Biomimetic catalysts of iron-based metal-organic frameworks with high peroxidase-mimicking activity for colorimetric biosensing.

The field of metal-organic framework (MOF)-based biomimetic catalysts has achieved great progress but is still in its infancy. The systematic investigation of the tailored construction of MOF-based biomimetic catalysts is required for further development. Herein, two iron-based MOFs, namely, [(Fe3O)2(H2O)4(HCOO)(L)2]n (HUST-5: H6L = hexakis(4-formylphenoxy) cyclotriphosphazene; HUST = Huazhong University of Science and Technology) and [(Fe3O)(H2O)3(L)]n (HUST-7) have been fabricated through the assembly of different iron clusters and hexa-carboxylate ligand under the control of the added acid species. The two MOFs exhibit distinct secondary building units (SBUs) and topological structures, which could be used as biomimetic catalysts for the systematic comparisons of structural characteristics and the catalytic activity. Both MOFs possess catalytic activity similar to that of natural peroxidases towards the catalysis of the oxidation of a variety of substrates. Significantly, HUST-5 and HUST-7 can effectively catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2 accompanied by significant colorimetric biosensing. With same compositions, different catalytic performances were obtained due to differences in the porous structures and characteristics of SBUs in two Fe-MOFs, which was also validated by theoretical calculation results. Furthermore, the phenomenon of colorimetric biosensing could be significantly suppressed by the addition of ascorbic acid (AA) during the oxidation process of TMB. It was observed from these findings that a facile colorimetric biosensing platform for detecting H2O2 and ascorbic acid has been successfully explored. Therefore, this work provides another unique perspective for the tailor-made preparation of stable MOF-based peroxidase mimics with excellent catalytic performance and colorimetric biosensing.

Metal-Organic Frameworks Based on Group 3 and 4 Metals.

Metal-organic frameworks (MOFs) based on group 3 and 4 metals are considered as the most promising MOFs for varying practical applications including water adsorption, carbon conversion, and biomedical applications. The relatively strong coordination bonds and versatile coordination modes within these MOFs endow the framework with high chemical stability, diverse structures and topologies, and interesting properties and functions. Herein, the significant progress made on this series of MOFs since 2018 is summarized and an update on the current status and future trends on the structural design of robust MOFs with high connectivity is provided. Cluster chemistry involving Y, lanthanides (Ln, from La to Lu), actinides (An, from Ac to Lr), Ti, and Zr is initially introduced. This is followed by a review of recently developed MOFs based on group 3 and 4 metals with their structures discussed based on the types of inorganic or organic building blocks. The novel properties and arising applications of these MOFs in catalysis, adsorption and separation, delivery, and sensing are highlighted. Overall, this review is expected to provide a timely summary on MOFs based on group 3 and 4 metals, which shall guide the future discovery and development of stable and functional MOFs for practical applications.

Crystallographic Visualization of Postsynthetic Nickel Clusters into Metal-Organic Framework.

Postsynthetic metalation (PSM) has been employed as a robust method for the postsynthetic modification of metal-organic frameworks (MOFs). However, the lack of relevant information that can be obtained for the postsynthetically introduced metallic ions has hindered the development of PSM applications. Thanks to the advancement in single-crystal X-ray diffraction (SCXRD) technology, there have been a few recent examples in which successful postsynthetic introduction of single metal ions into MOFs occurred at the defined chelating sites. These works have provided useful explanations about the complicated host-guest chemistry involved in PSMs. On the other hand, there are only limited examples with crystallographic snapshots of the postsynthetic installation of metal clusters into the pores of MOFs using an ordinary SCXRD due to the loss of crystallinity of parent matrix during the PSM process. Herein, by the careful selection of starting materials and controlling the reaction conditions, we report the first crystallographic visualization of metal clusters inserted into Zr-based MOFs via PSM. The structural advantages of the parent Zr-MOF, which are inherited from the stable Zr6 cluster and triazole-containing dicarboxylate ligand, ensure both the preservation of high crystallinity and the presence of flexible coordination sites for PSM. Furthermore, PSM of metal clusters in a MOF pore space enhances stability of the final samples while also imparting the functionality of a successful catalyst toward ethylene dimerization reaction. The related construction ideas and structural information detailed in this work can help lay the foundation for further advancements using the postmodification of MOFs as well as open new doors for the utilization of SCXRD technology in the field of MOFs.

Biological Antagonism Inspired Detoxification: Removal of Toxic Elements by Porous Polymer Networks.

Water contamination by toxic heavy elements is becoming an urgent problem in environmental science and separation technologies. However, the design of sophisticated absorbents with high stability and outstanding removal efficacy for ion coadsorption is still a technical challenge. Herein, inspired by biological Hg/Se antagonism detoxification, we have designed the first porous polymer network (PPN) for the concurrent removal of Hg/Se species in aqueous solutions. Remarkably, the MoS42- functionalized PPN-150-MoS4 exhibits a rapid and highly efficient simultaneous removal of toxic anions (SeO42- and SeO32-) and metals (Hg2+). The high thiophilicity of Hg2+ leads to 99.9% removal within minutes. More importantly, selenite and selenate, typically known for being difficult to remove from aqueous environments, can be removed by PPN-150-MoS4, exhibiting >99% removal within minutes when in the presence of Hg2+. At the same time, the removal efficiency for Se(IV) and Se(VI) oxoanions in the absence of Hg2+ is very low, reaching only 14% removal. Overall, PPN-150-MoS4 exhibits one of the highest adsorption capacities toward SeO32- (124 mg/g), making it a promising and cheap sorbent material for water remediation applications. This work provides a fresh route for detoxification and remediation strategies that aim to regulate the presence of toxic ions in nature. The material herein shall guide the state-of-the-art design of efficient water treatment techniques through a combination of biological antagonism and materials chemistry.

An efficient strategy for improving the luminescent sensing performance of a terbium(iii) metal-organic framework towards multiple substances.

By anchoring triazole units onto its skeleton, the luminescent sensing properties of a terbium(iii) metal-organic framework could be efficiently improved, including not only an expansion of the scale of analytes such as Fe3+, anions and nitroaromatic molecules, but also enhanced selectivity and sensitivity.

Creating Hierarchical Pores by Controlled Linker Thermolysis in Multivariate Metal-Organic Frameworks.

Sufficient pore size, appropriate stability, and hierarchical porosity are three prerequisites for open frameworks designed for drug delivery, enzyme immobilization, and catalysis involving large molecules. Herein, we report a powerful and general strategy, linker thermolysis, to construct ultrastable hierarchically porous metal-organic frameworks (HP-MOFs) with tunable pore size distribution. Linker instability, usually an undesirable trait of MOFs, was exploited to create mesopores by generating crystal defects throughout a microporous MOF crystal via thermolysis. The crystallinity and stability of HP-MOFs remain after thermolabile linkers are selectively removed from multivariate metal-organic frameworks (MTV-MOFs) through a decarboxylation process. A domain-based linker spatial distribution was found to be critical for creating hierarchical pores inside MTV-MOFs. Furthermore, linker thermolysis promotes the formation of ultrasmall metal oxide nanoparticles immobilized in an open framework that exhibits high catalytic activity for Lewis acid-catalyzed reactions. Most importantly, this work provides fresh insights into the connection between linker apportionment and vacancy distribution, which may shed light on probing the disordered linker apportionment in multivariate systems, a long-standing challenge in the study of MTV-MOFs.

Uncovering Two Principles of Multivariate Hierarchical Metal-Organic Framework Synthesis via Retrosynthetic Design.

Multivariate (MTV) hierarchical metal-organic frameworks (MOFs), which contain multiple regions arranged in ordered structures, show promise for applications such as gas separation, size-selective catalysis, and controlled drug delivery. However, the complexity of these hierarchical MOFs is limited by a lack of control during framework assembly. Herein, we report the controlled generation of hierarchical MOF-on-MOF structural formation under the guidance of two design principles, surface functionalization and retrosynthetic techniques for stability control. Accordingly, the tunability of spatial distributions, compositions, and crystal sizes has been achieved in these hierarchical systems. The resulting MOF-on-MOF hierarchical structures represent a unique crystalline porous material which contains a controllable distribution of functional groups and metal clusters that are associated together within a framework composite. This general synthetic approach not only expands the scope and tunability of the traditional MTV strategy to multicomponent materials, but also offers a facile route to introduce variants and sequences to sophisticated three-dimensional hierarchical and cooperative systems. As a proof of concept, the photothermal effects of a porphyrinic core-MOF are exploited to trigger the controlled guest release from a shell-MOF with high guest capacity, highlighting the integrated cooperative behaviors in multivariate hierarchical systems.