A tissue-like neurotransmitter sensor for the brain and gut.

Neurotransmitters play essential roles in regulating neural circuit dynamics both in the central nervous system as well as at the peripheral, including the gastrointestinal tract1-3. Their real-time monitoring will offer critical information for understanding neural function and diagnosing disease1-3. However, bioelectronic tools to monitor the dynamics of neurotransmitters in vivo, especially in the enteric nervous systems, are underdeveloped. This is mainly owing to the limited availability of biosensing tools that are capable of examining soft, complex and actively moving organs. Here we introduce a tissue-mimicking, stretchable, neurochemical biological interface termed NeuroString, which is prepared by laser patterning of a metal-complexed polyimide into an interconnected graphene/nanoparticle network embedded in an elastomer. NeuroString sensors allow chronic in vivo real-time, multichannel and multiplexed monoamine sensing in the brain of behaving mouse, as well as measuring serotonin dynamics in the gut without undesired stimulations and perturbing peristaltic movements. The described elastic and conformable biosensing interface has broad potential for studying the impact of neurotransmitters on gut microbes, brain-gut communication and may ultimately be extended to biomolecular sensing in other soft organs across the body.

Caged AIEgens: Multicolor and White Emission Triggered by Mechanical Activation.

Aggregation-induced emission luminogens (AIEgens) that respond to mechanical force are increasingly used as force probes, memory devices, and advanced security systems. Most of the known mechanisms to modulate mechanoresponsive AIEgens have been based on changes in aggregation states, involving only physical alterations. Instances that employ covalent bond cleavage are still rare. We have developed a novel mechanochemical uncaging strategy to unveil AIEgens with diverse emission characteristics using engineered norborn-2-en-7-one (NEO) mechanophores. These NEO mechanophores were covalently integrated into polymer molecules and activated in both the solution and solid states. This activation resulted in highly tunable fluorescence upon immobilization through solidification or aggregation, producing blue, green, yellow, and orange-red emissions. By designing the caged and uncaged forms as donor-acceptor pairs for Förster resonance energy transfer (FRET), we achieved multicolor mechanofluorescence, effectively broadening the color spectrum to include white emission. Additionally, we computationally explored the electronic structures of activated NEOs, providing insights into the observed regiochemical effects of the substituents. This understanding, together with the novel luminogenic characteristics of the caged and activated species, provides a highly tunable reporter that traces progress with continuous color evolution. This advancement paves the way for future applications of mechanoresponsive materials in areas like damage detection and bioimaging.

A Thermally Stable SO2-Releasing Mechanophore: Facile Activation, Single-Event Spectroscopy, and Molecular Dynamic Simulations.

Polymers that release small molecules in response to mechanical force are promising candidates as next-generation on-demand delivery systems. Despite advancements in the development of mechanophores for releasing diverse payloads through careful molecular design, the availability of scaffolds capable of discharging biomedically significant cargos in substantial quantities remains scarce. In this report, we detail a nonscissile mechanophore built from an 8-thiabicyclo[3.2.1]octane 8,8-dioxide (TBO) motif that releases one equivalent of sulfur dioxide (SO2) from each repeat unit. The TBO mechanophore exhibits high thermal stability but is activated mechanochemically using solution ultrasonication in either organic solvent or aqueous media with up to 63% efficiency, equating to 206 molecules of SO2 released per 143.3 kDa chain. We quantified the mechanochemical reactivity of TBO by single-molecule force spectroscopy and resolved its single-event activation. The force-coupled rate constant for TBO opening reaches ∼9.0 s-1 at ∼1520 pN, and each reaction of a single TBO domain releases a stored length of ∼0.68 nm. We investigated the mechanism of TBO activation using ab initio steered molecular dynamic simulations and rationalized the observed stereoselectivity. These comprehensive studies of the TBO mechanophore provide a mechanically coupled mechanism of multi-SO2 release from one polymer chain, facilitating the translation of polymer mechanochemistry to potential biomedical applications.

Construction and application of base-stable MOFs: a critical review.

Metal-organic frameworks (MOFs) are a new class of porous crystalline materials constructed from organic ligands and metal ions/clusters. Owing to their unique advantages, they have attracted more and more attention in recent years and numerous studies have revealed their great potential in various applications. Many important applications of MOFs inevitably involve harsh alkaline operational environments. To achieve high performance and long cycling life in these applications, high stability of MOFs against bases is necessary. Therefore, the construction of base-stable MOFs has become a critical research direction in the MOF field. This review gives a historic summary of the development of base-stable MOFs in the last few years. The key factors that can determine the robustness of MOFs under basic conditions are analyzed. We also demonstrate the exciting achievements that have been made by utilizing base-stable MOFs in different applications. In the end, we discuss major challenges for the further development of base-stable MOFs. Some possible methods to address these problems are presented.

Stable Metal-Organic Frameworks for Fluorescent Detection of Tetracycline Antibiotics.

The rapid detection of antibiotics in agricultural products is of great significance. In this work, two stable fluorescent metal-organic frameworks (MOFs), BUT-178 and BUT-179, are synthesized and used to detect tetracycline antibiotics. Among them, BUT-179 exhibits better performance in the detection of different tetracycline antibiotics in water and eggs. The limits of detection of BUT-179 toward tetracycline, aureomycin, oxytetracycline, and doxycycline all reach the nanomolar level. Furthermore, the cycling tests confirm that BUT-179 can be easily recovered and repeatedly used without an obvious performance loss. This work demonstrates the excellent application potential of MOFs for food safety, especially the fluorescence detection of antibiotics in foods.

A Practice of Reticular Chemistry: Construction of a Robust Mesoporous Palladium Metal-Organic Framework via Metal Metathesis.

Constructing stable palladium(II)-based metal-organic frameworks (MOFs) would unlock more opportunities for MOF chemistry, particularly toward applications in catalysis. However, their availability is limited by synthetic challenges due to the inertness of the Pd-ligand coordination bond, as well as the strong tendency of the Pd(II) source to be reduced under typical solvothermal conditions. Under the guidance of reticular chemistry, herein, we present the first example of an azolate Pd-MOF, BUT-33(Pd), obtained via a deuterated solvent-assisted metal metathesis. BUT-33(Pd) retains the underlying sodalite network and mesoporosity of the template BUT-33(Ni) and shows excellent chemical stability (resistance to an 8 M NaOH aqueous solution). With rich Pd(II) sites in the atomically precise distribution, it also demonstrates good performances as a heterogeneous Pd(II) catalyst in a wide application scope, including Suzuki/Heck coupling reactions and photocatalytic CO2 reduction to CH4. This work highlights a feasible approach to reticularly construct noble metal based MOFs via metal metathesis, in which various merits, including high chemical stability, large pores, and tunable functions, have been integrated for addressing challenging tasks.

In Situ Porphyrin Substitution in a Zr(IV)-MOF for Stability Enhancement and Photocatalytic CO2 Reduction.

Despite numerous inherent merits of metal-organic frameworks (MOFs), structural fragility has imposed great restrictions on their wider involvement in many applications, such as in catalysis. Herein, a strategy for enhancing stability and enabling functionality in a labile Zr(IV)-MOF has been proposed by in situ porphyrin substitution. A size- and geometry-matched robust linear porphyrin ligand 4,4'-(porphyrin-5,15-diyl)dibenzolate (DCPP2- ) is selected to replace the 4,4'-(1,3,6,8-tetraoxobenzo[lmn][3,8]phenanthroline-2,7(1H,3H,6H,8H)-diyl)dibenzoate (NDIDB2- ) ligand in the synthesis of BUT-109(Zr), affording BUT-110 with varied porphyrin contents. Compared to BUT-109(Zr), the chemical stability of BUT-110 series is greatly improved. Metalloporphyrin incorporation endows BUT-110 MOFs with high catalytic activity in the photoreduction of CO2 , in the absence of photosensitizers. By tuning the metal species and porphyrin contents in BUT-110, the resulting BUT-110-50%-Co is demonstrated to be a good photocatalyst for selective CO2 -to-CO reduction, via balancing the chemical stability, photocatalytic efficiency, and synthetic cost. This work highlights the advantages of in situ ligand substitution for MOF modification, by which uniform distribution and high content of the incoming ligand are accessible in the resulting MOFs. More importantly, it provides a promising approach to convert unstable MOFs, which mainly constitute the vast MOF database but have always been neglected, into robust functional materials.

Boosting Interfacial Charge-Transfer Kinetics for Efficient Overall CO2 Photoreduction via Rational Design of Coordination Spheres on Metal-Organic Frameworks.

The recombination of electron-hole pairs severely detracts from the efficiency of photocatalysts. This issue could be addressed in metal-organic frameworks (MOFs) through optimization of the charge-transfer kinetics via rational design of structures at atomic level. Herein, a pyrazolyl porphyrinic Ni-MOF (PCN-601), integrating light harvesters, active catalytic sites, and high surface areas, has been demonstrated as a superior and durable photocatalyst for visible-light-driven overall CO2 reduction with H2O vapor at room temperature. Kinetic studies reveal that the robust coordination spheres of pyrazolyl groups and Ni-oxo clusters endow PCN-601 with proper energy band alignment and ultrafast ligand-to-node electron transfer. Consequently, the CO2-to-CH4 production rate of PCN-601 far exceeds those of the analogous MOFs based on carboxylate porphyrin and the classic Pt/CdS photocatalyst by more than 3- and 20-fold, respectively. The reaction avoids the use of hole scavengers and proceeds in a gaseous phase which can take full advantage of the high gas uptake of MOFs. This work demonstrates that the rational design of coordination spheres in MOF structures not only reconciles the contradiction between reactivity and stability but also greatly promotes the interfacial charge transfer to achieve optimized kinetics, providing guidance for the design of highly efficient MOF photocatalysts.

Wrinkled Graphene Cages as Hosts for High-Capacity Li Metal Anodes Shown by Cryogenic Electron Microscopy.

Lithium (Li) metal has long been considered the "holy grail" of battery anode chemistry but is plagued by low efficiency and poor safety due to its high chemical reactivity and large volume fluctuation, respectively. Here we introduce a new host of wrinkled graphene cage (WGC) for Li metal. Different from recently reported amorphous carbon spheres, WGC show highly improved mechanical stability, better Li ion conductivity, and excellent solid electrolyte interphase (SEI) for continuous robust Li metal protection. At low areal capacities, Li metal is preferentially deposited inside the graphene cage. Cryogenic electron microscopy characterization shows that a uniform and stable SEI forms on the WGC surface that can shield the Li metal from direct exposure to electrolyte. With increased areal capacities, Li metal is plated densely and homogeneously into the outer pore spaces between graphene cages with no dendrite growth or volume change. As a result, a high Coulombic efficiency (CE) of ∼98.0% was achieved under 0.5 mA/cm2 and 1-10 mAh/cm2 in commercial carbonate electrolytes, and a CE of 99.1% was realized with high-concentration electrolytes under 0.5 mA/cm2 and 3 mAh/cm2. Full cells using WGC electrodes with prestored Li paired with Li iron phosphate showed greatly improved cycle lifetime. With 10 mAh/cm2 Li metal deposition, the WGC/Li composite anode was able to provide a high specific capacity of ∼2785 mAh/g. With its roll-to-roll compatible fabrication procedure, WGC serves as a highly promising material for the practical realization of Li metal anodes in next-generation high energy density secondary batteries.

Tailor-Made Pyrazolide-Based Metal-Organic Frameworks for Selective Catalysis.

The predesignable porous structures in metal-organic frameworks (MOFs) render them quite attractive as a host-guest platform to address a variety of important issues at the frontiers of science. In this work, a perfluorophenylene functionalized metalloporphyrinic MOF, namely, PCN-624, has been rationally designed, synthesized, and structurally characterized. PCN-624 is constructed by 12-connected [Ni8(OH)4(H2O)2Pz12] (Pz = pyrazolide) nodes and fluorinated 5,10,15,20-tetrakis(2,3,5,6-tetrafluoro-4-(1 H-pyrazol-4-yl)phenyl)-porphyrin (TTFPPP) linker with an ftw-a topological net. Notably, PCN-624 exhibits extinguished robustness under different conditions, including organic solvents, strong acid, and base aqueous solutions. The pore surface of PCN-624 is decorated with pendant perfluorophenylene groups. These moieties fabricate densely fluorinated nanocages resulting in the selective guest capture of the material. More importantly, PCN-624 can be employed as an efficient heterogeneous catalyst for the selective synthesis of fullerene-anthracene bisadduct. Owing to the high chemical robustness of PCN-624, it can be recycled over five times without significant loss of its catalytic activity. All of these results demonstrate that MOFs can serve as a powerful platform with great flexibility for functional design to solve various synthetic problems.

A Base-Resistant Metalloporphyrin Metal-Organic Framework for C-H Bond Halogenation.

A base-resistant porphyrin metal-organic framework (MOF), namely PCN-602 has been constructed with 12-connected [Ni8(OH)4(H2O)2Pz12] (Pz = pyrazolate) cluster and a newly designed pyrazolate-based porphyrin ligand, 5,10,15,20-tetrakis(4-(pyrazolate-4-yl)phenyl)porphyrin under the guidance of the reticular synthesis strategy. Besides its robustness in hydroxide solution, PCN-602 also shows excellent stability in aqueous solutions of F-, CO32-, and PO43- ions. Interestingly, the Mn3+-porphyrinic PCN-602, as a recyclable MOF catalyst, presents high catalytic activity for the C-H bond halogenation reaction in a basic system, significantly outperforming its homogeneous counterpart. For the first time, a porphyrinic MOF was thus used as an efficient catalyst in a basic solution with coordinating anions, to the best of our knowledge.

Seed-Mediated Synthesis of Metal-Organic Frameworks.

The synthesis of phase-pure metal-organic frameworks (MOFs) is of prime importance but remains a significant challenge because of the flexible and diversified coordination modes between metal ions and organic linkers. In this work, we report the synthesis of phase-pure MOFs via a facile seed-mediated approach. For several "accompanying" pairs of Zr-porphyrinic MOFs that are prone to yield mixtures, by fixing all reaction parameters except introducing seed crystals, MOFs in phase-pure forms have been obtained because the stage of MOF nucleation, which generates mixed nuclei, is bypassed. In addition, phase-pure MOF isomers with distinct pore structures have also been prepared through such an approach, revealing its versatility. To the best of our knowledge, this is an initial report on seed-assisted synthesis of phase-pure MOFs.

Pyrazolate-Based Porphyrinic Metal-Organic Framework with Extraordinary Base-Resistance.

Guided by a top-down topological analysis, a metal-organic framework (MOF) constructed by pyrazolate-based porphyrinic ligand, namely, PCN-601, has been rationally designed and synthesized, and it exhibits excellent stability in alkali solutions. It is, to the best of our knowledge, the first identified MOF that can retain its crystallinity and porosity in saturated sodium hydroxide solution (∼ 20 mol/L) at room temperature and 100 °C. This almost pushes base-resistance of porphyrinic MOFs (even if MOFs) to the limit in aqueous media and greatly extends the range of their potential applications. In this work, we also tried to interpret the stability of PCN-601 from both thermodynamic and kinetic perspectives.

Topology-guided design and syntheses of highly stable mesoporous porphyrinic zirconium metal-organic frameworks with high surface area.

Through a topology-guided strategy, a series of Zr6-containing isoreticular porphyrinic metal-organic frameworks (MOFs), PCN-228, PCN-229, and PCN-230, with ftw-a topology were synthesized using the extended porphyrinic linkers. The bulky porphyrin ring ligand effectively prevents the network interpenetration which often appears in MOFs with increased linker length. The pore apertures of the structures range from 2.5 to 3.8 nm, and PCN-229 demonstrates the highest porosity and BET surface area among the previously reported Zr-MOFs. Additionally, by changing the relative direction of the terminal phenyl rings, this series replaces a Zr8 cluster with a smaller Zr6 cluster in a topologically identical framework. The high connectivity of the Zr6 cluster yields frameworks with enhanced stability despite high porosity and ultralarge linker. As a representative example, PCN-230, constructed with the most extended porphyrinic linker, shows excellent stability in aqueous solutions with pH values ranging from 0 to 12 and demonstrates one of the highest pH tolerances among all porphyrinic MOFs. This work not only presents a successful example of rational design of MOFs with desired topology, but also provides a strategy for construction of stable mesoporous MOFs.

A Reversible Crystallinity-Preserving Phase Transition in Metal-Organic Frameworks: Discovery, Mechanistic Studies, and Potential Applications.

A quenching-triggered reversible single-crystal-to-single-crystal (SC-SC) phase transition was discovered in a metal-organic framework (MOF) PCN-526. During the phase transition, the one-dimensional channel of PCN-526 distorts from square to rectangular in shape while maintaining single crystallinity. Although SC-SC transformations have been frequently observed in MOFs, most reports have focused on describing the resulting structural alterations without shedding light on the mechanism for the transformation. Interestingly, modifying the occupancy or species of metal ions in the extra-framework sites, which provides mechanistic insight into the causes for the transformation, can forbid this phase transition. Moreover, as a host scaffold, PCN-526 presents a platform for modulation of the photoluminescence properties by encapsulation of luminescent guest molecules. Through judicious choice of these guest molecules, responsive luminescence caused by SC-SC transformations can be detected, introducing a new strategy for the design of novel luminescent MOF materials.

A highly stable zeotype mesoporous zirconium metal-organic framework with ultralarge pores.

Through topological rationalization, a zeotype mesoporous Zr-containing metal-organic framework (MOF), namely PCN-777, has been designed and synthesized. PCN-777 exhibits the largest cage size of 3.8 nm and the highest pore volume of 2.8 cm(3) g(-1) among reported Zr-MOFs. Moreover, PCN-777 shows excellent stability in aqueous environments, which makes it an ideal candidate as a support to incorporate different functional moieties. Through facile internal surface modification, the interaction between PCN-777 and different guests can be varied to realize efficient immobilization.

A series of highly stable mesoporous metalloporphyrin Fe-MOFs.

A series of mesoporous metalloporphyrin Fe-MOFs, namely PCN-600(M) (M = Mn, Fe, Co, Ni, Cu), have been synthesized using the preassembled [Fe3O(OOCCH3)6] building block. PCN-600 exhibits a one-dimensional channel as large as 3.1 nm and the highest experimental pore volume of 1.80 cm(3)g(-1) among all the reported porphyrinic MOFs. It also shows very high stability in aqueous solutions with pH values ranging from 2-11 and is to our knowledge the only mesoporous porphyrinic MOF stable under basic aqueous conditions. PCN-600(Fe) has been demonstrated as an effective peroxidase mimic to catalyze the co-oxidation reaction.

Symmetry-guided synthesis of highly porous metal-organic frameworks with fluorite topology.

Two stable, non-interpenetrated MOFs, PCN-521 and PCN-523, were synthesized by a symmetry-guided strategy. Augmentation of the 4-connected nodes in the fluorite structure with a rigid tetrahedral ligand and substitution of the 8-connected nodes by the Zr/Hf clusters yielded MOFs with large octahedral interstitial cavities. They are the first examples of Zr/Hf MOFs with tetrahedral linkers. PCN-521 has the largest BET surface area (3411 m(2) g(-1)), pore size (20.5×20.5×37.4 Å) and void volume (78.5%) of MOFs formed from tetrahedral ligands. This work not only demonstrates a successful implementation of rational design of MOFs with desired topology, but also provides a systematic way of constructing non-interpenetrated MOFs with high porosity.

A Glucose-Responsive Cannula for Automated and Electronics-Free Insulin Delivery.

Automated delivery of insulin based on continuous glucose monitoring is revolutionizing the way insulin-dependent diabetes is treated. However, challenges remain for the widespread adoption of these systems, including the requirement of a separate glucose sensor, sophisticated electronics and algorithms, and the need for significant user input to operate these costly therapies. Herein, a user-centric glucose-responsive cannula is reported for electronics-free insulin delivery. The cannula-made from a tough, elastomer-hydrogel hybrid membrane formed through a one-pot solvent exchange method-changes permeability to release insulin rapidly upon physiologically relevant varying glucose levels, providing simple and automated insulin delivery with no additional hardware or software. Two prototypes of the cannula are evaluated in insulin-deficient diabetic mice. The first cannula-an ends-sealed, subcutaneously inserted prototype-normalizes blood glucose levels for 3 d and controls postprandial glucose levels. The second, more translational version-a cannula with the distal end sealed and the proximal end connected to a transcutaneous injection port-likewise demonstrates tight, 3-d regulation of blood glucose levels when refilled twice daily. This proof-of-concept study may aid in the development of "smart" cannulas and next-generation insulin therapies at a reduced burden-of-care toll and cost to end-users.

Unlocking the potential: strategic synthesis of a previously predicted pyrazolate-based stable MOF with unique clusters and high catalytic activity.

The metal-organic framework (MOF) constructed from [Co4Pz8] clusters (Pz = pyrazolate) and 1,3,5-tris(pyrazolate-4-yl) benzene (BTP3-) ligands was structurally predicted many years ago, and expected to be a promising candidate for various applications owing to its unique clusters and highly open 3D framework structure. However, this MOF has not been experimentally prepared yet, despite extensive efforts were made. In this work, we present the successful construction of this MOF, hereinafter referred to as BUT-124(Co), by adopting a two-step synthesis strategy, involving the initial construction of a template framework (BUT-124(Cd)) followed by a post-synthetic metal metathesis process. The effects of various cobalt sources and solvents were systematically investigated, and an innovative stepwise metathesis strategy was employed to optimize the exchange rates and the porosity of the material. BUT-124(Co) demonstrates high catalytic activity in the oxygen evolution reaction (OER), achieving a competitive performance with an overpotential of 393 mV at a current density of 10 mA cm-2, and also affords remarkable long-term stability during potentiostatic electrolysis in 1 M KOH solution, surpassing the durability of many benchmark catalysts. This work not only introduces a novel MOF material with promising properties but also exemplifies a strategic synthesis approach for pyrazolate-based MOFs, paving the way for advancements in diverse application fields.