Nanoporous molecular frameworks are important in applications such as separation, storage and catalysis. Empirical rules exist for their assembly but it is still challenging to place and segregate functionality in three-dimensional porous solids in a predictable way. Indeed, recent studies of mixed crystalline frameworks suggest a preference for the statistical distribution of functionalities throughout the pores rather than, for example, the functional group localization found in the reactive sites of enzymes. This is a potential limitation for ‘one-pot’ chemical syntheses of porous frameworks from simple starting materials. An alternative strategy is to prepare porous solids from synthetically preorganized molecular pores. In principle, functional organic pore modules could be covalently prefabricated and then assembled to produce materials with specific properties. However, this vision of mix-and-match assembly is far from being realized, not least because of the challenge in reliably predicting three-dimensional structures for molecular crystals, which lack the strong directional bonding found in networks. Here we show that highly porous crystalline solids can be produced by mixing different organic cage modules that self-assemble by means of chiral recognition. The structures of the resulting materials can be predicted computationally, allowing in silico materials design strategies. The constituent pore modules are synthesized in high yields on gram scales in a one-step reaction. Assembly of the porous co-crystals is as simple as combining the modules in solution and removing the solvent. In some cases, the chiral recognition between modules can be exploited to produce porous organic nanoparticles. We show that the method is valid for four different cage modules and can in principle be generalized in a computationally predictable manner based on a lock-and-key assembly between modules.

Modular and predictable assembly of porous organic molecular crystals

Porphyrins and porphyrin derivatives have been widely explored for various applications owing to their excellent photophysical and electrochemical properties. However, inherent shortcomings, such as instability and self-quenching under physiological conditions, limit their biomedical applications. In recent years, metal-organic frameworks (MOFs) have received increasing attention. The construction of porphyrin-based MOFs by introducing porphyrin molecules into MOFs or using porphyrins as organic linkers to form MOFs can combine the unique features of porphyrins and MOFs as well as overcome the limitations of porphyrins. This Review summarizes important synthesis strategies for porphyrin-based MOFs including porphyrin@MOFs, porphyrinic MOFs, and composite porphyrinic MOFs, and highlights recent achievements and progress in the development of porphyrin-based MOFs for biomedical applications in tumor therapy and biosensing. Finally, the challenges and prospects presented by this class of emerging materials for biomedical applications are discussed.

https://onlinelibrary.wiley.com/doi/epdf/10.1002/anie.201909880

Porphyrin‐Based Metal–Organic Frameworks for Biomedical Applications

The effective capture of radioiodine, produced or released from nuclear-related activities, is of paramount importance for the sustainable development of nuclear energy. Here, a series of zirconium-based metal-organic frameworks (Zr-MOFs), with a Zr6(μ3-O)4(μ3-OH)4 cluster and various carboxylate linkers, were investigated for the capture of volatile iodine. Their adsorption kinetics and recyclability were investigated in dry and humid environments. The structural change of Zr-MOFs during iodine trapping was studied using powder X-ray diffraction and pore structure measurements. Experimental spectra (Raman and X-ray photoelectron spectroscopy) and density functional theory (DFT) calculations for the linkers and Zr clusters were performed to understand the trapping mechanism of the framework. When interacting with iodine molecules, MOF-808, NU-1000, and UiO-66, with highly connected and/or rigid linkers, have better structural stability than UiO-67 and MOF-867, which have flexible linkers with less connectivity. Particularly, MOF-808, with a rigid and tritopic benzenetricarboxylate linker, has the highest iodine adsorption capacity (2.18 g/g, 80 °C), as well as the largest pore volume after iodine elution. In contrast, UiO-67, with long linear ditopic linkers, exhibits the weakest stability and lowest adsorption capacity (0.53 g/g, 80 °C) because of its most serious collapse of pore structures. After incorporating with strong electron-donating imidazole/pyridine ligands, both the stability and adsorption capacity of MOF-808/NU-1000 decrease. DFT calculations verify that the N-heterocycle groups could enhance the affinity toward iodine by strong charge transfer. DFT calculations also suggest that the terminal -OH in MOF-808 has a strong affinity toward iodine (-54 kJ/mol I2) and water (-63 kJ/mol H2O) and a weak affinity toward NO2 (-27 kJ/mol NO2). With high adsorption capacity and excellent stability, MOF-808 shows great potential for the sustainable removal of radioiodine.

Iodine Capture Using Zr-Based Metal-Organic Frameworks (Zr-MOFs): Adsorption Performance and Mechanism.

Separation technology is central to industries as diverse as petroleum, pharmaceuticals, mining and life sciences Metal–organic cages, a class of molecular containers formed via coordination-driven self-assembly, show great promise as separation agents Precise control of the shape, size and functionalization of cage cavities enables them to selectively bind and distinguish a wide scope of physicochemically similar substances in solution Extensive research has, thus, been performed involving separations of high-value targets using coordination cages, ranging from gases and liquids to compounds dissolved in solution Enantiopure capsules also show great potential for the separation of chiral molecules The use of crystalline cages as absorbents, or the incorporation of cages into polymer membranes, could increase the selectivity and efficiency of separation processes This Review covers recent progress in using metal–organic cages to achieve separations, with discussion of the many methods of using them in this context Challenges and potential future developments are also discussed This Review discusses recent progress in the uses, challenges and future prospects for separations using metal–organic cages Precise control over the size, shape and functionalization of these cages enables their application for separations required in petroleum, pharmaceuticals, mining and life sciences

Metal–organic cages for molecular separations

https://www.cell.com/chem/pdf/S2451-9294(20)30631-8.pdf

A nitrogen-rich covalent organic framework for simultaneous dynamic capture of iodine and methyl iodide

The enrichment of radioactive iodine in the waste of nuclear industries threatens human health, and thus the efficient capture of iodine has attracted a great deal of attention in recent years. Porous organic polymers (POPs) and metal–organic frameworks (MOFs), new classes of porous materials, act as outstanding candidate adsorbent materials in this field due to their high surface areas, permanent tunable porosities, controllable structures, high thermal/chemical stabilities, versatility in molecular design and potential for post-synthetic modification. Herein, this review focuses on the research progress of these two types of porous materials for highly efficient iodine capture. We analyze and discuss some valid strategies for enhancing their iodine uptake, including increasing their surface area and pore volume, using organic building units with unique configurations and functions, introducing chemical functional groups to provide high-enthalpy binding sites, and further processing of POP and MOF materials. Indeed, there are many special structural and functional features found in porous POP and MOF materials, which make them unique and merit further exploration. Thus, we expect to see their usage grow as this field progresses.

Iodine capture in porous organic polymers and metal–organic frameworks materials

Porous cationic covalent triazine-based frameworks (CTFs) with imidazolium salts as tectons were prepared via ionothermal synthesis. The high-PF6 - -content CTF shows the CO2 adsorption of 44.7 cm3 g-1 and I2 capture capacity of 312 wt %. The influence of counterion species and contents on the porosities, CO2 adsorptions, and I2 capture capacities of the CTFs has been investigated.

Porous Cationic Covalent Triazine-Based Frameworks as Platforms for Efficient CO2 and Iodine Capture.

Polytriazine porous networks for effective iodine capture

A tetraphenylethylene-based covalent organic framework (TTPE-COF) with a rhomboid-shaped framework is constructed by a Schiff base reaction. Due to its porous structure and high surface area (681.27 m2 g−1), the TTPE-COF will be a meritorious adsorbent for gas storage (CO2 of 485.89 mg g−1 at 45 bar/318 K) and volatile organic compound (VOC) capture (benzene of 5.80 mmol g−1 and toluene of 5.20 mmol g−1 at 293 K). Furthermore, the TTPE-COF has good selectivity and detection effect for Fe3+, and the detection limit (LOD) of Fe3+ is 3.07 μM. The TTPE-COF has potential applications in adsorbents and fluorescent sensors.

A tetraphenylethylene-based covalent organic framework for waste gas adsorption and highly selective detection of Fe3+

Hybrid nanoparticles combining plasmonic and catalytic components have recently gained interest for their potential use in sunlight‐to‐chemical energy conversion. However, a deep understanding of the structure–performance that maximizes the use of the incoming energy remains elusive. Here, a suite of Au and Pd based nanostructures in core–shell and core‐satellites configurations are designed and their photocatalytic activity for Hydrogen (H2) generation under sunlight illumination is tested. Formic acid is employed as H2 source. Core‐satellite systems show a higher enhancement of the reaction upon illumination, compared to core–shell ones. Electromagnetic simulations reveal that a key difference between both configurations is the excitation of highly localized and asymmetric electric fields in the gap between both materials. In this scheme, the core Au particle acts as an antenna, efficiently capturing visible light via the excitation of localized plasmon resonances, while the surrounding Pd satellites transduce the locally‐enhanced electric field into catalytic activity. These findings advance the understanding of plasmon‐driven photocatalysis, and provide an important benchmark to guide the design of the next generation of plasmonic bimetallic nanostructures.

Wei Xie

Papers

Iodine capture in porous organic polymers and metal–organic frameworks materials

Porous Cationic Covalent Triazine-Based Frameworks as Platforms for Efficient CO2 and Iodine Capture.

Polytriazine porous networks for effective iodine capture

A tetraphenylethylene-based covalent organic framework for waste gas adsorption and highly selective detection of Fe3+

Tailoring Plasmonic Bimetallic Nanocatalysts Toward Sunlight‐Driven H2 Production