Water-Soluble Polyoxometal Clusters of Molybdenum (V) with Pyrazole and Triazole: Synthesis and Study of Cytotoxicity and Antiviral Activity

Among well-studied and actively developing compounds are polyoxometalates (POMs), which show application in many fields. Extending this class of compounds, we introduce a new subclass of polyoxometal clusters (POMCs) [Mo12O28(μ-L)8]4- (L = pyrazolate (pz) or triazolate (1,2,3-trz or 1,2,4-trz)), structurally similar to POM, but containing binuclear Mo2O4 clusters linked by bridging oxo- and organic ligands. The complexes obtained by ampoule synthesis from the binuclear cluster [Mo2O4(C2O4)2(H2O)2]2- in a melt of an organic ligand are soluble and stable in aqueous solutions. In addition to the detailed characterization in solid state and in aqueous solution, the biological properties of the compounds on normal and cancer cells were investigated, and antiviral activity against influenza A virus (subtype H5N1) was demonstrated.

PEGylation of Terminal Ligands as a Route to Decrease the Toxicity of Radiocontrast Re6-Clusters

The development of novel radiocontrast agents, mainly used for the visualization of blood vessels, is still an emerging task due to the variety of side effects of conventional X-ray contrast media. Recently, we have shown that octahedral chalcogenide rhenium clusters with phosphine ligands-Na2H14[{Re6Q8}(P(C2H4COO)3)6] (Q = S, Se)-can be considered as promising X-ray contrast agents if their relatively high toxicity related to the high charge of the complexes can be overcome. To address this issue, we propose one of the most widely used methods for tuning the properties of proteins and peptides-PEGylation (PEG is polyethylene glycol). The reaction between the clusters and PEG-400 was carried out in acidic aqueous media and resulted in the binding of up to five carboxylate groups with PEG. The study of cytotoxicity against Hep-2 cells and acute toxicity in mice showed a twofold reduction in toxicity after PEGylation, demonstrating the success of the strategy chosen. Finally, the compound obtained has been used for the visualization of blood vessels of laboratory rats by angiography and computed tomography.

Correction: Optical property trends in a family of {Mo6I8} aquahydroxo complexes

Correction for 'Optical property trends in a family of {Mo6I8} aquahydroxo complexes' by Margarita V. Marchuk et al., Dalton Trans., 2021, 50, 8794-8802, https://doi.org/10.1039/D1DT01293B.

Chemical Diversity of Mo5S5 Clusters with Pyrazole: Synthesis, Redox and UV-vis-NIR Absorption Properties

The chemistry of transition metal clusters has been intensively developed in the last decades, leading to the preparation of a number of compounds with promising and practically useful properties. In this context, the present work demonstrates the preparation and study of the reactivity, i.e., the possibility of varying the ligand environment, of new square pyramidal molybdenum chalcogenide clusters [{Mo5(μ3-S)i4(μ4-S)i(μ-pz)i4}(pzH)t5]1+/2+ (pzH = pyrazole, i = inner, t = terminal). The one-step synthesis starting from the octahedral Mo6Br12 cluster as well as the substitution of the apical pyrazole ligand or the selective bromination of the inner pyrazolate ligands were demonstrated. All the obtained compounds were characterized in detail using a series of physicochemical methods both in solid state (X-ray diffraction analysis, etc.) and in solution (nuclear magnetic resonance spectroscopy, mass spectrometry, etc.). In this work, redox properties and absorption in the ultraviolet-visible and near-infrared region of the obtained compounds were studied.

Silica-Based Materials Containing Inorganic Red/NIR Emitters and Their Application in Biomedicine

The low absorption of biological substances and living tissues in the red/near-infrared region (therapeutic window) makes luminophores emitting in the range of ~650-1350 nm favorable for in vitro and in vivo imaging. In contrast to commonly used organic dyes, inorganic red/NIR emitters, including ruthenium complexes, quantum dots, lanthanide compounds, and octahedral cluster complexes of molybdenum and tungsten, not only exhibit excellent emission in the desired region but also possess additional functional properties, such as photosensitization of the singlet oxygen generation process, upconversion luminescence, photoactivated effects, and so on. However, despite their outstanding functional applicability, they share the same drawback-instability in aqueous media under physiological conditions, especially without additional modifications. One of the most effective and thus widely used types of modification is incorporation into silica, which is (1) easy to obtain, (2) biocompatible, and (3) non-toxic. In addition, the variety of morphological characteristics, along with simple surface modification, provides room for creativity in the development of various multifunctional diagnostic/therapeutic platforms. In this review, we have highlighted biomedical applications of silica-based materials containing red/NIR-emitting compounds.

Multifunctional Oxidized Dextran as a Matrix for Stabilization of Octahedral Molybdenum and Tungsten Iodide Clusters in Aqueous Media

Due to their high abundance, polymeric character, and chemical tunability, polysaccharides are perfect candidates for the stabilization of photoactive nanoscale objects, which are of great interest in modern science but can be unstable in aqueous media. In this work, we have demonstrated the relevance of oxidized dextran polysaccharide, obtained via a simple reaction with H₂O₂, towards the stabilization of photoactive octahedral molybdenum and tungsten iodide cluster complexes [M₆I₈}(DMSO)₆](NO₃)₄ in aqueous and culture media. The cluster-containing materials were obtained by co-precipitation of the starting reagents in DMSO solution. According to the data obtained, the amount and ratio of functional carbonyl and carboxylic groups as well as the molecular weight of oxidized dextran strongly affect the extent of stabilization, i.e., high loading of aldehyde groups and high molecular weight increase the stability, while acidic groups have some negative impact on the stability. The most stable material based on the tungsten cluster complex exhibited low dark and moderate photoinduced cytotoxicity, which together with high cellular uptake makes these polymers promising for the fields of bioimaging and PDT.

Improved Synthesis of (TBA)2[W6Br14] Paving the Way to Further Study of Bromide Cluster Complexes

Octahedral cluster complexes of molybdenum and tungsten, [M₆X₈Y₆]^n- (M = Mo, W; X, Y = Cl, Br, I), are promising active components in various fields, including biomedicine and solar energy. Cluster complexes draw considerable attention due to their X-ray opacity, red/near-IR luminescence, and ability to convert triplet molecular oxygen to active singlet oxygen under UV and visible irradiation. Among the octahedral cluster complexes of molybdenum and tungsten, compounds with a {W₆Br₈}⁴⁺ core are the least studied. There are only a few examples of compounds with substituted terminal ligands, and their properties are not well understood. Among other things, this is due to more labor-intensive and expensive methods for obtaining the starting compounds in comparison with molybdenum counterparts. In this paper, we describe the synthesis of an octahedral cluster complex, (TBA)₂[W₆Br₁₄] (TBA⁺ = tetrabutylammonium), in gram quantities, starting from simple substances─W, Br₂, and Bi─in 70% yield. The formation of pentanuclear tungsten cluster complexes was recorded as a byproduct. Compounds with substituted terminal ligands (TBA)₂[W₆Br₈Y₆] (Y = NO₃, Cl, I) were obtained. We also discuss the instability of (TBA)₂[W₆Br₈(NO₃)₆] under light exposure, the optical properties of a series of compounds (TBA)₂[W₆Br₈Y₆] (Y = Cl, Br, I), and the effect of terminal ligands on the chemical shifts in ¹⁸³W NMR spectra in dimethyl sulfoxide-d₆. The presented approach to the synthesis of one of the main precursors of various bromide cluster complexes on a gram scale can stimulate the study of their properties and development of new functional materials based on them.

Nano TiO2 and Molybdenum/Tungsten Iodide Octahedral Clusters: Synergism in UV/Visible-Light Driven Degradation of Organic Pollutants

Emissions of various organic pollutants in the environment becomes a more and more acute problem in the modern world as they can lead to an ecological disaster in foreseeable future. The current situation forces scientists to develop numerous methods for the treatment of polluted water. Among these methods, advanced photocatalytic oxidation is a promising approach for removing organic pollutants from wastewater. In this work, one of the most common photocatalysts-titanium dioxide-was obtained by direct aqueous hydrolysis of titanium (IV) isopropoxide and impregnated with aqueous solutions of octahedral cluster complexes [{M₆I₈}(DMSO)₆](NO₃)₄ (M = Mo, W) to overcome visible light absorption issues and increase overall photocatalytic activity. XRPD analysis showed that the titania is formed as anatase-brookite mixed-phase nanoparticles and cluster impregnation does not affect the morphology of the particles. Complex deposition resulted in the expansion of the absorption up to ~500 nm and in the appearance of an additional cluster-related band gap value of 1.8 eV. Both types of materials showed high activity in the photocatalytic decomposition of RhB under UV- and sunlight irradiation with effective rate constants 4-5 times higher than those of pure TiO₂. The stability of the catalysts is preserved for up to 5 cycles of photodegradation. Scavengers' experiments revealed high impact of all of the active species in photocatalytic process indicating the formation of an S-scheme heterojunction photocatalyst.

Oxygen-Sensitive Photo- and Radioluminescent Polyurethane Nanoparticles Modified with Octahedral Iodide Tungsten Clusters

The development of cancer treatment techniques able to cure tumors located deep in the body is an urgent task for scientists and physicians. One of the most promising methods is X-ray-induced photodynamic therapy (X-PDT), since X-rays have unlimited penetration through tissues. In this work, octahedral iodide tungsten clusters, combining the properties of a scintillator and photosensitizer, are considered as a key component of nanosized polyurethane (pU) particles in the production of materials promising for X-PDT. Cluster-containing pU nanoparticles obtained here demonstrate bright photo- and X-ray-induced emission in both solid and water dispersion, great efficiency in the generation of singlet oxygen, and high sensitivity regarding photoluminescence intensity in relation to oxygen concentration. Additionally, incorporation of the cluster complex into the pU matrix greatly increases its stability against hydrolysis in water and under X-rays.

Stabilization of Octahedral Metal Halide Clusters by Host-Guest Complexation with γ-Cyclodextrin: Toward Nontoxic Luminescent Compounds

γ-Cyclodextrin (γ-CD) interacts in aqueous solution with octahedral halide clusters Na₂[{M₆X₈}Cl₆] (M = Mo, W; X = Br, I) to form robust inclusion supramolecular complexes [{M₆X₈}Cl₆@2γ-CD]^2-. Single-crystal X-ray diffraction analyses revealed two conformational organizations within the adduct depending on the nature of the inner halide X within the {M₆X₈} core. Using ³⁵Cl NMR and UV-vis as complementary techniques, the kinetics of the hydrolysis process were shown to increase with the following order: {W₆I₈} < {W₆Br₈} ≈ {Mo₆I₈} < {Mo₆Br₈}. The complexation with γ-CD drastically enhances the hydrolytic stability of luminescent [{M₆X₈}Cl₆]^2- cluster-based units, which was quantitatively proved by the same techniques. The resulting host-guest complexation provides a protective shell against contact with water and offers promising horizons for octahedral clusters in biology as revealed by the low dark cytotoxicity and cellular uptake.

Neutral Mo6Q8-clusters with terminal phosphane ligands – a route to water-soluble molecular units of Chevrel phases

Neutral clusters [{Mo6Q8}(Ph2PC2H4COOH)6] (Q = S or Se) readily dissolve in slightly alkaline water forming a highly stable solution. Compounds are redox-active and demonstrate absorbance in all major regions of the spectra – UV, visible and NIR.

The role of hydrolysis in biological effects of molybdenum cluster with DMSO ligands

Biological applications of octahedral molybdenum cluster complexes are complicated by their hydrolytic instability, since hydrolysis leads to irreversible changes in the structure and properties of these compounds. On the other hand, if such changes are thoroughly investigated and understood, the hydrolysis process can become an important tool for regulating specific biological effects of the clusters. In this work, we demonstrate how the luminescence and biological properties (cellular uptake, cytotoxicity in the dark and photodynamic effect) of highly unstable cluster complex [{Mo₆I₈}(DMSO)₆](NO₃)₄ change along with the degree of hydrolysis. Particularly, cluster solution preliminarily aged in water demonstrated lower dark and higher photoinduced cytotoxicity and higher cellular uptake in comparison with fresh solution.

Self-Assembled Microporous M-HOFs Based on an Octahedral Rhenium Cluster with Benzimidazole

Substitution of apical halide ligands in [{Re₆Seⁱ₈}X^a₆]^3- (X = Cl, Br) by benzimidazole (bimzH) accompanied by a self-assembly process leads to the formation of microporous Re₆-based hydrogen-bonded organic frameworks (Re₆-HOFs) constructed on N-H···X hydrogen bonds and π-π-stacking interactions between bimzH ligands. Re₆-HOFs demonstrate sorption properties with a Brunauer-Emmett-Teller surface area of up to 443 m² g^-1 and luminescence with a quantum yield and an emission lifetime of up to 0.16 and 16 μs, respectively. The compounds obtained complement small groups of transition-metal cluster-based HOFs, which are a perspective for the development of multifunctional frameworks.

Optical property trends in a family of {Mo6I8} aquahydroxo complexes

Luminescence is one of the key properties of octahedral molybdenum cluster complexes and the basis for most areas of their possible practical applications. Nevertheless, the factors affecting the optical properties of the clusters are insufficiently studied and establishing them will allow us to tune both absorption and emission more precisely. In this work, we obtained two new cationic [{Mo6I8}(H2O)4(OH)2](An)2·nH2O (An = NO3-, n = 3; An = OTs-, n = 2, OTs- - p-toluenesulfonate), and two neutral [{Mo6I8}(H2O)2(OH)4]·nH2O (n = 2, 12) aquahydroxo complexes. Due to the similar compositions of the clusters obtained, we determined the influence of crystal packing and ligand environment on the absorption and photo- and radioluminescence properties. Thus, the four-component nature of the cluster emission was established using Gaussian deconvolution of the photoluminescence spectra. It was shown that the influence of both ligand type and crystal density decreases when moving to the red (lower-energy) part of the spectra, with only the first two components located in the blue (higher-energy) part of the spectra being strongly affected. Also, it was found that protonation of two hydroxo ligands leads to a significant decrease in absorption in the visible spectral region.

"Host in Host" Supramolecular Core-Shell Type Systems Based on Giant Ring-Shaped Polyoxometalates

Herein, we show how the chaotropic effect arising from reduced molybdate ions in acidified aqueous solution is able to amplify drastically weak supramolecular interactions. Time-resolved Small Angle X-ray Scattering (SAXS) analysis suggests that molybdenum-blue oligomeric species form huge aggregates in the presence of γ-cyclodextrin (γ-CD) which results in the fast formation of nanoscopic {Mo₁₅₄ }-based host-guest species, while X-ray diffraction analysis reveals that the ending-point of the scenario results in an unprecedented three-component well-ordered core-shell-like motif. A similar arrangement was found by using preformed hexarhenium chalcogenide-type cluster [Re₆ Te₈ (CN)₆ ]^4- as exogenous guest. This seminal work brings better understanding of the self-assembly processes in general and gives new opportunities for practical applications in the design of complex multicomponent materials via the simplicity of the non-covalent chemistry.

A water-soluble octahedral molybdenum cluster complex as a potential agent for X-ray induced photodynamic therapy

X-ray-induced photodynamic therapy (X-PDT) has recently evolved into a suitable modality to fight cancer. This technique, which exploits radiosensitizers producing reactive oxygen species, allows for a reduction of the radiation dose needed to eradicate cancer in the frame of the radiotherapy treatment of deep tumors. The use of transition metal complexes able to directly produce singlet oxygen, O₂(¹Δ_g), upon X-ray irradiation constitutes a promising route towards the optimization of the radiosensitizer's architecture. In our endeavour to conceive pertinent agents for X-PDT, we designed an octahedral molybdenum cluster complex (Mo₆) with iodine inner ligands, and carboxylated apical ligands bearing ethylene oxide organic functions. The sodium salt of this complex is highly soluble in aqueous media and displays red luminescence which is efficiently quenched by oxygen to produce O₂(¹Δ_g) in a high quantum yield. Furthermore, due to its high radiodensity, the complex exhibits radioluminescence in aqueous media, with the same spectral features as for photoluminescence, indicating the production of O₂(¹Δ_g) upon X-ray irradiation. The uptake of the complex by Hep-2 and MRC-5 cells is negligible during the first hours of incubation, then considerably increases in connection with the hydrolysis of the apical ligands. The complex exhibits low toxicity in vitro and induces a radiotoxic effect, noticeable against cancerous Hep-2 cells but negligible against normal MRC-5 cells, at X-ray doses that do not affect cell viability otherwise. The first evaluation of in vivo toxicity of an Mo₆ complex on a mouse model evidences a moderate and delayed toxic effect on kidneys, with an intravenous LD₅₀ value of 390 ± 30 mg kg^-1, possibly connected with hydrolysis-induced aggregation of the complex. Overall, this complex displays attractive features as a singlet oxygen radiosensitizer for X-PDT, highlighting the potential of transition metal cluster complexes towards this modality.

The role of gold nanoparticles' aspect ratio in plasmon-enhanced luminescence and the singlet oxygen generation rate of Mo6 clusters

Here we present a study on the effect of the aspect ratio (AR) of gold nanoparticles on the emission intensity and singlet oxygen production rate of hexamolybdenum cluster-doped silica particles. It was shown that these parameters can be enhanced gradually up to 6.7- and 13-fold with the AR.

Hofmeister effect in the Keggin-type polyoxotungstate series

The chaotropic character of Keggin-type polyoxotungstate anions was evaluated with respect to their ability to bind to γ-cyclodextrin (γ-CD) by varying the global charge density of the nanometer-sized polyanion.

Heterogeneous photoactive antimicrobial coatings based on a fluoroplastic doped with an octahedral molybdenum cluster compound

Despite the wide variety of strategies developed to combat pathogenic microorganisms, the infectious diseases they cause remain a worldwide health issue. Hence, the search for new disinfectants, which prevent infection spread, constitutes an extremely urgent task. One of the most promising methods is the use of photoactive compounds - photosensitizers, capable of generating reactive oxygen species, in particular, singlet oxygen (O2(1Δg)), which causes rapid and effective death of microorganisms of all types. In this work, we propose the utilization of the powdered cluster complex (Bu4N)2[{Mo6I8}(OTs)6] as a photoactive additive to commercially available fluoroplastic lacquer F-32L to create heterogeneous self-sterilizing coatings. We show that soaking of the prepared films in water for 60 days did not lead to a decrease in their photosensitization properties indicating their excellent stability. Moreover, the use of the cluster complex in the solid state allowed significant expansion of the operating wavelength range, which covers the UV region and a large part of the visible region (250-650 nm). The films displayed high photoantimicrobial activity against five common pathogens (bacteria and fungi) under white-light irradiation. Overall, the properties demonstrated make these materials promising for practical use in everyday outdoor and indoor disinfection since they are active under both sunlight and artificial lighting.

Single-domain antibody C7b for address delivery of nanoparticles to HER2-positive cancers

Monoclonal antibodies (mAb) demonstrate great potential as immunotherapy agents for the treatment of diseases such as cancer as well as tagging for the targeted delivery of multicomponent therapeutic or diagnostic systems. Nevertheless, the large physical size, poor stability of mAbs and abnormal allergic reactions still remain the main issues affecting their generalised use. Single-domain antibodies (sdAb) are seen as the next generation of antibody derived therapeutics and diagnostics. This work presents the optimised production method for HER2-specific sdAb C7b, which led to an ∼11-fold increase in protein yield. In addition, the in vitro and in vivo efficiencies of the targeted delivery of a model nanoparticle cargo (50 nm silica particles doped with Mo6 phosphorescent clusters) conjugated to C7b against those conjugated to HER2-specific trastuzumab is benchmarked. Specifically, this paper demonstrates the significantly higher rate of accumulation in and excretion from xenograft cancer tissue of nanoparticles with C7b, which is of particular importance for diagnostics, i.e. delivery of imaging agents.

Water-Soluble Rhenium Clusters with Triazoles: The Effect of Chemical Structure on Cellular Internalization and the DNA Binding of the Complexes

Here we explore the effect of the nature of organic ligands in rhenium cluster complexes [Re₆ Q₈ L₆ ]^4- (where Q=S or Se, and L=benzotriazole, 1,2,3-triazole or 1,2,4-triazole) on the biological properties of the complexes, in particular on the cellular toxicity, cellular internalization and localization. Specifically, the study describes the synthesis and detailed characterization of the structure, luminescence and electrochemical properties of the four new Re₆ clusters with 1,2,3- and 1,2,4-triazoles. Biological assays of these complexes are also discussed in addition to those with benzotriazole using cervical cancer (HeLa) and immortalized human fibroblasts (CRL-4025) as model cell lines. Our study demonstrates that the presence of hydrophobic and π-bonding rich units such as the benzene ring in benzotriazole significantly enhances cellular internalization of rhenium clusters. These ligands facilitate binding of the clusters to DNA, which results in increased cytotoxicity of the complexes.

Synthesis and cytotoxicity of hybrids of 1,3,4- or 1,2,5-oxadiazoles tethered from ursane and lupane core with 1,2,3-triazole

Ursane and lupane type (1-((5-aryl-1,3,4-oxadiazol-2-yl)methyl)-1H-1,2,3-triazol-4-yl)methyl and (1-((4-methyl-2-oxido-1,2,5-oxadiazol-3-yl)methyl)-1H-1,2,3-triazol-4-yl)methyl hybrids were prepared by 1,3-cycloaddition reactions of azole-derived azides with alkyne esters connected to positions C-3 and C-28 of triterpene core and tested for cytotoxicity. Hybrid compounds of 1,3,4-oxadiazoles attached at positions 3- and 28- of triterpenoid frame via triazole spacer and combinations of 1,2,5-oxadiazole or 1,3,4-oxadiazole, tethered with succinate linker and 1,2,3-triazole at the position 3- of the ursane backbone, were inactive in relation to all the cancer cells tested. Eventually, combinations of furoxan fragment and 1,2,3-triazole linked to C-28 position of triterpene backbone demonstrated marked cytotoxic activity towards MCF-7 and HepG2 cells. The most active ester of ursolic acid with (1-((4-methyl-2-oxido-1,2,5-oxadiazol-3-yl)methyl)-1H-1,2,3-triazol-4-yl)methyl substituent and 3-O-acetyl group was superior in activity and selectivity over doxorubicin and ursolic acid on MCF-7 cells. The length of the carbon spacer group may be of crucial importance for cytotoxicity. The introduction of the additional ester linker between the C-28 of triterpenoid and triazole or changing triazole spacer between furoxan moiety and triterpenoid core resulted in activity decrease against all the tested cells. In accordance with molecular modeling results, the activity of new derivatives may be explained in terms of the interaction of the new hybrid molecules and Mdm2 binding sites.

Cyclodextrin-Assisted Hierarchical Aggregation of Dawson-type Polyoxometalate in the Presence of {Re6Se8} Based Clusters

The association of metallic clusters (CLUS) and polyoxometalates (POM) into hierarchical architectures is achieved using γ-cyclodextrin (γ-CD) as a supramolecular connector. The new self-assembled systems, so-called CLUSPOM, are formed from Dawson-type polyoxometalate [P₂W₁₈O₆₂]^6- and electron-rich rhenium clusters. It is worth noting that a cluster-based cation [{Re₆Se₈}(H₂O)₆]²⁺ on one hand and a cluster-based anion on the other hand [{Re₆Se₈}(CN)₆]^4- can be associated with the anionic POM. In the absence of the supramolecular connector, a "CLUSPOM salt" was obtained from aqueous solution of the cationic cluster and the polyoxometalate. In this solid, the arrangement between the polymetallic building blocks is mainly governed by long-range Coulombic interactions. In the presence of γ-CD, the Dawson anion and the cationic cluster are assembled differently, forming a hierarchical supramolecular solid, K₂[{Re₆Se₈}(H₂O)₆]₂{[P₂W₁₈O₆₂]@2γ-CD}·42H₂O, where the organic macrocycle acts as a ditopic linker between the inorganic building blocks. In such an edifice, the short-range molecular recognition dominates the long-range Coulombic interactions leading to a specific three-dimensional organization. Interestingly, the assembling of anionic POM [P₂W₁₈O₆₂]^6- with the anionic rhenium cluster [{Re₆Se₈}(CN)₆]^4- is also achieved with γ-CD despite the repulsive forces between the nanosized anions. The resulting solid, K₁₀{[{Re₆Se₈}(CN)₆]@2γ-CD}[P₂W₁₈O₆₂]·33H₂O, is built from 1:2 inclusion complexes {[{Re₆Se₈}(CN)₆]@2γ-CD}^4- linked by a POM unit interacting with the exterior wall of the organic macrocycle. Multinuclear NMR and small-angle X-ray scattering investigations support supramolecular preorganization in aqueous solution prior to crystallization.

From Specific γ-CD/[Nb6 Cl12 (H2 O)6 ]2+ Recognition to Biological Activity Tuning

Specific molecular recognition of γ-cyclodextrin (γ-CD) by the cationic hexanuclear niobium [Nb₆ Cl₁₂ (H₂ O)₆ ]²⁺ cluster complex in aqueous solutions results in a 1:1 supramolecular assembly {[Nb₆ Cl₁₂ (H₂ O)₆ ]@γ-CD}²⁺ . NMR spectroscopy, isothermal titration calorimetry (ITC), and ESI-MS were used to study the interaction between the inorganic cluster and the organic macrocycle. Such molecular association affects the biological activity of [Nb₆ Cl₁₂ (H₂ O)₆ ]²⁺ , decreasing its cytotoxicity despite enhanced cellular uptake. The 1:1 stoichiometry is maintained in solution over a large window of the reagents' ratio, but crystallization by slow evaporation produces a 1:2 host-guest complex [Nb₆ Cl₁₂ (H₂ O)₆ @(γ-CD)₂ ]Cl₂ ⋅20 H₂ O featuring the cluster encapsulated between two molecules of γ-CD. The 1:2 complex was characterized by XRD, elemental analysis, IR spectroscopy, and thermogravimetric analysis (TGA). Quantum chemical calculations were performed to model host-guest interaction.

Soluble Molecular Rhenium Cluster Complexes Exhibiting Multistage Terminal Ligands Reduction

Substitution of terminal halide ligands of octahedral rhenium cluster complexes [Re₆Q₈X₆]^4- in a melt of 4,4'-bipyridine (bpy) led to us obtaining four new compounds with the general formula trans-[Re₆Q₈(bpy)₄X₂] (Q = S or Se; X = Cl or Br) in high yield. In contrast to most of the known molecular rhenium cluster complexes with heteroaromatic terminal ligands, compounds 1-4 are soluble in organic solvents. This made it possible to carry out a detailed characterization of the new compounds both in solids and in solutions. In particular, it was shown that compounds 1-4 in the DMSO solution exhibit four reversible reduction processes. A comparison of the obtained data with the results of DFT calculations of the electronic structure suggests that these processes correspond to two-electron reduction of all four bpy ligands. The reduction potentials are shifted to the positive region compared with the potential of free bipyridine, and the value of the shift depends on the composition of the cluster core. The presence of four transitions also suggests that electronic exchange between terminal ligands in the cis-position is possible. The study of the luminescence of the compounds showed that emission maxima of selenide clusters almost coincide with those of sulfide ones, while luminescence spectra of the complexes with chloride terminal ligands (1 and 3) are slightly blue-shifted relative to the spectra of the complexes with bromide ligands (2 and 4).

Photodynamic properties of tungsten iodide clusters incorporated into silicone: A2[M6I8L6]@silicone

The light-induced antibacterial and antifungal properties of A₂[M₆I₈L₆] with M = Mo and W, A = organic cation, L = ligand have been studied. The photoactive compounds (TBA)₂[W₆I₈(C₇H₇SO₃)₆] and (TBA)₂[W₆I₈(COOCF₃)₆] have been incorporated into a permeable silicone matrix and were measured for their application in the decomposition of multi-resistant bioactive species (hospital germs) such as S. aureus and P. aeruginosa as well as fungi. In addition, we present a new high volume synthesis route for these types of cluster compounds departing from the soluble compound W₆I₂₂.

The light-induced antibacterial and antifungal properties of A₂[M₆I₈L₆] with M = Mo and W, A = organic cation, L = ligand have been studied.

Water-soluble Re6-clusters with aromatic phosphine ligands – from synthesis to potential biomedical applications

New hexarhenium clusters exhibit radio- and photoluminescence, have low cytotoxicity, are capable of penetrating into cells and exhibit photodynamic toxicity.

Tuning the chaotropic effect as an assembly motif through one-electron transfer in a rhenium cluster

As small change as one electron transfer within the hydrophilic rhenium cluster [{Re₆Se₈}(CN)₆]^4−/3− induces dramatic alteration in supramolecular self-assembly properties with γ-cyclodextrin as a result of chaotropic effect driven process.

Luminescent silica mesoparticles for protein transduction

Unlike silica nanoparticles, the potential of silica mesoparticles (SMPs) (i.e. particles of submicron size) for biological applications in particular the in vitro (let alone in vivo) cellular delivery of biological cargo has so far not been sufficiently studied. Here we examine the potential of luminescent (namely, octahedral molybdenum cluster doped) SMPs synthesised by a simple one-pot reaction for the labelling of cells and for protein transduction into larynx carcinoma (Hep-2) cells using GFP as a model protein. Our data demonstrates that the SMPs internalise into the cells within half an hour. This results in cells that detectably luminesce via conventional methods. In addition, the particles are non-toxic both in darkness and upon photo-irradiation. The SMPs were modified to allow their functionalisation by a protein, which then delivered the protein (GFP) efficiently into the cells. Thus, the luminescent SMPs offer a cheap and trackable alternative to existing materials for cellular internalisation of proteins, such as the HIV TAT protein and commercial protein delivery agents (e.g. Pierce™).

Polyelectrolyte-coated ultra-small nanoparticles with Tb(III)-centered luminescence as cell labels with unusual charge effect on their cell internalization

The present work reports ultra-small polyelectrolyte-coated water insoluble Tb(III) complex species with bright Tb(III)-centered luminescence resulted from efficient ligand-to-metal energy transfer as efficient labels for Hep-2 cells. The flow cytometry data revealed the enhanced cellular uptake of negatively charged nanoparticles coated by the polystyrenesulfonate (PSS)-monolayer versus the positively charged nanoparticles. The latter are obtained by layer-by-layer deposition of polyethyleneimine (PEI) onto PSS-coated ones. Confocal and TEM images of Hep-2 cells exposed by the colloids confirm favorable cell internalization of the PSS- compared to PEI-PSS-coated colloids illustrating unusual charge-effect. Dynamic light scattering data indicate significant effect of the biological background exemplified by serum bovine albumin and phosphatidylcholine-based bilayers on the exterior charge and aggregation behavior of the colloids. The obtained results reveal the PSS-coated nanoparticles based on water insoluble Tb(III) complex as promising cell labels.

Host-Guest Binding Hierarchy within Redox- and Luminescence-Responsive Supramolecular Self-Assembly Based on Chalcogenide Clusters and γ-Cyclodextrin

Water-soluble salts of anionic [Re₆ Q₈ (CN)₆ ]^4- (Q=S, Se, Te) chalcogenide octahedral rhenium clusters react with γ-cyclodextrin (γ-CD) producing a new type of inclusion compounds. Crystal structures determined through single-crystal X-ray diffraction analysis revealed supramolecular host-guest assemblies resulting from close encapsulations of the octahedral cluster within two γ-CDs. Interestingly, nature of the inner Q ligands influences strongly the host-guest conformation. The cluster [Re₆ S₈ (CN)₆ ]^4- interacts preferentially with the primary faces of the γ-CD while the bulkier clusters [Re₆ Se₈ (CN)₆ ]^4- and [Re₆ Te₈ (CN)₆ ]^4- exhibit specific interactions with the secondary faces of the cyclic host. Furthermore, analysis of the crystal packing reveals additional supramolecular interactions that lead to 2D infinite arrangements with [Re₆ S₈ (CN)₆ ]^4- or to 1D "bamboo-like" columns with [Re₆ Se₈ (CN)₆ ]^4- and [Re₆ Te₈ (CN)₆ ]^4- species. Solution studies, using multinuclear NMR methods, ESI-MS and Isothermal titration calorimetry (ITC) corroborates nicely the solid-state investigations showing that supramolecular pre-organization is retained in aqueous solution even in diluted conditions. Furthermore, ITC analysis showed that host-guest stability increases significantly ongoing from S to Te. At last, we report herein that deep inclusion alters significantly the intrinsic physical-chemical properties of the octahedral clusters, allowing redox tuning and near IR luminescence enhancement.

Silica nanoparticles with Tb(III)-centered luminescence decorated by Ag0 as efficient cellular contrast agent with anticancer effect

The present work introduces composite luminescent nanoparticles (Ag⁰-Tb³⁺-SNs), where ultra-small nanosilver (4 ± 2 nm) is deposited onto amino-modified silica nanoparticles (35±6 nm) doped by green luminescent Tb(III) complexes. Ag⁰-Tb³⁺-SNs are able to image cancer (Hep-2) cells in confocal microscopy measurements due to efficient cell internalization, which is confirmed by TEM images of the Hep-2 cells exposed by Ag⁰-Tb³⁺-SNs. Comparative analysis of the cytotoxicity of normal fibroblasts (DK-4) and cancer cells (Hep-2) incubated with various concentrations of Ag⁰-Tb³⁺-SNs revealed the concentration range where the toxic effect on the cancer cells is significant, while it is insignificant towards the nonmalignant fibroblasts cells. The obtained results reveal Ag⁰-Tb³⁺-SNs as good cellular contrast agent able to induce the cancer cells death, which makes them promising theranostic in cancer diagnostics and therapy.

A comparative study of hydrophilic phosphine hexanuclear rhenium cluster complexes' toxicity

The octahedral rhenium cluster compound Na2H8[{Re6Se8}(P(C2H4CONH2)(C2H4COO)2)6] has recently emerged as a very promising X-ray contrast agent for biomedical applications. However, the synthesis of this compound is rather challenging due to the difficulty in controlling the hydrolysis of the initial P(C2H4CN)3 ligand during the reaction process. Therefore, in this report we compare the in vitro and in vivo toxicity of Na2H8[{Re6Se8}(P(C2H4CONH2)(C2H4COO)2)6] with those of related compounds featuring the fully hydrolysed form of the phosphine ligand, namely Na2H14[{Re6Q8}(P(C2H4COO)3)6] (Q = S or Se). Our results demonstrate that the cytotoxicity and acute in vivo toxicity of the complex Na2H8[{Re6Se8}(P(C2H4CONH2)(C2H4COO)2)6] solutions were considerably lower than those of compounds with the fully hydrolysed ligand P(C2H4COOH)3. Such behavior can be explained by the higher osmolality of Na2H14[{Re6Q8}(P(C2H4COO)3)6] versus Na2H8[{Re6Se8}(P(C2H4CONH2)(C2H4COO)2)6].