Superstructures of Zeolitic Imidazolate Frameworks to Single- and Multiatom Sites for Electrochemical Energy Conversion

The exploration of electrocatalysts with high catalytic activity and long-term stability for electrochemical energy conversion is significant yet remains challenging. Zeolitic imidazolate framework (ZIF)-derived superstructures are a source of atomic-site-containing electrocatalysts. These atomic sites anchor the guest encapsulation and self-assembly of aspheric polyhedral particles produced using microreactor fabrication. This review provides an overview of ZIF-derived superstructures by highlighting some of the key structural types, such as open carbon cages, 1D superstructures, hollow structures, and the interconversion of superstructures. The fundamentals and representative structures are outlined to demonstrate the role of superstructures in the construction of materials with atomic sites, such as single- and dual-atom materials. Then, the roles of ZIF-derived single-atom sites for the electroreduction of CO₂ and electrochemical synthesis of H₂ O₂ are discussed, and their electrochemical performance for energy conversion is outlined. Finally, the perspective on advancing single- and dual-atom electrode-based electrochemical processes with enhanced redox activity and a low-impedance charge-transfer pathway for cathodes is provided. The challenges associated with ZIF-derived superstructures for electrochemical energy conversion are discussed.

Biocatalytic self-assembled synthetic vesicles and coacervates: From single compartment to artificial cells

Compartmentalization is an intrinsic feature of living cells that allows spatiotemporal control over the biochemical pathways expressed in them. Over the years, a library of compartmentalized systems has been generated, which includes nano to micrometer sized biomimetic vesicles derived from lipids, amphiphilic block copolymers, peptides, and nanoparticles. Biocatalytic vesicles have been developed using a simple bag containing enzyme design of liposomes to multienzymes immobilized multi-vesicular compartments for artificial cell generation. Additionally, enzymes were also entrapped in membrane-less coacervate droplets to mimic the cytoplasmic macromolecular crowding mechanisms. Here, we have discussed different types of single and multicompartment systems, emphasizing their recent developments as biocatalytic self-assembled structures using recent examples. Importantly, we have summarized the strategies in the development of the self-assembled structure to improvise their adaptivity and flexibility for enzyme immobilization. Finally, we have presented the use of biocatalytic assemblies in mimicking different aspects of living cells, which further carves the path for the engineering of a minimal cell.

Triple-Layered Metal-Organic Framework Hybrid for Tandem Response-Driven Enhanced Chemotherapy

The precise release of drugs is essential to improve cancer therapeutic efficacy. In this work, a tandem responsive strategy was developed based on a triple-layered metal-organic framework (MOF) hybrid. The MOF nanoprobe was stepwise fabricated with a telomerase-responsive inner, a pH-sensitive MOF filling and H₂ O₂ -responsive coordination complex shell of Fe³⁺ and eigallocatechin gallate (EGCG). In the tumor microenvironment, the shell was dissociated by endogenous H₂ O₂ and simultaneously produced highly reactive hydroxyl radicals by a Fenton reaction. Meanwhile, the released EGCG could downregulate the expression of P-glycoprotein responsible for drug resistance. After the dissociation of the framework by protons, telomerase could trigger the release of the drug from the DNA duplex on the exposed inner shell. By integrating confined drug release, inhibited efflux pump and chemodynamic therapy, the all-in-one chemotherapy strategy was identified with enhanced therapeutic efficacy in drug-resistant cancer cells.

Pickering Emulsion-Based Microreactors for Size-Selective Interfacial Enzymatic Catalysis

In this study, we have developed a mild and effective method to prepare a metal-organic framework (MOF)-based microcapsule by the self-assembly of pre-synthesized zeolite imidazolate framework-8 (ZIF-8) nanoparticles at the oil-water interface combined with deposition of a dense ZIF-8 coating outside the capsule. By introducing the enzyme Candida antarctica lipase B (CalB) directly into the stabilizer ZIF-8 or the water phase of Pickering emulsion during the preparation process, we achieved that the enzyme was immobilized within the shell (CalB@ZIF-8@cap) or in the cavity (ZIF-8@cap-CalB) of the microcapsules, respectively. The resulting CalB-loaded microcapsules were robust and had a core-shell structure proved by scanning electron microscopy. Meanwhile, Fourier transform infrared spectroscopy was conducted to confirm the encapsulation of enzymes in the microcapsules and their position in the microcapsules was confirmed by fluorescence microscopy. Furthermore, through the comparison of transesterification reactions between a pair of small substrates and a pair of larger ones, the two types of CalB-loaded microcapsules showed great catalytic activity, stability and size selectivity, and the catalytic activity of CalB@ZIF-8@cap was slightly higher than that of ZIF-8@cap-CalB. Importantly, due to the large size of the microcapsules, the catalyst could be separated from the reaction system by sedimentation, thereby reducing the energy consumption for separation. These kinds of multifunctional MOF-enzyme composites may open up new opportunities for the biocatalysis and microreactor.

In situ assembled ZIF superstructures via an emulsion-free soft-templating approach

Assembling well-defined MOF superstructures remains challenging as it requires easily removable hard templates or readily available immiscible solutions for an emulsion-based soft-template approach. In this work, a single-step emulsion-free soft templating approach is reported to spontaneously prepare hollow ZIF-8 and ZIF-67 colloidosomes with no further purification. These superstructures can load different enzymes regardless of the size and charge with a high encapsulation efficiency of 99%. We envisage that this work will expand the repertoires of MOF superstructures by the judicious selection of precursors and the reaction medium.

The Progress and Prospect of Zeolitic Imidazolate Frameworks in Cancer Therapy, Antibacterial Activity, and Biomineralization

The progressive development of zeolitic imidazolate frameworks (ZIFs), as a subfamily of metal-organic frameworks (MOFs), and their unique features, including tunable pore size, large surface area, high thermal stability, and biodegradability/biocompatibility, have made them attractive in the field of biomedicine, especially for drug delivery and biomineralization applications. The high porosity of ZIFs gives them the opportunity for encapsulating a high amount of therapeutic drugs, proteins, imaging cargos, or a combination of them to construct advanced multifunctional drug delivery systems (DDSs) with combined therapeutic and imaging capabilities. This review summarizes recent strategies on the design and fabrication of ZIF-based nansystems and their exploration in the biomedical field. First, recent developments for the adjustment of particle size, functionality, and morphology of ZIFs are discussed, which are important for achieving optimized therapeutic/theranostic nanosystems. Second, recent trends on the application of ZIF nanocarriers for the loading of diverse cargos, including anticancer medicines, antibiotic drugs, enzymes, proteins, photosensitizers, as well as imaging and photothermal agents, are investigated in order to understand how multifunctional DDSs can be designed based on the ZIF nanoparticles to treat different diseases, such as cancer and infection. Finally, prospects on the future research direction and applications of ZIF-based nanomedicines are discussed.

Rational Construction of a 2D PbII Coordination Polymer as a Sensitive Turn-Off Fluorescent Switch for Fe3+, Cr2O72−, and NFT

A PbII coordination polymer, [Pb(L)2]n (denoted as complex 1), was generated successfully by the assembly process of PbII and 5-fluoronicotinic acid (HL) under solvothermal synthesis. The obtained 1 was characterised by element analysis, powder and single-crystal X-ray diffraction, thermogravimetric analysis, and UV-vis and fluorescent spectroscopy. The resultant 1 has an outstanding application as a fluorescent sensor for Fe3+, Cr2O72−, and NFT with excellent selectivity and reusability.