Metal-organic Assemblies Research Articles

Modulating intramolecular charge transfer via π-d conjugative effect in coordination polymers toward photo-thermo-electric conversion

The prospect of harnessing sunlight to generate cost-effective heat and electricity presents a captivating opportunity to address water scarcity and electricity shortages. Photothermal materials with a broad absorption spectrum are indispensable for effectively harnessing solar energy and converting it into heat/electricity. Herein, we developed an intramolecular charge transfer strategy via conjugated effect to regulate solar absorption and photothermal conversion ability of M-DABDT (M = Fe/Co/Ni/Cu/Zn, DABDT = 2,5-diaminobenzene-1,4-dithiol), overcoming a common limitation of narrow absorption and low photothermal efficiency in traditional metal-organic assemblies. The density functional theory calculations reveal that altering transition metal ions induces the structural torsion of organic linkers, resulting in a significant change in dihedral angle from 89.96° to 2.57°. The structural change significantly facilitates the charge transfer and electron relaxation, ultimately promoting the conversion of light to heat. Under one sun irradiation, the maximum temperature of Fe-DABDT can reach approximately 92.5 ℃. More significantly, the integration of M-DABDT CPs and thermoelectric devices under normal solar irradiation results in an extraordinary open circuit voltage (238 mV) and maximum power density (364.5 μW m−2), processing a peak output voltage density of 76.9 V m−2 at 11:00 a.m. in the presence of outdoor sunlight. This strategy presents an avenue for developing metal-organic solar absorbers for photo-thermo-electric conversion systems.

Rational design of metal–organic cages to increase the number of components via dihedral angle control

The general principles of discrete, large self-assemblies composed of numerous components are not unveiled and the artificial formation of such entities is a challenging topic. In metal–organic cages, design strategies for tuning the coordination directions in multitopic ligands by the bend and twist angles were previously developed to solve this problem. In this study, the importance of remote geometric communications between components is emphasized, realizing several types of metal–organic assemblies based on dihedral angle control in multitopic ligands although they have the same coordination directions. Self-assembly of a tritopic ligand with dihedral angles θ = 36.5° and a cis-protected Pd(II) ion affords M9L6 and M12L8 cages as kinetic and thermodynamic products, respectively, whereas an M12L8 sheet is formed when θ = 90°. Geometric analyses of strains in the subcomponent rings reveals that remote geometric communications among neighboring multitopic ligands through coordination bonds are key for large assemblies.

Asymmetric Charge Distribution in One-dimensional Metal-Organic Assemblies to Promote Photocatalytic Hydrogen Evolution.

The local charge distribution of photocatalyst is crucial to the catalytic activity due to its influence on the charge separation process. Herein, we report two one-dimensional Ni-based metal-organic assemblies for efficient photocatalytic hydrogen evolution without using noble-metal cocatalysts. By adjusting the aromatic ring in the center of the tricarboxylic ligand, the photocatalytic hydrogen evolution activity was increased from 1715 to 2652 μmol h-1 g-1. The detailed mechanism study shows that the introduced nitrogen atoms in the ligands of the metal-organic coordination assembly could modulate the local charge distribution, and yielding a significant enhancement of the molecular dipole moment which engenders a propulsive force for the effective separation and transport of photoinduced charge carriers. This work provides insights into the local charge distribution via ligand modulation for enhancing the activity of photocatalysts.

The Influence of Light-Generated Radicals for Highly Efficient Solar-Thermal Conversion in an Ultra-Stable 2D Metal-Organic Assembly.

Solar-thermal water evaporation is a promising strategy for clean water production, which needs the development of solar-thermal conversion materials with both high efficiency and high stability. Herein, we reported an ultra-stable cobalt(II)-organic assembly NKU-123 with light-generated radicals, exhibiting superior photothermal conversion efficiency and high stability. Under the irradiation of 808 nm light, the temperature of NKU-123 rapidly increases from 25.5 to 215.1 °C in 6 seconds. The solar water evaporator based on NKU-123 achieves a high solar-thermal water evaporation rate of 1.442 and 1.299 kg m-2 h-1 under 1-sun irradiation with a water evaporation efficiency of 97.8 and 87.9 % for pure water and seawater, respectively. A detailed mechanism study revealed that the formation of light-generated radicals leads to an increase of spin density of NKU-123 for enhancing the photothermal effect, which provides insights into the design of highly efficient photothermal materials.

A critical overview on impact of different nano-catalytic assemblies for photodegradation of tetracycline

Abstract Recently, the removal of tetracycline, a toxic material, from aquatic medium has been a trending subject of research. Several different technologies including adsorption, biological removal method, solvent extraction, coagulation, chemical reduction, photocatalysis and ion exchange method for removal of tetracyclines from wastewater have been reported. However, photocatalysis of tetracyclines (TC) has gained huge interest because of more efficient mineralization of TC into CO2 and water. Several different nanomaterial based photocatalytic assemblies for the removal of tetracyclines have been widely reported for the removal of tetracyclines which have not been critically reviewed in the literature. This study provides an overview of recent progress of classification, synthesis, characterizations, mechanism of inorganic and metal organic framework nanocatalytic assemblies on photocatalysis of tetracyclines in aquatic medium. Additionally, kinetics and factors affecting the photocatalysis of tetracyclines have been discussed briefly. Future perspectives have also been presented for further advancement in this area.

Steric and Geometrical Frustration Generate Two Higher-Order CuI12L8 Assemblies from a Triaminotriptycene Subcomponent.

The use of copper(I) in metal-organic assemblies leads readily to the formation of simple grids and helicates, whereas higher-order structures require complex ligand designs. Here, we report the clean and selective syntheses of two complex and structurally distinct CuI12L8 frameworks, 1 and 2, which assemble from the same simple triaminotriptycene subcomponent and a formylpyridine around the CuI templates. Both represent new structure types. In T-symmetric 1, the copper(I) centers describe a pair of octahedra with a common center but whose vertices are offset from each other, whereas in D3-symmetric 2, the metal ions form a distorted hexagonal prism. The syntheses of these architectures illustrate how more intricate CuI-based complexes can be prepared via subcomponent self-assembly than has been possible to date through consideration of the interplay between the subcomponent geometry and solvent and electronic effects.

Visualization of drug release in a chemo-immunotherapy nanoplatform via ratiometric 19F magnetic resonance imaging.

Visualization of drug release in vivo is crucial for improving therapeutic efficacy and preventing inappropriate medication dosing, yet, challenging. Herein, we report a pH-activated chemo-immunotherapy nanoplatform with visualization of drug release in vivo by ratiometric 19F magnetic resonance imaging (19F MRI). This nanoplatform consists of ultra-small histamine-modified perfluoro-15-crown-5-ether (PFCE) nanodroplets loaded with doxorubicin (Dox), which are packaged in trifluoromethyl-containing metal-organic assemblies via coordination-driven self-assembly. The chemical shifts of two types of 19F atoms in the nanoplatform are significantly different in 19F nuclear magnetic resonance (NMR) spectra, which facilitates the implementation of ratiometric 19F MRI without any signal crosstalk. In an acidic tumor microenvironment, this nanoplatform gradually degrades, which results in a sustained drug release with a real-time change in the ratiometric 19F MRI signal. Therefore, a linear correlation between the Dox release profile and ratiometric 19F MRI signal is established to visualize Dox release. Moreover, the pH-triggered disassembly of the nanoplatform leads to cell pyroptosis, which evokes immunogenic cell death (ICD), resulting in the regression of the primary tumor and inhibition of distal tumor growth. This study provides the proof-of-concept application of ratiometric 19F MRI to visualize drug release in vivo.

Design of Metal–Organic Assemblies via Shape Complementarity and Conformational Constraints in Dual Curvature Ligands

Design of Metal–Organic Assemblies via Shape Complementarity and Conformational Constraints in Dual Curvature Ligands

9,10-Bis(diphenylmethylene)-9,10-dihydroanthracene-based metal-organic assemblies with aggregation-induced emission for multiple sensing

Developing novel emissive supramolecular assemblies with elegant architectures and tunable performance remains highly desirable yet challenging. Herein, we report the design and synthesis of several 9,10-bis(diphenylmethylene)-9,10-dihydroanthracene-based metal-organic assembles with aggregation-induced emission characteristics. Such assemblies feature intriguing thermochromic and mechanochromic properties, i.e., distinguishable fluorescence responses in terms of emission wavelength and intensity under variable temperatures and pressures. Moreover, these assemblies can serve as excellent fluorescent sensors for the detection of polysaccharide molecules. Due to the differentiated charge type and density, the assembles display distinct sensing mechanisms toward different polysaccharide molecules. This study provides novel perspectives for the synthesis of butterfly-like platinum(II) supramolecular coordination complexes with multistimuli-responsiveness for polysaccharide sensing, which will facilitate the development of stimuli-responsive materials

Construction of dual-hydrophilic metal-organic framework with hierarchical porous structure for efficient glycopeptide enrichment

As an important role in life activities, it is necessary and important to study protein glycosylation. The pre-enrichment of N-glycopeptides is a significant step in glycoproteomics research. According to the inherent size, hydrophilicity and other properties of N-glycopeptides, affinity materials designed to match them will be able to separate N-glycopeptides from complex samples. In this work, we designed and prepared dual-hydrophilic hierarchical porous metal-organic frameworks (MOFs) nanospheres by metal-organic assembly (MOA) based template method and post-synthesis modification strategy. The hierarchical porous structure significantly improved the diffusion rate and binding sites for N-glycopeptide enrichment. Furthermore, the combination of hydrophilic MOFs and small molecules endowed the as-prepared MOFs nanospheres excellent hydrophilicity, which is conducive to the enrichment of N-glycopeptides based on hydrophilic interaction liquid chromatography (HILIC). Therefore, the nanospheres showed surprising enrichment ability for N-glycopeptides such as excellent selectivity (1/500, human serum immunoglobulin G/bovine serum albumin, m/m) and extremely low detective limitation (0.5 fmol). Meanwhile, 550 N-glycopeptides were identified from rat liver samples, proving its application potential in glycoproteomics research and providing design idea for porous affinity materials.

Metal-Organic Assembly Strategy for the Synthesis of Layered Metal Chalcogenide Anodes for Na+ /K+ -Ion Batteries.

Layered transition metal chalcogenides (MX, M=Mo, W, Sn, V; X=S, Se, Te) have large ion transport channels and high specific capacity, making them promising for large-sized Na+ /K+ energy-storage technologies. Nevertheless, slow reaction kinetics and huge volume expansion will induce an undesirable electrochemical performance. Numerous efforts have been devoted to designing MX anodes and enhancing their electrochemical performance. Based on the metal-organic assembly strategy, nanostructural engineering, combination with carbon materials, and component regulation can be easily realized, which effectively boost the performance of MX anodes. In this Review, we present a comprehensive overview on the synthesis of MX nanostructure using the metal-organic assembly strategy, which can realize the design of MX nanostructures, based on self-sacrificial templates, host@guest tailored templates, post-modified layer and derivative templates. The preparation routes and structure evolution are mainly discussed. Then, Mo-, W-, Sn-, V-based chalcogenides used for Na+ /K+ energy storage are reviewed, and the relationship between the structure and the electrochemical performance, as well as the energy storage mechanism are emphasized. In addition, existing challenges and future perspectives are also presented.

Chirality-Dependent Copper-Diphenylalanine Assemblies with Tough Layered Structure and Enhanced Catalytic Performance.

Chiral regulation to prepare functional materials has aroused considerable interest in recent years. However, little is known on the effect of chirality of ligands in the metal-organic coordination assembly process. We report the self-assembly of diphenylalanine peptide (Phe-Phe, FF), the core fragment of Aβ protein, with metal copper ion (Cu2+) into metal-organic assemblies with chirality-encoded structures and properties. The chirality-dependent metal-dipeptide assembles with different morphologies and supramolecular chirality were obtained by facile changing of the FF chirality. Single-crystal results indicate that (L)-FF coordinated with Cu2+ into a cross-chain structure with a five-coordinated style, while the racemates of (L+D)-FF with Cu2+ crystallized into an (L)-Cu2+-(D)-Cu2+ alternated four-coordinating structure, enabling a higher mechanical and catalytic performance. The Young's modulus of (L+D)-FF-Cu is as high as 34.36 GPa, which is 2.45 times higher than that of (L)-FF-Cu. Furthermore, both of them follow the characteristic enzyme kinetics and show higher catalytic activity than natural laccase at the same mass concentration. Specifically, the calculated catalytic efficiency (kcat/KM) of (L+D)-FF-Cu is 1.14 times higher than that of (L)-FF-Cu, and the (L+D)-FF-Cu shows significantly enhanced stability and reusability compared with (L)-FF-Cu. The results reveal that highly functional materials could be constructed by encoding the chirality of molecular building blocks.

Transformation networks of metal-organic cages controlled by chemical stimuli.

The flexibility of biomolecules enables them to adapt and transform as a result of signals received from the external environment, expressing different functions in different contexts. In similar fashion, coordination cages can undergo stimuli-triggered transformations owing to the dynamic nature of the metal–ligand bonds that hold them together. Different types of stimuli can trigger dynamic reconfiguration of these metal–organic assemblies, to switch on or off desired functionalities. Such adaptable systems are of interest for applications in switchable catalysis, selective molecular recognition or as transformable materials. This review highlights recent advances in the transformation of cages using chemical stimuli, providing a catalogue of reported strategies to transform cages and thus allow the creation of new architectures. Firstly we focus on strategies for transformation through the introduction of new cage components, which trigger reconstitution of the initial set of components. Secondly we summarize conversions triggered by external stimuli such as guests, concentration, solvent or pH, highlighting the adaptation processes that coordination cages can undergo. Finally, systems capable of responding to multiple stimuli are described. Such systems constitute composite chemical networks with the potential for more complex behaviour. We aim to offer new perspectives on how to design transformation networks, in order to shed light on signal-driven transformation processes that lead to the preparation of new functional metal–organic architectures.

Molecularly engineered graphene oxide anchored metal organic assembly: An active site economic bi-functional electrocatalyst

Low-temperature fuel cells are the most promising sustainable energy technology as they use hydrogen, an environmentally clean fuel. However, the sluggish kinetics of oxygen electrochemistry, a chronic issue, is holding them from commercialization. Herein, we address this issue through a molecular level design of a Graphene oxide anchored Metal Organic Molecular Assembly (G-MOMA) based catalyst. This non-precious metal catalyst consists of Ni and Fe ions ligated by graphene oxide supported terpyridine, a unique molecular assembly design that maximizes the utilization of active metal centers. This G-MOMA catalyst brings down an over potential (240 mV) for oxygen evolution reaction (OER) as close as that of the bench mark catalyst Ru/C with an impressive Tafel slope of 58 mV/dec and a cyclic stability of >30,000 cycles. G-MOMA excels in oxygen reduction reaction (ORR) too with an onset at 0.88 V (vs RHE). The remarkably stable G-MOMA catalyst surprises with an excellent bi-functionality towards both OER and ORR with an overall potential difference of mere 0.77 V, which is 180 mV and 70 mV lesser than the standard Pt/C and Ru/C catalysts, respectively. The G-MOMA catalyst is well in the activity range of the state-of-art bi-functional catalysts and yet cheaper by many folds.

Topologically non-trivial metal-organic assemblies inhibit β2-microglobulin amyloidogenesis

Inhibiting amyloid aggregation through high-turnover dynamic interactions could be an efficient strategy that is already used by small heat-shock proteins in different biological contexts. We report the interactions of three topologically non-trivial, zinc-templated metal-organic assemblies, a [2]catenane, a trefoil knot (TK), and Borromean rings, with two β 2 -microglobulin (β2m) variants responsible for amyloidotic pathologies. Fast exchange and similar patterns of preferred contact surface are observed by NMR, consistent with molecular dynamics simulations. In vitro fibrillation is inhibited by each complex, whereas the zinc-free TK induces protein aggregation and does not inhibit fibrillogenesis. The metal coordination imposes structural rigidity that determines the contact area on the β2m surface depending on the complex dimensions, ensuring in vitro prevention of fibrillogenesis. Administration of TK, the best protein-contacting species, to a disease-model organism, namely a Caenorhabditis elegan s mutant expressing the D76N β2m variant, confirms the bioactivity potential of the knot topology and suggests new developments. Topologically non-trivial (TnT) species may engage labile supramolecular interactions Proteins can be ideal targets of TnT metal-templated structures Protein fibrillogenesis can be inhibited by TnT metal-organic assemblies Rigidity and dimensions of the TnT assemblies modulate interactions with proteins Prakasam et al. report that topologically non-trivial metal-organic species inhibit the in vitro fibrillogenesis of the paradigmatic amyloidogen β 2 -microglobulin and the effects of the D76N mutant expression in a Caenorhabditis elegans disease model. Acting as small-molecule chaperones, the metal-templated assemblies suppress the formation of soluble protofibrillar oligomers by engaging labile supramolecular interactions that interfere with protein-protein pairing.

Glucose Binding Drives Reconfiguration of a Dynamic Library of Urea-Containing Metal-Organic Assemblies.

A bis-urea-functionalized ditopic subcomponent assembled with 2-formylpyridine and FeII , resulting in a dynamic library of metal-organic assemblies: an irregular FeII4 L6 structure and three FeII2 L3 stereoisomers: left- and right-handed helicates and a meso-structure. This library reconfigured in response to the addition of monosaccharide derivatives, which served as guests for specific library members, and the rate of saccharide mutarotation was also enhanced by the library. The (P) enantiomer of the FeII2 L3 helical structure bound β-D-glucose selectively over α-D-glucose. As a consequence, the library collapsed into the (P)-FeII2 L3 helicate following glucose addition. The α-D-glucose was likewise transformed into the β-D-anomer during equilibration and binding. Thus, β-D-glucose and (P)-3 amplified each other in the product mixture, as metal-organic and saccharide libraries geared together into a single equilibrating system.

Glucose Binding Drives Reconfiguration of a Dynamic Library of Urea‐Containing Metal–Organic Assemblies

AbstractA bis‐urea‐functionalized ditopic subcomponent assembled with 2‐formylpyridine and FeII, resulting in a dynamic library of metal–organic assemblies: an irregular FeII4L6 structure and three FeII2L3 stereoisomers: left‐ and right‐handed helicates and a meso‐structure. This library reconfigured in response to the addition of monosaccharide derivatives, which served as guests for specific library members, and the rate of saccharide mutarotation was also enhanced by the library. The (P) enantiomer of the FeII2L3 helical structure bound β‐D‐glucose selectively over α‐D‐glucose. As a consequence, the library collapsed into the (P)‐FeII2L3 helicate following glucose addition. The α‐D‐glucose was likewise transformed into the β‐D‐anomer during equilibration and binding. Thus, β‐D‐glucose and (P)‐3 amplified each other in the product mixture, as metal–organic and saccharide libraries geared together into a single equilibrating system.

Metal Organic Frame-Upconverting Nanoparticle Assemblies for the FRET Based Sensor Detection of Bisphenol A in High-Salt Foods.

To resolve the occurrence of unfulfillable detection in high-salts foods, we used fluorescence resonant energy transfer (FRET) sensors based on nanoparticle upconversion. In this study, we developed a novel FRET sensor for the detection of bisphenol A (BPA) in high-salt foods. We based this approach on the assembly of aptamer modified upconversion nanoparticles (DNA1-UCNPs) and complementary DNA modified metal organic frames (DNA2-MOFs), which possessed corresponding wavelength absorption. Targeting BPA signal transduction was performed using the BPA aptamer, via competitive recognition between the BPA analyte and complementary DNA sequences in a high-salt solution. Sensor adaption in high-salt samples was attributed to functional hydrophilic groups, modified in the MOFs, and the enhanced colloidal stability of these MOFs. The MOF-UCNP assembly displayed considerable analytical performance in terms of BPA detection, with a linear range of 0.1–100 nM, and a limit of detection (LOD) of 0.02 nM, in a 340 mM NaCl food sample (the energy drink, Gatorade). Thus, this method provides a solid basis for small molecules detection in high-salt foods.

Intrinsic Effect of Pyridine-N-Position on Structural Properties of Cu-Based Low-Dimensional Coordination Frameworks.

Metal-organic assemblies have received significant attention for catalytic and other applications, including gas and energy storage, due to their porosity and thermal/chemical stability. Here, we report the synthesis and physicochemical characterization of three metallosupramolecular assemblies consisting of isomeric ambidentate pyridyl-β-diketonate ligands L1–L3 and Cu(II) metal ions. It has been demonstrated that the topology and dimensionality of generated supramolecular aggregates depend on the location of the pyridine nitrogen donor atom in L1–L3. This is seen in characterization of two distinct 2D polymeric assemblies, i.e., [Cu(L1)2]n and [Cu(L2)2]n, in which both β-diketonate and pyridine groups are coordinated to the Cu(II) center, as well as in characterization of the mononuclear 1D complex Cu(L3)2, in which the central atom is bound only by two β-diketonate units.

Regioselective Photochemical Cycloaddition Reactions of Diolefinic Ligands in Coordination Polymers.

The pure diolefinic ligand 1,4-bis(pyridin-4-yl)-1,3-butadiene (bpbde) is photostable in the crystalline state. With the assistance of coordination-driven metal-organic assemblies, the photoreactivity of this diolefinic ligand can be significantly enhanced. A hydrothermal reaction of bpbde with Cd(NO3 )2 ⋅4 H2 O and the auxiliary ligand adipic acid resulted in the formation of a two-dimensional photoreactive coordination polymer (CP), [Cd(adipate)(bpbde)]n (1). When the aliphatic carboxylic acid was replaced by pimelic acid, another photoreactive CP [Cd(pimelate)(bpbde)]n (2) with a three-dimensional framework was obtained. With irradiation of 365 nm UV light, the bpbde ligands in crystalline 1 and 2 underwent a regioselective photochemical [2+2] cycloaddition reaction and converted to 3,4,7,8-tetra(pyridin-4-yl)tricyclo[4.2.0.02,5 ]octane (tptco) and 1,3-bis(pyridin-4-yl)-2,4-bis(2-(pyridin-4-yl)vinyl)cyclobutane (bpbpvcb), respectively. The results provide an interesting insight into the rational design of highly regio- or stereoselective photocatalytic reactions for the formation of special organic molecules.