(Al)-FA, FA: fumaric acid), and their thermodynamic binding affinities and specificities were measured. Electron microscopy, powder X-ray diffraction, and gas adsorption analysis confirmed that the peptide-functionalized frameworks retained similar characteristics compared to their as-synthesized counterparts. Confocal laser-scanning microscopy demonstrated that peptide was localized on the surface of the frameworks, whereas surface area measurements showed no evidence of pore blockage. Finally, we measured the pH-dependent release of fluorescein from peptide-functionalized frameworks and discovered that peptide binding can attenuate fluorescein release by improving framework stability under low pH conditions. Our results demonstrate that phage display can be used as a general method to identify specific peptide sequences with strong binding affinity to water-stable metal-organic frameworks and that these peptides can alter drug release kinetics by affecting framework stability in aqueous environments.

Catalytic Transfer Hydrogenation of Biomass-Derived Carbonyls over Hafnium-Based Metal-Organic Frameworks

A series of highly crystalline, porous, hafnium-based metal-organic frameworks (Hf-MOFs) have been shown to catalyze the transfer hydrogenation reaction of levulinic ester to produce γ-valerolactone by using isopropanol as a hydrogen donor. The results are compared with their zirconium-based counterparts. The role of the metal center in Hf-MOFs has been identified and reaction parameters optimized. NMR studies using isotopically labeled isopropanol provide evidence that the transfer hydrogenation occurs through a direct intermolecular hydrogen transfer route. The catalyst, Hf-MOF-808, can be recycled several times with only a minor decrease in catalytic activity. The generality of the procedure has been demonstrated by accomplishing the transformation with aldehydes, ketones, and α,β-unsaturated carbonyl compounds. The combination of Hf-MOF-808 with the Brønsted-acidic Al-Beta zeolite gives the four-step one-pot transformation of furfural to γ-valerolactone in good yield of 75 %.

Epoxy Nanocomposites Containing Zeolitic Imidazolate Framework-8

Zeolitic imidazole framework-8 (ZIF-8) is utilized as a functional filler and a curing agent in the preparation of epoxy nanocomposites. The imidazole group on the surface of the ZIF-8 initiates epoxy curing, resulting in covalent bonding between the ZIF-8 crystals and epoxy matrix. A substantial reduction in dielectric constant and increase in tensile modulus were observed. The implication of the present study for utilization of metal-organic framework to improve physical and mechanical properties of polymeric matrixes is discussed.

Crystallization and structural properties of a family of isotopological 3D-networks: the case of a 4,4′-bipy ligand–M2+ triflate system

Desolvation process characterization of a flexible coordination network performed by time-resolved single-crystal X-ray diffraction. Influence of the metal centre on the network stability.

Growth-modulating agents for the synthesis of Al-MOF-type materials based on assembled 1D structural subdomains

Specific long-alkyl aromatic mono-carboxylate linkers, combined with metallic nodes, favors the formation of 1D metalorganic nanoribbon-type structural sub-units which are assembled to generate novel organized Al-MOF-type solids.

Structure activity relationships in metal–organic framework catalysts for the continuous flow synthesis of propylene carbonate from CO2 and propylene oxide

Studies of MOF catalysts under continuous flow have led to the discovery of a new catalyst for carbonation of propylene oxide.

Synthesis of core–shell ZIF-67@Co-MOF-74 catalyst with controllable shell thickness and enhanced photocatalytic activity for visible light-driven water oxidation

Core–shell ZIF-67@Co-MOF-74 catalysts with improved photocatalytic properties were synthesized via the ligand exchange method.

An efficient and sustainable catalytic reduction of carbon–carbon multiple bonds, aldehydes, and ketones using a Cu nanoparticle decorated metal organic framework

Economical, reusable, eco-friendly sustainable process is reported that involve low amount of hydrazine hydrate.

An efficient halometallate ionic liquid functionalized mesoporous ZSM-5 for the reduction of carbon–carbon multiple bonds

Bi-functional activity and highly dispersed active sites present in halometallate ionic liquid functionalized mesoporous ZSM-5 makes it a unique and superior catalyst compared to various other catalysts reported in the literature.

Influence of nanoscale structuralisation on the catalytic performance of ZIF-8: a cautionary surface catalysis study

Nanoscale structuralisation is demonstrated to influence the stability and catalytic properties of zeolitic imidazolate framework-8.

Synthesis of glycerol carbonate over a 2D coordination polymer built with Nd3+ions and organic ligands

The production of glycerol carbonate from glycerol and urea using a 2D coordination polymer as the heterogeneous catalyst.

A Co-MOF nanosheet array as a high-performance electrocatalyst for the oxygen evolution reaction in alkaline electrolytes

A Co-MOF nanosheet array on Ni foam (Co-MOF/NF) acts as a superior electrocatalyst for the oxygen evolution reaction, needing an overpotential of only 311 mV to drive a geometrical catalytic current density of 50 mA cm⁻² in 1.0 M KOH.

Copper-catalyzed oxidative coupling of arylboronic acids with aryl carboxylic acids: Cu3(BTC)2 MOF as a sustainable catalyst to access aryl esters

A straightforward and sustainable methodology for the synthesis of commercially important aryl esters via a C–O cross-coupling reaction was demonstrated using the Cu₃(BTC)₂ metal–organic framework.

Zwitterionic Manganese and Gadolinium Metal-Organic Frameworks as Efficient Contrast Agents for in Vivo Magnetic Resonance Imaging

Two water-stable three-dimensional Mn- and Gd-based metal-organic frameworks (MOFs), {[Mn₂(Cmdcp)₂(H₂O)₂]·H₂O}_n (1) and {[Gd(Cmdcp)(H₂O)₃](NO₃)·3H₂O}_n (2, H₃CmdcpBr = N-(4-carboxy benzyl)-(3,5-dicarboxyl)pyridinium bromide), have been prepared and analyzed. In vitro magnetic resonance imaging indicated that MOFs 1 and 2 possess relaxivity r₁ values of 17.50 and 13.46 mM^-1·S^-1, respectively, which are superior to that of the control Gd-DTPA (r₁ = 4.87 mM^-1·S^-1, DTPA = diethylene triamine pentaacetate). MOFs 1 and 2 also possessed good biocompatibility and low cytotoxicity against a model cell line. In vivo magnetic resonance images of treated Kunming mice indicated that kidneys showed remarkably positive signal enhancement after 15 min with intravenous administration of MOF 1 and the hyperintensity of both kidneys persisted for about 240 min with no obvious tissue damage. MOF 1 is therefore promising in vivo probes for imaging intravascular diseases and renal dysfunction.

Greening the Processes of Metal-Organic Framework Synthesis and their Use in Sustainable Catalysis

Given the shortage of sustainable resources and the increasingly serious environmental issues in recent decades, the demand for clean technologies and sustainable feedstocks is of great interest to researchers worldwide. With regard to the fields of energy saving and environmental remediation, the key point is the development of efficient catalysts, not only in terms of facile synthesis methods, but also the benign utilization of such catalysts. This work reviews the use of metal-organic frameworks (MOFs) and MOF-based materials in these fields. The definition of MOFs and MOF-based materials will be primarily introduced followed by a brief description of the characterization and stability of MOF-related materials under the applied conditions. The greening of MOF synthesis processes will then be discussed and catalogued by benign solvents and conditions and green precursors of MOFs. Furthermore, their suitable application in sustainable catalysis will be summarized, focusing on several typical atom-economic reactions, such as the direct introduction of H₂ or O₂ and C-C bond formation. Approaches towards reducing CO₂ emission by MOF-based catalysts will be described with special emphasis on CO₂ fixation and CO₂ reduction. In addition, driven by the explosive growth of energy consumption in the last century, much research has gone into biomass, which represents a renewable alternative to fossil fuels and a sustainable carbon feedstock for chemical production. The advanced progress of biomass-related transformations is also illustrated herein. Fundamental insights into the nature of MOF-based materials as constitutionally easily recoverable heterogeneous catalysts and as supports for various active sites is thoroughly discussed. Finally, challenges facing the development of this field and the outlook for future research are presented.

Postsynthetic Modification of ZIF-90 for Potential Targeted Codelivery of Two Anticancer Drugs

Combination therapy has been regarded as a promising strategy for cancer treatment due to the enhanced anticancer efficacy achieved by blocking multiple drug resistance pathways. In this work, a drug carrier based on nanoscale ZIF-90 for the codelivery of two anticancer drugs has been synthesized by covalently attaching doxorubicin (DOX) to the surface of ZIF-90 via Schiff base reaction of amino group in DOX and aldehyde group of imidazole-2-carboxaldehyde (ICA) ligand and encapsulating 5-fluorouracil (5-FU) into the pores of the framework. The results of drug loading measurements show that the loading amount of drugs was estimated as high as 36.35 and 11-13.5 wt % for 5-FU and DOX, respectively. Moreover, we demonstrated that the carrier had the potential of cancer-targeted delivery of drugs for the collapse of framework under the pH environment around cancer cells and subsequently releasing drugs. Drug release at pH 5.5, imitating the environment of tumor, can reach over 95%, and the release time is less 16 h, meaning a more effective and faster release of drugs around tumoral cells than that in a normal environment. This is the first report for cancer-targeted codelivery of two different chemical drugs based on nanoscale metal-organic frameworks (NMOFs).

Heterogeneous Catalysis in Zeolites, Mesoporous Silica, and Metal-Organic Frameworks

Crystalline porous materials are important in the development of catalytic systems with high scientific and industrial impact. Zeolites, ordered mesoporous silica, and metal-organic frameworks (MOFs) are three types of porous materials that can be used as heterogeneous catalysts. This review focuses on a comparison of the catalytic activities of zeolites, mesoporous silica, and MOFs. In the first part of the review, the distinctive properties of these porous materials relevant to catalysis are discussed, and the corresponding catalytic reactions are highlighted. In the second part, the catalytic behaviors of zeolites, mesoporous silica, and MOFs in four types of general organic reactions (acid, base, oxidation, and hydrogenation) are compared. The advantages and disadvantages of each porous material for catalytic reactions are summarized. Conclusions and prospects for future development of these porous materials in this field are provided in the last section. This review aims to highlight recent research advancements in zeolites, ordered mesoporous silica, and MOFs for heterogeneous catalysis, and inspire further studies in this rapidly developing field.

MOF catalysts in biomass upgrading towards value-added fine chemicals

The development of new synthetic routes from biomass sources towards already existing molecules, which are then called bio-based molecules, or the transformation of biomass into new building blocks and materials will be of great impact. This review presents a critical comparison between MOFs and other catalysts (e.g. zeolites) for biomass transformation.

Silver(i) coordination polymers with 3,3′,5,5′-tetrasubstituted 4,4′-bipyridine ligands: towards new porous chiral materials

The first homochiral metal–organic framework (MOF) based on an atropisomeric 4,4′-bipyridine ligand is described.

Cyclic gas-phase heterogeneous process in a metal–organic framework involving a nickel nitrosyl complex

The cubic metal–organic framework MFU-4l ([Zn₅Cl₄(BTDD)₃], H₂-BTDD = bis(1H-1,2,3-triazolo[4,5-b],[4′,5′-i])dibenzo[1,4]dioxin) featuring large pore apertures can be modified post-synthetically via partial or complete substitution of peripheral metal sites and chloride side-ligands, thus opening a route towards a large variety of functionalized MOFs. In this way, Ni-MFU-4l-nitrite (or Ni-MFU-4l-NO₂) with an analytically determined chemical composition [Zn_2.6Ni_2.4(NO₂)_2.9Cl_1.1(BTDD)₃], containing accessible Ni–NO₂ units, was prepared. Ni-MFU-4l-NO₂ undergoes selective heterogeneous gas-phase reduction by carbon monoxide at 350 °C, leading to formation of Ni–NO units at the peripheral sites of the MFU-4l framework (Ni-MFU-4l-NO). The crystallinity and porosity of the MFU-4l framework are completely retained upon this transformation. The so-formed nickel nitrosyl complex, showing high thermal stability, readily reacts with nitrogen monoxide at room temperature, producing Ni–NO₂ units and dinitrogen monoxide (N₂O). Hence, the reaction of Ni-MFU-4l-NO₂ with CO followed by NO represents a cyclic process with an overall stoichiometry 2NO + CO → N₂O + CO₂, in which the Ni-MFU-4l framework serves as a catalyst. It can be considered as a model process for the removal of highly toxic NO and CO gases, which are converted to non-toxic CO₂ and N₂O. Diffuse reflectance infrared Fourier transform spectroscopic studies show that at least 10 cycles can be repeated. The framework's reactivity drops down by ca. 50% after 10 cycles, which is most likely due to the accumulation of highly reactive NO₂ and N₂O₄ contaminants. Therefore, further investigations on characterizing reaction intermediates should be done in order to improve the catalyst's performance. Our results confirm the potential of MFU-4l frameworks as selective single-site catalysts for heterogeneous gas-phase transformations and provide a motivation for further studies.

Surface acid–base catalytic activity of ZIF-8 revealed by super-resolution fluorescence microscopy

Fluorescence microscopy uncovers the surface-only catalytic activity of ZIF-8, but its accessibility is improved via extra porosity introduction by oleic acid treatment.

Highly shape- and regio-selective peroxy–trifluoromethylation of styrene by metal–organic framework Cu3(BTC)2

The peroxy and trifluoromethyl groups play important roles in pharmacy, but it is challenging to introduce both of them selectively into the target molecules in a homogeneous catalytic system.