The antibacterial activity of polyoxometalates: structures, antibiotic effects and future perspectives

Mechanism of the antimicrobial activity induced by phosphatase inhibitor sodium ortho-vanadate

The present study describes a novel antimicrobial mechanism based on Sodium Orthovanadate (SOV), an alkaline phosphatase inhibitor. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM) were employed to examine the surface morphologies of the test organism, Escherichia coli (E. coli), during various antibacterial phases. Our results indicated that SOV kills bacteria by attacking cell wall growth and development, leaving E. coli's outer membrane intact. Our antimicrobial test indicated that the MIC of SOV for both E. coli and Lactococcus lactis (L. lactis) is 40 μM. A combination of quantum mechanical calculations and vibrational spectroscopy revealed that divanadate from SOV strongly coordinates with Ca2+ and Mg2+, which are the activity centers for the phosphatase that regulates bacterial cell wall synthesis. The current study is the first to propose the antibacterial mechanism caused by SOV attacking cell wall.

Non-Covalent and Covalent Binding of New Mixed-Valence Cage-like Polyoxidovanadate Clusters to Lysozyme

The high-resolution X-ray structures of the model protein lysozyme in the presence of the potential drug [VIVO(acetylacetonato)2] from crystals grown in 1.1 M NaCl, 0.1 M sodium acetate at pH 4.0 reveal the binding to the protein of different and unexpected mixed-valence cage-like polyoxidovanadates (POVs): [V15O36(OH2)]5-, which non-covalently interacts with the lysozyme surface, [V15O33(OH2)]+ and [V20O51(OH2)]n- (this latter based on an unusual {V18O43} cage) which covalently bind the protein. EPR spectroscopy confirms the partial oxidation of VIV to VV and the formation of mixed-valence species. The results indicate that the interaction with proteins can stabilize the structure of unexpected - both for dimension and architecture - POVs, not observed in aqueous solution.

Two High-Nuclear Wheel-Hub-Shaped Transition-Metal-Doped Polyoxovanadates

The first two unprecedented high-nuclear wheel-hub-shaped transition-metal-doped polyoxovanadates, [M8Mo4W4V20P20] [M = Ni (1), Co (2)], have been assembled under solvothermal conditions. The center of the cluster consists of two {Ni4(oa)4} rings as the center hole, four {MoO4} units acting as the spokes, and four {WV5(PPOA)5} molecular building blocks serving as the tire. Compound 1 exhibits good catalytic properties and recyclability in oxidative desulfurization reactions.

The effect of ionic versus covalent functionalization of polyoxometalate hybrid materials with coordinating subunits on their stability and interaction with DNA

Inorganic-organic hybrid materials that combine both Polyoxometalates (POMs) and metal ion coordinating subunits (CSUs) represent promising multifunctional materials. Though their individual components are often biologically active, utilization of hybrid materials in bioassays significantly depends on the functionalization method and thus resulting stability of the system. Quite intriguingly, these aspects were very scarcely studied in hybrid materials based on the Wells-Dawson POM (WD POM) scaffold and remain unknown. We chose two model WD POM hybrid systems to establish how the functionalization mode (ionic vs. covalent) affects their stability in biological medium and interaction with nucleic acids. The synthetic scope and limitations of the covalent POM-terpyridine hybrids were demonstrated and compared with the ionic Complex-Decorated Surfactant Encapsulated-Clusters (CD-SECs) hybrids. The nature of POM and CSU binding can be utilized to modulate the stability of the hybrid and the extent of DNA binding. The above systems show potential to behave as model cargo-platforms for potential utilization in medicine and pharmacy.

Zeolitic imidazolate framework-8 encapsulated with Mo-based polyoxometalates as surfaces with antibacterial activity against Escherichia coli

Bacterial infections represent a major global health concern, causing millions of deaths and a significant economic burden. The development of antibacterial nanoporous surfaces with potential mechano-bactericidal effects can revolutionize infection control practices. In this study, a hybrid material of zeolitic imidazolate framework-8 (ZIF-8) doped with phosphomolybdic acid (PMA) was synthesized and characterized by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and N2 sorption isotherms. PMA@ZIF-8 performance as an antibacterial agent against E. coli was superior to that of its individual constituents, suggesting a synergistic effect of PMA and ZIF-8. The incorporation of PMA into ZIF-8 significantly enhanced its antibacterial efficacy, as evidenced by a twofold reduction in MIC (375 μg mL-1 vs. 750 μg mL-1) and a 4.35 times increase in the bactericidal kinetics rate constant. The time-kill curve experiment revealed that PMA@ZIF-8 achieved a 3-log reduction within 7 hours, whereas ZIF-8 required 24 hours to reach the same level of reduction. The density functional theory (DFT) calculated bandgap of PMA@ZIF-8 was significantly less than that of ZIF-8. Also, PMA@ZIF-8 has caused the elimination of 56.72% of the thiol group as detected by Ellman's assay. Accordingly, PMA@ZIF-8 can be both computationally and experimentally demonstrated as an oxidative nanozyme. PMA@ZIF-8's surface topology revealed nanorod protrusions, suggesting a potential mechano-bactericidal effect, which was confirmed by live/dead assay on PMA@ZIF-8-coated glass. This study highlights the potential of the PMA@ZIF-8 hybrid as a highly effective antibacterial agent, holding promise for creating multifunctional antibacterial surfaces.

Unveiling the agonistic properties of Preyssler-type Polyoxotungstates on purinergic P2 receptors

The Preyssler-type polyoxotungstate ({P5W30}) belongs to the family of polyanionic metal-oxides formed by group V and VI metal ions, such as V, Mo and W, commonly known as polyoxometalates (POMs). POMs have demonstrated inhibitory effect on a significant number of ATP-binding proteins in vitro. Purinergic P2 receptors, widely expressed in eukaryotic cells, contain extracellularly oriented ATP-binding sites and play many biological roles with health implications. In this work, we use the immortalized mouse hippocampal neuronal HT-22 cells in culture to study the effects of {P5W30} on the cytosolic Ca2+ concentration. Changes in cytosolic Ca2+ concentration were monitored using fluorescence microscopy of HT-22 cells loaded with the fluorescent Ca2+ indicator Fluo3. 31P-Nuclear magnetic resonance measurements of {P5W30} indicate its stability in the medium used for cytosolic Ca2+ measurements for over 30 min. The findings reveal that addition of {P5W30} to the extracellular medium induces a sustained increase of the cytosolic Ca2+ concentration within minutes. This Ca2+ increase is triggered by extracellular Ca2+ entry into the cells and is dose-dependent, with a half-of-effect concentration of 0.25 ± 0.05 μM {P5W30}. In addition, after the {P5W30}-induced cytosolic Ca2+ increase, the transient Ca2+ peak induced by extracellular ATP is reduced up to 100% with an apparent half-of-effect concentration of 0.15 ± 0.05 μM {P5W30}. Activation of metabotropic purinergic P2 receptors affords about 80% contribution to the increase of Fluo3 fluorescence elicited by {P5W30} in HT-22 cells, whereas ionotropic receptors contribute, at most, with 20%. These results suggest that {P5W30} could serve as a novel agonist of purinergic P2 receptors.

A High Nucleus Cu-Incorporated Giant Phosphotungstate with Photocatalytic Oxidation C-H of Toluene

Exploring a novel photocatalyst for catalytic oxidation of toluene is a sustainable strategy for energy conversion in times of an energy crisis. However, designing an effective photocatalyst for the conversion of toluene remains challenging. Herein, a novel organic monophosphonate-modified high nucleus Cu-incorporated polyoxotungstate, K8H33[{Cu0.5(H2O)4}{Cu2(O3PCH2COO)(1,4,9-α-P2W15O56)}]4·Cl·60H2O (1), has been intentionally synthesized by a self-assembly process utilizing conventional aqueous method. It reveals that 1 contains a polyanion of [{Cu0.5(H2O)}4{Cu2(O3PCH2COO)(1,4,9-α-P2W15O56)}]440- composed of four Dawson-type {1,4,9-α-P2W15} subunits, forming an oval-shaped structure and further connecting into a three-dimensional (3D) framework by lateral {Cu(H2O)4}2+. Interestingly, the trivacant {1,4,9-α-P2W15} subunits were observed in the organophosphonate acid-functionalized polyoxometalates for the first time. Notably, 1 exhibits a wonderful performance in catalytic oxidation of the recalcitrant C(sp3)-H bond of toluene to benzoic acid with a conversion as high as 97% under visible light utilizing O2 as an oxidant.

The good, the bad, and the ugly of metals as antimicrobials

We are now moving into the antimicrobial resistance (AMR) era where more antibiotic resistant bacteria are now the majority, a problem brought on by both misuse and over use of antibiotics. Unfortunately, the antibiotic development pipeline dwindled away over the past decades as they are not very profitable compounds for companies to develop. Regardless researchers over the past decade have made strides to explore alternative options and out of this we see revisiting historical infection control agents such as toxic metals. From this we now see a field of research exploring the efficacy of metal ions and metal complexes as antimicrobials. Such antimicrobials are delivered in a variety of forms from metal salts, alloys, metal complexes, organometallic compounds, and metal based nanomaterials and gives us the broad term metalloantimicrobials. We now see many effective formulations applied for various applications using metals as antimicrobials that are effective against drug resistant strains. The purpose of the document here is to step aside and begin a conversation on the issues of use of such toxic metal compounds against microbes. This critical opinion mini-review in no way aims to be comprehensive. The goal here is to understand the benefits of metalloantimicrobials, but also to consider strongly the disadvantages of using metals, and what are the potential consequences of misuse and overuse. We need to be conscious of the issues, to see the entire system and affect through a OneHealth vision.

Polyoxometalate-Polymer Directed Macromolecular Architectonics of Silver Nanoparticles as Effective Antimicrobials

A novel inorganic-organic-inorganic ternary bioactive material formulated on antimicrobial peptide-based polymer has been reported. Supramolecular approach has been employed to incorporate molecularly crowded tyrosine-based polymer stabilized silver nanoparticles into membrane bound vesicles exploiting polyoxometalate-triggered surface templating strategy. Utilizing the covalent reversible addition fragmentation chain transfer (RAFT) polymerization and exploiting templated supramolecular architectonics at biopolymer interface, the bioactive ternary polymeric nanohybrids have been designed against Shigellosis leveraging the antibacterial activities of silver nanoparticle, cationic amphiphilic tyrosine polymer and inorganic polyoxometalate. The detail investigation against Shigella flexneri 2a cell line demonstrates that the collaborative mechanism of the ternary hybrid composite enhances the bactericidal activity in comparison to only polyoxometalate and polymer stabilized silver nanoparticle with an altered mechanism of action which is established via detailed biological analysis.

Injectable hydrogel harnessing foreskin mesenchymal stem cell-derived extracellular vesicles for treatment of chronic diabetic skin wounds

Chronic skin wounds are a serious complication of diabetes with a high incidence rate, which can lead to disability or even death. Previous studies have shown that mesenchymal stem cells derived extracellular vesicles (EVs) have beneficial effects on wound healing. However, the human foreskin mesenchymal stem cell (FSMSCs)-derived extracellular vesicle (FM-EV) has not yet been isolated and characterized. Furthermore, the limited supply and short lifespan of EVs also hinder their practical use. In this study, we developed an injectable dual-physical cross-linking hydrogel (PSiW) with self-healing, adhesive, and antibacterial properties, using polyvinylpyrrolidone and silicotungstic acid to load FM-EV. The EVs were evenly distributed in the hydrogel and continuously released. In vivo and vitro tests demonstrated that the synergistic effect of EVs and hydrogel could significantly promote the repair of diabetic wounds by regulating macrophage polarization, promoting angiogenesis, and improving the microenvironment. Overall, the obtained EVs-loaded hydrogels developed in this work exhibited promising applicability for the repair of chronic skin wounds in diabetes patients.

Detailed Study on the Interfacial Interaction between Different Polyoxometalates and Tetronic Block Copolymers Exploring the Langmuir-Blodgett Technique

Polyoxometalates (POMs) interact with various biologically relevant entities. A basic understanding of this interaction is very important for various applications in the biological field. In this work, the focus is on the study of the interaction between tetronics and Keggin POMs. T701 and T90R4 are the two tetronics considered here; they have different solubilities in water due to different PPO/PEO ratios. The arrangement of PPO and PEO is also different with respect to the central ethylenediamine groups. Three different Keggin-type POMs, phosphomolybdic acid (PMA), phosphotungstic acid (PTA), and silicotungstic acid (STA), with different charge densities are chosen for an elaborate investigation using Langmuir-Blodgett technique. The observation is analyzed thoroughly, which shows both electrostatic interaction and adsorption of POMs on the PPO blocks of the tetronics due to the chaotropic effect, which is responsible for the binding of POMs (in subphase) with the tetronic monolayer. This interaction results in an expanded yet rigid monolayer for POM-tetronic association on the surface. Surface pressure vs mean molecular area isotherm is the key characterization to reach the conclusion. UV-vis spectroscopy, NMR, ITC, ellipsometric studies, FTIR, and SEM also serve as supportive characterization techniques.

Bioorthogonal chemistry of polyoxometalates - challenges and prospects

Bioorthogonal chemistry has enabled scientists to carry out controlled chemical processes in high yields in vivo while minimizing hazardous effects. Its extension to the field of polyoxometalates (POMs) could open up new possibilities and new applications in molecular electronics, sensing and catalysis, including inside living cells. However, this comes with many challenges that need to be addressed to effectively implement and exploit bioorthogonal reactions in the chemistry of POMs. In particular, how to protect POMs from the biological environment but make their reactivity selective towards specific bioorthogonal tags (and thereby reduce their toxicity), as well as which bioorthogonal chemistry protocols are suitable for POMs and how reactions can be carried out are questions that we are exploring herein. This perspective conceptualizes and discusses advances in the supramolecular chemistry of POMs, their click chemistry, and POM-based surface engineering to develop innovative bioorthogonal approaches tailored to POMs and to improve POM biological tolerance.

Gold Nanoparticles Capped with a Novel Titanium(IV)-Containing Polyoxomolybdate Cluster: Selective and Enhanced Bactericidal Effect Against Escherichia coli

Bacterial infections are a public health threat of increasing concern in medical care systems; hence, the search for novel strategies to lower the use of antibiotics and their harmful effects becomes imperative. Herein, the antimicrobial performance of four polyoxometalate (POM)-stabilized gold nanoparticles (Au@POM) against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as Gram-negative and Gram-positive bacteria models, respectively, is studied. The bactericidal studies performed, both in planktonic and sessile forms, evidence the antimicrobial potential of these hybrid nanostructures with selectivity toward Gram-negative species. In particular, the Au@GeMoTi composite with the novel [Ti2 (HGeMo7 O28 )2 ]10- POM capping ligand exhibits outstanding bactericidal efficiency with a minimum inhibitory concentration of just 3.12 µm for the E. coli strain, thus outperforming the other three Au@POM counterparts. GeMoTi represents the fourth example of a water-soluble TiIV -containing polyoxomolybdate, and among them, the first sandwich-type structure having heteroatoms in high-oxidation state. The evaluation of the bactericidal mechanisms of action points to the cell membrane hyperpolarization, disruption, and subsequent nucleotide leakage and the low cytotoxicity exerted on five different cell lines at antimicrobial doses demonstrates the antibiotic-like character. These studies highlight the successful design and development of a new POM-based nanomaterial able to eradicate Gram-negative bacteria without damaging mammalian cells.

Effects of the tetravanadate [V4O12]4- anion on the structural, magnetic, and biological properties of copper/phenanthroline complexes

The aim to access linked tetravanadate [V4O12]4- anion with mixed copper(II) complexes, using α-amino acids and phenanthroline-derived ligands, resulted in the formation of four copper(II) complexes [Cu(dmb)(Gly)(OH2)]2[Cu(dmb)(Gly)]2[V4O12]·9H2O (1) [Cu(dmb)(Lys)]2[V4O12]·8H2O (2), [Cu(dmp)2][V4O12]·C2H5OH·11H2O (3), and [Cu(dmp)(Gly)Cl]·2H2O (4), where dmb = 4,4'-dimethioxy-2,2'-bipyridine; Gly = glycine; Lys = lysine; and dmp = 2,9-dimethyl-1,10-phenanthroline. The [V4O12]4- anion is functionalized with mixed copper(II) units in 1 and 2; while in 3, it acts as a counterion of two [Cu(dmp)]2+ units. Compound 4 crystallized as a unit that did not incorporate the vanadium cluster. All compounds present magnetic couplings arising from Cu⋯O/Cu⋯Cu bridges. Stability studies of water-soluble 3 and 4 by UV-Vis spectroscopy in cell culture medium confirmed the robustness of 3, while 4 appears to undergo ligand scrambling over time, resulting partially in the stable species [Cu(dmp)2]+ that was also identified by electrospray ionization mass spectrometry at m/z = 479. The in vitro cytotoxicity activity of 3 and 4 was determined in six cancer cell lines; the healthy cell line COS-7 was also included for comparative purposes. MCF-7 cells were more sensitive to compound 3 with an IC50 value of 12 ± 1.2 nmol. The tested compounds did not show lipid peroxidation in the TBARS assay, ruling out a mechanism of action via reactive oxygen species formation. Both compounds inhibited cell migration at 5 µM in wound-healing assays using MCF-7, PC-3, and SKLU-1 cell lines, opening a new window to study the anti-metastatic effect of mixed vanadium-copper(II) systems.

Electron-Sponge Nature of Polyoxometalates for Next-Generation Electrocatalytic Water Splitting and Nonvolatile Neuromorphic Devices

Designing next-generation molecular devices typically necessitates plentiful oxygen-bearing sites to facilitate multiple-electron transfers. However, the theoretical limits of existing materials for energy conversion and information storage devices make it inevitable to hunt for new competitors. Polyoxometalates (POMs), a unique class of metal-oxide clusters, have been investigated exponentially due to their structural diversity and tunable redox properties. POMs behave as electron-sponges owing to their intrinsic ability of reversible uptake-release of multiple electrons. In this review, numerous POM-frameworks together with desired features of a contender material and inherited properties of POMs are systematically discussed to demonstrate how and why the electron-sponge-like nature of POMs is beneficial to design next-generation water oxidation/reduction electrocatalysts, and neuromorphic nonvolatile resistance-switching random-access memory devices. The aim is to converge the attention of scientists who are working separately on electrocatalysts and memory devices, on a point that, although the application types are different, they all hunt for a material that could exhibit electron-sponge-like feature to realize boosted performances and thus, encouraging the scientists of two completely different fields to explore POMs as imperious contenders to design next-generation nanodevices. Finally, challenges and promising prospects in this research field are also highlighted.

Self-Assembly of Polyoxometalate-Based Nanoparticle Surfactants in Solutions

Nanoparticle surfactants (NPSs) are an emergent class of amphiphiles attractive for their controllable assembly at the liquid-liquid interface. In this work, intriguing self-assembly behavior and stimuli-responsiveness of NPSs in homogeneous solutions are presented. With β-cyclodextrin-grafted polyoxometalates (POMs) and ferrocene (or azobenzene)-terminated polystyrene in water/tetrahydrofuran, POM-based NPSs are formed via host-guest interactions and self-organize to vesicles driven by solvent-phobic effects. The tunable supramolecular interactions allow these assemblies to be responsive to redox or light stimulus, respectively, affording an on-demand assembly/disassembly capacity that shows promise in delivery and release applications.

Polyoxometalate-Guanosine Monophosphate Hydrogels with Haloperoxidase-like Activity for Antibacterial Performance

Haloperoxidases represent an important class of enzymes that nature adopts as a defense mechanism to combat the colonial buildup of microorganisms on surfaces, commonly known as biofouling. Subsequently, there has been tremendous focus on the development of artificial haloperoxidase mimics that can catalyze the oxidation of X- (halide ion) in the presence of H2O2 to form HOX. The natural intermediate HOX disrupts the bacterial quorum sensing, thus preventing biofilm formation. Herein, we report a simple method for the formation of supramolecular hydrogels through the self-assembly of Keggin-structured polyoxometalates, phosphotungstic acid, and silicotungstic acid with the small biomolecule guanosine monophosphate (GMP) in an aqueous medium. The polyoxometalate-GMP hydrogels that contained highly entangled nanofibers were mechanically robust and showed thixotropic properties. The gelation of the polyoxometalates with GMP not only rendered manifold enhancement in biocompatibility but also the fibril network in the hydrogel provided high water wettability and the polyoxometalates acted as an efficient haloperoxidase mimic to trigger oxidative iodination, as demonstrated by a haloperoxidase assay. The antifouling activity of the phosphotungstic acid-GMP hydrogel was demonstrated against both Gram-positive and Gram-negative bacteria, which showed enhanced antibacterial performance of the hydrogel as compared to the polyoxometalate alone. We envision that the polyoxometalate-GMP hydrogels may facilitate mechanically robust coatings in a simple pathway that can be useful for antifouling applications.

Reactivity of metal-oxo clusters towards biomolecules: from discrete polyoxometalates to metal-organic frameworks

Metal-oxo clusters hold great potential in several fields such as catalysis, materials science, energy storage, medicine, and biotechnology. These nanoclusters of transition metals with oxygen-based ligands have also shown promising reactivity towards several classes of biomolecules, including proteins, nucleic acids, nucleotides, sugars, and lipids. This reactivity can be leveraged to address some of the most pressing challenges we face today, from fighting various diseases, such as cancer and viral infections, to the development of sustainable and environmentally friendly energy sources. For instance, metal-oxo clusters and related materials have been shown to be effective catalysts for biomass conversion into renewable fuels and platform chemicals. Furthermore, their reactivity towards biomolecules has also attracted interest in the development of inorganic drugs and bioanalytical tools. Additionally, the structural versatility of metal-oxo clusters allows for the efficiency and selectivity of the biomolecular reactions they promote to be readily tuned, thereby providing a pathway towards reaction optimization. The properties of the catalyst can also be improved through incorporation into solid supports or by linking metal-oxo clusters together to form Metal-Organic Frameworks (MOFs), which have been demonstrated to be powerful heterogeneous catalysts. Therefore, this review aims to provide a comprehensive and critical analysis of the state of the art on biomolecular transformations promoted by metal-oxo clusters and their applications, with a particular focus on structure-activity relationships.

All-Inorganic Polyoxometalates Act as Superchaotropic Membrane Carriers

Polyoxometalates (POMs) are known antitumoral, antibacterial, antiviral, and anticancer agents and considered as next-generation metallodrugs. Herein, a new biological functionality in neutral physiological media, where selected mixed-metal POMs are sufficiently stable and able to affect membrane transport of impermeable, hydrophilic, and cationic peptides (heptaarginine, heptalysine, protamine, and polyarginine) is reported. The uptake is observed in both, model membranes as well as cells, and attributed to the superchaotropic properties of the polyoxoanions. In view of the structural diversity of POMs these findings pave the way toward their biomedical application in drug delivery or for cell-biological uptake studies with biological effector molecules or staining agents.

Tungsten-based polyoxometalate nanoclusters with remarkable reactive oxygen species-scavenging activity efficiently quenched luminol-based electrochemiluminescence for sensitive detection of Her-2

This study aimed to develop a quenching-type electrochemiluminescence (ECL) immunosensor for human epidermal growth factor receptor (Her-2) detection. Firstly, Pd/NiFeOx nanoflowers decorated by in situ formation of gold nanoparticles (Au NPs) and 2D Ti3C2 MXene nanosheets were synthesized (AuPd/NiFeOx/Ti3C2) as carriers to load luminol and primary antibodies. Impressively, AuPd/NiFeOx/Ti3C2 with excellent peroxidase-like activity could accelerate the decomposition of the coreactant H2O2 generating more reactive oxygen species (ROSs) under the working potential from 0 to 0.8 V, resulting in highly efficient ECL emission at 435-nm wavelengths. The introduction of tungsten-based polyoxometalate nanoclusters (W-POM NCs) which exhibit remarkable ROSs-scavenging activity as secondary antibody labels could improve the sensitivity of immunosensors. The ZnO nanoflowers were employed to encapsulate minute-sized W-POM NCs, and polydopamine was self-polymerized on the surface of Zn(W-POM)O to anchor secondary antibodies. The mechanism of the quenching strategy was explored and it was found that W-POM NCs could consume ROSs by the redox reaction of W5+ resulting in W6+. The proposed ECL immunosensor displayed a wide linear response range of 0.1 pg·mL-1 to 50 ng·mL-1, and a low detection limit of 0.036 pg mL-1 (S/N = 3). The recoveries ranged from 93.9 to 99.4%, and the relative standard deviation (RSD) was lower than 10%. This finding is promising for the design of detecting new protein biomarkers.

Stabilization and Binding of [V4 O12 ]4- and Unprecedented [V20 O54 (NO3 )]n- to Lysozyme upon Loss of Ligands and Oxidation of the Potential Drug VIV O(acetylacetonato)2

High-resolution crystal structures of lysozyme in the presence of the potential drug VIV O(acetylacetonato)2 under two different experimental conditions have been solved. The crystallographic study reveals the loss of the ligands, the oxidation of VIV to VV and the subsequent formation of adducts of the protein with two different polyoxidovanadates: [V4 O12 ]4- , which interacts with lysozyme non-covalently, and the unprecedented [V20 O54 (NO3 )]n- , which is covalenty bound to the side chain of an aspartate residue of symmetry related molecules.

Decavanadate-Bearing Guanidine Derivatives Developed as Antimicrobial and Antitumor Species

To obtain biologically active species, a series of decavanadates (Hpbg)4[H2V10O28]·6H2O (1) (Htbg)4[H2V10O28]·6H2O; (2) (Hgnd)2(Hgnu)4[V10O28]; (3) (Hgnu)6[V10O28]·2H2O; and (4) (pbg = 1-phenyl biguanide, tbg = 1-(o-tolyl)biguanide, gnd = guanidine, and gnu = guanylurea) were synthesized and characterized by several spectroscopic techniques (IR, UV-Vis, and EPR) as well as by single crystal X-ray diffraction. Compound (1) crystallizes in space group P-1 while (3) and (4) adopt the same centrosymmetric space group P21/n. The unusual signal identified by EPR spectroscopy was assigned to a charge-transfer π(O)→d(V) process. Both stability in solution and reactivity towards reactive oxygen species (O2- and OH·) were screened through EPR signal modification. All compounds inhibited the development of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis bacterial strains in a planktonic state at a micromolar level, the most active being compound (3). However, the experiments conducted at a minimal inhibitory concentration (MIC) indicated that the compounds do not disrupt the biofilm produced by these bacterial strains. The cytotoxicity assayed against A375 human melanoma cells and BJ human fibroblasts by testing the viability, lactate dehydrogenase, and nitric oxide levels indicated compound (1) as the most active in tumor cells.

A polyoxomolybdate-based hybrid nano capsule as an antineoplastic agent

Polyoxometalates (POMs) are versatile anionic clusters which have attracted a lot of attention in biomedical investigations. To counteract the increasing resistance effect of cancer cells and the high toxicity of chemotherapeutic treatments, POM-based metallodrugs can be strategically synthesized by adjusting the stereochemical and physicochemical features of POMs. In the present report a polyoxomolybdate (POMo) based organic-inorganic hybrid solid (C6H16N)(C6H15N)2[Mo8O26]·3H2O, solid 1, has been synthesized and its antitumoral activities have been investigated against three cancer cell lines namely, A549 (Lung cancer), HepG2 (Liver cancer), and MCF-7 (Breast cancer) with IC50 values 56.2 μmol L-1, 57.3 μmol L-1, and 55.2 μmol L-1 respectively. The structural characterization revealed that solid 1 consists of an octa molybdate-type cluster connected by three triethylamine molecules via hydrogen bonding interactions. The electron microscopy analysis suggests the nanocapsule-like morphology of solid 1 in the size range of 50-70 nm. The UV-vis absorption spectra were used to assess the binding ability of synthesized POM-based solid 1 to calf thymus DNA (ctDNA), which further explained the binding interaction between POMo and ctDNA and the binding constant was calculated to be 2.246 × 103 giving evidence of groove binding.

Ni/Mn-Complex-Tethered Tetranuclear Polyoxovanadates: Crystal Structure and Inhibitory Activity on Human Hepatocellular Carcinoma (HepG-2)

Polyoxometalates (POMs) exhibit unique structural characteristics and excellent physical and chemical properties, which have attracted significant attention from scholars in the fields of anticancer research and chemotherapy. Herein, we successfully synthesized and structurally characterized two novel polyoxovanadates (POVs), denoted as POVs-1 and POVs-2, where [M(1-vIM)4]2[VV4O12]·H2O (M: NiII and MnII, 1-vinylimidazole abbreviated as 1-vIM) serve as ligands. The two POVs are isomeric and consist of fundamental structural units, each comprising one [V4O12]4- cluster, two [M(1-vIM)4]2+ cations, and one water molecule. Subsequently, we evaluated the cell viability of human hepatocellular carcinoma (HepG-2) cells treated with the synthesized POVs using the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazoliumbromide) assay. And the changes in cell nucleus morphology, mitochondrial membrane potential (Δψm), and reactive oxygen species levels in HepG-2 exposed to POVs were monitored using specific fluorescent staining techniques. Both hybrid POVs showed potent inhibitory activities, induing apoptosis in HepG-2 cells along with significant mitochondria dysfunction and a burst of reactive oxygen species. Notably, the inhibitory effects of POVs-2 were more pronounced than those of POVs-1, which is primarily attributed to the different transition metal ions present. These findings underscore the intricate relationship between the metal components, structural characteristics, and the observed antitumor activities in HepG-2 cells.

Combined Experimental and Computational Study of V-Substituted Lindqvist Polyoxotungstate: Screening by Docking for Potential Antidiabetic Activity

In the current work, a novel vanadotungstate compound, (C6H9N2)4[V2W4O19]·2H2O (1), is isolated by a simple stepwise synthesis method and characterized by a combined experimental and computational study. Molecular docking is conducted for the first time for this kind of substituted Lindqvist polyoxometalates to elucidate for potential antidiabetic activity. Hence, the modeling results revealed a significant docking score of the reported compound to bind to the active sites of α-glucosidase with the lowest binding energy of -5.7 kcal/mol, where the standard drug acarbose (ACB) had -4.6 kcal/mol binding energy. The stability of binding was enhanced by strong H-bonding, van der Waals, and electrostatic interactions occurring in the three-dimensional (3D) supramolecular network of polyanionic vanadotungstate subunits templated with organic moieties as shown by X-ray diffraction and Hirshfeld analyses. Furthermore, density functional theory (DFT) calculations supported with photophysical measurements are also discussed to predict the most chemical and biological reactivity. In this view, the complete description of electronic and biological features of (1) is enhanced by determination of the highest occupied molecular orbital (HOMO)/least unoccupied molecular orbital (LUMO) energy, electronic density, ionization potential, electron affinity, etc. These chemical descriptors, intermolecular interactions, docking score, and binding free energy estimation are essential in understanding the reactivity of this bioactive compound offering potential inhibition of the α-glucosidase enzyme.

In Vitro, Oral Acute, and Repeated 28-Day Oral Dose Toxicity of a Mixed-Valence Polyoxovanadate Cluster

Polyoxovanadates (POV) are a subgroup of polyoxometalates (POM), which are nanosized clusters with reported biological activities. This manuscript describes the first toxicity evaluation of a mixed-valence polyoxovanadate, pentadecavanadate, (Me4N)6[V15O36Cl], abbreviated as V15. Cytotoxicity experiments using peripheral blood mononuclear cells (PBMC), larvae of Artemia salina Leach, and in vivo oral acute and repeated 28-day doses in mice was carried out. The LC50 values in PBMC cells and A. salina were 17.5 ± 5.8 μmol L-1, and 17.9 µg L-1, respectively, which indicates high cytotoxic activity. The toxicity in mice was not observed upon acute exposure in a single dose, however, the V15 repeated 28-day oral administration demonstrated high toxicity using 25 mg/kg, 50 mg/kg and, 300 mg/kg doses. The biochemical and hematological analyses during the 28-day administration of V15 showed significant alteration of the metabolic parameters related to the kidney and liver, suggesting moderate toxicity. The V15 toxicity was attributed to the oxidative stress and lipid peroxidation, once thiobarbituric acid (TBAR) levels significantly increased in both males and females treated with high doses of the POV and also in males treated with a lower dose of the POV. This is the first study reporting a treatment-related mortality in animals acutely administrated with a mixed-valence POV, contrasting with the well-known, less toxic decavanadate. These results document the toxicity of this mixed-valence POV, which may not be suitable for biomedical applications.

Gallium(III)- and Thallium(III)-Encapsulated Polyoxopalladates: Synthesis, Structure, Multinuclear NMR, and Biological Activity Studies

Three gallium(III)- and thallium(III)-containing polyoxopalladates (POPs) have been synthesized and structurally characterized in the solid state and in solution, namely, the phosphate-capped 12-palladate nanocubes [XPd12O8(PO4)8]13- (X = GaIII, GaPd12P8; X = TlIII, TlPd12P8) and the 23-palladate double-cube [Tl2IIIPd23P14O70(OH)2]20- (Tl2Pd23P14). The cuboid POPs, GaPd12P8 and TlPd12P8, are solution stable as verified by the respective 31P, 71Ga, and 205Tl nuclear magnetic resonance (NMR) spectra. Of prime interest, the spin-spin coupling schemes allowed for an intimate study of the solution behavior of the TlIII-containing POPs via a combination of 31P and 205Tl NMR, including the stoichiometry of the major fragments of Tl2Pd23P14. Moreover, biological studies demonstrated the antitumor and antiviral activity of GaPd12P8 and TlPd12P8, which were validated to be as efficient as cis-platinum against human melanoma and acute promyelocytic leukemia cells. Furthermore, GaPd12P8 and TlPd12P8 exerted inhibitory activity against two herpetic viruses, HSV-2 and HCMV, in a dose-response manner.

The interaction on HSA and the antibacterial activity from four polyoxometalate hybrids based on berberine

Four organic-polyoxometalate hybrids BR4[SiW12O40] (BR-SiW), BR3[PMo12O40] (BR-PMo), BR4K[EuSiW11O40]·2H2O (BR-EuSiW) and BR6Na3[EuW10O36] (BR-EuW) were fabricated by the polyoxometalates (POMs) anions and berberine cations (BR) noted for the alkaloids in traditional Chinese herbal medicine. These hybrids have been characterized and confirmed. The interaction between hybrids and human serum albumin (HSA) was investigated in a buffer solution (pH 7.4) using ultraviolet-visible light absorption and fluorescence techniques. The classical Stern-Volmer equation was used to analyze the fluorescence quenching at three temperatures (296, 303 and 310 K), and the static quenching mechanism for interaction was proposed. The Thermodynamic parameters, enthalpy, entropy change, and Gibbs free energy of hybrids interacting on HSA were calculated by Scatchard equation. The results indicated that therewas one binding site on the protein and BR-POMs all showed stronger binding force than that of raw materials. Synchronous fluorescence results showed that the binding sites of BR-POMs and HSA were not effectively affected the surrounding microenvironment. The following antibacterial experiments implied that inhibitory effect of hybrids were synergistic effect from organic active ingredient and POMs but the simple combination. All these data were prepared for further research on biology.

Fine-tuning non-covalent interactions between hybrid metal-oxo clusters and proteins

Interactions between the protein Hen Egg White Lysozyme (HEWL) and three different hybrid Anderson-Evans polyoxometalate clusters - AE-NH2 (δ-[MnMo6O18{(OCH2)3CNH2}2]3-), AE-CH3 (δ-[MnMo6O18{(OCH2)3CCH3}2]3-) and AE-Biot (δ-[MnMo6O18{(OCH2)3CNHCOC9H15N2OS}2]3-) - were studied via tryptophan fluorescence spectroscopy and single crystal X-ray diffraction. Quenching of tryptophan fluorescence was observed in the presence of all three hybrid polyoxometalate clusters (HPOMs), but the extent of quenching and the binding affinity were greatly dependent on the nature of the organic groups attached to the cluster. Control experiments further revealed the synergistic effect of the anionic polyoxometalate core and organic ligands towards enhanced protein interactions. Furthermore, the protein was co-crystallised with each of the three HPOMs, resulting in four different crystal structures, thus allowing for the binding modes of HPOM-protein interactions to be investigated with near-atomic precision. All crystal structures displayed a unique mode of binding of the HPOMs to the protein, with both functionalisation and the pH of the crystallisation conditions influencing the interactions. From the crystal structures, it was determined that HPOM-protein non-covalent complexes formed through a combination of electrostatic attraction between the polyoxometalate cluster and positively charged surface regions of HEWL, and direct and water-mediated hydrogen bonds with both the metal-oxo inorganic core and the functional groups of the ligand, where possible. Hence, functionalisation of metal-oxo clusters shows great potential in tuning their interactions with proteins, which is of interest for several biomedical applications.

Polyoxometalate K6[P2Mo18O62] Inactivates Escherichia coli O157:H7 by Inducing recA Expression and Apoptosis-like Bacterial Death

Polyoxometalates have emerged as promising bactericidal agents. In the current study, the bactericidal activity of polyoxometalate K₆[P₂Mo₁₈O₆₂] against Escherichia coli (E. coli) O157:H7 and its possible underlying mechanisms were explored. The obtained results demonstrated that K₆[P₂Mo₁₈O₆₂] could effectively kill E. coli O157:H7 at millimolar levels. Moreover, K₆[P₂Mo₁₈O₆₂] treatment also induced significant increases in recA protein expression and further triggered characteristic apoptosis-like bacterial death events such as DNA fragmentation and phosphatidylserine exposure. In conclusion, polyoxometalate K₆[P₂Mo₁₈O₆₂] possesses a desirable antibacterial activity, and induction of bacterial apoptosis-like death might be involved in its underlying bactericidal mechanisms.

Speciation atlas of polyoxometalates in aqueous solutions

Speciation is the key parameter in solution chemistry that describes the composition, concentration, and oxidation state of each chemical form of an element present in a sample. The speciation study of complex polyatomic ions has remained challenging because of the large number of factors affecting stability and the limited number of direct methods. To address these challenges, we developed the speciation atlas of 10 polyoxometalates commonly used in catalytic and biological applications in aqueous solutions, where the speciation atlas provides both a species distribution database and a predictive model for other polyoxometalates to be used. Compiled for six different polyoxometalate archetypes with three types of addenda ions based on 1309 nuclear magnetic resonance spectra under 54 different conditions, the atlas has revealed a previously unknown behavior of polyoxometalates that may account for their potency as biological agents and catalysts. The atlas is intended to promote the interdisciplinary use of metal oxides in various scientific fields.

Synthesis, Characterization, and Antibacterial Activity of Ni-Substituted Krebs-type Sandwich-Tungstobismuthates Functionalized with Amino Acids

Four new Ni-substituted Krebs-type sandwich-tungstobismuthates, K₄Ni₂[{Ni(β-ala)(H₂O)₂}₂{Ni(H₂O)}₂{Ni(H₂O)(η²-β-ala)}₂(B-β-BiW₉O₃₃)₂]·49H₂O {(β-ala)₄(Ni₃)₂(BiW₉)₂}, K_3.5Na_6.5[{Ni(η³-L-asp)}₂(WO₂)₂(B-β-BiW₉O₃₃)₂]·36H₂O·L-asp {(L-asp)₂(NiW)₂(BiW₉)₂}, K₄Na₆[{Ni(gly)(H₂O)₂}₂(WO₂)₂(B-β-BiW₉O₃₃)₂]·86H₂O {(gly)₂(NiW)₂(BiW₉)₂}, and K₂Na₈[{Ni(η²-serinol) (H₂O)}₂{Ni(H₂O)₂}₂(B-β-BiW₉O₃₃)₂]·42H₂O {(serinol)₂Ni₄(BiW₉)₂} have been synthesized by one-pot solution methods. All compounds have been characterized in the solid state by single-crystal X-ray diffraction (SXRD), powder X-ray diffraction (PXRD), elemental and thermogravimetric analyses, and infrared spectroscopy (IR), as well as by UV-vis spectroscopy in solution. The antibacterial activity of all compounds was studied against four bacterial strains by the determination of the minimum inhibitory concentration (MIC). The results showed that only {(β-ala)₄(Ni₃)₂(BiW₉)₂} demonstrates antibacterial activity (MIC is in the range from 8 to 256 μg/mL) compared to three other Ni-Krebs sandwiches.

Adaptive Responses of a Peroxidase-like Polyoxometalate-Based Tri-Assembly to Bacterial Microenvironment (BME) Significantly Improved the Anti-Bacterial Effects

The present study presents the tertiary assembly of a POM, peptide, and biogenic amine, which is a concept to construct new hybrid bio-inorganic materials for antibacterial applications and will help to promote the development of antivirus agents in the future. To achieve this, a Eu-containing polyoxometalate (EuW₁₀) was first co-assembled with a biogenic amine of spermine (Spm), which improved both the luminescence and antibacterial effect of EuW₁₀. Further introduction of a basic peptide from HPV E6, GL-22, induced more extensive enhancements, both of them being attributed to the cooperation and synergistic effects between the constituents, particularly the adaptive responses of assembly to the bacterial microenvironment (BME). Further intrinsic mechanism investigations revealed in detail that the encapsulation of EuW₁₀ in Spm and further GL-22 enhanced the uptake abilities of EuW₁₀ in bacteria, which further improved the ROS generation in BME via the abundant H₂O₂ involved there and significantly promoted the antibacterial effects.

Evaluating the durability and performance of polyoxometalate-ionic liquid coatings on calcareous stones: Preventing biocolonisation in outdoor environments

Rock-based materials exposed to outdoor environments are naturally colonised by an array of microorganisms, which can cause dissolution and fracturing of the natural stone. Biocolonisation of monuments and architectures of important cultural heritage therefore represents an expensive and recurring problem for local authorities and private owners alike. In this area, preventive strategies to mitigate biocolonisation are generally preferred to curative approaches, such as mechanical cleaning by brush or high-pressure cleaning, to remove pre-existing patina. The aim of this work was to study the interaction between biocidal polyoxometalate-ionic liquid (POM-IL) coatings and calcareous stones and evaluate the capacity of these coatings to prevent biocolonisation through a series of accelerated ageing studies in climate chambers, carried out in parallel with a two-year period of outdoor exposure in north-eastern France. Our experiments show that POM-IL coatings did not affect water vapour transfer nor significantly alter the total porosity of the calcareous stones. Simulated weathering studies replicating harsh (hot and wet) climatic weather conditions demonstrated that the colour variation of POM-IL-coated stones did not vary significantly with respect to the natural uncoated stones. Accelerated biocolonisation studies performed on the weathered POM-IL-coated stones proved that the coatings were still capable of preventing colonisation by an algal biofilm. However, a combination of colour measurements, chlorophyll fluorescence data, and scanning electron microscopy imaging of stones aged outdoors in northern France for two years showed that coated and uncoated stone samples showed signs of colonisation by fungal mycelium and phototrophs. Altogether, our results demonstrate that POM-ILs are suitable as preventative biocidal coatings for calcareous stones, but the correct concentrations must be chosen to achieve a balance between porosity of the stone, the resulting colour variation and the desired duration of the biocidal effect over longer periods of time, particularly in outdoor environments.

Exploring the Reactivity of Polyoxometalates toward Proteins: From Interactions to Mechanistic Insights

The latest advances in the study of the reactivity of metal-oxo clusters toward proteins showcase how fundamental insights obtained so far open new opportunities in biotechnology and medicine. In this Perspective, these studies are discussed through the lens of the reactivity of a family of soluble anionic metal-oxo nanoclusters known as polyoxometalates (POMs). POMs act as catalysts in a wide range of reactions with several different types of biomolecules and have promising therapeutic applications due to their antiviral, antibacterial, and antitumor activities. However, the lack of a detailed understanding of the mechanisms behind biochemically relevant reactions-particularly with complex biological systems such as proteins-still hinders further developments. Hence, in this Perspective, special attention is given to reactions of POMs with peptides and proteins showcasing a molecular-level understanding of the reaction mechanism. In doing so, we aim to highlight both existing limitations and promising directions of future research on the reactivity of metal-oxo clusters toward proteins and beyond.

Role of Multiple Vanadium Centers on Redox Buffering and Rates of Polyvanadomolybdate-Cu(II)-Catalyzed Aerobic Oxidations

A recent report established that the tetrabutylammonium (TBA) salt of hexavanadopolymolybdate TBA₄H₅[PMo₆V₆O₄₀] (PV₆Mo₆) serves as the redox buffer with Cu(II) as a co-catalyst for aerobic deodorization of thiols in acetonitrile. Here, we document the profound impact of vanadium atom number (x = 0-4 and 6) in TBA salts of PV_xMo_12-xO₄₀^(3+x)- (PVMo) on this multicomponent catalytic system. The PVMo cyclic voltammetric peaks from 0 to -2000 mV vs Fc/Fc⁺ under catalytic conditions (acetonitrile, ambient T) are assigned and clarify that the redox buffering capability of the PVMo/Cu catalytic system derives from the number of steps, the number of electrons transferred each step, and the potential ranges of each step. All PVMo are reduced by varying numbers of electrons, from 1 to 6, in different reaction conditions. Significantly, PVMo with x ≤ 3 not only has much lower activity than when x > 3 (for example, the turnover frequencies (TOF) of PV₃Mo₉ and PV₄Mo₈ are 8.9 and 48 s^-1, respectively) but also, unlike the latter, cannot maintain steady reduction states when the Mo atoms in these polyoxometalate (POMs) are also reduced. Stopped-flow kinetics measurements reveal that Mo atoms in Keggin PVMo exhibit much slower electron transfer rates than V atoms. There are two kinetic arguments: (a) In acetonitrile, the first formal potential of PMo₁₂ is more positive than that of PVMo₁₁ (-236 and -405 mV vs Fc/Fc⁺); however, the initial reduction rates are 1.06 × 10^-4 s^-1 and 0.036 s^-1 for PMo₁₂ and PVMo₁₁, respectively. (b) In aqueous sulfate buffer (pH = 2), a two-step kinetics is observed for PVMo₁₁ and PV₂Mo₁₀, where the first and second steps are assigned to reduction of the V and Mo centers, respectively. Since fast and reversible electron transfers are key for the redox buffering behavior, the slower electron transfer kinetics of Mo preclude these centers functioning in redox buffering that maintains the solution potential. We conclude that PVMo with more vanadium atoms allows the POM to undergo more and faster redox changes, which enables the POM to function as a redox buffer dictating far higher catalytic activity.

Comparative Spectroscopic and Electrochemical Study of V(V)-Substituted Keggin-Type Phosphomolybdates and -Tungstates

Vanadium-substituted Keggin-type heteropolyanions have been studied for a wide variety of applications, ranging from catalysis to antiviral/antimicrobial agents. While the V-substituted phosphomolybdates [PVxMo12−xO40](3+x)− have been well investigated in this context, comparatively little is known about the corresponding phosphotungstates [PVxW12-xO40](3+x)−. We have succeeded in synthesizing the sodium salts of the whole series [PVxW12−xO40](3+x)−, for x = 1 to 6, and characterised them spectroscopically (FT-IR, UV-Vis, 31P-, and 51V-NMR) and electrochemically (CV and SWV). Thereby, direct comparisons between the vanadium-substituted phosphomolybdates and -tungstates, with substitution degrees from 1 to 6, can be established, which provides a solid basis for further investigations of potential applications.

Polyoxometalates Impact as Anticancer Agents

Polyoxometalates (POMs) are oxoanions of transition metal ions, such as V, Mo, W, Nb, and Pd, forming a variety of structures with a wide range of applications. Herein, we analyzed recent studies on the effects of polyoxometalates as anticancer agents, particularly their effects on the cell cycle. To this end, a literature search was carried out between March and June 2022, using the keywords "polyoxometalates" and "cell cycle". The effects of POMs on selected cell lines can be diverse, such as their effects in the cell cycle, protein expression, mitochondrial effects, reactive oxygen species (ROS) production, cell death and cell viability. The present study focused on cell viability and cell cycle arrest. Cell viability was analyzed by dividing the POMs into sections according to the constituent compound, namely polyoxovanadates (POVs), polyoxomolybdates (POMos), polyoxopaladates (POPds) and polyoxotungstates (POTs). When comparing and sorting the IC₅₀ values in ascending order, we obtained first POVs, then POTs, POPds and, finally, POMos. When comparing clinically approved drugs and POMs, better results of POMs in relation to drugs were observed in many cases, since the dose required to have an inhibitory concentration of 50% is 2 to 200 times less, depending on the POMs, highlighting that these compounds could become in the future an alternative to existing drugs in cancer therapy.

Recent Advances in Hybrid Materials of Metal Nanoparticles and Polyoxometalates

Polyoxometalates (POMs), anionic metal-oxygen nanoclusters that possess various composition-dependent properties, are widely used to modify the existing properties of metal nanoparticles and to endow them with new ones. Herein, we present an overview of recent advances in hybrid materials that consist of metal nanoparticles and POMs. Following a brief introduction on the inception of this area and its development, representative properties and applications of these materials in various fields such as electrochemistry, photochemistry, and catalysis are introduced. We discuss how the combination of two classic inorganic materials facilitates cooperative and synergistic behavior, and we also give personal perspectives on the future development of this field.

Polyoxometalate-peptide hybrid materials: from structure-property relationships to applications

Organo-functionalisation of polyoxometalates (POMs) represents an effective approach to obtain diverse arrays of functional structures and materials, where the introduction of organic moieties into the POM molecules can dramatically change their surface chemistry, charge, polarity, and redox properties. The synergistic combination of POMs and peptides, which perform a myriad of essential roles within cellular biochemistry, including protection and transport in living organisms, leads to functional hybrid materials with unique properties. In this Perspective article, we present the principal synthetic routes to prepare and characterise POM-peptide hybrids, together with a comprehensive description of how their properties - such as redox chemistry, stereochemistry and supramolecular self-assembly - give rise to materials with relevant catalytic, adhesive, and biomedical applications. By presenting the state-of-the-art of the POM-peptide field, we show specifically how emerging chemical approaches can be harnessed to develop tailored POM-peptide materials with synergistic properties for applications in a variety of disciplines.

Oxo-Replaced Polyoxometalates: There Is More than Oxygen

The presence of oxo-ligands is one of the main required characteristics for polyoxometalates (POMs), although some oxygen ions in a metallic environment can be replaced by other nonmetals, while maintaining the POM structure. The replacement of oxo-ligands offers a valuable approach to tune the charge distribution and connected properties like reducibility and hydrolytic stability of POMs for the development of tailored compounds. By assessing the reported catalytic and biological applications and connecting them to POM structures, the present review provides a guideline for synthetic approaches and aims to stimulate further applications where the oxo-replaced compounds are superior to their oxo-analogues. Oxo-replacement in POMs deserves more attention as a valuable tool to form chemically activated precursors for the synthesis of novel structures or to upgrade established structures with extraordinary properties for challenging applications.

Grafting of Anionic Decahydro-Closo-Decaborate Clusters on Keggin and Dawson-Type Polyoxometalates: Syntheses, Studies in Solution, DFT Calculations and Electrochemical Properties

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.

Inhibition of SERCA and PMCA Ca2+-ATPase activities by polyoxotungstates

Plasma membrane calcium ATPases (PMCA) and sarco(endo) reticulum calcium ATPases (SERCA) are key proteins in the maintenance of calcium homeostasis. Herein, we compare for the first time the inhibition of SERCA and PMCA calcium pumps by several polyoxotungstates (POTs), namely by Wells-Dawson phosphotungstate anions [P₂W₁₈O₆₂]^6- (intact, {P₂W₁₈}), [P₂W₁₇O₆₁]^10- (monolacunary, {P₂W₁₇}), [P₂W₁₅O₅₆]^12- (trilacunary, {P₂W₁₅}), [H₂P₂W₁₂O₄₈]^12- (hexalacunary, {P₂W₁₂}), [H₃P₂W₁₅V₃O₆₂]^6- (trivanadium-substituted, {P₂W₁₅V₃}) and by Preyssler-type anion [NaP₅W₃₀O₁₁₀]^14- ({P₅W₃₀}). The speciation in the solutions of tested POTs was investigated by ³¹P and ⁵¹V NMR spectroscopy. The tested POTs inhibited SERCA Ca²⁺-ATPase activity, whereby the Preyssler POT showed the strongest effect, with an IC₅₀ value of 0.37 μM. For {P₂W₁₇} and {P₂W₁₅V₃} higher IC₅₀ values were determined: 0.72 and 0.95 μM, respectively. The studied POTs showed to be more potent inhibitors of PMCA Ca²⁺-ATPase activity, with lower IC₅₀ values for {P₂W₁₇}, {P₅W₃₀} and {P₂W₁₅V₃}.

Computational and experimental elucidation of the boosted stability and antibacterial activity of ZIF-67 upon optimized encapsulation with polyoxometalates

Water microbial purification is one of the hottest topics that threats human morbidity and mortality. It is indispensable to purify water using antimicrobial agents combined with several technologies and systems. Herein, we introduce a class of nanosized metal organic framework; Zeolitic imidazolate framework (ZIF-67) cages encapsulated with polyoxometalates synthesized via facile one-step co-precipitation method. We employed two types of polyoxometalates bioactive agents; phosphotungstic acid (PTA) and phosphomolybdic acid (PMA) that act as novel antibacterial purification agents. Several characterization techniques were utilized to investigate the morphological, structural, chemical, and physical properties such as FESEM, EDS, FTIR, XRD, and N₂ adsorption/desorption isotherms techniques. The antibacterial assessment was evaluated using colony forming unit (CFU) against both Escherichia coli and Staphylococcus aureus as models of Gram-negative and Gram-positive bacteria, respectively. The PTA@ZIF-67 showed higher microbial inhibition against both Gram-positive and Gram-negative bacteria by 98.8% and 84.6%, respectively. Furthermore, computational modeling using density functional theory was conducted to evaluate the antibacterial efficacy of PTA when compared to PMA. The computational and experimental findings demonstrate that the fabricated POM@ZIF-67 materials exhibited outstanding bactericidal effect against both Gram-negative and Gram-positive bacteria and effectively purify contaminated water.

Polyoxometalate-based nanocomposites for antitumor and antibacterial applications

Polyoxometalates (POMs), as emerging inorganic metal oxides, have been shown to have significant biological activity and great medicinal value. Nowadays, biologically active POM-based organic-inorganic hybrid materials have become the next generation of antibacterial and anticancer drugs because of their customizable molecular structures related to their highly enhanced antitumor activity and reduced toxicity to healthy cells. In this review, the current developed strategies with POM-based materials for the purpose of antibacterial and anticancer activities from different action principles inducing cell death and hyperpolarization, cell plasma membrane destruction, interference with bacterial respiratory chain and inhibiting bacterial growth are overviewed. Moreover, specific interactions between POM-based materials and biomolecules are highlighted for a better understanding of their antibacterial and anticancer mechanisms. POMs have great promise as next-generation antibacterial and anticancer drugs, and this review will provide a valuable systematic reference for the further development of POM-based nanomaterials.