Search Results (19)

Polyoxometalates (POMs) represent a broad class of anionic inorganic (V, Mo, W) clusters with versatile structures of chemical and physical properties. POMs are inhibitors of many enzymes, including P-type ATPases, well-known to be a target of several approved drugs. Herein, two new hybrid POMs with Mo and mixed V/W, namely (C₂H₈N₁)₆[V₂Mo₁₈O₆₂].3H₂O (1) and (C₄H₁₆N₃)₄[V₂W₄O₁₉]₃.12H₂O (2), were synthesized via wet chemical methods in aqueous solution, and their purity was confirmed and characterized by single X-ray diffraction and infrared spectroscopy. The cations are dimethylammonium ((C₂H₈N)⁺) and diethylenetriammonium ((C₄H₁₆N₃)³⁺), respectively. POMs biological activities were investigated, specifically their inhibitory potential against Ca²⁺-ATPase. The sarcoplasmic reticulum Ca²⁺-ATPase activities were measured spectrophotometrically using the coupled enzyme pyruvate kinase/lactate dehydrogenase assay. For the Ca²⁺-ATPase activity, Dawson (1) showed an IC₅₀ value of 3.4 μM, whereas Lindqvist (2) displayed a value of 45.1 μM. The Ca²⁺-ATPase inhibitory potential of these POMs can be correlated with the net charge (namely 6- and 4-) and the charge density (namely 0.33 and 0.67). A structure–activity-relationship was established for a series of 17 POMs Ca²⁺-ATPase inhibitors correlating IC₅₀ values and POMs net charge and POMs charge density. The described features make Dawson (1) and Lindqvist (2) attractive POMs in a wide range of chemistry fields as well as in biomedical applications. Full article

Polyoxotungstate nanoclusters have recently emerged as promising contrast agents for computed tomography (CT). In order to evaluate their clinical potential, in this study, we evaluated the in vitro CT imaging properties, potential toxic effects in vivo, and tissue distribution of monolacunary Wells–Dawson polyoxometalate, α₂-K₁₀P₂W₁₇O₆₁^.20H₂O (mono-WD POM). Mono-WD POM showed superior X-ray attenuation compared to other tungsten-containing nanoclusters (its parent WD-POM and Keggin POM) and the standard iodine-based contrast agent (iohexol). The calculated X-ray attenuation linear slope for mono-WD POM was significantly higher compared to parent WD-POM, Keggin POM, and iohexol (5.97 ± 0.14 vs. 4.84 ± 0.05, 4.55 ± 0.16, and 4.30 ± 0.09, respectively). Acute oral (maximum-administered dose (MAD) = 960 mg/kg) and intravenous administration (1/10, 1/5, and 1/3 MAD) of mono-WD POM did not induce unexpected changes in rats’ general habits or mortality. Results of blood gas analysis, CO-oximetry status, and the levels of electrolytes, glucose, lactate, creatinine, and BUN demonstrated a dose-dependent tendency 14 days after intravenous administration of mono-WD POM. The most significant differences compared to the control were observed for 1/3 MAD, being approximately seventy times higher than the typically used dose (0.015 mmol W/kg) of tungsten-based contrast agents. The highest tungsten deposition was found in the kidney (1/3 MAD—0.67 ± 0.12; 1/5 MAD—0.59 ± 0.07; 1/10 MAD—0.54 ± 0.05), which corresponded to detected morphological irregularities, electrolyte imbalance, and increased BUN levels. Full article

Micro-computed tomography (microCT) is a common tool for the visualization of the internal composition of organic tissues. Collagen comprises approximately 25–35% of the whole-body protein content in mammals, and the structure and arrangement of collagen fibers contribute significantly to the integrity of tissues. Collagen type I is also frequently used as a key structural component in tissue-engineered and bioprinted tissues. However, the imaging of collagenous tissues is limited by their inherently low X-ray attenuation, which makes them indistinguishable from most other soft tissues. An imaging contrast agent that selectively alters X-ray attenuation is thus essential to properly visualize collagenous tissue using a standard X-ray tube microCT scanner. This review compares various contrast-enhanced techniques reported in the literature for MicroCT visualization of collagen-based tissues. An ideal microCT contrast agent would meet the following criteria: (1) it diffuses through the tissue quickly; (2) it does not deform or impair the object being imaged; and (3) it provides sufficient image contrast for reliable visualization of the orientation of individual fibers within the collagen network. The relative benefits and disadvantages of each method are discussed. Lugol’s solution (I₃K), phosphotungstic acid (H₃PW₁₂O₄₀), mercury(II) chloride (HgCl₂), and Wells–Dawson polyoxometalates came closest to fitting the criteria. While none of the contrast agents discussed in the literature met all criteria, each one has advantages to consider in the context of specific lab capabilities and imaging priorities. Full article

The oxygen reduction reaction (ORR) is a key cathodic reaction in energy-converting systems, such as fuel cells (FCs). Thus, it is of utmost importance to develop cost-effective and efficient electrocatalysts (ECs) without noble metals to substitute the Pt-based ones. This study focuses on polyoxometalate (POM)-based ECs for ORR applications. A Wells–Dawson POM salt K₇ [P₂W₁₇(FeOH₂)O₆₁].·20H₂O was immobilised onto graphene flakes and multiwalled carbon nanotubes doped with nitrogen, denominated as P₂W₁₇Fe@GF_N8 and P₂W₁₇Fe@MWCNT_N8. The successful preparation of the composites was proved with various characterisation techniques, including FTIR, XPS and SEM. Both materials showed good ORR performance in an alkaline medium with similar potential onset values of ~0.84 V vs. RHE and diffusion-limiting current densities of −3.9 and −3.3 mA cm⁻² for P₂W₁₇Fe@MWCNT_N8 and P₂W₁₇Fe@GF_N8, respectively. Furthermore, both composites presented low Tafel slopes (48–58 mV dec⁻¹). Chronoamperometric tests revealed that the as-prepared nanocomposites rendered a significant improvement achieving between 90 and 94% of current retention in tolerance to methanol in comparison with Pt/C, and moderate to good long-term electrochemical stability with current retentions comprised between 68 and 88%. This work reinforces the use of POMs as important electroactive species for the preparation of alternative ORR electrocatalysts, exhibiting good activity, stability and selectivity towards the ORR in the presence of methanol. Full article

Herein we report the synthesis of a new class of compounds associating Keggin and Dawson-type Polyoxometalates (POMs) with a derivative of the anionic decahydro-closo-decaborate cluster [B₁₀H₁₀]²⁻ through aminopropylsilyl ligand (APTES) acting as both a linker and a spacer between the two negatively charged species. Three new adducts were isolated and fully characterized by various NMR techniques and MALDI-TOF mass spectrometry, notably revealing the isolation of an unprecedented monofunctionalized SiW₁₀ derivative stabilized through intramolecular H-H dihydrogen contacts. DFT as well as electrochemical studies allowed studying the electronic effect of grafting the decaborate cluster on the POM moiety and its consequences on the hydrogen evolution reaction (HER) properties. Full article

The increase in bacterial resistance to antibiotics has led researchers to find new compounds or find combinations between different compounds with potential antibacterial action and with the ability to prevent the development of antibiotic resistance. Polyoxotungstates (POTs) are inorganic clusters that may fulfill that need, either individually or in combination with antibiotics. Herein, we report the ability of the polyoxotungstates (POTs) with Wells-Dawson P₂W₁₈, P₂W₁₇, P₂W₁₅, and Preyssler P₅W₃₀ type structures to differently affect Gram-negative and Gram-positive microorganisms, either susceptible or resistant to antibiotics. The compound P₅W₃₀ showed the highest activity against the majority of the tested bacterial strains in comparison with the other tested POTs (P₂W₁₅, P₂W₁₇ and P₂W₁₈) that did not show inhibition zones for the Gram-negative bacteria, A. baumanii I73775, E. coli DSM 1077, E. coli I73194, K. pneumoniae I7092374, and P. aeruginosa C46281). Generally, the results evidenced that Gram-positive bacteria are more susceptible to the POTs tested. The compound P₅W₃₀ was the one most active against S. aureus ATCC 6538 and MRSA16, reaching <0.83 mg·mL⁻¹ (100 μM) and 4.96 mg·mL⁻¹ (600 μM), respectively. Moreover, it was verified by NMR spectroscopy that the most promising POT, P₅W₃₀, remains intact under all the experimental conditions, after 24 h at 37 °C. This prompted us to further evaluate the anti-quorum sensing activity of P₅W₃₀ using the biosensor Chromobacterium violaceum CV026, as well as its antibiofilm activity both individually and in combination with the antibiotic cefoxitin against the methicillin-resistant Staphylococcus aureus 16 (MRSA16). P₅W₃₀ showed a synergistic antibacterial effect with the antibiotic cefoxitin and chloramphenicol against MRSA16. Moreover, the antibiofilm activity of P₅W₃₀ was more pronounced when used individually, in comparison with the combination with the antibiotic cefoxitin. Finally, the antiviral activity of P₅W₃₀ was tested using the coliphage Qβ, showing a dose-dependent response. The maximum inactivation was observed at 750 μM (6.23 mg·mL⁻¹). In sum, P₅W₃₀ shows anti-quorum sensing and antibiofilm activities besides being a potent antibacterial agent against S. aureus and to exhibit antiviral activities against enteric viruses. Full article

In the present study, an anti-bacterial film (Carr/POM film) was prepared through the incorporation of Wells-Dawson polyoxometalate K₆[Mo₁₈O₆₂P₂] into κ-carrageenan-based polymers using the tape-casting method. The mechanical properties, thermal stability, and morphology of the prepared film were characterized. The obtained results showed that incorporation of K₆[Mo₁₈O₆₂P₂] significantly affected the morphology and structure of the films. Moreover, the polyoxometalate-based film demonstrated desirable bactericidal activity against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive). Carr/POM (@8 mg/mL) film resulted in an obvious inhibition zone around the film in Kirby-Bauer disk diffusion test, which could also remove 99% of S. aureus and E. coli on plastic, glass, and stainless steel. In addition, this anti-bacterial film also demonstrated good biodegradability, which could be decomposed in soil in around 1 week. In conclusion, the polyoxometalate-based film showed good anti-bacterial property against food-borne pathogenic microbes, suggesting the prepared film has great potential to be developed as promising food packaging. Full article

The hydrolysis of the iron-binding blood plasma glycoprotein transferrin (Tf) has been examined at pH = 7.4 in the presence of a series of Zr-substituted polyoxometalates (Zr-POMs) including Keggin (Et₂NH₂)₁₀[Zr(PW₁₁O₃₉)₂]∙7H₂O (Zr-K 1:2), (Et₂NH₂)₈[{α-PW₁₁O₃₉Zr-(μ-OH) (H₂O)}₂]∙7H₂O (Zr-K 2:2), Wells-Dawson K₁₅H[Zr(α₂-P₂W₁₇O₆₁)₂]·25H₂O (Zr-WD 1:2), Na₁₄[Zr₄(α-P₂W₁₆O₅₉)₂(μ₃-O)₂(μ-OH)₂(H₂O)₄]·57H₂O (Zr-WD 4:2) and Lindqvist (Me₄N)₂[ZrW₅O₁₈(H₂O)₃] (Zr-L 1:1), (nBu₄N)₆[(ZrW₅O₁₈(μ–OH))₂]∙2H₂O (Zr-L 2:2)) type POMs. Incubation of transferrin with Zr-POMs resulted in formation of 13 polypeptide fragments that were observed on sodium dodecyl sulfate poly(acrylamide) gel electrophoresis (SDS-PAGE), but the hydrolysis efficiency varied depending on the nature of Zr-POMs. Molecular interactions between Zr-POMs and transferrin were investigated by using a range of complementary techniques such as tryptophan fluorescence, circular dichroism (CD), ³¹P-NMR spectroscopy, in order to gain better understanding of different efficiency of investigated Zr-POMs. A tryptophan fluorescence quenching study revealed that the most reactive Zr-WD species show the strongest interaction toward transferrin. The CD results demonstrated that interaction of Zr-POMs and transferrin in buffer solution result in significant secondary structure changes. The speciation of Zr-POMs has been followed by ³¹P-NMR spectroscopy in the presence and absence of transferrin, providing insight into stability of the catalysts under reaction condition. Full article

Organic solar cells, characterized by a symmetrical regular layered structure, are very promising systems for developing green, low cost, and flexible solar energy conversion devices. Despite the efficiencies being appealing (over 17%), the technological transfer is still limited by the low durability. Several processes, in bulk and at interface, are responsible. The quick downgrading of the performance is due to a combination of physical and chemical degradations. These phenomena induce instability and a drop of performance in working conditions. Close monitoring of these processes is mandatory to understand the degradation pathways upon device operation. Here, an unconventional approach based on Energy Dispersive X-ray Reflectivity (ED-XRR) performed in-situ is used to address the role of Wells–Dawson polyoxometalate (K₆-P₂W₁₈O₆₂, hereafter K6-P2W18) as hole transporting layer in organic photovoltaics. The results demonstrate that K6-P2W18 thin films, showing ideal bulk and interface properties and superior optical/morphological stability upon prolonged illumination, are attractive candidates for the interface of durable OPV devices. Full article

Polyoxometalates (POMs) are of increasing interest due to their proven anticancer activities. Aquaporins (AQPs) were found to be overexpressed in tumors bringing particular attention to their inhibitors as anticancer drugs. Herein, we report for the first time the ability of polyoxotungstates (POTs), such as of Wells–Dawson P₂W₁₈, P₂W₁₂, and P₂W₁₅, and Preyssler P₅W₃₀ structures, to affect aquaporin-3 (AQP3) activity and impair melanoma cell migration. The tested POTs were revealed to inhibit AQP3 function with different effects, with P₂W₁₈, P₂W₁₂, and P₅W₃₀ being the most potent (50% inhibitory concentration (IC₅₀) = 0.8, 2.8, and 3.2 µM), and P₂W₁₅ being the weakest (IC50 > 100 µM). The selectivity of P₂W₁₈ toward AQP3 was confirmed in yeast cells transformed with human aquaglyceroporins. The effect of P₂W₁₂ and P₂W₁₈ on melanoma cells that highly express AQP3 revealed an impairment of cell migration between 55% and 65% after 24 h, indicating that the anticancer properties of these compounds may in part be due to the blockage of AQP3-mediated permeability. Altogether, our data revealed that P₂W₁₈ strongly affects AQP3 activity and cancer cell growth, unveiling its potential as an anticancer drug against tumors where AQP3 is highly expressed. Full article

A triol-functionalized 2,2′-bipyridine (bpy) derivative has been synthesized and used for the tris-alkoxylation of polyoxometalate (POM) precursors. The resultant POM-bpy conjugates of the Wells–Dawson- and Anderson-type feature a C–C bond as a linkage between the POM and bpy fragments. This structural motif is expected to increase the hydrolytic stability of the compounds. This is of particular relevance with respect to the application of POM-bpy metal complexes, as photocatalysts, in the hydrogen-evolution reaction (HER) in an aqueous environment. Accordingly, Rh(III) and Ir(III) complexes of the POM-bpy ligands have been prepared and characterized. These catalyst-photosensitizer dyads have been analyzed with respect to their electrochemical and photophysical properties. Cyclic and square-wave voltammetry, as well as UV/vis absorption and emission spectroscopy, indicated a negligible electronic interaction of the POM and metal-complex subunits in the ground state. However, emission–quenching experiments suggested an efficient intramolecular electron-transfer process from the photo-excited metal centers to the POM units to account for the non-emissive nature of the dyads (thus, suggesting a strong interaction of the subunits in the excited state). In-depth photophysical investigations, as well as a functional characterization, i.e., the applicability in the HER reaction, are currently ongoing. Full article

A Ru-doped phospho-tungstic Wells–Dawson polyoxometalate (POM) was successfully applied as homogeneous catalyst for glycerol hydrogenolysis in aqueous media. The synthesized compound showed superior catalytic activity compared to classical homogeneous/heterogeneous Ru catalysts like RuCl₃ and Ru/C under identical reaction conditions, whereas the analogous POM doped with Pd or Pt proved far less activity. Detailed characterization of the POMs was performed using ³¹P-NMR to identify characteristic phosphorous peaks of the heteroatoms, infrared spectroscopy (ATR-FTIR) to confirm characteristic P-O and W-O-W vibrations, powder XRD for comparison of crystal structures, and X-ray fluorescence (XRF) and inductive-coupled plasma (ICP) analysis to determine elemental composition. Variation of the reaction parameters for the best performing Ru-doped POM catalyst showed that substrate concentration played an important role for both product selectivity and conversion. Moreover, medium hydrogen pressure and high stirring speed were key factors to obtain highly selective conversion of glycerol to 1,2-propanediol. Full article

The reaction of [α-P₂W₁₅O₅₆]¹²⁻ with Mn^II and Dy^III in an aqueous basic solution led to the isolation of an all inorganic heterometallic aggregate Na₁₀(OH₂)₄₂[{Dy(H₂O)₆}₂Mn₄P₄W₃₀O₁₁₂(H₂O)₂]·17H₂O (Dy₂Mn₄-P₂W₁₅). Single-crystal X-ray diffraction revealed that Dy₂Mn₄-P₂W₁₅ crystallizes in the triclinic system with space group P $\overline{1}$ , and consists of a tetranuclear manganese(II)-substituted sandwich-type phosphotungstate [Mn₄(H₂O)₂(P₂W₁₅O₅₆)₂]¹⁶⁻ (Mn₄-P₂W₁₅), Na, and Dy^III cations. Compound Dy₂Mn₄-P₂W₁₅ exhibits a 1D ladder-like chain structure based on sandwich-type segments and dysprosium cations as linkers, which are further connected into a three-dimensional open framework by sodium cations. The title compound was structurally and compositionally characterized in solid state by single-crystal XRD, powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric (TGA), and elemental analyses. Further, the absorption and emission electronic spectra in aqueous solutions of Dy₂Mn₄-P₂W₁₅ and Mn₄-P₂W₁₅ were studied. Also, magnetic properties were studied and compared with the magnetic behavior of [Mn₄(H₂O)₂(P₂W₁₅O₅₆)₂]¹⁶⁻. Full article

We have successfully synthesized K₁₇{[{KIn₂(μ-OH)₂}(α,α-Si₂W₁₈O₆₆)]₂[In₆(μ-OH)₁₃(H₂O)₈]}·35H₂O (potassium salt of In₁₀-open), an open-Wells–Dawson polyoxometalate (POM) containing ten indium metal atoms. This novel compound was characterized by X-ray crystallography, ²⁹Si NMR, FTIR, complete elemental analysis, and TG/DTA. X-ray crystallography results for {[{KIn₂(μ-OH)₂}(α,α-Si₂W₁₈O₆₆)]₂[In₆(μ-OH)₁₃(H₂O)₈]}¹⁷⁻ (In₁₀-open) revealed two open-Wells–Dawson units containing two In³⁺ ions and a K⁺ ion, [{KIn₂(μ-OH)₂}(α,α-Si₂W₁₈O₆₆)]¹¹⁻, connected by an In₆-hydroxide cluster moiety, [In₆(μ-OH)₁₃(H₂O)₈]⁵⁺. In₁₀-open is the first example of an open-Wells–Dawson POM containing a fifth-period element. Moreover, to the best of our knowledge, it exhibits the highest nuclearity among the indium-containing POMs reported to date. Full article