Polyoxometalate HIV-1 protease inhibitors. A new mode of protease inhibition

Nanoproteases: Alternatives to Natural Protease for Biotechnological Applications

Some nanomaterials with intrinsic protease-like activity have the advantages of good stability, biosafety, low price, large-scale preparation and unique property of nanomaterials, which are promising alternatives for natural proteases in various applications. An especial term, "nanoprotease", has been coined to stress the intrinsic proteolytic property of these nanomaterials. As a new generation of artificial proteases, they have become a burgeoning field, attracting many researchers to design and synthesize high performance nanoproteases. In this review, we summarize recent progress on all types of nanoproteases with regard of their activity, mechanism and application and introduce a new and effective strategy for engineering high-performance nanoproteases. In addition, we discuss the challenges and opportunities of nanoprotease research in the future.

Recent advances in lanthanide-based POMs for photoluminescent applications

Since the first formation of the famous "Peacock-Weakley" anions [Ln(W5O18)2]8/9-, a steady stream of breakthroughs have been made in the chemistry of multitalented lanthanide (Ln)-based polyoxometalates (POMs) for their potentially desirable properties. In particular, LnIII ions are generally recognised as the "vitamins of the modern industry" owing to their ability to cover a wide emission range, endowing Ln-based POMs with great potential for versatile and diverse luminescence-related applications. In this frontier, we discuss the synthesis strategies and intramolecular energy transfer in Ln-based POM derivatives. Then, the progressive improvements achieved with Ln-based POMs in photoluminescence applications are highlighted, focusing mainly on luminescent and fluorescent probes. Finally, the challenges for Ln-based POM materials for photoluminescence applications are discussed.

Two Unprecedented Germanoniobate Frameworks Based on High-Nuclearity Peanut-Shaped {Ge12Nb38} Clusters

By variation of the amount of GeO2, two organic-inorganic hybrid germanoniobate frameworks with 6-connected pcu and 10-connected bct topologies were constructed from peanut-shaped {α-Ge12Nb38} and {β-Ge12Nb38} clusters, respectively. The {α-Ge12Nb38} and {β-Ge12Nb38} clusters contain the most Ge centers of germanoniobates reported so far. The compounds exhibit proton conduction properties with a conductivity of 3.04 × 10-4 S·cm-3 for 1 and 1.62 × 10-4 S·cm-3 for 2 at 85 °C and 98% RH. The water vapor adsorption capacities for 1 and 2 are 5.86 and 4.40 mmol·g-1, respectively.

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.

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.

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.

Contrasting Trivalent Lanthanide and Actinide Complexation by Polyoxometalates via Solution-State NMR

Deciphering the solution chemistry and speciation of actinides is inherently difficult due to radioactivity, rarity, and cost constraints, especially for transplutonium elements. In this context, the development of new chelating platforms for actinides and associated spectroscopic techniques is particularly important. In this study, we investigate a relatively overlooked class of chelators for actinide binding, namely, polyoxometalates (POMs). We provide the first NMR measurements on americium-POM and curium-POM complexes, using one-dimensional (1D) ³¹P NMR, variable-temperature NMR, and spin-lattice relaxation time (T₁) experiments. The proposed POM-NMR approach allows for the study of trivalent f-elements even when only microgram amounts are available and in phosphate-containing solutions where f-elements are typically insoluble. The solution-state speciation of trivalent americium, curium, plus multiple lanthanide ions (La³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Yb³⁺, and Lu³⁺), in the presence of the model POM ligand PW₁₁O₃₉^7- was elucidated and revealed the concurrent formation of two stable complexes, [M^III(PW₁₁O₃₉)(H₂O)_x]^4- and [M^III(PW₁₁O₃₉)₂]^11-. Interconversion reaction constants, reaction enthalpies, and reaction entropies were derived from the NMR data. The NMR results also provide experimental evidence of the weakly paramagnetic nature of the Am³⁺ and Cm³⁺ ions in solution. Furthermore, the study reveals a previously unnoticed periodicity break along the f-element series with the reversal of T₁ relaxation times of the 1:1 and 1:2 complexes and the preferential formation of the long T₁ species for the early lanthanides versus the short T₁ species for the late lanthanides, americium, and curium. Given the broad variety of POM ligands that exist, with many of them containing NMR-active nuclei, the combined POM-NMR approach reported here opens a new avenue to investigate difficult-to-study elements such as heavy actinides and other radionuclides.

Decoding drug resistant mechanism of V32I, I50V and I84V mutations of HIV-1 protease on amprenavir binding by using molecular dynamics simulations and MM-GBSA calculations

Mutations V32I, I50V and I84V in the HIV-1 protease (PR) induce drug resistance towards drug amprenavir (APV). Multiple short molecular dynamics (MSMD) simulations and molecular mechanics generalized Born surface area (MM-GBSA) method were utilized to investigate drug-resistant mechanism of V32I, I50V and I84V towards APV. Dynamic information arising from MSMD simulations suggest that V32I, I50V and I84V highly affect structural flexibility, motion modes and conformational behaviours of two flaps in the PR. Binding free energies calculated by MM-GBSA method suggest that the decrease in binding enthalpy and the increase in binding entropy induced by mutations V32I, I50V and I84V are responsible for drug resistance of the mutated PRs on APV. The energetic contributions of separate residues on binding of APV to the PR show that V32I, I50V and I84V highly disturb the interactions of two flaps with APV and mostly drive the decrease in binding ability of APV to the PR. Thus, the conformational changes of two flaps in the PR caused by V32I, I50V and I84V play key roles in drug resistance of three mutated PR towards APV. This study can provide useful dynamics information for the design of potent inhibitors relieving drug resistance.

Promising application of polyoxometalates in the treatment of cancer, infectious diseases and Alzheimer's disease

As shown in studies conducted in recent decades, polyoxometalates (POMs), as inorganic metal oxides, have promising biological activities, including antitumor, anti-infectious and anti-Alzheimer’s activities, due to their special structures and properties. However, some side effects impede their clinical applications to a certain extent. Compared with unmodified POMs, POM-based inorganic–organic hybrids and POM-based nanocomposite structures show significantly enhanced bioactivity and reduced side effects. In this review, we introduce the biological activities of POMs and their derivatives and highlight the side effects of POMs on normal cells and organisms and their possible mechanisms of action. We then propose a development direction for overcoming their side effects. POMs are expected to constitute a new generation of inorganic metal drugs for the treatment of cancer, infectious diseases, and Alzheimer's disease.

Graphical abstract

Computational Modelling of the Interactions Between Polyoxometalates and Biological Systems

Polyoxometalates (POMs) structures have raised considerable interest for the last years in their application to biological processes and medicine. Within this area, our mini-review shows that computational modelling is an emerging tool, which can play an important role in understanding the interaction of POMs with biological systems and the mechanisms responsible of their activity, otherwise difficult to achieve experimentally. During recent years, computational studies have mainly focused on the analysis of POM binding to proteins and other systems such as lipid bilayers and nucleic acids, and on the characterization of reaction mechanisms of POMs acting as artificial metalloproteases and phosphoesterases. From early docking studies locating binding sites, molecular dynamics (MD) simulations have allowed to characterize the nature of POM···protein interactions, and to evaluate the effect of the charge, size, and shape of the POM on protein affinity, including also, the atomistic description of chaotropic character of POM anions. Although these studies rely on the interaction with proteins and nucleic acid models, the results could be extrapolated to other biomolecules such as carbohydrates, triglycerides, steroids, terpenes, etc. Combining MD simulations with quantum mechanics/molecular mechanics (QM/MM) methods and DFT calculations on cluster models, computational studies are starting to shed light on the factors governing the activity and selectivity for the hydrolysis of peptide and phosphoester bonds catalysed by POMs.

Two high-nuclearity isopolyoxoniobates containing {Nb54 O151}-based helical nanotubes for the decomposition of chemical warfare agent simulants

Two inorganic-organic hybrid isopolyoxoniobates (1 and 2) based on new high-nuclearity {Nb₅₄O₁₅₁} clusters have been synthesized under hydrothermal conditions. In particular, the combination of the unique {Nb₅₄O₁₅₁} clusters with copper-amine complexes has led to rare helical nanotubes, which are further linked by alkali metal cations or copper-amine complexes into two 2D similar bamboo-raft-like layered networks (1 and 2), respectively. Compound 1 exhibits effective base-catalytic decomposition of chemical warfare agent simulants dimethyl methylphosphonate (DMMP) and diethyl cyanophosphonate (DECP).

Rare-earth ions as antibacterial agents for woven wool fabric

Woven fabrics were bestowed with antibacterial property by the simple adsorption of rare-earth metal ions, and the underlying mechanism was investigated using electron spin resonance (ESR) spectroscopy. The adsorption of Ce³⁺ ions on wool, silk, and cotton fabrics resulted in significant inhibition of Staphylococcus aureus (a gram-positive bacterium), with maximum antibacterial activities (viable bacterial count compared to the reference) of 4.7, 5.8, and 5.2, respectively. Even after 50 wash cycles, the values remained at 3.9, 2.9, and 4.8, respectively. The adsorption of La³⁺ and Gd³⁺ ions on wool fabrics also resulted in antibacterial activities of 5.8 and 5.9, respectively. In addition, wool adsorbed with Ce³⁺ exhibits a satisfactory antibacterial activity of 6.2 against Escherichia coli (a gram-negative bacterium). Such bacterial inhibition is attributed to Fenton reactions between the adsorbed rare-earth ions and hydrogen peroxide (H₂O₂) produced during bacterial metabolism, as determined from the ESR spectra collected using the spin trap method in the presence of H₂O₂. The safety of cerium nitrate was also investigated, and no significant issues arose, indicating that it was a safe antibacterial agent. This facile method of imparting antibacterial properties to natural fabrics may be useful for preventing infections in humans.

Mechanistic Advantages of Organotin Molecular EUV Photoresists

Extreme ultraviolet (EUV)-induced radiation exposure chemistry in organotin-oxo systems, represented by the archetypal [(R-Sn)₁₂O₁₄(OH)₆](A)₂ cage, has been investigated with density functional theory. Upholding existing experimental evidence of Sn-C cleavage-dominant chemistry, computations have revealed that either electron attachment or ionization can single-handedly trigger tin-carbon bond cleavage, partially explaining the current EUV sensitivity advantage of metal oxide systems. We have revealed that tin atoms at different parts of the molecule react differently to ionization and electron attachment and have identified such selectivity as a result of local coordination chemistry instead of the macro geometry of the molecule. An ionization-deprotonation pathway has also been identified to explain the observed evolution of an anion conjugate acid upon exposure and anion mass dependence in resist sensitivity.

Can polyoxometalates (POMs) prevent of coronavirus 2019-nCoV cell entry? Interaction of POMs with TMPRSS2 and spike receptor domain complexed with ACE2 (ACE2-RBD): Virtual screening approaches

The unexpected appearance and global spread of COVID-19 create significant difficulties for healthcare systems and present an unusual challenge for the fast discovery of medicines to combat this fatal disease. Screening metallodrugs libraries from the medicinal inorganic chemistry society may expand the studied ‘chemical space’ and improve the probability of discovering effective anti-COVID drugs, including polyoxometalates. POMs are an oxygen-rich family of inorganic cluster systems that have previously been tested for antiviral action against different types of viruses. Human angiotensin-converting enzyme 2 (ACE2), human transmembrane protease serine 2 (TMPRSS2), and the SARS-CoV-2 spike glycoprotein are required for host cell-mediated viral entrance. Targeting these proteins demonstrates potential possibilities for preventing infections and transmissions in the initial stage. As a result, POMs with known antiviral effects were investigated for this purpose using molecular docking and dynamic simulations. This research shows that POMs can prevent SARS CoV-2 from entering cells by blocking TMPRSS2, which SARS-CoV-2 uses for spike glycoprotein priming. They may also engage with ACE2 and the spike glycoprotein and disrupt their binding by blocking the active sites. We think that a thorough investigation of POMs as possible anti-COVID-19 drugs will provide significant opportunities.

Incorporating highly basic polyoxometalate anions comprising Nb or Ta into nanoscale reaction fields of porous ionic crystals

Polyoxometalates (POMs) are oxide cluster anions composed of high-valence early transition metals and are widely used as catalysts. Yet base catalysis of POMs remains an ongoing challenge; group V (V, Nb, and Ta) elements form more negatively charged POMs than group VI (Mo and W) elements, and in particular, polyoxoniobates and polyoxotantalates are known to show strong basicity in solution due to the highly negative surface oxygen atoms. Herein, we report for the first time porous ionic crystals (PICs) comprising Nb or Ta. The PICs are composed of Dawson-type Nb/W or Ta/W mixed-addenda POMs with oxo-centered trinuclear Cr^III carboxylates and potassium ions as counter cations to control the crystal structure. Among the PICs, those with Nb or Ta tri-substituted POMs exhibit the highest yield (78-82%) and selectivity (99%) towards the Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate (353 K, 6 h), which is a typical base-catalyzed reaction, as reusable solid catalysts, and they can also catalyze the reaction of other active methylene compounds. A detailed investigation into the crystal structures together with DFT calculations and in situ IR spectroscopy with methanol as a basic probe molecule shows that the exposure of [Nb₃O₁₃] or [Ta₃O₁₃] units with highly negative surface oxygen atoms to the pore surface of PICs is crucial to the catalytic performance. These findings based on the composition-structure-function relationships show that Nb- and Ta-containing PICs can serve as platforms for rational designing of heterogeneous base catalysts.

Nanomaterials for Modulating the Aggregation of β-Amyloid Peptides

The aberrant aggregation of amyloid-β (Aβ) peptides in the brain has been recognized as the major hallmark of Alzheimer's disease (AD). Thus, the inhibition and dissociation of Aβ aggregation are believed to be effective therapeutic strategiesforthe prevention and treatment of AD. When integrated with traditional agents and biomolecules, nanomaterials can overcome their intrinsic shortcomings and boost their efficiency via synergistic effects. This article provides an overview of recent efforts to utilize nanomaterials with superior properties to propose effective platforms for AD treatment. The underlying mechanismsthat are involved in modulating Aβ aggregation are discussed. The summary of nanomaterials-based modulation of Aβ aggregation may help researchers to understand the critical roles in therapeutic agents and provide new insight into the exploration of more promising anti-amyloid agents and tactics in AD theranostics.

Polyoxometalates as Effective Nano-inhibitors of Amyloid Aggregation of Pro-inflammatory S100A9 Protein Involved in Neurodegenerative Diseases

Pro-inflammatory and amyloidogenic S100A9 protein is central to the amyloid-neuroinflammatory cascade in neurodegenerative diseases. Polyoxometalates (POMs) constitute a diverse group of nanomaterials, which showed potency in amyloid inhibition. Here, we have demonstrated that two selected nanosized niobium POMs, Nb₁₀ and TiNb₉, can act as potent inhibitors of S100A9 amyloid assembly. Kinetics analysis based on ThT fluorescence experiments showed that addition of either Nb₁₀ or TiNb₉ reduces the S100A9 amyloid formation rate and amyloid quantity. Atomic force microscopy imaging demonstrated the complete absence of long S100A9 amyloid fibrils at increasing concentrations of either POM and the presence of only round-shaped and slightly elongated aggregates. Molecular dynamics simulation revealed that both Nb₁₀ and TiNb₉ bind to native S100A9 homo-dimer by forming ionic interactions with the positively charged Lys residue-rich patches on the protein surface. The acrylamide quenching of intrinsic fluorescence showed that POM binding does not perturb the Trp 88 environment. The far and near UV circular dichroism revealed no large-scale perturbation of S100A9 secondary and tertiary structures upon POM binding. These indicate that POM binding involves only local conformational changes in the binding sites. By using intrinsic and 8-anilino-1-naphthalene sulfonate fluorescence titration experiments, we found that POMs bind to S100A9 with a K_d of ca. 2.5 μM. We suggest that the region, including Lys 50 to Lys 54 and characterized by high amyloid propensity, could be the key sequences involved in S1009 amyloid self-assembly. The inhibition and complete hindering of S100A9 amyloid pathways may be used in the therapeutic applications targeting the amyloid-neuroinflammatory cascade in neurodegenerative diseases.

Preparation of cerium molybdates and their antiviral activity against bacteriophage Φ6 and SARS-CoV-2

Two cerium molybdates (Ce₂Mo₃O₁₂ and γ-Ce₂Mo₃O₁₃) were prepared using either polymerizable complex method or hydrothermal process. The obtained powders were almost single-phase with different cerium valence. Both samples were found to have antiviral activity against bacteriophage Φ6. Especially, γ-Ce₂Mo₃O₁₃ exhibited high antiviral activity against both bacteriophage Φ6 and SARS-CoV-2 coronavirus, which causes COVID-19. A synergetic effect of Ce and molybdate ion was inferred along with the specific surface area as key factors for antiviral activity.

Hybrid Polyoxometalate Salt Adhesion by Butyltin Functionalization

Polyoxometalate (POM)-based ionic liquids, with nearly infinite compositional variations to fine-tune antimicrobial and physical properties, function as water purification filters, anticorrosion/antibacterial coatings for natural stones, self-repairing acid-resistant coatings, catalysts, and electroactive, stable solvents. By combining hydrophobic quaternary ammonium cations (QACs; tetraheptylammonium and trihexyltetradecylammonium) with butyltin-substituted polyoxotungstates [(BuSn)₃(α-SiW₉O₃₇)] via repeated solvent extraction-ion exchange, we obtained phase-pure hybrid POM salts (referred to as such because they melt above room temperature). If the solvent extraction process is performed only once, then solids with high salt contamination and considerably lower melting temperatures are obtained. Solution-phase behavior, based on POM-QAC interactions, was similar for all formulations in polar and nonpolar organic solvents, as observed by X-ray scattering and multinuclear magnetic resonance spectroscopy. However, solid thin films of the butyltin-functionalized hybrid POM salts were significantly more stable and adhesive than their inorganic analogues. We attribute this to the favorable hydrophobic interactions between the butyltin groups and the QACs. All synthesized hybrid POM salts display a potent antimicrobial activity toward Escherichia coli. These studies provide fundamental form-function understanding of hybrid POM salts, based on interactions between ions in these complex hybrid phases.

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.

Synthesis, Anti-Tumor Activity and Apoptosis-Inducing Effect of Novel Dimeric Keggin-Type Phosphotungstate

A dimeric Keggin-type phosphotungstate (ODA)₁₀[(PW₁₁FeO₃₉)₂O]·9H₂O (abbreviated as ODA₁₀[(PW₁₁Fe)₂], ODA = octadecyltrimethylammonium bromide) was synthesized and investigated comprehensively its antitumor activity on MCF-7 and A549 cells. The dimeric structure and amorphous morphology were characterized by FT-IR, UV-vis-DRS, SEM and XRD. The in vitro MTT assay of ODA₁₀[(PW₁₁Fe)₂] showed anticancer activity on MCF-7 and A549 cells in a dose- and time-dependent manner, and the IC₅₀ values for MCF-7 and A549 cells at 48 h were 5.83 μg/ml and 3.23 μg/ml, respectively. The images of the ODA₁₀[(PW₁₁Fe)₂]-treated cells observed by inverted biological microscope exhibited the characteristic morphology of apoptosis. Flow cytometric analysis showed cell apoptosis and cycle arrested at S phase induced by ODA₁₀[(PW₁₁Fe)₂]. The above results illuminated the main mechanism of the antitumor action of ODA₁₀[(PW₁₁Fe)₂] on MCF-7 and A549 cells, indicating that this dimeric phosphotungstate is a promising anticancer drug.

Minerals in biology and medicine

Natural minerals ('stone drugs') have been used in traditional Chinese medicines for over 2000 years, but there is potential for modern-day use of inorganic minerals to combat viral infections, antimicrobial resistance, and for other areas in need of new therapies and diagnostic aids. Metal and mineral surfaces on scales from milli-to nanometres, either natural or synthetic, are patterned or can be modified with hydrophilic/hydrophobic and ionic/covalent target-recognition sites. They introduce new strategies for medical applications. Such surfaces have novel properties compared to single metal centres. Moreover, 3D mineral particles (including hybrid organo-minerals) can have reactive cavities, and some minerals have dynamic movement of metal ions, anions, and other molecules within their structures. Minerals have a unique ability to interact with viruses, microbes and macro-biomolecules through multipoint ionic and/or non-covalent contacts, with potential for novel applications in therapy and biotechnology. Investigations of mineral deposits in biology, with their often inherent heterogeneity and tendency to become chemically-modified on isolation, are highly challenging, but new methods for their study, including in intact tissues, hold promise for future advances.

A Series of Cube-Shaped Polyoxoniobates Encapsulating Octahedral Cu12X m O n Clusters With Hydrolytic Decomposition for Chemical Warfare Agents

This study reported a series of cube-shaped polyoxoniobates, {MCu₁₂O₈)(Cu₁₂X_mO_n)(Nb₇(OH)O₂₁)₈} [M = Nb(1, 2), Ln³⁺(3), X = I(1, m = 3, n = 3; 2, m = 5, n = 1), Br(3, m = 5, n = 1)]. As the first octahedral Cu₁₂X_mO_n cluster incorporated polyoxoniobate, the cube-shaped three-shell structure of {MCu₁₂O₈)(Cu₁₂X_mO_n)(Nb₇(OH)O₂₁)₈} polyanion contains a {MCu₁₂O₈} body-centered cuboctahedron, a {Cu₁₂X_mO_n} octahedron and a {Cu₁₂(Nb₇(OH)O₂₁)₈} cube. Compounds 1, 2, 3 show effective catalytic activities for the hydrolytic decomposition of chemical warefare agent simulants.

Recent Progress in Ionic Coassembly of Cationic Peptides and Anionic Species

Peptide assembly has been extensively exploited as a promising platform for the creation of hierarchical nanostructures and tailor-made bioactive materials. Ionic coassembly of cationic peptides and anionic species is paving the way to provide particularly important contribution to this topic. In this review, the recent progress of ionic coassembly soft materials derived from the electrostatic coupling between cationic peptides and anionic species in aqueous solution is systematically summarized. The presentation of this review starts from a brief background on the general importance and advantages of peptide-based ionic coassembly. After that, diverse combinations of cationic peptides with small anions, macro- and/or oligo-anions, anionic polymers, and inorganic polyoxometalates are described. Emphasis is placed on the hierarchical structures, value-added properties, and applications. The molecular design of cationic peptides and the general principles behind the ionic coassembled structures are discussed. It is summarized that the combination of interesting and unique characteristics that arise both from the chemical diversity of peptides and the wide range of anionic species may contribute in a variety of output, including drug delivery, tissue engineering, gene transfection, and antibacterial activity. The emergent new phenomena and findings are illustrated. Finally, the outlook for the peptide-based ionic coassembly systems is also presented.

Effects of cerium and tungsten substitution on antiviral and antibacterial properties of lanthanum molybdate

Powders of cerium (Ce)-substituted and tungsten (W)-substituted La₂Mo₂O₉ (LMO) were prepared using polymerizable complex method. Their antiviral and antibacterial performances were then evaluated using bacteriophage Qβ, bacteriophage Φ6, Escherichia coli, and Staphylococcus aureus. The obtained powders, which were almost single-phase, exhibited both antiviral and antibacterial properties. Effects of dissolved ions on their antiviral activity against bacteriophage Qβ were remarkable. A certain contribution of direct contact to the powder surface was also inferred along with the dissolved ion effect for antiviral activity against bacteriophage Φ6. Dissolved ion effects and pH values suggest that both Mo and W are in the form of polyacids. Antiviral activity against bacteriophage Φ6 was improved by substituting Ce for La in LMO. Similarly to LMO, Ce-substituted LMO exhibited hydrophobicity. Inactivation of alkaline phosphatase enzyme proteins was inferred as one mechanism of the antiviral and antibacterial activities of the obtained powders.

•

Ce and W were partially substituted in La₂Mo₂O₉ (LMO).

•

These powders inactivated E. coli, S. aureus, bacteriophage Qβ, and bacteriophage Φ6.

•

Inactivation of alkaline phosphatase enzyme proteins on these materials was confirmed.

•

Antiviral activity against bacteriophage Φ6 of LMO was improved by substituting Ce.

•

Hydrophobicity and UV shielding performance were also confirmed for this material.

Nanolipid-loaded Preyssler polyoxometalate: Synthesis, characterization and invitro inhibitory effects on HepG2 tumor cells

Polyoxometalate-based drugs have been selected by some researchers as alternative antitumor substances with promising results in suppression of tumor growth because of low toxicity towards the human body and high activity. In this research, for the first time, nanolipid-loaded Preyssler polyoxometalate with diameters of 230-250 nm was synthesized and characterized by the Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Analysis (EDAX), Atomic Force Microscopy (AFM), and Infrared (IR) spectroscopy. The nanoliposomes were found to be nearly spherical, without any agglomeration with the Entrapment Efficiency of 53.8%. In -vitro antitumor activity of the synthesized nanoliposomes was investigated using the MTT method on HepG2 tumor cells. Our findings showed enhanced anticancer activity for the nanolipid-loaded Preyssler (NLP) compared to the Sorafenib as a commercially drug at 72 h. Selectivity of the synthesized NLP and Sorafenib for cancer cells versus primary HFF cells was obtained as 4.2 and 2.2, respectively. The IC50 value of the loaded nanoliposomes for cancer cells and normal cells was equal to 470 and 2000 μg/mL, respectively at 72 h, which was much better compared to that of the Sorafenib (7 and 16 μg/mL, respectively).

Anti-flavivirus activity of polyoxometalate

Viruses in the Flaviviridae family such as Zika virus (ZIKV), dengue virus (DENV), and Japanese encephalitis virus (JEV) are major public health concerns. The development of antiviral agents against these viruses is urgently needed. We have previously discovered that the Keggin structured polyoxometalate POM-12 has potent inhibitory activity against hepatitis C virus, another member of the Flaviviridae family. In this study, we tested its antiviral activity of DENV, JEV and ZIKV, and found that POM-12 dramatically inhibited their infection with IC50 value of 1.16 μM, 1.9 μM and 0.64 μM, respectively. Mechanistic studies indicated that POM-12 directly disrupted the integrity of these virions. Moreover, POM-12 also targeted the post-entry steps of viral replication of JEV, but having no similar activities on ZIKV and DENV. The differential actions of POM-12 on these viruses suggest that surface topology and charge of virion may have influence on its drug effect, and thus POM-12 may be modified to more efficiently inhibit these and other similar viruses.

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.

Polyoxometalates in Biomedicine: Update and Overview

BACKGROUND

Polyoxometalates (POMs) are negatively charged metal-oxo clusters of early transition metal ions in high oxidation states (e.g., WVI, MoVI, VV). POMs are of interest in the fields of catalysis, electronics, magnetic materials and nanotechnology. Moreover, POMs were shown to exhibit biological activities in vitro and in vivo, such as antitumor, antimicrobial, and antidiabetic.

METHODS

The literature search for this peer-reviewed article was performed using PubMed and Scopus databases with the help of appropriate keywords.

RESULTS

This review gives a comprehensive overview of recent studies regarding biological activities of polyoxometalates, and their biomedical applications as promising anti-viral, anti-bacterial, anti-tumor, and anti-diabetic agents. Additionally, their putative mechanisms of action and molecular targets are particularly considered.

CONCLUSION

Although a wide range of biological activities of Polyoxometalates (POMs) has been reported, they are to the best of our knowledge not close to a clinical trial or a final application in the treatment of diabetes or infectious and malignant diseases. Accordingly, further studies should be directed towards determining the mechanism of POM biological actions, which would enable fine-tuning at the molecular level, and consequently efficient action towards biological targets and as low toxicity as possible. Furthermore, biomedical studies should be performed on solutionstable POMs employing physiological conditions and concentrations.

Structural, spectral characterization and molecular docking analyses of mer-ruthenium (II) complexes containing the bidentate chelating ligands

In this study, we analyzed some monofunctional Ru (II) complexes containing chlorine, bromine and fluorine atoms around the central atom. The best calculation level among HF, B3LYP and M062X methods for [Ru (Cl-Ph-tpy)(NN)X]⁺ (X = F, Cl, Br) was determined in the light of Benchmark analysis and according to this analysis results, the best level is shown as B3LYP-LANL2DZ/6-31G(d). In addition to this, the spectroscopic data (IR, NMR and UV-Vis) were also obtained in agreement with experimental results. The tendency of anticancer activity and structural activity relationship (SAR) parameters are predicted with some quantum chemical methods. Surface and contour diagrams, as well as electron densities on mentioned complexes were interpreted through theoretically obtained results. Finally, the anticancer activity tendency of the relevant complexes on the human cervical carcinoma cell line (ID: 1 M17) is supported by molecular docking calculations.

H5PV2Mo10O40 encapsulated into Cu3(BTC)2 as an efficient heterogeneous nanocrystalline catalyst for styrene epoxidation

The nanocrystalline catalyst HPMoV@Cu₃(BTC)₂ prepared using a liquid-assisted grinding method showed excellent catalytic activity for the epoxidation of styrene in O₂.

Intrathecal Administration of Nanoclusters for Protecting Neurons against Oxidative Stress in Cerebral Ischemia/Reperfusion Injury

Oxidative stress is one of the important mechanisms in cerebral ischemia/reperfusion (I/R) injury. Antioxidants with high brain accumulation are highly desired to help prevent cerebral I/R injury. Herein, intrathecal injection of polyoxometalate (POM) nanoclusters as nano-antioxidants with preferential brain uptake were applied for neuronal protection in cerebral I/R injury. Using powerful positron emission tomography imaging, the uptake of nano-antioxidants in the brain was non-invasively and real-timely monitored. Our results demonstrated that POM nanoclusters rapidly reached the ischemic penumbra after intrathecal injection and effectively scavenged reactive oxygen species (ROS) for inhibiting oxidative stress. The infarct size was reduced, and neurological function was restored in cerebral I/R injury rat models. As a proof-of-concept, the intrathecal injection of nano-antioxidants is an excellent therapeutic strategy to ameliorate cerebral I/R injury.

Features of Vibrational and Electronic Structures of Decavanadate Revealed by Resonance Raman Spectroscopy and Density Functional Theory

Polyoxometalates are known to be inhibitors of a diverse collection of enzymes, although the specific interactions that lead to this bioactivity are still unclear. Spectroscopic characterization may be an invaluable if indirect tool for remedying this problem, yet this requires clear, cogent assignment of polyoxometalate spectra before the complicating effect of their binding to large biomolecules can be considered. We report the use of FT-IR and resonance Raman spectroscopies alongside density functional theory to describe the vibrational and electronic structures of decavanadate, [V₁₀O₂₈]^6-. Our computational model, which reproduced the majority of vibrational features to within 10 cm^-1, was used to identify an axial oxo ligand as the most likely position of the acidic proton in the related cluster [HV₁₀O₂₈]^5-. As resonance Raman spectroscopy can directly interrogate chromophores embedded in complex systems, this approach may be of general use in answering structural questions about polyoxometalate-enzyme systems.

Chirality-Selected Chemical Modulation of Amyloid Aggregation

Due to the composed α-helical/β-strand structures, β-amyloid peptide (Aβ) is sensitive to chiral environments. The orientation and chirality of the Aβ strand strongly influence its aggregation. Aβ-formed fibrils have a cascade of chirality. Therefore, for selectively targeting amyloid aggregates, chirality preference can be one key issue. Inspired by the natural stereoselectivity and the β-sheet structure, herein, we synthesized a series of d- and l-amino acid-modified polyoxometalate (POM) derivatives, including positively charged amino acids (d-His and l-His) and negatively charged (d-Glu and l-Glu) and hydrophobic amino acids (d-Leu, l-Leu, d-Phe, and l-Phe), to modulate Aβ aggregation. Intriguingly, Phe-modified POMs showed a stronger inhibition effect than other amino acid-modified POMs, as evidenced by multiple biophysical and spectral assays, including fluorescence, circular dichroism, NMR, molecular dynamic simulations, and isothermal titration calorimetry. More importantly, d-Phe-modified POM had an 8-fold stronger inhibition effect than l-Phe-modified POM, indicating high enantioselectivity. Furthermore, in vivo studies demonstrated that the chiral POM derivatives crossed the blood-brain barrier, extended the life span of AD transgenic Caenorhabditis elegans CL2006 strain, and had low cytotoxicity, even at a high dosage.

Stabilizing γ-Alkyltin-Oxo Keggin Ions by Borate Functionalization

We report a hierarchical self-assembly engineering of tin-oxo clusters from nanosized hydrophobic clusters to a single-layer film of assembled clusters. These clusters are derivatives of the previously reported Na-centered butyltin Keggin ions, but they are bicapped with butyltin and with borate ligands. The formulas γ-[( n-BuSn)₁₄(OCH₃)₁₀(OH)₃O₉(NaO₄)(HBO₃)₂] and γ-[( n-BuSn)₁₄(OCH₃)₁₀(OH)₃O₉(NaO₄)(PhBO₂)₂] were determined from single-crystal X-ray diffraction and bulk solution characterization including small-angle X-ray scattering, electrospray ionization mass spectrometry, and multinuclear and multidimensional NMR (¹¹⁹Sn, ¹³C, and ¹H). Solution characterization confirms that borate functionalization inhibits the solution-phase β-γ Keggin isomer interconversion that was recognized prior for uncapped butyltin clusters, and in this case, the γ isomer is favored. The assembly of the γ-NaSn₁₄BO₃ clusters into a homogeneous Langmuir-Blodgett monolayer is the first step toward creating nanopatterned films for microelectronic devices.