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

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.

Structure-Activity Relationships for the Affinity of Chaotropic Polyoxometalate Anions towards Proteins

The influence of the composition of chaotropic polyoxometalate (POM) anions on their affinity to biological systems was studied by means of atomistic molecular dynamics (MD) simulations. The variations in the affinity to hen egg-white lysozyme (HEWL) were analyzed along two series of POMs whereby the charge or the size and shape of the metal cluster are modified systematically. Our simulations revealed a quadratic relationship between the charge of the POM and its affinity to HEWL as a consequence of the parabolic growth of POM⋅⋅⋅water interaction with the charge. As the charge increases, POMs become less chaotropic (more kosmotropic) increasing the number and the strength of POM-water hydrogen bonds and structuring the solvation shell around the POM. This atomistic description explains the proportionally larger desolvation energies and less protein affinity for highly charged POMs, and consequently, the preference for moderate charge densities (q/M=0.33). Also, our simulations suggest that POM⋅⋅⋅protein interactions are size-specific. The cationic pockets of HEWL protein show a preference for Keggin-like structures, which display the optimal dimensions (≈1 nm). Finally, we developed a quantitative multidimensional model for protein affinity with predictive ability (r² =0.97; q² =0.88) using two molecular descriptors that account for the charge density (charge per metal atom ratio; q/M) and the size and shape (shape weighted-volume; V_S ).

The Aquaporin-3-Inhibiting Potential of Polyoxotungstates

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

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.

Bis(ethylmaltolato)oxidovanadium(iv) inhibited the pathogenesis of Alzheimer's disease in triple transgenic model mice

Vanadium compounds have been reported to mimic the anti-diabetes effects of insulin on rodent models, but their effects on Alzheimer's disease (AD) have rarely been explored. In this paper, 9-month-old triple transgenic AD model mice (3×Tg-AD) received bis(ethylmaltolato)oxidovanadium(iv) (BEOV) at doses of 0.2 mmol L^-1 (68.4 μg mL^-1) and 1.0 mmol L^-1 (342 μg mL^-1) for 3 months. BEOV at both doses was found to improve contextual memory and spatial learning in AD mice. It also improved glucose metabolism and protected neuronal synapses in the AD brain, as evidenced respectively by ¹⁸F-labeled fluoro-deoxyglucose positron emission tomography (¹⁸F-FDG-PET) scanning and by transmission electron microscopy. Inhibitory effects of BEOV on β-amyloid (Aβ) plaques and neuronal impairment in the cortex and hippocampus of fluorescent AD mice were visualized three-dimensionally by applying optical clearing technology to brain slices before confocal laser scanning microscopy. Western blot analysis semi-quantitatively revealed the altered levels of Aβ₄₂ in the brains of wildtype, AD, and AD treated with 0.2 and 1.0 mmol L^-1 BEOV mice (70.3%, 100%, 83.2% and 56.8% in the hippocampus; 82.4%, 100%, 66.9% and 42% in the cortex, respectively). The mechanism study showed that BEOV increased the expression of peroxisome proliferator-activated receptor γ (PPARγ) (140%, 100%, 142% and 160% in the hippocampus; 167%, 100%, 124% and 133% in the cortex) to inactivate the JAK2/STAT3/SOCS-1 pathway and to block the amyloidogenesis cascade, thus attenuating Aβ-induced insulin resistance in AD models. BEOV also reduced protein tyrosine phosphatase 1B (PTP1B) expression (74.8%, 100%, 76.5% and 53.8% in the hippocampus; 71.8%, 100%, 94.2% and 81.8% in cortex) to promote insulin sensitivity and to stimulate the PI3K/Akt/GSK3β pathway, subsequently reducing tau hyperphosphorylation (phosphorylated tau396 levels were 51.1%, 100%, 56.1% and 50.2% in the hippocampus; 22.2%, 100%, 36.1%, and 24% in the cortex). Our results suggested that BEOV reduced the pathological hallmarks of AD by targeting the pathways of PPARγ and PTP1B in 3×Tg AD mice.

Polyoxometalates function as indirect activators of a G protein-coupled receptor

A series of multivalent polyoxovanadates were found to activate signaling of a G protein coupled receptor, the luteinizing hormone receptor.

Recent advances: peptides and self-assembled peptide-nanosystems for antimicrobial therapy and diagnosis

Bacterial infections, especially the refractory treatment of drug-resistant bacteria, are one of the greatest threats to human health. Self-assembling peptide-based strategies can specifically detect the bacteria at the site of infection in the body and kill it.

Research progress on the inhibition of enzymes by polyoxometalates

Polyoxometalates (POMs) are a kind of inorganic cluster metal complex with various biological activities, such as anti-Alzheimer's disease, antibacterial, anti-cancer, anti-diabetes, anti-virus and so on.

A silver-substituted phosphomolybdate prevents the growth of bacteria without affecting the balance of reactive oxygen species

A novel 2D nanoscale silver-substituted Strandberg-type phosphomolybdate shows good inhibitory effect on the growth of Escherichia coli.

Ionic strength effect on regulating the synthetic assembly of polyoxometalate clusters with slow magnetic relaxation behavior

Three novel polyoxometalate (POM) clusters of K10Na10[Dy3(H2O)6Ni(H2O)(W3O11)(B-α-SbW9O33)3]·(H2O)45 (1), (NH4)5K4Na8[Dy3(H2O)6SbV(H2O)(W3O11)(B-α-SbW9O33)3]·(H2O)50 (2), and (NH4)9Na[Ni2(H2O)6(WO2)2(B-β-SbW9O33)2]·(H2O)24 (3) were successfully obtained using the same precursor under different ionic strength conditions. Structural analysis showed that compounds 1-3 possess discrepant structural characteristics in 1 M KCl, 1 M NH4Cl, and saturated NH4Cl, respectively. Among them, 2 is the first reported lanthanide cluster including both Sb3+ and Sb5+ in POM derivatives. Furthermore, the analysis of ac magnetic data proved that 1 and 2 embodied dramatic field-induced slow magnetic relaxation, and the effective barrier of 2 was estimated as Ueff/KB = 21.10 K based on the Orbach process. It was found that the structure and magnetic properties of POM materials can be regulated using an effective and satisfactory ionic strength-controlled strategy.

Co(ii) and Zn(ii) pyrazolyl-benzimidazole complexes with remarkable antibacterial activity

Three pseudopolymorphs based on a coordination complex of a pyrazolyl-benzimidazole ligand have been synthesized and characterized by single crystal X-diffraction, and showed remarkable antibacterial properties.

Polyoxometalates in solution: speciation under spotlight

The review covers stability and transformations of classical polyoxometalates in aqueous solutions and provides their ion-distribution diagrams over a wide pH range.

Selenotungstates incorporating organophosphonate ligands and metal ions: synthesis, characterization, magnetism and catalytic efficiency in the Knoevenagel condensation reaction

Three new sandwich-type selenotungstate anion structures and Co1 show superior catalytic performance in the Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate under mild conditions.

A hexaniobate expanded by six [Hg(cyclam)]2+ complexes via Hg–O bonds yields a positively charged polyoxoniobate cluster

The room temperature reaction of Hg(NO3)2 · H2O, cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane) and K8{Nb6O19} · 16 H2O in a mixture of H2O and DMSO led to crystallization of the novel compound {[Hg(cyclam)]6Nb6O19}(NO3)4 · 14 H2O, which is the first mercury containing polyoxoniobate. The structure consists of a {Nb6O19}8− cluster core which is expanded by six [Hg(cyclam)]2+ complexes via Hg–μ 2-O–Nb bond formation. The title compound contains a positively charged polyoxoniobate cluster. The crystal water molecules form small aggregates by O–H · · · O hydrogen bonding which are joined into larger aggregates by N–O · · · H–O hydrogen bonding integrating the nitrate anions.

Synthesis, structural characterisation, and cytotoxicity studies of Bi, W, and Mo containing homo- and hetero-bimetallic polyoxometalates

Three new and different homo- and hetero-bimetallic polyoxometalate (POM) species have been synthesised by simple one-pot synthetic methods utilising naturally occurring bismite (Bi₂O₃) (or Bi(NO₃)₃·5H₂O) and aryl sulfonic acids. The POM species isolated are (NH₄)₁₄[Bi₂W₂₂O₇₆]·14H₂O (1·14H₂O), (NH₄)[Bi(DMSO)₇][Mo₈O₂₆]·H₂O (2·H₂O) and [(NH₄)₄(Mo₃₆O₁₀₈(OH)₄·16H₂O)]·45H₂O (3·45H₂O). The compounds have been characterised by X-ray crystallography, energy dispersive X-ray spectroscopy (EDX), powdered X-ray diffraction (PXRD), mass spectrometry (ESI-MS), Raman spectroscopy, thermogravimetric (TGA) and ICP analyis. In vitro cytoxicity and proliferation studies conducted on 1 and 3, highlight the low toxicity of these species.

In vitro study of the protective effect of manganese against vanadium-mediated nuclear and mitochondrial DNA damage

We aimed to study the effect of vanadium(V) exposure on cell viability, nuclear DNA (nDNA) and mitochondrial DNA (mtDNA) and to elucidate if these effects can be reverted by co-exposure to V and manganese (Mn). HepG2 cells were incubated with various concentrations of bis(maltolato)oxovanadium(IV) or MnCl2 for 32 h for viability study. The higher concentrations (59   μM V, 54 nM Mn and 59   μM V+54 nM Mn) were used to study DNA damage and uptake of V and Mn. Comet assay was used for the study of nDNA damage; mtDNA damage was studied by determining deletions and number of copies of the ND1/ND4 mtDNA region. Cellular content of V and Mn was determined using ICPMS. Cellular exposure to 59   μM V decreased viability (14%) and damaged nDNA and mtDNA. This effect was partially prevented by the co-exposure to V + Mn. Exposure to V increased the cellular content of V and Mn (812.3% and 153.5%, respectively). Exposure to Mn decreased the content of V and Mn (62% and 56%, respectively). Exposure to V + Mn increased V (261%) and decreased Mn (56%) content. The positive effects on cell viability and DNA damage when incubated with V + Mn could be due to the Mn-mediated inhibition of V uptake.

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.

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.

Preparation of polyoxometalate-doped aminosilane-modified silicate hybrid as a new barrier of chem-bio toxicant

Nanohybrid membranes based on the Keggin-type polyoxometalate (POM) H5PV2Mo10O40 and aminosilane-modified silicate (Ormosil and Ormosil(NR4+Cl-)) hybrids were synthesized as a new barrier to protect against simulants of chemical and biological toxicant. The 31P NMR and XPS results indicated that POM was bound to the Ormosil and Ormosil(NR4+Cl-) hybrids after impregnation. The antibacterial effects of the hybrids and hybrid-impregnated fabrics against Gram-negative and Gram-positive bacteria were investigated with zone of inhibition, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and plate-counting method. The MIC/MBC values of Ormosil(NR4+Cl-)/POM and Ormosil/POM against bacteria were 0.267/2.67 and 2.67/26.7, respectively, and the percentage reduction of bacteria was approximately 100% after 20 laundry cycles of their fabrics. The reaction products and mechanisms of the adsorptive degradation of 2-chloroethylethylsulfide (CEES) by hybrids were investigated with 13C NMR. The results of this study showed that POM-doped Ormosil systems are capable of destroying bacteria and CEES.

One-pot synthesis of a new generation of hybrid bisphosphonate polyoxometalate gold nanoparticles as antibiofilm agents

A reduced polyoxovanadate functionalized with bisphosphonate molecules was synthesized and used to prepare in one step hybrid organic-inorganic polyoxometalate decorated gold nanoparticles. These new composites were shown to strongly inhibit P. aeruginosa and S. epidermidis biofilm growth, with the three components constituting the nanoparticles (Au0 core, vanadium and alendronate) acting synergistically.

The Synthesis and Biological Function of a Novel Sandwich-Type Complex Based on {SbW9 } and Flexible bpp Ligand

A novel sandwich-type complex [Na(H₂ O)₄ ][{Na₃ (H₂ O)₅ }{Mn₃ (bpp)₃ } (SbW₉ O₃₃ )₂ }]·8H₃ O (MnSbW-bpp) (bpp = 1,3-bis(4-pyridyl) propane) is synthesized and characterized by elemental analysis, IR, thermogravimetric analysis, and single-crystal X-ray diffraction. The MnSbW-bpp compound is the first sandwich case bridged by a flexible ligand. Its biological function of MnSbW-bpp in antitumor activity is also determined in vitro and in vivo. The inhibitory proliferation and induction of apoptosis are performed by flow cytometry assay, S180 (sarcoma) tumor xenograft in ICR mice, the color Doppler ultrasound monitor, and TdT-mediated dUTP-biotin nick end labeling assay. The results show that the novel compound-MnSbW-bpp-is synthesized and identified by its physical and chemical characteristics, such as the fluorescent and paramagnetic activities. MnSbW-bpp indicates a potency inhibition of human cancer lines, such as SGC-7901, HT-29, HepG2, Hela, U2OS, SaoS2, and HMC cells. MnSbW-bpp also inhibits the growth of tumor xenograft in mice, induced cell apoptosis, and released cytochrome c in vivo and in vitro. Thus, MnSbW-bpp, as a new compound, possesses the potent inhibition of cancer cells, which indicates that the MnSbW-bpp has potential merit for the further evaluation of a novel antitumor agent.

Inhibition of Na+/K+- and Ca2+-ATPase activities by phosphotetradecavanadate

Polyoxometalates (POMs) are promising inorganic inhibitors for P-type ATPases. The experimental models used to study the effects of POMs on these ATPases are usually in vitro models using vesicles from several membrane sources. Very recently, some polyoxotungstates, such as the Dawson anion [P₂W₁₈O₆₂]^6-, were shown to be potent P-type ATPase inhibitors; being active in vitro as well as in ex-vivo. In the present study we broaden the spectrum of highly active inhibitors of Na⁺/K⁺-ATPase from basal membrane of epithelial skin to the bi-capped Keggin-type anion phosphotetradecavanadate Cs_5.6H_3.4PV₁₄O₄₂ (PV₁₄) and we confront the data with activity of other commonly encountered polyoxovanadates, decavanadate (V₁₀) and monovanadate (V₁). The X-ray crystal structure of PV₁₄ was solved and contains two trans-bicapped α-Keggin anions H_xPV₁₄O₄₂^(9-x)-. The anion is built up from the classical Keggin structure [(PO₄)@(V₁₂O₃₆)] capped by two [VO] units. PV₁₄ (10 μM) exhibited higher ex-vivo inhibitory effect on Na⁺/K⁺-ATPase (78%) than was observed at the same concentrations of V₁₀ (66%) or V₁ (33%). Moreover, PV₁₄ is also a potent in vitro inhibitor of the Ca²⁺-ATPase activity (IC₅₀ 5 μM) exhibiting stronger inhibition than the previously reported activities for V₁₀ (15 μM) and V₁ (80 μM). Putting it all together, when compared both P-typye ATPases it is suggested that PV₁₄ exibited a high potential to act as an in vivo inhibitor of the Na⁺/K⁺-ATPase associated with chloride secretion.

Exploring Wells-Dawson Clusters Associated With the Small Ribosomal Subunit

The polyoxometalate P₂W₁₈O626-, the Wells-Dawson cluster, stabilized the ribosome sufficiently for the crystallographers to solve the phase problem and improve the structural resolution. In the following we characterize the interaction of the Wells-Dawson cluster with the ribosome small subunit. There are 14 different P₂W₁₈O626- clusters interacting with the ribosome, and the types of interactions range from one simple residue interaction to complex association of multiple sites including backbone interactions with a Wells-Dawson cluster. Although well-documented that bridging oxygen atoms are the main basic sites on other polyoxometalate interaction with most proteins reported, the W=O groups are the main sites of the Wells-Dawson cluster interacting with the ribosome. Furthermore, the peptide chain backbone on the ribosome host constitutes the main sites that associate with the Wells-Dawson cluster. In this work we investigate the potential of one representative pair of closely-located Wells-Dawson clusters being a genuine Double Wells-Dawson cluster. We found that the Double Wells-Dawson structure on the ribosome is geometrically sound and in line with other Double Wells-Dawson clusters previously observed in the solid state and solution. This information suggests that the Double Wells-Dawson structure on the ribosome is real and contribute to characterization of this particular structure of the ribosome.

Regioselective synthesis and characterization of monovanadium-substituted β-octamolybdate [VMo7O26]5

The monovanadium-substituted polyoxometalate anion [VMo7O26]5-, exhibiting a β-octamolybdate archetype structure, was selectively prepared as pentapotassium [hexaikosaoxido(heptamolybdenumvanadium)]ate hexahydrate, K5[VMo7O26]·6H2O (VMo7), by oxidation of a reduced vanadomolybdate solution with hydrogen peroxide in a fast one-pot approach. X-ray structure analysis revealed that the V atom occupies a single position in the cluster that differs from the other positions by the presence of one doubly-bonded O atom instead of two terminal oxide ligands in all other positions. The composition and structure of VMo7 was also confirmed by elemental analyses and IR spectroscopy. The selectivity of the synthesis was inspected by a 51V NMR investigation which showed that this species bound about 95% of VV in the crystallization solution. Upon dissolution of VMo7 in aqueous solution, the [VMo7O26]5- anion is substantially decomposed, mostly into [VMo5O19]3-, α-[VMo7O26]4- and [V2Mo4O19]4-, depending on the pH.

Antibacterial activity of chitosan nano-composites and carbon nanotubes: A review

Bacteriological contamination of water sources is a major challenge that has a detrimental impact on both the environment and human health. This imposes the search for the most efficient disinfectant. Despite their antibacterial efficiency, traditional methods can often form disinfection byproducts through their reaction with organic and inorganic compounds. Substitutes for conventional bacterial inactivation methods should not produce harmful byproducts and must also be cost effective. Nanotechnology is an attractive option that is suited for surface reactions as nanostructures offer large surface to volume ratios. Technologies using chitosan-modified nanocomposites and carbon nanotubes have proven to offer promising alternatives for bacterial inactivation. To enhance their antibacterial efficiency, such technologies have been modified chemically and physically and have as well been associated with other treatment techniques. However, despite their high bacterial disinfection efficacy and lack of treatment byproducts, the vagueness in bacterial inactivation mechanisms and complexity in materials preparation have often obscured their wide scale application. The aim of this manuscript is to review the recent advances in bacterial disinfection using nanomaterials, in the form of chitosan and carbon nanotubes. The rapid rate of research and the notable progress in this area dictate the frequent compilation and dissemination of recent introductions to this field. Existing gaps in the literature are thus also highlighted and reported discrepancies are pinpointed so that roadmaps for future studies may be figured.

Impact of copper and iron binding properties on the anticancer activity of 8-hydroxyquinoline derived Mannich bases

The anticancer activity of 8-hydroxyquinolines relies on complex formation with redox active copper and iron ions. Here we employ UV-visible spectrophotometry and EPR spectroscopy to compare proton dissociation and complex formation processes of the reference compound 8-hydroxyquinoline (Q-1) and three related Mannich bases to reveal possible correlations with biological activity. The studied derivatives harbor a CH2-N moiety at position 7 linked to morpholine (Q-2), piperidine (Q-3), and chlorine and fluorobenzylamino (Q-4) substituents. Solid phase structures of Q-3, Q-4·HCl·H2O, [(Cu(HQ-2)2)2]·(CH3OH)2·Cl4·(H2O)2, [Cu(Q-3)2]·Cl2 and [Cu(HQ-4)2(CH3OH)]·ZnCl4·CH3OH were characterized by single-crystal X-ray diffraction analysis. In addition, the redox properties of the copper and iron complexes were studied by cyclic voltammetry, and the direct reaction with physiologically relevant reductants (glutathione and ascorbic acid) was monitored. In vitro cytotoxicity studies conducted with the human uterine sarcoma MES-SA/Dx5 cell line reveal the significant cytotoxicity of Q-2, Q-3, and Q-4 in the sub- to low micromolar range (IC50 values 0.2-3.3 μM). Correlation analysis of the anticancer activity and the metal binding properties of the compound series indicates that, at physiological pH, weaker copper(ii) and iron(iii) binding results in elevated toxicity (e.g.Q4: pCu = 13.0, pFe = 6.8, IC50 = 0.2 μM vs.Q1: pCu = 15.1, pFe = 13.0 IC50 = 2.5 μM). Although the studied 8-hydroxyquinolines preferentially bind copper(ii) over iron(iii), the cyclic voltammetry data revealed that the more cytotoxic ligands preferentially stabilize the lower oxidation state of the metal ions. A linear relationship between the pKa (OH) and IC50 values of the studied 8-hydroxyquinolines was found. In summary, we identify Q-4 as a potent and selective anticancer candidate with significant toxicity in drug resistant cells.

Interaction of Vanadium(IV) Species with Ubiquitin: A Combined Instrumental and Computational Approach

The interaction of V^IVO²⁺ ion and five V^IVOL₂ compounds with potential pharmacological application, where L indicates maltolate (ma), kojate (koj), acetylacetonate (acac), 1,2-dimethyl-3-hydroxy-4(1 H)-pyridinonate (dhp), and l-mimosinate (mim), with ubiquitin (Ub) was studied by EPR, ESI-MS, and computational (docking and DFT) methods. The free metal ion V^IVO²⁺ interacts with Glu, Asp, His, Thr, and Leu residues, but the most stable sites (named 1 and 2) involve the coordination of (Glu16, Glu18) and (Glu24, Asp52). In the system with V^IVOL₂ compounds, the type of binding depends on the vanadium concentration. When the concentration is in the mM range, the binding occurs with cis-VOL₂(H₂O), L = ma, koj, dhp, and mim, or with VO(acac)₂: in the first case, the equatorial coordination of His68, Glu16, Glu18, or Asp21 residues yields species with formula n[VOL₂]-Ub where n = 2-3, while with VO(acac)₂ only noncovalent surface interactions are revealed. When the concentration of V is on the order of micromolar, the mono-chelated species VOL(H₂O)₂⁺ with L = ma, koj, acac, dhp, and mim, favored by the hydrolysis, interact with Ub, and adducts with composition n[VOL]-Ub ( n = 1-2) are observed with the contemporaneous coordination of (Glu18, Asp21) or (Glu16, Glu18), and (Glu24, Asp52) or (Glu51, Asp52) donors. The results of this work suggest that the combined application of spectroscopic, spectrometric, and computational techniques allow the complete characterization of the ternary systems formed by a V compound and a model protein such as ubiquitin. The same approach can be applied, eventually changing the spectroscopic/spectrometric techniques, to study the interaction of other metal species with other proteins.

Synthesis, characterization, and POM-protein interactions of a Fe-substituted Krebs-type Sandwich-tungstoantimonate

ABSTRACT

The novel iron-substituted Krebs-type polyoxotungstate (C12N4H11)4Na2H5[(Fe(H2O)3)2((FeO2)0.5(WO2)0.5)2(β-SbW9O33)2] (Fe-1) has been synthesized using ortho-phenylenediamine (opda) as a precursor for the in situ formation of the counter cation 2,3-diaminophenazinium (C12N4H11)+ (2,3-DAP). Fe-1 has been thoroughly characterized in the solid state by single-crystal X-ray diffraction (SXRD), powder X-ray diffraction (PXRD), IR spectroscopy, and elemental analysis as well as in solution by UV-Vis spectroscopy. The crystal structure of Fe-1 reveals π-π-interactions between the aromatic systems of the unconventional 2,3-DAP counter cation. POM-protein interaction studies using SDS-PAGE revealed a non-proteolytic behavior of Fe-1 towards Human Serum Albumin (HSA) as a model protein.

GRAPHICAL ABSTRACT

Keggin-type polyoxotungstates as mushroom tyrosinase inhibitors - A speciation study

Mushroom tyrosinase abPPO4 is a commercially relevant polyphenol oxidase and has been being targeted for numerous inhibition studies including polyoxometalates (POMs). In the present work, its diphenolase activity was inhibited at pH 6.8 by a series of structurally related polyoxotungstates (POTs) of the α-Keggin archetype, exhibiting the general formula [Xⁿ⁺W₁₂O₄₀]⁽⁸⁻ⁿ⁾⁻ in order to elucidate charge-dependent activity correlations. Kinetic data were obtained from the dopachrome assay and ¹⁸³W NMR was applied to obtain crucial insights into the actual Keggin POT speciation in solution, facilitating a straightforward assignment of inhibition effects to the identified POT species. While [PW₁₂O₄₀]³⁻ was completely hydrolyzed to its moderately active lacunary form H_x[PW₁₁O₃₉]^(7−x)− (K_i = 25.6 mM), [SiW₁₂O₄₀]⁴⁻ showed the most pronounced inhibition effects with a K_i of 4.7 mM despite of partial hydrolysis to its ineffective lacunary form H_x[SiW₁₁O₃₉]^(8−x)−. More negative Keggin cluster charges of 5− and 6− generally resulted in preclusion of inhibitory efficacy as well as hydrolysis, but with the Ni-substituted cluster [PW₁₁O₃₉{Ni(H₂O)}]⁵⁻ enzymatic inhibition was clearly restored (K_i = 9.7 mM). The inhibitory capacity of the structurally intact Keggin POTs was found to be inversely correlated to their net charge. The here applied speciation strategy is of utmost importance for any biological POM application to identify the actually active POM species.

Polyoxometalates as Potential Next-Generation Metallodrugs in the Combat Against Cancer

Polyoxometalates (POMs) are an emerging class of inorganic metal oxides, which over the last decades demonstrated promising biological activities by the virtue of their great diversity in structures and properties. They possess high potential for the inhibition of various tumor types; however, their unspecific interactions with biomolecules and toxicity impede their clinical usage. The current focus of the field of biologically active POMs lies on organically functionalized and POM-based nanocomposite structures as these hybrids show enhanced anticancer activity and significantly reduced toxicity towards normal cells in comparison to unmodified POMs. Although the antitumor activity of POMs is well documented, their mechanisms of action are still not well understood. In this Review, an overview is given of the cytotoxic effects of POMs with a special focus on POM-based hybrid and nanocomposite structures. Furthermore, we aim to provide proposed mode of actions and to identify molecular targets. POMs are expected to develop into the next generation of anticancer drugs that selectively target cancer cells while sparing healthy cells.

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.

Ionic Liquid Stabilized Niobium Oxoclusters Catalyzing Oxidation of Sulfides with Exceptional Activity

We present here a new class of niobium oxoclusters that are stabilized effectively by carboxylate ionic liquids. These functionalized ILs are designated as [TBA][LA], [TBA][PA], and [TBA][HPA] in this work, in which TBA represents tetrabutylammonium and LA, PA, and HPA refer to lactate, propionate, 3-hydroxypropionate anions, respectively. The as-synthesized Nb oxoclusters have been characterized by use of elemental analysis, NMR, IR, XRD, TGA, HRTEM. It was found that [TBA][LA]-stabilized Nb oxoclusters (Nb-OC@[TBA][LA]) are uniformly dispersed with an average particle size of 2-3 nm and afforded exceptionally high catalytic activity for the selective oxidation of various thioethers. The turnover number with Nb-OC@[TBA][LA] catalyst was over 56 000 at catalyst loading as low as 0.0033 mol % (1 ppm). Meantime, the catalyst also showed the high activity for the epoxidation of olefins and allylic alcohols by using only 0.065 mol % of catalyst (50 ppm). The characterization of ⁹³ Nb NMR spectra revealed that the Nb oxoclusters underwent structural transformation in the presence of H₂ O₂ but regenerated to their initial state at the end of the reaction. In particular, the highly dispersed Nb oxoclusters can absorb a large amount of polar organic solvents and thus were swollen greatly, which exhibited "pseudo" liquid phase behavior, and enabled the substrate molecules to be highly accessible to the catalytic center of Nb oxocluster units.

Polyoxomolybdates as α-glucosidase inhibitors: Kinetic and molecular modeling studies

Noninsulin dependent diabetes mellitus is a serious global disease that is treated by inhibiting α-glucosidase to reduce the glucose content in the blood. Several incompletely satisfactory therapeutic drugs are already on the market. In this report, we showed that polyoxomolybdates based on Keggin-type architecture are promising candidates. Kinetic studies indicate that H₃PMo₁₂O₄₀, Na₄PMo₁₁VO₄₀, Na₆PMo₁₁FeO₄₀ and Na₇PMo₁₁CoO₄₀ strongly inhibit α-glucosidase with IC₅₀ values of 6.14 ± 0.38 μM, 52.33 ± 1.41 μM, 161.90 ± 7.68 μM and 103.10 ± 2.88 μM, respectively. Moreover, H₃PMo₁₂O₄₀, Na₄PMo₁₁VO₄₀, and Na₇PMo₁₁CoO₄₀ are reversible, competitive inhibitors with K_I values of 0.018 mM, 0.146 mM and 0.121 mM, respectively. Na₆PMo₁₁FeO₄₀ inhibited α-glucosidase in a reversible noncompetitive manner with K_I and K_IS of 0.312 mM and 0.412 mM, respectively. Molecular docking simulation suggested that H₃PMo₁₂O₄₀ binds into the substrate binding site in accordance with competitive inhibition behavior and offered, in addition, an initial insight into the polypeptide-inhibitor interactions. This work presents a promising new perspective for designing effective α-glucosidase inhibitors and further demonstrates the enormous potential of polyoxomolybdates as enzyme inhibitors.