Many sophisticated chemical and physical properties of porous materials strongly rely on the presence of the metal ions within the structures. Whereas homogeneous distribution of metals is ...conveniently realized in metal–organic frameworks (MOFs), the limited stability potentially restricts their practical implementation. From that perspective, the development of metal–covalent organic frameworks (MCOFs) may address these shortcomings by incorporating active metal species atop highly stable COF backbones. This Minireview highlights examples of MCOFs that tackle important issues from their design, synthesis, characterization to cutting‐edge applications.
MCOFs (metal–covalent organic frameworks) hold high promise in combining the advantages of MOFs (metal–organic frameworks) and COFs (covalent organic frameworks), thus realizing a balanced mix of crystallinity, porosity, stability, tunability, and functionality. This Minireview summarizes the recent progress of MCOFs regarding design strategy, synthesis, structural characterization, and their cutting‐edge applications.
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.
We herein report a facile preparation of graphene oxide (GO) membranes including three steps: (1) mild freeze–thaw exfoliation to get large GO nanosheets, (2) purification of exfoliated GO nanosheets ...through pH adjustment, and (3) spin coating to fabricate smooth GO membranes with uniformly aligned GO nanosheets. The fabricated GO membranes are subject to single gas permeation tests, with the obtained gas permeance in the order He > H2 ≫ CH4 > CO2 > N2 ≫ SF6, indicating a dominant molecular sieving separation mechanism. The H2/CO2 mixed gas permeation tests reveal H2 permeance up to 3.4 × 10–7 mol/(m2·s·Pa) and a H2/CO2 separation factor up to 240, which are among the best of all the reported membranes for H2/CO2 separation. The separation factor drops to 47 at a higher temperature of 120 °C, but the H2 permeance is further increased to 6.7 × 10–7 mol/(m2·s·Pa), ensuring a higher gas separation throughput under higher temperatures. This study paves the way toward large-scale production and application of GO membranes as promising gas separation materials.
Photodynamic therapy (PDT) has been a well-accepted clinical treatment for malignant tumors owing to its noninvasiveness and high spatiotemporal selectivity. However, the efficiency of PDT is still ...severely hindered by an inherent aggregation-caused quenching (ACQ) effect of traditional photosensitizers (PSs), the presence of B-cell lymphoma 2 (Bcl-2), an antiapoptosis protein in cells, and hypoxia in the tumor microenvironment. To address these issues, hybrid nanospheres containing Fe3+, aggregation-induced emission (AIE) PS, and Bcl-2 inhibitor of sabutoclax were constructed via coordination-driven self-assembly in aqueous media. Once the hybrid nanospheres are taken up by tumor cells, intracellular O2 concentration is observed to increase via Fenton reaction driven by Fe3+, whereas intracellular PDT resistance of the AIE PS was mitigated by sabutoclax. The design of the multifunctional hybrid nanospheres demonstrates a prospective nanoplatform for image-guided enhanced PDT of tumors.
Nature has protein channels (e.g., aquaporins) that preferentially transport water molecules while rejecting even the smallest hydrated ions. Aspirations to create robust synthetic counterparts have ...led to the development of a few one-dimensional channels. However, replicating the performance of the protein channels in these synthetic water channels remains a challenge. In addition, the dimensionality of the synthetic water channels also imposes engineering difficulties to align them in membranes. Here we show that zero-dimensional porous organic cages (POCs) with nanoscale pores can effectively reject small cations and anions while allowing fast water permeation (ca. 10
water molecules per second) on the same magnitude as that of aquaporins. Water molecules are found to preferentially flow in single-file, branched chains within the POCs. This work widens the choice of water channel morphologies for water desalination applications.
Three chiral robust diene-based porous organic frameworks (POFs) are prepared. POF- is shown to be an efficient heterogeneous catalyst after metallation for asymmetric conjugation addition with up to ...93% ee, and it can also function as a new chiral stationary phase for gas chromatographic separation of racemates.
Advanced porous materials (APMs)—such as metal‐organic frameworks (MOFs) and porous organic polymers (POPs)—have emerged as an exciting research frontier of chemistry and materials science. Given ...their tunable pore size and extensive diversity, APMs have found widespread applications. In addition, adding dynamic functional groups to porous solids furthers the development of stimuli‐responsive materials. By incorporating moving elements—molecular rotors—into the porous frameworks, molecular‐rotor‐driven advanced porous materials (MR‐APMs) can respond reversibly to chemical and physical stimuli, thus imparting dynamic functionalities that have not been found in conventional porous materials. This Minireview discusses exemplary MR‐APMs in terms of their design, synthesis, rotor dynamics, and potential applications.
Molecular‐rotor‐driven advanced porous materials (MR‐APMs) can expand the chemical and physical properties of conventional rigid porous solids and drive the development of sophisticated stimuli‐responsive materials. This Minireview emphasizes the strategies for the localization and characterization of molecular rotors in porous materials as well as the exploration of their rotor‐induced specific functionalities.
A highly fluorescent coordination cage Zn8L4I8 has been constructed by treating enantiopure pyridyl‐functionalized metallosalalen units (L) with zinc(II) iodide and characterized by a variety of ...techniques including microanalysis, thermogravimetric analysis (TGA), circular dichroism (CD) spectroscopy, and single‐crystal and powder X‐ray diffraction. Strong intermolecular π–π, CH⋅⋅⋅π, and CH⋅⋅⋅I interactions direct packing of the cage molecules to generate a 3D polycage network interconnected by pentahedral cages formed by adjacent pentamers. The cage has an amphiphilic helical cavity decorated with chiral NH functionalities capable of interactions with guest species such as saccharides. The fluorescence of the cage was greatly enhanced by five enantiomeric saccharides in solution, with enantioselectivity factors of 2.480–4.943, and by five enantiomeric amines in the solid state, with enantioselective fluorescence enhancement ratios of 1.30–3.60. This remarkable chiral sensing of both saccharides and amines with impressive enantioselectivity may result from the steric confinement of the cavity as well as its conformational rigidity. It holds great promise for the development of novel chiral cage materials for sensing applications.
Cage‐based chiral sensor: A highly fluorescent coordination cage Zn8L4I8 can be prepared from enantiopure pyridyl‐functionalized metallosalalen units (L). The cage has an amphiphilic helical cavity decorated with chiral NH functionalities and supramolecular interactions generate a 3D polycage network interconnected by pentahedral cages formed by adjacent pentamers (see graphic). The fluorescence of the cage is greatly enhanced either in solution or in the solid state in the presence of enantiomeric saccharides or amines, respectively, with significant enantioselectivity factors.
Fluorescent porous materials have been under intensive investigation recently, because of their wide applications in molecular recognition and chemical sensing. However, it is a great challenge to ...achieve size selectivity and sensing linearity for molecular recognition. Herein, we report a series of porous organic frameworks (POFs) containing flexible tetraphenylethylene (TPE) moieties as molecular rotors with responsive fluorescent behavior. These fluorescent POFs exhibit size-selective turn-on fluorescence for the effective chemical sensing of volatile organic compounds (VOCs), which can be attributed to the different degrees of motion restriction of flexible TPE rotors by various VOCs, leading to the partially freezing of rotors in more fluorescent conformations. Significantly, a linear aggregation-induced emission (AIE) relationship is observed between the fluorescent POFs and the VOCs over a wide range of concentrations, which is highly beneficial for quantitative sensing applications. The gas-phase detection of arene vapors using POFs is also proven with unprecedentedly high sensitivity, selectively, and recyclability. The mechanism of responsive fluorescence in POFs is further investigated using molecular simulations and density functional theory (DFT) calculations.
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