Novel morphological mono-metallic substituted polyoxometalate immobilized 3-(aminopropyl)-imidazole photocatalysts for visible-light driven degradation: Anti-bacterial activity, membrane bacterial activity applications

A novel keggin-type tetra-metalates substituted polyoxometalate was functionalized by 3-(aminopropyl)-imidazole (3-API) supporting a ligand substitution method. In this paper, polyoxometalate (POMs) (NH₄)₃ [PMo₁₂O₄₀] and transition metal substituted of (NH₄)₃ [{PM^IVMo₁₁O₄₀}.(H₂O)] (M = Mn, V) are used as one of the adsorbents. The 3-API/POMs hybrid have been synthesized and used as adsorbent for the photo-catalysis of azo-dye molecule degradation after visible-light illumination as a simulated organic contaminant in water. The transition metal (M = M^IV, V^IV) substituted keggin-type anions (MPOMs) were synthesized, which reveals the degradation of methyl orange (MO) of about 94.0 % and 88.6 %. Immobilizing high redox ability POMs as an efficient acceptor of photo generated electron, on metal 3-API. In the presence of visible light irradiation result reveals that 3-API/POMs (89.9 %) have incredibly achieved after certain irradiation time and at specific conditions (3)-API/POMs; photo-catalysts dose = 5mg/100 ml, pH = 3 and MO dye concentration = 5 ppm). As the surface of POM catalyst has strong absorption of azo-dye MO molecule engaged as a molecular exploration through photo catalytic reactant. From the SEM images it is clear that the synthesized POMs based materials and POMs conjugated MO have varieties of morphological changes observed such as flakes, rods and spherical like structures. Anti-bacterial study reveals that the process of targeted microorganism occur higher activity against pathogenic bacterium for 180 min of visible-light irradiation is measured in terms of zone of the inhibition. Furthermore, the photo catalytic degradation mechanism of MO using POM, metaled POMs and 3-API/POMs also has been discussed.

Two Polyoxometalate-Encapsulated Two-Fold Interpenetrating Metal-Organic Frameworks for the Detection, Discrimination, and Degradation of Phenolic Pollutants

Phenols are widely used for commercial production, while they pose a hazard to the environment and human health. Thus, investigation of convenient and efficient methods for the detection, discrimination, and degradation of phenols becomes particularly important. Herein, two new polyoxometalate (POM)-based compounds, [Co₂(btap)₄(H₂O)₄][SiW₁₂O₄₀] (Co-POM) and [Ni₂(btap)₄(H₂O)₄][SiW₁₂O₄₀] (Ni-POM) (btap = 3,5-bis(triazol-1-yl)pyridine), are prepared via a hydrothermal synthesis method. The compounds show a fascinating structural feature of a POM-encapsulated twofold interpenetrating dia metal-organic framework. More importantly, besides the novel structures, the compound Co-POM realizes three functions, namely, the simultaneous detection, discrimination, and degradation of phenols. Specifically, Co-POM shows an excellent colorimetric detection performance toward phenol with a detection limit (LOD) ca. 1.32 μM, which is lower than most reported colorimetric detectors for phenol. Also, a new colorimetric sensor system based on Co-POM can discriminate phenol, 4-chlorophenol, and o-cresol with ease. Further, Co-POM exhibits a photocatalytic degradation property for 4-chlorophenol under irradiation of visible light with the highest degradation rate at 62% after irradiation for 5 h. Therefore, this work provides the first example of a POMs-based multifunctional material for achieving the detection, discrimination, and degradation of phenolic pollutants.

Recent Advances in Polyoxometalates with Enzyme-like Characteristics for Analytical Applications

Artificial enzymes based on inorganic solids with both enzyme-mimetic activities and the special material features has been a promising candidate to overcome many deleterious effects of native enzymes in analytical applications. Polyoxometalates (POMs) are an importance class of molecular metal-oxygen anionic clusters. Their outstanding physicochemical properties, versatility and potential applications in energy conversion, magnetism, catalysis, molecular electronics and biomedicine have long been studied. However, the analytical applications of them is limited. Recently, the intrinsic enzymatic activities of POMs have also been found and become an area of growing interest. In this review, along with other reports, we aimed to classify the enzymatic activity of POMs, summarize the construction of POMs-based enzymes, and survey their recent advances in analytical fields. Finally, the current challenges and trends of the polyoxometalates with enzymatic activity in future chemo-/bio-sensing applications are briefly discussed.

Oxygen-Powered Flower-like FeMo6@CeO2 Self-cascade Nanozyme: Turn-on Enhancement Fluorescence Sensor

Enzyme cascade reactions in organisms have sparked tremendous interest for their coupled catalysis-facilitated efficient biochemical reactions. However, multi-enzyme cascade nanozymes remain largely unpracticed. In the work, flower-like porous ceria-based integrated...

Polyoxometalate-Based Nanomaterials Toward Efficient Cancer Diagnosis and Therapy

As an emerging class of inorganic metal oxides, organically functionalized polyoxometalates (POMs) or POM-based nanohybrids have been demonstrated promising potential for the inhibition of various cancer types by the virtue of their diversity in structures and significantly reduced toxicity. This contribution summarizes the latest achievement of POM-based nanomaterials in cancer diagnosis and various therapeutics to put forward our fundamental viewpoints on the design principles of modified POMs based on their application. In addition, major challenges and perspectives in this field are also discussed. We expect that this review will provide a valuable and systematic reference for the further development of POM-based nanomaterials.

Preparation of laccase mimicking nanozymes and their catalytic oxidation of phenolic pollutants

The construction of a nanozyme that mimics a natural enzyme is a promising strategy to obtain a highly stable catalyst.

A polypyrrole-coated eightfold-helical Wells-Dawson POM-based Cu-FKZ framework for enhanced colorimetric sensing

To explore a novel colorimetric biosensor with high sensibility and selectivity, a new Wells-Dawson-type polyoxometalate (POM)-based metal-organic framework (MOF) with an eightfold helix, [Cu₉(FKZ)₁₂(H₂O)₈][H₃P₂W₁₈O₆₂]₂·4H₂O (CuFKZP₂W₁₈) (HFKZ = 1-(2,4-difluorophenyl)-1,1-bis[(1H-1,2,4-triazol-1-yl)methyl] ethanol), was successfully synthesized; then, polypyrrole (PPy) was introduced to fabricate CuFKZP₂W₁₈/PPy(n) nanocomposites (n = 7%, 15%, 30%) via a facile in situ oxidation polymerization process. All the results indicate that CuFKZP₂W₁₈/PPy(15%) as a colorimetric biosensor exhibits lower limits of detection (0.07 μM towards H₂O₂ and 0.627 μM towards ascorbic acid), smaller K_m values (0.106 mM for H₂O₂ and 0.042 mM for o-phenylenediamine) and higher sensitivity (0.0227 1 μM^-1 towards H₂O₂ and 0.0025 1 μM^-1 to ascorbic acid) than most reported enzyme mimetics to the best of our knowledge.

AuNPs@PMo12nanozyme: highly oxidase mimetic activity for sensitive and specific colorimetric detection of acetaminophen

The design of a highly specific and sensitive approach for the quantitative and qualitative determination of acetaminophen (AP) is crucial from a human health point of view. In this study, AuNPs@PMo₁₂, as a nanozyme, has been developed for the highly sensitive and selective detection of AP with 3,3′,5,5′-tetramethylbenzidine (TMB) within a few seconds without adding oxidizing reagents (e.g. H₂O₂). Synthesized nanosensors are able to oxidize TMB to yellow-brown oxidized TMB (oxTMB). The maximum peak wavelength of oxTMB was observed at 450 nm. The addition of AP and then increasing its concentration led to the production of different products in blue color. In experimental measurements, the limit of detection was obtained as 14.52 mg L⁻¹. The quantitative determination of AP concentrations can be carried out using UV-vis spectroscopy. The design of nanosensors is cost-effective and application of them in H₂O₂-free and enzyme-free conditions provides a rapid sensing approach for practical use in disease monitoring and diagnosis.

The design of a highly specific and sensitive approach for the quantitative and qualitative determination of acetaminophen (AP) is crucial from a human health point of view.

Sonochemical synthesis of polyoxometalate-stabilized gold nanoparticles for point-of-care determination of acetaminophen levels: preclinical study in an animal model

The aim of this study is the accurate and rapid detection of acetaminophen (AP) for point-of-care (POC) clinical diagnosis. Acetaminophen overdose causes acute liver failure and currently there is a lack of rapid quantitative detection methods for this drug in the emergency room. Here, low-frequency sonication (20 kHz) in the presence of phosphomolybdic acid (PMo₁₂) was used to reduce Au³⁺ to Au⁰ and stabilize the resulting spherical Au⁰ nanoparticles (herein AuNPs). These AuNPs@PMo₁₂ were used as nano-probes for the selective detection of acetaminophen in the presence of other commercial drugs. The optical sensing method we describe is based on the aggregation of AuNPs@PMo₁₂ in the presence of acetaminophen, which produces a red-shift in the absorption spectrum of the AuNPs@PMo₁₂, which is characterised by a color change from red to purple that is visible to the naked eye. Furthermore, the quantitative determination of acetaminophen concentrations can be carried out using the eyedropper function in Microsoft's PowerPoint or open access ImageJ software, using RGB (red, green, and blue) values. To prove the feasibility of this novel nanosensor, the concentration of acetaminophen was measured in over-the-counter pharmaceutical tablets and in serum samples taken from mice. This simple sensing approach offers high stability, selectivity, rapid detection time, and cost saving compared to other detection methods, which therefore opens the way for the development of quantitative POC acetaminophen detection using polyoxometalate-stabilized metal nanoparticles.

The aim of this study is the accurate detection of acetaminophen (AP) for point-of-care (POC) clinical diagnosis. The concentration of acetaminophen was measured in over-the-counter pharmaceutical tablets and in serum samples taken from mice.

The Intrinsic Enzyme Activities of the Classic Polyoxometalates

The mimicking enzyme activities of eighteen classic POMs with different structures, Keggin (H₃PW₁₂O₄₀, H₄SiW₁₂O₄₀, H₄GeW₁₂O₄₀, K₄GeW₁₂O₄₀, H₃PMo₁₂O₄₀, H₄SiMo₁₂O₄₀ and Eu₃PMo₁₂O₄₀), Wells-Dawson (H₆P₂Mo₁₈O₆₂, α-(NH₄)₆P₂W₁₈O₆₂ and α-K₆P₂W₁₈O₆₂·14H₂O), lacunary-Keggin (Na₈H[α-PW₉O₃₄], Na₁₀[α-SiW₉O₃₄], Na₁₀[α-GeW₉O₃₄] and K₈[γ-SiW₁₀O₃₆]), the transition-metal substituted-type (α-1,2,3-K₆H[SiW₉V₃O₃₄] and H₅PMo₁₀V₂O₄₀), sandwich-type (K₁₀P₂W₁₈Fe₄(H₂O)₂O₆₈) and an isopolyoxotungstate (Na₁₀H₂W₁₂O₄₂) were screened and compared. The mechanisms and reaction conditions of POMs with mimicking enzyme-like activities were also analyzed. The results shown that the structures, the hybrid atoms, the coordination atoms, the substituted metal atoms, pH and substrate are the effect factors for the enzyme mimic activities of POM. Among the eighteen POMs, H₃PW₁₂O₄₀, H₄SiW₁₂O₄₀, H₄GeW₁₂O₄₀, α-(NH₄)₆P₂W₁₈O₆₂, α-K₆P₂W₁₈O₆₂·14H₂O, Na₈H[α-PW₉O₃₄], Na₁₀[α-SiW₉O₃₄], Na₁₀[α-GeW₉O₃₄], K₈[γ-SiW₁₀O₃₆], K₁₀P₂W₁₈Fe₄(H₂O)₂O₆₈ and Na₁₀H₂W₁₂O₄₂ had the peroxidase activities. Eu₃PMo₁₂O₄₀, H₃PMo₁₂O₄₀, H₄SiMo₁₂O₄₀, α-1,2,3-K₆H [SiW₉V₃O₃₄], H₆P₂Mo₁₈O₆₂ and H₅PMo₁₀V₂O₄₀ showed the oxidase-like activities. K₄GeW₁₂O₄₀ did not show the peroxidase and oxidase activities. The Na₈H[α-PW₉O₃₄], Na₁₀[α-SiW₉O₃₄] and Na₁₀[α-GeW₉O₃₄] showed intrinsic enzyme activities at alkaline conditions, which were different from other type of POMs. The sandwich-type K₁₀P₂W₁₈Fe₄(H₂O)₂O₆₈ displayed the strongest peroxidase activity, which is similar to natural horseradish peroxidase.

POMOF/SWNT Nanocomposites with Prominent Peroxidase-Mimicking Activity for l-Cysteine "On-Off Switch" Colorimetric Biosensing

In order to explore novel colorimetric biosensors with high sensibility and selectivity, two new Keggin polyoxometalates (POMs)-based Cu-trz (1,2,4-triazole) metal-organic frameworks (MOFs) with suitable specific surface areas and multiple active sites were favorably fabricated; then single-walled carbon nanotubes (SWNTs) were merged with new POMOFs to construct POMOF/SWNT nanocomposites. Herein, POMOF/SWNT nanocomposites as peroxidase mimics were explored for the first time, and the peroxidase-mimicking activity of the prepared POMOF/SWNT nanocomposites is heavily dependent on the mass ratio of POMOFs and SWNTs, in which the maximum activity is achieved at the mass ratio of 2.5:1 (named PMNT-2). More importantly, PMNT-2 exhibits the lowest limit of detection (0.103 μM) among all reported materials to date and the assumable selectivity toward l-cysteine (l-Cys) detection. With these findings, a convenient, sensitive, and effective "on-off switch" colorimetric platform for l-Cys detection has been successfully developed, providing a promising prospect in the biosensors and clinical diagnosis fields.

Enhancing the colorimetric detection of H2O2 and ascorbic acid on polypyrrole coated fluconazole-functionalized POMOFs

A new fluconazole-functionalized polyoxometalate-based metal-organic framework (POMOF) [Ag₃(FKZ)₂(H₂O)₂][H₃SiW₁₂O₄₀] (AgFKZSiW₁₂) was successfully constructed, and its polypyrrole (PPy) coated composite AgFKZSiW₁₂@PPy was also obtained via a facile 'in situ' oxidation polymerization process. The peroxidase-like activity evaluation indicates that the maximized synergistic effect from the integration of PPy, SiW₁₂ clusters, HFKZ drug molecules, and Ag ions deeply enhanced the overall performance. More importantly, AgFKZSiW₁₂@PPy exhibits the fastest response time (30 s) among all the reported peroxidase mimics to date, including the pristine AgFKZSiW₁₂ (2 min). Moreover, the AgFKZSiW₁₂@PPy-based colorimetric biosensing platform towards H₂O₂ and ascorbic acid (AA) exhibits limits of detection (LOD) as low as 0.12 μM and 2.7 μM, respectively. This work reveals a promising prospect in medical diagnosis and biotechnology for colorimetric biosensor fabrication with high performance through the introduction of PPy.

Mo-Based crystal POMOFs with a high electrochemical capacitor performance

The capacitor performance of newly synthesized crystalline POMOFs was higher than those of the majority of reported POMOF-, state-of-the-art MOF- and POM-based materials.

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)

An updated comprehensive review to help researchers understand nanozymes better and in turn to advance the field.

Potential bio-protective effect of copper compounds: mimicking SOD and peroxidases enzymes and inhibiting acid phosphatase as a target for anti-osteoporotic chemotherapeutics

Copper complexes with transformed methimazole ligand have been synthesized and characterized by elemental analysis, conductivity measurements, thermogravimetric analysis, EPR, FTIR and UV-Vis spectroscopies. Results support their stoichiometries and geometrical structures: [Cu(C₄H₅N₂S)₂Cl₂]·2H₂O(1), [Cu(C₈H₁₀N₄S)SO₄H₂O](2) and [Cu(C₈H₁₀N₄S)SO₄](3). ((C₄H₅N₂)₂S: bis(l-methylimidazol-2-yl)sulfide; (C₄H₅N₂S)₂ = Bis[bis(l-methylimidazol-2-yl)disulfide]) Concurrently, the structurally distinct soluble species corresponding to complexes (1) and (2) were subsequently used in an in vitro investigation of their potential biological properties. In view of their possible pharmaceutical activity, the complexes were in vitro evaluated as phosphatase acid inhibitors. Their radical bio-protective effects were also studied measuring the effect against DPPH^• and O₂^•- radicals. Additional catalytic properties as peroxidase mimics were evaluated using Michaelis-Menten kinetic model by means of phenol red and pyrogallol assays. The complexes exhibited catalytic bromination activity and the ability to oxidize pyrogallol substrate indicating that they can be considered as functional models. The relationships between the structures and the in vitro biological activities have also been considered. Serum protein albumin has attracted the greatest interest as drug carrier and the affinity of biological/pharmaceutical compound is relevant to the development of new medicine. In that sense, interaction studies by fluorescence and EPR spectroscopies were performed showing the binding capacity of the complexes.

Two novel Dawson-like tungstoantimonates with difunctional photocatalytic and magnetic properties

Two novel inorganic-organic hybrids containing the pyramidal SbO₃ group in Dawson-like POMs based on an organic ligand with different coordination modes, namely {Ni(phen)₃}₃[SbW₁₈O₆₀]·(H₃O)₃·7H₂O (1) and [Cu^I(phen)(H₂O)₃]{[Cu(phen)₂(H₂O)₂]₂[SbW₁₈O₆₀]}·2H₂O (2) (phen = 1,10-phenanthroline), have been synthesized. The catalytic property of compound 1 was studied as the first case for an {M₁₈} cluster containing the pyramidal SbO₃ group. Remarkably, compound 1 has excellent photocatalytic activity for RhB degradation and the probable mechanism of degradation was discussed. Additionally, the 2D-IR correlation spectra (2D-IR COS) under magnetic perturbation were recorded to analyze the magnetic properties of compound 1. The 2D-IR COS under thermo perturbation were recorded to verify the presence of H-bonding interactions.

Intrinsic peroxidase-like activity and enhanced photo-Fenton reactivity of iron-substituted polyoxometallate nanostructures

Fe-substituted heteropolyacid nanostructures are developed for the efficient degradation of pollutants via Fenton and photo-Fenton reactions and show efficient artificial enzyme-like activity for oxidation.