Im Kampf gegen Krebs: Polyoxometallate als nächste Generation metallhaltiger Medikamente

Prussian blue nanoparticle-based pH-responsive self-assembly for enhanced photothermal and chemotherapy of tumors

In recent years, there has been growing interest in size-transformable nanoplatforms that exhibit active responses to acidic microenvironments, presenting promising prospects in the field of nanomedicine for tumor therapy. However, the design and fabrication of such size-adjustable nanotherapeutics pose significant challenges compared to size-fixed nanocomposites, primarily due to their distinct pH-responsive requirements. In this study, we developed pH-activated-aggregating nanosystems to integrate chemotherapy and photothermal therapy by creating size-transformable nanoparticles based on Prussian blue nanoparticles (PB NPs) anchored with acid-responsive polyoxometalates (POMs) quantum dots via electrostatic interactions (PPP NPs). Subsequently, we utilized doxorubicin (DOX) as a representative drug to formulate PPPD NPs. Notably, PPPD NPs exhibited a significant response to acidic conditions, resulting in changes in surface charge and rapid aggregation of PPP NPs. Furthermore, the aggregated PPP NPs demonstrated excellent photothermal properties under near-infrared laser irradiation. Importantly, PPPD NPs prolonged their retention time in tumor cells via a size-transformation approach. In vitro cellular assays revealed that the anticancer efficacy of PPPD NPs was significantly enhanced. The IC50 values for the PPPD NPs groupand the PPPD NPs + NIR group were 50.11 μg/mL and 30.9 μg/mL. Overall, this study introduces a novel strategy for cancer therapy by developing size-aggregating nano-drugs with stimuli-responsive properties, holding promise for improved therapeutic outcomes in future combination approaches involving photothermal therapy and chemotherapy.

Tris-Functionalized Polyoxotungstovanadate-Mediated Antitumor Efficacy Involves Multiple Cell Death Pathways

Polyoxometalates (POMs) are promising inorganic drug candidates for cancer chemotherapy. They are becoming attractive because of their easy accessibility and low cost. Herein, we report the synthesis and antitumor activity studies of four Lindqvist-type POMs with mixed-addenda atoms Na2[V4W2O16{(OCH2)3CR}] (R=-CH2OH, -CH3, -CH2CH3) and (Bu4N)2[V3W3{(OCH2)3CH2OOCCH2CH3}]. Compared with the current clinical applied antitumor drug 5-fluorouracil (5-FU) or Gemcitabine, analysis of MTT/CCK-8 assay, colony formation and wound healing assay revealed that the {V4W2} POMs had acceptable cytotoxicity in normal cells (293T) and significant inhibitory effects on cell proliferation and migration in three human tumor cell lines: human lung carcinoma cells (A549), human cervical carcinoma cells (HeLa), and human breast cancer cells (MCF-7). Interestingly, among the POMs analyzed, the therapeutic index (TI) of the {V4W2} POM with R= -CH2OH was relatively the most satisfactory. Thus, it was subsequently used for further studies. Flow cytometry analysis showed it prompted cellular apoptosis rate. qRT-PCR and Western blotting analysis indicated that multiple cell death pathways were activated including apoptosis, autophagy, necroptosis and pyroptosis during the POM-mediated antitumor process. In conclusion, our study shows that the polyoxotungstovanadate has great potential to be developed into a broad-spectrum antitumor chemotherapeutic drug.

Surface Engineering Promoted Insulin-Sensitizing Activities of Sub-Nanoscale Vanadate Clusters through Regulated Pharmacokinetics and Bioavailability

The therapeutic application of vanadium compounds is plagued by their poor bioavailability and potential adverse effects. Herein, 1 nm polyoxovanadate (POV) clusters are functionalized with alkyl chains of various lengths and studied for the effect of surface engineering on their preclinical pharmacokinetics and typical insulin-sensitizing activity. The concentrations of surface engineered POVs in plasma, urine, and feces are monitored after a single administration to rats. The POVs exhibit a two-compartment profile of in vivo kinetics, and the surface engineering effect plays an important role in renal clearance of the POVs comparable to small molecules. POVs functionalized with long alkyl chains show much shorter elimination half time t_1/2β and higher elimination fractions (50%) within 48 h than pristine POVs, suggesting favorable elimination kinetics to mitigate the possible side effects of vanadium. Meanwhile, long alkyl chain modification leads to a 76% increment of oral bioavailability in contrast to unmodified POVs. As suggested by glucose tolerance tests and sub-chronic toxicity tests, the above two factors contribute to the enhanced therapeutic efficacy of POVs while mitigating their adverse effects. The surface engineering protocol provides a feasible approach to the optimization of the bioavailability and pharmacokinetic properties of POVs for promoted insulin-sensitizing activities.

Selective Adsorption of Hemoglobin in Human Whole Blood with a Nickel Monosubstituted Silicotungstic Acid Hybrid

A nickel monosubstituted polyoxometalate (POM)/polyaniline organic-inorganic hybrid SiW₁₁Ni/PANI was synthesized using the liquid-phase method at room temperature to achieve the solidification of water-soluble POMs. The SiW₁₁Ni/PANI hybrid was characterized by scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction, and zeta potential. On the basis of π-π stacking and affinity interaction between the SiW₁₁Ni/PANI hybrid and proteins, the SiW₁₁Ni/PANI hybrid showed good adsorption selectivity to hemoglobin (Hb). At pH 7.0, 0.5 mg of SiW₁₁Ni/PANI resulted in an adsorption efficiency of 92.4% for 1 mL of 100 μg mL^-1 Hb. The adsorption behavior of Hb on the surface of the hybrid fitted with the Langmuir model, and the maximum adsorption capacity was 692 mg g^-1. The adsorbed Hb was eluted by BR (0.04 mol L^-1, pH 9), providing a recovery of 94%. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis assay results indicated that the Hb in human whole blood could selectively be adsorbed by the SiW₁₁Ni/PANI hybrid, and the obtained Hb was with high purity. It could expand the application of POMs in life science due to the application of the POM hybrid in protein isolation/purification.

Thermal Structure Transformation and Application as a Negative Staining Reagent for SARS‐CoV‐2 Observation of Methylammonium Vanadate

The solid‐state thermal structure transformation of methylammonium vanadate, (CH₃NH₃)VO₃, from −150 °C to 350 °C is reported. Variable‐temperature X‐ray single‐crystal structure analysis at 23, 0, −50, −100, and −150 °C reveal (CH₃NH₃)VO₃ comprises of methylammonium cations and “snake‐like” ([VO₃]⁻)_n anion chains propagating along the c‐direction in the Pna2₁ space group. In between −150 and −100 °C, we observe a reversible structural transformation due to the re‐orientation of the methylammonium cations in the crystal packing, which is also confirmed by the reversible profiles observed in differential scanning calorimetry. The methylammonium vanadate is stable until at ca. 100 °C and further heating releases methylamine and water and V₂O₅ is formed at ca. 275 °C . Furthermore, we show that the methylammonium vanadate can be used as a negative staining reagent for visualizing SARS‐CoV‐2, allowing us to discern the spike proteins from the body of the virus using transmission electron microscopy.

Trisubstituted 4f- and 4d tungstoantimonates as artificial phosphoesterases for nerve agent degradation

Three new trisubstituted 4f- and 4d tungstoantimonates (TA) K₃Na₂₁[(M(CH₃COO))₃(HPO₃)(WO₄)(SbW₉O₃₃)₃]·nH₂O {M₃(HPO₃)Sb₃W₂₈} (M = Gd^III, Y^III, Yb^III, n = 35–36) were synthesized using a double-template synthetic approach. Following their characterization in the solid state employing single- and powder X-ray diffraction (XRD), IR-spectroscopy, and elemental – and thermogravimetric analyses (TGA), {M₃(HPO₃)Sb₃W₂₈} were subjected to a comprehensive set of solution characterization methods including UV/vis- and multinuclear ³¹P and ¹³C NMR spectroscopy. All representatives were shown to be highly active, recyclable, and stable Lewis-acid catalysts towards the nerve agent simulant O,O-dimethyl O-(4-nitrophenyl) phosphate (DMNP) at neutral pH (in Tris–HCl [125 mM] at pD 7.0 25 °C). Control experiments showing catalytic activity of the unsubstituted trilacunary TA [SbW₉O₃₃]⁹⁻ suggest the non-innocence of Tris in the DMNP hydrolysis for the first time.

With 3 Mio. people worldwide being yearly exposed to organophosphates (OPs), accounting for approximately 300 000 deaths, OPs are a current threat to mankind. This work reports on {M₃(HPO₃)Sb₃W₂₈} and {SbW₉} as recyclable OP degradation catalysts.

Host-Guest Complexation Between Cyclodextrins and Hybrid Hexavanadates: What are the Driving Forces?

Host-guest complexes between native cyclodextrins (α-, β- and γ-CD) and hybrid Lindqvist-type polyoxovanadates (POVs) [V₆ O₁₃ ((OCH₂ )₃ C-R)₂ ]^2- with R = CH₂ CH₃ , NO₂ , CH₂ OH and NH(BOC) (BOC = N-tert-butoxycarbonyl) were studied in aqueous solution. Six crystal structures determined by single-crystal X-ray diffraction analysis revealed the nature of the functional R group strongly influences the host-guest conformation and also the crystal packing. In all systems isolated in the solid-state, the organic groups R are embedded within the cyclodextrin cavities, involving only a few weak supramolecular contacts. The interaction between hybrid POVs and the macrocyclic organic hosts have been deeply studied in solution using ITC, cyclic voltammetry and NMR methods (1D ¹ H NMR, and 2D DOSY, and ROESY). This set of complementary techniques provides clear insights about the strength of interactions and the binding host-guest modes occurring in aqueous solution, highlighting a dramatic influence of the functional group R on the supramolecular properties of the hexavanadate polyoxoanions (association constant K_1:1 vary from 0 to 2 000 M^-1 ) while isolated functional organic groups exhibit only very weak intrinsic affinity with CDs. Electrochemical and calorimetric investigations suggest that the driving force of the host-guest association involving larger CDs (β- and γ-CD) is mainly related to the chaotropic effect. In contrast, the hydrophobic effect supported by weak attractive forces appears as the main contributor for the formation of α-CD-containing host-guest complexes. In any cases, the origin of driving forces is clearly related to the ability of the macrocyclic host to desolvate the exposed moieties of the hybrid POVs.

Wells-Dawson phosphotungstates as mushroom tyrosinase inhibitors: a speciation study

In order to elucidate the active polyoxotungstate (POT) species that inhibit fungal polyphenol oxidase (AbPPO4) in sodium citrate buffer at pH 6.8, four Wells-Dawson phosphotungstates [α/β-P^V₂W^VI₁₈O₆₂]^6- (intact form), [α₂-P^V₂W^VI₁₇O₆₁]^10- (monolacunary), [P^V₂W^VI₁₅O₅₆]^12- (trilacunary) and [H₂P^V₂W^VI₁₂O₄₈]^12- (hexalacunary) were investigated. The speciation of the POT solutions under the dopachrome assay (50 mM Na-citrate buffer, pH 6.8; L-3,4-dihydroxyphenylalanine as a substrate) conditions were determined by ¹⁸³W-NMR, ³¹P-NMR spectroscopy and mass spectrometry. The intact Wells-Dawson POT [α/β-P^V₂W^VI₁₈O₆₂]^6- shows partial (~ 69%) disintegration into the monolacunary [α₂-P^V₂W^VI₁₇O₆₁]^10- anion with moderate activity (K_i = 9.7 mM). The monolacunary [α₂-P^V₂W^VI₁₇O₆₁]^10- retains its structural integrity and exhibits the strongest inhibition of AbPPO4 (K_i = 6.5 mM). The trilacunary POT [P^V₂W^VI₁₅O₅₆]^12- rearranges to the more stable monolacunary [α₂-P^V₂W^VI₁₇O₆₁]^10- (~ 62%) accompanied by release of free phosphates and shows the weakest inhibition (K_i = 13.6 mM). The hexalacunary anion [H₂P^V₂W^VI₁₂O₄₈]^12- undergoes time-dependent hydrolysis resulting in a mixture of [H₂P^V₂W^VI₁₂O₄₈]^12-, [P^V₈W^VI₄₈O₁₈₄]^40-, [P^V₂W^VI₁₉O₆₉(H₂O)]^14- and [α₂-P^V₂W^VI₁₇O₆₁]^10- which together leads to comparable inhibitory activity (K_i = 7.5 mM) after 48 h. For the solutions of [α/β-P^V₂W^VI₁₈O₆₂]^6-, [α₂-P^V₂W^VI₁₇O₆₁]^10- and [P^V₂W^VI₁₅O₅₆]^12- the inhibitory activity is correlated to the degree of their rearrangement to [α₂-P^V₂W^VI₁₇O₆₁]^10-. The rearrangement of hexalacunary [H₂P^V₂W^VI₁₂O₄₈]^12- into at least four POTs with a negligible amount of monolacunary anion interferes with the correlation of activity to the degree of their rearrangement to [α₂-P^V₂W^VI₁₇O₆₁]^10-. The good inhibitory effect of the Wells-Dawson [α₂-P^V₂W^VI₁₇O₆₁]^10- anion is explained by the low charge density of its protonated forms H_x[α₂-P^V₂W^VI₁₇O₆₁]^(10-x)- (x = 3 or 4) at pH 6.8.

The Smallest Polyoxotungstate Retained by TRIS-Stabilization

A polycondensation reaction of the orthotungstate anion WO₄^2–, buffered at pH 7.5 in a TRIS-HCl (0.15 M) solution, results in the first example of a discrete polyoxotungstate anion, with just two W ions stabilized with TRIS ligands. It was isolated and characterized as Na₂[W^VI₂O₆(C₄O₃NH₁₀)₂]·6H₂O by single-crystal and powder X-ray diffraction, FT-IR spectroscopy, thermogravimetrical analysis (TGA), and elemental analysis in solid state and by electro-spray ionization mass spectrometry (ESI-MS), ¹³C, and ¹⁸³W NMR, as well as Raman spectroscopy in solution. This synthesis demonstrates the crucial and new role of the added tris-alkoxy ligand in the development of a new hybrid TRIS-isopolytungstate with the lowest known nuclearity (so far) and the terminal oxygens substituted with two nitrogen atoms arising from amines of the TRIS ligands.

We report on the synthesis and characterization of a new hybrid isopolytungstate Na₂[W^VI₂O₆(C₄O₃NH₁₀)₂]·6H₂O with the, so far, lowest known nuclearity and the terminal oxygen atoms substituted with nitrogen arising from amine.

Increased in vitro Anti-HIV Activity of Caffeinium-Functionalized Polyoxometalates

Polyoxometalates (POMs), molecular metal oxide anions, are inorganic clusters with promising antiviral activity. Herein we report increased anti-HIV-1 activity of a POM when electrostatically combined with organic counter-cations. To this end, Keggin-type cerium tungstate POMs have been combined with organic methyl-caffeinium (Caf) cations, and their cytotoxicity, antiviral activity and mode of action have been studied. The novel compound, Caf4 K[β2 -CeSiW11 O39 ]×H2 O, exhibits sub-nanomolar antiviral activity and inhibits HIV-1 infectivity by acting on an early step of the viral infection cycle. This work demonstrates that combination of POM anions and organic bioactive cations can be a powerful new strategy to increase antiviral activity of these inorganic compounds.

High Proton-Conductivity in Covalently Linked Polyoxometalate-Organoboronic Acid-Polymers

The controlled bottom-up design of polymers with metal oxide backbones is a grand challenge in materials design, as it could give unique control over the resulting chemical properties. Herein, we report a 1D-organo-functionalized polyoxometalate polymer featuring a purely inorganic backbone. The polymer is self-assembled from two types of monomers, inorganic Wells-Dawson-type polyoxometalates, and aromatic organo-boronates. Their covalent linkage results in 1D polymer strands, which combine an inorganic oxide backbone (based on B-O and Nb-O linkages) with functional organic side-chains. The polymer shows high bulk proton conductivity of up to 1.59×10-1  S cm-1 at 90 °C and 98 % relative humidity. This synthetic approach could lead to a new class of organic-inorganic polymers where function can be designed by controlled tuning of the monomer units.

Defect {(WVIO7)WVI4} and Full {(WVIO7)WVI5} Pentagonal Units as Synthons for the Generation of Nanosized Main Group V Heteropolyoxotungstates

We report on the synthesis and characterization of three new nanosized main group V heteropolyoxotungstates K_xNa_y[H₂(XW^VI₉O₃₃)(W^VI₅O₁₂)(X₂W^VI₂₉O₁₀₃)]·nH₂O {X₃W₄₃} (x = 11, y = 16, and n = 115.5 for X = Sb^III; x = 20, y = 7, and n = 68 for X = Bi^III) and K₈Na₁₅[H₁₆(Co^II(H₂O)₂)_0.9(Co^II(H₂O)₃)₂(W^VI_3.1O₁₄)(Sb^IIIW^VI₉O₃₃)(Sb^III₂W^VI₃₀O₁₀₆)(H₂O)]·53H₂O {Co₃Sb₃W₄₂}. On the basis of the key parameters for the one-pot synthesis strategy of {Bi₃W₄₃}, a rational step-by-step approach was developed using the known Krebs-type polyoxotungstate (POT) K₁₂[Sb^V₂W^VI₂₂O₇₄(OH)₂]·27H₂O {Sb₂W₂₂} as a nonlacunary precursor leading to the synthesis and characterization of {Sb₃W₄₃} and {Co₃Sb₃W₄₂}. Solid-state characterization of the three new representatives {Bi₃W₄₃}, {Sb₃W₄₃}, and {Co₃Sb₃W₄₂} by single-crystal and powder X-ray diffraction (XRD), IR spectroscopy, thermogravimetric analysis (TGA), energy-dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), and elemental analysis, along with characterization in solution by UV/vis spectroscopy shows that {Bi₃W₄₃}, {Sb₃W₄₃}, and {Co₃Sb₃W₄₂} represent the first main group V heteropolyoxotungstates encapsulating a defect {(W^VIO₇)W^VI₄} ({X₃W₄₃}, X = Bi^III and Sb^III) or full {(W^VIO₇)W^VI₅} ({Co₃Sb₃W₄₂}) pentagonal unit. With 43 tungsten metal centers, {X₃W₄₃} (X = Bi^III and Sb^III) are the largest unsubstituted tungstoantimonate– and bismuthate clusters reported to date. By using time-dependent UV/vis spectroscopy, the isostructural representatives {Sb₃W₄₃} and {Bi₃W₄₃} were subjected to a comprehensive study on their catalytic properties as homogeneous electron-transfer catalysts for the reduction of K₃[Fe^III(CN)₆] as a model substrate revealing up to 5.8 times higher substrate conversions in the first 240 min (35% for {Sb₃W₄₃}, 29% for {Bi₃W₄₃}) as compared to the uncatalyzed reaction (<6% without catalyst after 240 min) under otherwise identical conditions.

We report on the synthesis and characterization of three new tungsten-based defect {(W^VIO₇)W^VI₄}K_xNa_y[H₂(XW^VI₉O₃₃)(W^VI₅O₁₂)(X₂W^VI₂₉O₁₀₃)]·nH₂O {X₃W₄₃} (x = 11, y = 16, and n = 115.5 for X = Sb^III; x = 20, y = 7, and n = 68 for Bi^III) or full pentagonal {(W^VIO₇)W^VI₅} unit K₈Na₁₅[H₁₆(Co^II(H₂O)₂)_0.9(Co^II(H₂O)₃)₂(W^VI_3.1O₁₄)(Sb^IIIW^VI₉O₃₃)(Sb^III₂W^VI₃₀O₁₀₆)(H₂O)]·53H₂O {Co₃Sb₃W₄₂} encapsulating main group V representatives. With 43 W centers, {Sb₃W₄₃} and {Bi₃W₄₃} exhibit the highest nuclearity among unsubstituted tungstoantimonates and bismuthates reported to date. The catalytic properties of {Sb₃W₄₃} and {Bi₃W₄₃} as homogeneous electron-transfer catalysts for the reduction of K₃[Fe^III(CN)₆] to K₄[Fe^II(CN)₆] was investigated.

Intrinsic Molybdenum-Based POMOFs with Impressive Gas Adsorptions and Photochromism

Novel molybdenum(VI/V) POM-based self-constructed frameworks [Mo^VI ₁₂ O₂₄ (μ₂ -O)₁₂ (trz)₆ (H₂ O)₆ ] ⋅ 6Hma ⋅ 18H₂ O (1, Htrz=1H-1,2,3-triazole, ma=methylamine), [Mo^VI ₇ O₁₄ (μ₂ -O)₈ (trz)₅ (H₂ O)] ⋅ 7Hma ⋅ 5H₂ O (2), Na₃ [Mo^V ₆ O₆ (μ₂ -O)₉ (Htrz)₃ (trz)₃ ] ⋅ 7.5H₂ O (3) and [Mo^V ₈ O₈ (μ₂ -O)₁₂ (Htrz)₈ ] ⋅ 30H₂ O (4) have been covalently decorated with tri-coordinated deprotonated/protonated 1,2,3-triazoles. Channels with an inner diameter of 7.5 Å were found in 1, whereas a tunnel composed of stacking molecules with an inner diameter of 4.1 Å along the b-axis exists in 2; it is occupied by free disordered methylamines, showing selective adsorption of O₂ and CO₂ at 25 °C. Obvious downfield shifts were observed by ¹³ C NMR spectroscopies for methylamines inside the confined channels in 1 and 2. There are diversified pores in 3 and 4, which are formed by the molecules themselves and intermolecular accumulations. Adsorption tests indicate that 3 and 4 are fine adsorption materials for CH₄ and CO₂ under low pressure that rely on the environments built by the POMs. Correspondingly, 1 and 2 display reversible photoresponsive thermochromism that is subtlety influenced by the channels. The polyoxometalate organic frameworks (POMOFs) with multiple functional adsorptions are easy to assemble. Their photo-/thermoresponse properties offer a new pathway for the self-constructions of one-off hybrid materials that possess the good properties of both POMs and MOFs.

Multicomponent Self-Assembly of a Giant Heterometallic Polyoxotungstate Supercluster with Antitumor Activity

The hierarchical aggregation of molecular nanostructures from multiple components is a grand synthetic challenge, which requires highly selective linkage control. We demonstrate how two orthogonal linkage groups, that is, organotin and lanthanide cations, can be used to drive the aggregation of a giant molecular metal oxide superstructure. The title compound {[(Sn(CH3 )2 )2 O]4 {[CeW5 O18 ] [TeW4 O16 ][CeSn(CH3 )2 ]4 [TeW8 O31 ]4 }2 }46- (1 a) features dimensions of ca. 2.2×2.3×3.4 nm3 and a molecular weight of ca. 25 kDa. Structural analysis shows the hierarchical aggregation from several independent subunits. Initial biomedical tests show that 1 features an inhibitory effect on the proliferation of HeLa cells based on an apoptosis pathway. In vivo experiments in mice reveal the antiproliferative activity of 1 and open new paths for further development of this new compound class.

Formation of Nanoscale [Ge4 O16 Al48 (OH)108 (H2 O)24 ]20+ from Condensation of ϵ-GeAl12 8+ Keggin Polycations*

Keggin-type polyaluminum cations belong to a unique class of compounds with their large positive charge, hydroxo bridges, and divergent isomerization/oligomerization. Previous reports indicated that oligomerization of this species can only occur through one isomer (δ), but herein we report the isolation of largest Keggin-type cluster that occurs through self-condensation of four ϵ-isomers ϵ-GeAl₁₂ ⁸⁺ to form [Ge₄ O₁₆ Al₄₈ (OH)₁₀₈ (H₂ O)₂₄ ]²⁰⁺ cluster (Ge₄ Al₄₈ ). The cluster was crystallized and structurally characterized by single-crystal X-ray diffraction (SCXRD) and the elemental composition was confirmed by ICP-MS and SEM-EDS. Additional dynamic light scattering experiments confirms the presence of the Ge₄ Al₄₈ in thermally aged solutions. DFT calculations reveal that a single atom Ge substitution in tetrahedral site of ϵ-isomer is the key for the formation of Ge₄ Al₄₈ because it activates deprotonation at key surface sites that control the self-condensation process.

Interweaving Disciplines to Advance Chemistry: Applying Polyoxometalates in Biology

This Viewpoint brings awareness of the challenges and subsequent breakthroughs at the intersection of different disciplines, illustrated by the example of the influence biological entities exerted on a huge class of inorganic coordination compounds, called polyoxometalates (POMs). We highlight the possible effects of biological systems on POMs that need to be considered, thereby emphasizing the depth and complexity of interdisciplinary work. We map POMs’ structural, electrochemical, and stability properties in the presence of biomolecules and stress the potential challenges related to inorganic coordination chemistry carried out in biological systems. This Viewpoint shows that new chemistry is available at the intersections between disciplines and aims to guide the community toward a discussion about current as well as future trends in truly interdisciplinary work.

We discuss the investigation of polyoxometalates in biological systems as one future direction of chemistry. Highly interesting, new, and sometimes spectacular findings and applications can be obtained from correctly carried out interdisciplinary research. In this Viewpoint, the challenges of truly interdisciplinary work and concepts for overcoming boundaries while working on intertwining disciplines are discussed.

Inhibition of Mitochondrial ATP Synthesis and Regulation of Oxidative Stress Based on {SbW8 O30 } Determined by Single-Cell Proteomics Analysis

The 10-nuclear heteroatom cluster modified {SbW₈ O₃₀ } was successfully synthesized and exhibited inhibitory activity (IC₅₀ =0.29 μM). Based on proteomics analysis, Na₄ Ni₂ Sb₂ W₂ -SbW₈ inhibited ATP production by affecting the expression of 16 related proteins, hindering metabolic functions in vivo and cell proliferation due to reactive oxygen species (ROS) stress. In particular, the low expression of FAD/FMN-binding redox enzymes (relative expression ratio of the experimental group to the control=0.43843) could be attributed to the redox mechanism of Na₄ Ni₂ Sb₂ W₂ -SbW₈ , which was consistent with the effect of polyoxometalates (POMs) and FMN-binding proteins on ATP formation. An electrochemical study showed that Na₄ Ni₂ Sb₂ W₂ -SbW₈ combined with FMN to form Na₄ Ni₂ Sb₂ W₂ -SbW₈ -2FMN complex through a one-electron process of the W atoms. Na₄ Ni₂ Sb₂ W₂ -SbW₈ acted as catalase and glutathione peroxidase to protect the cell from ROS stress, and the inhibition rates were 63.3 % at 1.77 μM of NADPH and 86.06 % at 10.62 μM of 2-hydroxyterephthalic acid. Overall, our results showed that POMs can be specific oxidative/antioxidant regulatory agents.

Polyoxometalate-Based Nanomaterials Toward Efficient Cancer Diagnosis and Therapy

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

Aluminum-Substituted Keggin Germanotungstate [HAl(H2O)GeW11O39]4-: Synthesis, Characterization, and Antibacterial Activity

We report on the new monosubstituted aluminum Keggin-type germanotungstate (C₄H₁₂N)₄[HAlGeW₁₁O₃₉(H₂O)]·11H₂O ([Al(H₂O)GeW₁₁]^4–), which has been synthesized at room temperature via rearrangement of the dilacunary [γ-GeW₁₀O₃₆]^8– polyoxometalate precursor. [Al(H₂O)GeW₁₁]^4– has been characterized thoroughly both in the solid state by single-crystal and powder X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and elemental analysis as well as in solution by cyclic voltammetry (CV) ¹⁸³W, ²⁷Al NMR and UV–vis spectroscopy. A study on the antibacterial properties of [Al(H₂O)GeW₁₁]^4– and the known aluminum(III)-centered Keggin polyoxotungstates (Al-POTs) α-Na₅[AlW₁₂O₄₀] (α-[AlW₁₂O₄₀]^5–) and Na₆[Al(AlOH₂)W₁₁O₃₉] ([Al(AlOH₂)W₁₁O₃₉]^6–) revealed enhanced activity for all three Al-POTs against the Gram-negative bacterium Moraxella catarrhalis (minimum inhibitory concentration (MIC) up to 4 μg mL^–1) and the Gram-positive Enterococcus faecalis (MIC up to 128 μg mL^–1) compared to the inactive Al(NO₃)₃ salt (MIC > 256 μg mL^–1). CV indicates the redox activity of the Al-POTs as a dominating factor for the observed antibacterial activity with increased tendency to reduction, resulting in increased antibacterial activity of the POT.

We report on the synthesis and thorough characterization of the new monosubstituted aluminum germanotungstate (C₄H₁₂N)₄[HAlGeW₁₁O₃₉(H₂O)]·11H₂O ([Al(H₂O)GeW₁₁]⁴⁻), which has been subjected to an antibacterial study including the previously reported α-Na₅[AlW₁₂O₄₀] and Na₆[Al(AlOH₂)W₁₁O₃₉]. All three aluminum-substituted polyoxotungstates (Al-POTs) revealed enhanced activity against Moraxella catarrhalis and Enterococcus faecalis compared to the inactive Al(NO₃)₃ salt. On the basis of cyclic voltammetry studies, the redox activity of the POTs is suggested to have an impact on their overall antibacterial activity.

Synthesis, Characterization, and Phosphoesterase Activity of a Series of 4f- and 4d-Sandwich-Type Germanotungstates [(n-C4H9)4N]l/mH2[(M(H2O)3)(γ-GeW10O35)2] (M = CeIII, NdIII, GdIII, ErIII, l = 7; ZrIV, m = 6)

We report on a family of five new 4f- and 4d-doped sandwich-type germanotungstates with the general formula [(n-C₄H₉)₄N]_l/mH₂[(M(H₂O)₃)(γ-GeW₁₀O₃₅)₂]·3(CH₃)₂CO [M(H₂O)₃(GeW₁₀)₂] (M = Ce^III, Nd^III, Gd^III, Er^III, l = 7; Zr^IV, m = 6), which have been synthesized at room temperature in an acetone–water mixture. Among the compound series, [Zr(H₂O)₃(GeW₁₀)₂]^8–, which has been obtained in the presence of 30% H₂O₂, represents the first example of a 4d-substituted germanotungstate incorporating the intact dilacunary [γ-Ge^IVW₁₀O₃₆]^8– building block. All compounds were characterized thoroughly in the solid state by single-crystal and powder X-ray diffraction (XRD), IR spectroscopy, thermogravimetric analysis (TGA), and elemental analysis and in solution by NMR and UV–vis spectroscopy. The phosphoesterase activity of [Ce(H₂O)₃(GeW₁₀)₂]^9– and [Zr(H₂O)₃(GeW₁₀)₂]^8– toward the model substrates 4-nitrophenyl phosphate (NPP) and O,O-dimethyl O-(4-nitrophenyl) phosphate (DMNP) was monitored with ¹H- and ³¹P-NMR spectroscopy revealing an acceleration of the hydrolytic reaction by an order of magnitude (k_corr = 3.44 (±0.30) × 10^–4 min^–1 for [Ce(H₂O)₃(GeW₁₀)₂]^9– and k_corr = 5.36 (±0.05) × 10^–4 min^–1 for [Zr(H₂O)₃(GeW₁₀)₂]^8–) as compared to the uncatalyzed reaction (k_uncat = 2.60 (±0.10) × 10^–5 min^–1). [Ce(H₂O)₃(GeW₁₀)₂]^9– demonstrated improved antibacterial activity toward Moraxella catarrhalis (MIC 32 μg/mL), compared to the unsubstituted [GeW₁₀O₃₆]^8– POM (MIC 64 μg/mL).

We report on the synthesis and characterization of five new monosubstituted 4f- and 4d-germanotungstates [(n-C₄H₉)₄N]_l/mH₂[(M(H₂O)₃)(γ-GeW₁₀O₃₅)₂]·3(CH₃)₂CO [M(H₂O)₃(GeW₁₀)₂] (M = Ce^III, Nd^III, Gd^III, Er^III, l = 7; Zr^IV; m = 6). The phosphoesterase properties of [Ce(H₂O)₃(GeW₁₀)₂]⁹⁻ and [Zr(H₂O)₃(GeW₁₀)₂]⁸⁻ were investigated by probing the hydrolytic activity toward 4-nitrophenyl phosphate (NPP) and O,O-dimethyl O-(4-nitrophenyl) phosphate (DMNP). Antibacterial tests revealed inhibiting activity of [Ce(H₂O)₃(GeW₁₀)₂]⁹⁻ against Moraxella catarrhalis.

Cation-Directed Synthetic Strategy Using 4f Tungstoantimonates as Nonlacunary Precursors for the Generation of 3d-4f Clusters

The first synthetic pathway using a series of four nonlacunary 4f-heterometal-substituted polyoxotungstate clusters Na₂₁[(Ln(H₂O)(OH)₂(CH₃COO))₃(WO₄)(SbW₉O₃₃)₃]·nH₂O (NaLnSbW₉; Ln = Tb^III, Dy^III, Ho^III, Er^III, Y^III) as precursors for the directed preparation of nine new 3d–4f heterometallic tungstoantimonates K₅Na₁₂H₃[TM(H₂O)Ln₃(H₂O)₅(W₃O₁₁)(SbW₉O₃₃)₃]·nH₂O (KTMLnSbW₉; TM = Co^II, Ni^II; Ln = Tb^III, Dy^III, Ho^III, Er^III, Y^III) has been developed. Systematic studies revealed an increased K content in the aqueous acidic reaction mixture to be the key step in the cation-directed preparation of 3d–4f compounds; among those, the Co-containing members represent the first examples of KCoLnSbW₉ (Ln = Tb^III, Dy^III, Ho^III, Er^III, Y^III) heterometallic tungstoantimonates exhibiting the SbW₉ building block. All 13 compounds have been characterized thoroughly in the solid state by powder and single-crystal X-ray diffraction (XRD), revealing a cyclic trimeric polyoxometalate architecture with three SbW₉ units encapsulating a planar triangle of Ln^III ions in the case of NaLnSbW₉ and a heterometallic core of one TM^II and three Ln^III for KTMLnSbW₉ (TM = Co^II, Ni^II; Ln = Tb^III, Dy^III, Ho^III, Er^III, Y^III). The results obtained by XRD are supplemented by complementary characterization methods in the solid state such as IR spectroscopy, thermogravimetric analysis, and elemental analysis as well as in solution by UV–vis spectroscopy. Detailed magnetic studies on the representative compounds KTMDySbW₉ (TM = Co^II, Ni^II) and KCoYSbW₉ of the series revealed field-induced slow magnetic relaxation.

The first step-by-step synthetic protocol using preformed 4f tungstoantimonate clusters as nonlacunary precursors for the controlled preparation and thorough characterization of a family of nine new 3d−4f heterometallic polyoxometalates [TM(H₂O)Ln₃(H₂O)₅(W₃O₁₁)(SbW₉O₃₃)₃]^20- (KTMLnSbW₉) (TM = Co^II, Ni^II; Ln = Tb^III, Dy^III, Ho^III, Er^III, Y^III) is reported. Magnetic studies on the Dy^III-containing representatives [TM(H₂O)Dy₃(H₂O)₅(W₃O₁₁)(SbW₉O₃₃)₃]²⁰⁻ (TM = Co^II, Ni^II) show single-molecule-magnet behavior.

Binding of a Fatty Acid-Functionalized Anderson-Type Polyoxometalate to Human Serum Albumin

The Anderson-type hexamolybdoaluminate functionalized with lauric acid (LA), (TBA)₃[Al(OH)₃Mo₆O₁₈{(OCH₂)₃CNHCOC₁₁H₂₃}]·9H₂O (TBA-AlMo₆-LA, where TBA = tetrabutylammonium), was prepared via two synthetic routes and characterized by thermogravimetric and elemental analyses, mass spectrometry, IR and ¹H NMR spectroscopy, and powder and single-crystal X-ray diffraction. The interaction of TBA-AlMo₆-LA with human serum albumin (HSA) was investigated via fluorescence and circular dichroism spectroscopy. The results revealed that TBA-AlMo₆-LA binds strongly to HSA (63% quenching at an HSA/TBA-AlMo₆-LA ratio of 1:1), exhibiting static quenching. In contrast to TBA-AlMo₆-LA, the nonfunctionalized polyoxometalate, Na₃(H₂O)₆[Al(OH)₆Mo₆O₁₈]·2H₂O (AlMo₆), showed weak binding toward HSA (22% quenching at a HSA/AlMo₆ ratio of 1:25). HSA binding was confirmed by X-ray structure analysis of the HSA-Myr-AlMo₆-LA complex (Myr = myristate). These results provide a promising lead for the design of novel polyoxometalate-based hybrids that are able to exploit HSA as a delivery vehicle to improve their pharmacokinetics and bioactivity.

A fatty acid-functionalized Anderson-type polyoxometalate, (TBA)₃[Al(OH)₃Mo₆O₁₈{(OCH₂)₃CNHCOC₁₁H₂₃}]·9H₂O (TBA-AlMo₆-LA), was synthesized and characterized in detail. The final organic−inorganic hybrid shows an increased affinity toward the transport protein human serum albumin (HSA) in comparison to its unmodified counterpart, Na₃(H₂O)₆[Al(OH)₆Mo₆O₁₈)]·2H₂O (AlMo₆). This is of medical importance because HSA is a well-known drug carrier and can therefore serve as a delivery system for AlMo₆. This study provides a rational design for the synthesis of bioactive polyoxometalates with enhanced pharmacokinetic properties.

Organoplatinum-Substituted Polyoxometalate Inhibits β-amyloid Aggregation for Alzheimer's Therapy

Aggregated β-amyloid (Aβ) is widely considered as a key factor in triggering progressive loss of neuronal function in Alzheimer's disease (AD), so targeting and inhibiting Aβ aggregation has been broadly recognized as an efficient therapeutic strategy for curing AD. Herein, we designed and prepared an organic platinum-substituted polyoxometalate, (Me₄ N)₃ [PW₁₁ O₄₀ (SiC₃ H₆ NH₂ )₂ PtCl₂ ] (abbreviated as Pt^II -PW₁₁ ) for inhibiting Aβ₄₂ aggregation. The mechanism of inhibition on Aβ₄₂ aggregation by Pt^II -PW₁₁ was attributed to the multiple interactions of Pt^II -PW₁₁ with Aβ₄₂ including coordination interaction of Pt²⁺ in Pt^II -PW₁₁ with amino group in Aβ₄₂ , electrostatic attraction, hydrogen bonding and van der Waals force. In cell-based assay, Pt^II -PW₁₁ displayed remarkable neuroprotective effect for Aβ₄₂ aggregation-induced cytotoxicity, leading to increase of cell viability from 49 % to 67 % at a dosage of 8 μm. More importantly, the Pt^II -PW₁₁ greatly reduced Aβ deposition and rescued memory loss in APP/PS1 transgenic AD model mice without noticeable cytotoxicity, demonstrating its potential as drugs for AD treatment.

Twining Poly(polyoxometalate) Chains into Nanoropes

Organic polymers and inorganic clusters belong to two different disciplines and have completely different properties and structures. When a cluster is attached to the backbone of a polymer as a pendant, the resultant hybrid polymers (polyclusters) exhibit unique behaviours totally different from those of conventional polymers owing to the nanoscale size of the cluster and its particular interactions. Herein, the aggregation of a poly(polyoxometalate)-a polynorbornene backbone with inorganic polyoxometalate cluster pendants-upon addition of a non-solvent to its dilute solution is reported. A three-dimensional network of tangled and snake-like nanothreads was observed. Direct visualisation of individual nanoscale clusters enabled identification of single chains within the nanothreads. These observations suggest that during the process of aggregation, the hybrid polymer forms curved or extended chains as a consequence of an armouring effect in which the collapsed cluster pendants wrap around the backbone. The collapse occurs because they become less soluble in the solvent/non-solvent mixture. The extended chains then become entwined and form nanoropes consisting of multiple chains wound around each other. This study provides a deeper understanding of the nature of polyclusters and should also prove useful for their future development and application.

Vanadium in Biological Action: Chemical, Pharmacological Aspects, and Metabolic Implications in Diabetes Mellitus

Vanadium compounds have been primarily investigated as potential therapeutic agents for the treatment of various major health issues, including cancer, atherosclerosis, and diabetes. The translation of vanadium-based compounds into clinical trials and ultimately into disease treatments remains hampered by the absence of a basic pharmacological and metabolic comprehension of such compounds. In this review, we examine the development of vanadium-containing compounds in biological systems regarding the role of the physiological environment, dosage, intracellular interactions, metabolic transformations, modulation of signaling pathways, toxicology, and transport and tissue distribution as well as therapeutic implications. From our point of view, the toxicological and pharmacological aspects in animal models and humans are not understood completely, and thus, we introduced them in a physiological environment and dosage context. Different transport proteins in blood plasma and mechanistic transport determinants are discussed. Furthermore, an overview of different vanadium species and the role of physiological factors (i.e., pH, redox conditions, concentration, and so on) are considered. Mechanistic specifications about different signaling pathways are discussed, particularly the phosphatases and kinases that are modulated dynamically by vanadium compounds because until now, the focus only has been on protein tyrosine phosphatase 1B as a vanadium target. Particular emphasis is laid on the therapeutic ability of vanadium-based compounds and their role for the treatment of diabetes mellitus, specifically on that of vanadate- and polioxovanadate-containing compounds. We aim at shedding light on the prevailing gaps between primary scientific data and information from animal models and human studies.

Polyoxometalates: more than a phasing tool in protein crystallography

Protein crystallography is the most widely used method for determining the molecular structure of proteins and obtaining structural information on protein–ligand complexes at the atomic level. As the structure determines the functions and properties of a protein, crystallography is of immense importance for nearly all research fields related to biochemistry. However, protein crystallography suffers from some major drawbacks, whereby the unpredictability of the crystallization process represents the main bottleneck. Crystallization is still more or less a ‘trial and error’ based procedure, and therefore, very time and resource consuming. Many strategies  have been developed in the past decades to improve or enable the crystallization of proteins, whereby the use of so-called additives, which are mostly small molecules that make proteins more amenable to crystallization, is one of the most convenient and successful methods. Most of the commonly used additives are, however, restricted to particular crystallization conditions or groups of proteins. Therefore, a more universal additive addressing a wider range of proteins and being applicable to a broad spectrum of crystallization conditions would represent a significant advance in the field of protein crystallography. In recent years, polyoxometalates (POMs) emerged as a promising group of crystallization additives due to their unique structures and properties. In this regard, the tellurium-centered Anderson–Evans polyoxotungstate [TeW₆O₂₄]⁶⁻ (TEW) showed its high potential as crystallization additive. In this lecture text, the development of POMs as tools in protein crystallography are discussed with a special focus on the so far most successful cluster TEW.