The interactions of polyoxovanadates (POVs) with proteins have increasingly attracted interest in recent years due to their potential biomedical applications. This is especially the case because of their redox and catalytic properties, which make them interesting for developing artificial metalloenzymes. Organic-inorganic hybrid hexavanadates in particular offer several advantages over all-inorganic POVs. However, they have been scarcely investigated in biological systems even though, as shown in this work, hybrid hexavanadates are highly stable in aqueous solutions up to relatively high pH. Therefore, a novel bis-biotinylated hexavanadate was synthesized and shown to selectively interact with two biotin-binding proteins, avidin and streptavidin. Bridging interactions between multiple proteins led to their self-assembly into supramolecular bio-inorganic hybrid systems that have potential as artificial enzymes with the hexavanadate core as a redox-active cofactor. Moreover, the structure and charge of the hexavanadate core were determined to enhance the binding affinity and slightly alter the secondary structure of the proteins, which affected the size and speed of formation of the assemblies. Hence, tuning the polyoxometalate (POM) core of hybrid POMs (HPOMs) with protein-binding ligands has been demonstrated to be a potential strategy for controlling the self-assembly process while also enabling the formation of novel POM-based biomaterials that could be of interest in biomedicine.

OBJECTIVE: Lindqvist-type polyoxometalates (POMs) exhibit potential antitumor activities. This study aimed to examine the effects of Lindqvist-type POMs against breast cancer and the underlying mechanism.
METHODS: Using different cancer cell lines, the present study evaluated the antitumor activities of POM analogues that were modified at the body skeleton based on molybdenum-vanadium-centered negative oxygen ion polycondensations with different side strains. Cell colony formation assay, autophagy detection, mitochondrial observation, qRT-PCR, Western blotting, and animal model were used to evaluate the antitumor activities of POMs against breast cancer cells and the related mechanism.
RESULTS: MO-4, a Lindqvist-type POM linking a proline at its side strain, was selected for subsequent experiments due to its low half maximal inhibitory concentration in the inhibition of proliferation of breast cancer cells. It was found that MO-4 induced the apoptosis of multiple types of breast cancer cells. Mechanistically, MO-4 activated intracellular mitophagy by elevating mitochondrial reactive oxygen species (ROS) levels and resulting in apoptosis. In vivo, breast tumor growth and distant metastasis were significantly reduced following MO-4 treatment.
CONCLUSIONS: Collectively, the results of the present study demonstrated that the novel Lindqvist-type POM MO-4 may exhibit potential in the treatment of breast cancer.

To improve the performance of Lithium-Sulfur (Li-S) batteries, the reaction catalysts of lithium polysulfides (LiPSs) reactions should have the characteristics of large surface area, efficient atomic utilization, high conductivity, small size, good stability, and strong adjustability. Herein, Anderson-type polyoxometalate ([TMMo6O24]n-, TM = Co, Ni, Fe, represented by TMMo6 POMs) are used as the modified materials for Li-S battery separator. By customizing the central metal atoms, this work gains insights into the layer-by-layer electron transfer mechanism between TMMo6 units and LiPSs, similar to the collision effect of a bowling ball. Theoretical analysis and in situ experimental characterization show that the changes of CoMo6 units with moderate binding energy and lowest Gibbs free energy result in the formation of robust polar bonds and prolonged S─S bonds after adsorption. Hence, the representative Li-S battery with CoMo6 and graphene composite modified separator has a high initial capacity of 1588.6 mA h g-1 at 0.2 C, excellent cycle performance of more than 3000 cycles at 5 C, and uniform Li+ transport over 1900 h. More importantly, this work has revealed the inherent contradiction between the kinetics and thermodynamics, achieving a stable cycle in the temperature range of -20 to 60 °C.

Alzheimer\'s disease (AD) is a devastating neurodegenerative disease that affects ∼50 million people globally. The accumulation of amyloid-β (Aβ) plaques, a predominant pathological feature of AD, plays a crucial role in AD pathogenesis. In this respect, Aβ has been regarded as a highly promising therapeutic target for AD treatment. Polyoxometalates (POMs) are a novel class of metallodrugs being developed as modulators of Aβ aggregation, owing to their negative charge, polarity, and three-dimensional structure. Unlike traditional discrete inorganic complexes, POMs contain tens to hundreds of metal atoms, showcasing remarkable tunability and diversity in nuclearities, sizes, and shapes. The easily adjustable and structurally variable nature of POMs allows for their favorable interactions with Aβ. This mini-review presents a balanced overview of recent progress in using POMs to mitigate amyloidosis. Clear correlations between anti-amyloid activities and structural features of POMs are also elaborated in detail. Finally, we discuss the current challenges and future prospects of POMs in combating AD.

As a new type of artificial enzyme, a nanozyme is an ideal substitute for natural enzymes and has been successfully applied in many fields. However, in the application of biomolecular detection, most nanozymes have the disadvantages of long reaction times or high detection limits, prompting researchers to search for new efficient nanozymes. In this work, the enzyme-like activities of three polyoxometalate-based iron-organic complexes ([Fe(bpp)2](Mo6O19), [Fe(bpp)2]2(Mo8O26)·2CH3OH, and [Fe(bpp)2]4H[Na(Mo8O26)]3), namely, FeMo6, Fe2Mo8, and Fe4Mo8Na, were analyzed. All three polyoxometalate-based iron-organic complexes were found to be capable of catalyzing hydrogen peroxide (H2O2) to oxidize 3,3\',5,5\'-tetramethylbenzidine and o-phenylenediamine, resulting in visible color changes, further exhibiting peroxidase-like activity. Results showed that Fe4Mo8Na had more active sites due to its long chain structure, endowing more prominent peroxidase-like activity compared with Fe2Mo8 and FeMo6. A colorimetric sensing platform for H2O2 and ascorbic acid detection based on Fe4Mo8Na was established. The linear response range for H2O2 detection was 0.5-100 μM, and the detection limit was 0.143 μM. The linear response for ascorbic acid detection ranges from 0 to 750 μM with a detection limit of 1.07 μM. This study provides a new perspective for developing new nanozymes and expanding the sensing and detection application of nanozymes.

Non-oxidative intercalation of graphite avoids damage to graphene lattices and is a suitable method to produce high-quality graphene. However, the yield of exfoliated graphene is low in this process due to the poor delamination efficiency of guest species. In this study, a Brønsted acid intercalation protocol is developed involving polyoxometalate (POM) clusters (H6P2W18O62) as guests and intercalation of graphite is realized at the sub-nanometer scale. Theoretical simulation based on DFT elucidates the stepwise intercalation mechanism of Brønsted acid molecules and clusters. Unlike common molecules/ionic guests, intercalation of POM clusters induces large expansion and extensive donor-acceptor interactions among graphite interlayers. This significantly weakens the van der Waals forces and promotes exfoliation efficiency of graphene layers. The exfoliated graphene possesses outstanding features of large lateral size, thin thickness, and high purity, and shows excellent performance as the anode for high power sodium-ion batteries. This work proffers a new pathway toward non-oxidative intercalation of graphite for large-scale production of graphene.

Polyoxometalate (POM)-based ionic liquids (POM-ILs) are gaining increasing attention due to their diverse structures and functionalities. POMs in POM-ILs not only act as essential structural building blocks but also play a crucial role in their functional performance. With the incorporation of POMs, POM-ILs find applications in various fields such as chemical catalysis, energy science, materials science, sensors, and more. The abundant availability of POMs and other building blocks in POM-ILs, along with their versatile combination possibilities, present promising opportunities for the future. Rather than focusing solely on discovering new structures of POM-ILs, current developments in this field emphasize exploring their functions, leading to the emergence of numerous new applications. Summarizing these advancements aids in understanding the latest trends and facilitates rapid evolution. This review examines the recent five years\' worth of results to analyze the new functions of POM-ILs, categorizing them based on their unique characteristics.

Polyoxometalates (POMs) are nanosized molecular metal oxide anion clusters with tuneable structures and functionalities, and they exhibit a redox chemistry and catalytic activity in multielectron redox processes. These are typically poor electrical conductors (<10-10 Scm-1), which is attributed to negligible electronic interactions among anions in the solid state. Since the reduced electrons on the d0 metals in POMs are delocalized, electrical conductivity was improved when judicious pathways for the electrons were created by bridging the POMs. Utilized with the electronic interactions between bridging oxygen atoms with the highest occupied molecular orbital in the POMs and the metal dz2 orbitals in the multinuclear platinum complexes, and three mixed-valent assemblies were synthesized and characterized. Simply mixing Keggin-type or Dawson-type POMs with tetranuclear or trinuclear platinum complexes in solution afforded three single crystals, and all three compounds were paramagnetic with mixed oxidation states and better conductivities at room temperature than the parent compounds.

The pronounced conductivity of tin dioxide (SnO2) nanoparticles makes it an ideal multifunctional electrode material, while the challenge is to stabilize the quantum dot (QD) SnO2 nanocore in water. An Anderson-type polyoxomolybdate, (NH4)6[Mo7O24], is employed as an inorganic ligand to stabilize a ca. 6 nm SnO2 QD (Mox@SnO2). X-ray scattering and diffraction studies confirm the tetragonal SnO2 nanocore in Mox@SnO2. Elemental analyses are in good agreement with the mass spectrometric detection of the [Mo7O24]6- cluster present in Mox@SnO2. The ionic POMs attached to the SnO2 surface through [Mo-O-Sn] covalent linkages have been established by surface zeta potential, shift of the [Mo = O]t Raman vibration, and extended X-ray absorption fine structure (EXAFS) analyses. The presence of the [Mo7O24]6- cluster in the Mox@SnO2 is responsible for the remarkable aqueous stability of Mox@SnO2 in the pH range of 3-9. Dominant oxygen vacancy in the SnO2 core, identified by EXAFS data and the anisotropic electron paramagnetic resonance (EPR) signals (g ∼ 2.4 and 1.9), results in facile electronic conduction in Mox@SnO2 while being deposited on the electrode surface. Mox@SnO2 acts as an active catalyst for the electrocatalytic nitrate reduction (eNOR) to ammonia with 94% faradaic efficiency (FE) at -0.2 V vs RHE and a yield rate of 28.9 mg h-1 cm-2. The stability of Mox@SnO2 in acidic pH provides scope to reuse the Mox@SnO2 electrode at least four times with notable NH3 selectivity and a superior production rate (239.06 mmol g-1(cat) h-1). This study demonstrates the essential role of POM in stabilizing SnO2 QD, harnessing its electrochemical activity toward electrocatalytic ammonia production.

Heazlewoodite nickel sulfide (Ni3S2) is advocated as a promising nonnoble catalyst for electrochemical water splitting because of its unique structure configuration and high conductivity. However, the low active sites and strong sulfur-hydrogen bonds (S-Hads) formed on Ni3S2 surface greatly inhibit the desorption of Hads and reduce the hydrogen and oxygen evolution reaction (HER and OER) activity. Doping is a valid strategy to stimulate the intrinsic catalytic activity of pristine Ni3S2 via modifying the active site. Herein, the Ni foam supported Fe and Mo co-doped Ni3S2 electrocatalysts (Fe-MoS2/Ni3S2@NF) have been constructed using Keplerate polyoxomolybdate {Mo72F30} as precursor through a facile hydrothermal process. Experimental results certificate that Fe and Mo co-doping can effectively tune the local electronic structure, facilitate the interfacial electron transfer, and improve the intrinsic activity. Consequently, the Fe-MoS2/Ni3S2@NF display more excellent HER and OER activity than MoS2/Ni3S2@NF and bare Ni3S2@NF by delivering the 10 and 50 mA cm-2 current densities at ultra-low overpotentials of 74/175 and 80/160 mV for HER and OER. Moreover, when coupled in an alkaline electrolyzer, Fe-MoS2/Ni3S2@NF approached the current of 10 mA cm-2 under a cell voltage of 1.60 V and exhibit excellent stability. The strategy to realize tunable catalytic behaviors via foreign metal doping provides a new avenue to optimize the water splitting catalysts.