Luminescent Hydrogel Particles Prepared by Self-Assembly of β‑Cyclodextrin Polymer and Octahedral Molybdenum Cluster Complexes

A series of luminescent octahedral molybdenum cluster complexes were obtained by treating Na₂[Mo₆I₈(OMe)₆] with icosahedral <i>closo</i>-dicarbaborane C-carboxylic acids in refluxing tetrahydrofuran. The study of the photophysical properties of Na₂[Mo₆I₈(1-OOC-1,2-<i>closo</i>-C₂B₁₀H₁₁)₆] (<b>1</b>), Na₂[Mo₆I₈(1-OOC-1,7-<i>closo</i>-C₂B₁₀H₁₁)₆] (<b>2</b>), and Na₂[Mo₆I₈(1-OOC-1,12-<i>closo</i>-C₂B₁₀H₁₁)₆] (<b>3</b>) in acetonitrile revealed a red luminescence with high quantum yields up to 0.93 for <b>2</b>, an efficient quenching of the luminescence by oxygen, and high quantum yields of singlet oxygen formation of approximately 0.7. Self-assembly between compound <b>2</b> and β-cyclodextrin polymer led to monodisperse hydrogel particles with a diameter of approximately 200 nm and unchanged luminescence spectra and kinetics features over 14 days. In contrast, bare cluster complex <b>2</b> in water formed aggregates and hydrolyzed over the time as indicated by a progressive red shift of the luminescence maxima. The invariance of key photophysical parameters of the hydrogel particles coupled with a high oxygen sensitivity of the luminescence are attractive features for long-term biological experiments involving optical oxygen probing. In addition, this hydrogel is a singlet oxygen sensitizer in water with promising properties for photodynamic therapy

X‑ray Inducible Luminescence and Singlet Oxygen Sensitization by an Octahedral Molybdenum Cluster Compound: A New Class of Nanoscintillators

Newly synthesized octahedral molybdenum cluster compound (<i>n</i>-Bu₄N)₂­[Mo₆I₈(OOC-1-adamantane)₆] revealed uncharted features applicable for the development of X-ray inducible luminescent materials and sensitizers of singlet oxygen, O₂(¹Δ_g). The compound exhibits a red-NIR luminescence in the solid state and in solution (e.g., quantum yield of 0.76 in tetrahydrofuran) upon excitation by UV–vis light. The luminescence originating from the excited triplet states is quenched by molecular oxygen to produce O₂(¹Δ_g) with a high quantum yield. Irradiation of the compound by X-rays generated a radioluminescence with the same emission spectrum as that obtained by UV–vis excitation. It proves the formation of the same excited triplet states regardless of the excitation source. By virtue of the described behavior, the compound is suggested as an efficient sensitizer of O₂(¹Δ_g) upon X-ray excitation. The luminescence and radioluminescence properties were maintained upon embedding the compound in polystyrene films. In addition, polystyrene induced an enhancement of the radioluminescence intensity via energy transfer from the scintillating polymeric matrix. Sulfonated polystyrene nanofibers were used for the preparation of nanoparticles which form stable dispersions in water, while keeping intact the luminescence properties of the embedded compound over a long time period. Due to their small size and high oxygen diffusivity, these nanoparticles are suitable carriers of sensitizers of O₂(¹Δ_g). The presented results define a new class of nanoscintillators with promising properties for X-ray inducible photodynamic therapy

Antibacterial, Antiviral, and Oxygen-Sensing Nanoparticles Prepared from Electrospun Materials

A simple nanoprecipitation method was used for preparation of stable photoactive polystyrene nanoparticles (NPs, diameter 30 ± 10 nm) from sulfonated electrospun polystyrene nanofiber membranes with encapsulated 5,10,15,20-tetraphenylporphyrin (TPP) or platinum octaethylporphyrin (Pt-OEP). The NPs prepared with TPP have strong antibacterial and antiviral properties and can be applied to the photooxidation of external substrates based on photogenerated singlet oxygen. In contrast to nanofiber membranes, which have limited photooxidation ability near the surface, NPs are able to travel toward target species/structures. NPs with Pt-OEP were used for oxygen sensing in aqueous media, and they presented strong linear responses to a broad range of oxygen concentrations. The nanofiber membranes can be applied not only as a source of NPs but also as an effective filter for their removal from solution

Synthesis and Crystal and Electronic Structures of the Na₂(Sc₄Nb₂)(Nb₆O₁₂)₃ Octahedral Niobium Cluster Oxide. Structural Correlations between A<i>_n</i>BM₆L₁₂(Z) Series and Chevrel Phases

We report here the synthesis and crystal and electronic structures of the Na2(Sc4Nb2)(Nb6O12)3 niobium oxide whose structure is related to that of Ti2Nb6O12. It constitutes a new member of the larger AnBM6L12(Z) families (A = monovalent cation located in tetrahedral cavities of units, B = monovalent or trivalent cations located in octahedral cavities of units, M = rare earth, Zr, or Nb, Z = interstitial except for M = Nb). The structural relationships between the AnBM6L12(Z) series (M6Li12La6 unit-based compounds with a M6Li6Li-a6/2La-i6/2 cluster framework) and Chevrel Phases (M6Li8La6 unit-based compounds with a M6Li2Li-a6/2La-i6/2 cluster framework) are shown in terms of M6L18 and M6L14 unit packing. Despite a topology similar to that encountered in Chevrel Phases, intercalation properties are not expected in the Nb6Oi6Oi-a6/2Oa-i6/2 cluster framework-based compounds. Finally, it is shown, from theoretical LMTO calculations, that a semiconducting behavior is expected for a maximum VEC of 14 in the Nb6Oi6Oi-a6/2Oa-i6/2 cluster framework

X‑ray Inducible Luminescence and Singlet Oxygen Sensitization by an Octahedral Molybdenum Cluster Compound: A New Class of Nanoscintillators

Newly synthesized octahedral molybdenum cluster compound (<i>n</i>-Bu₄N)₂­[Mo₆I₈(OOC-1-adamantane)₆] revealed uncharted features applicable for the development of X-ray inducible luminescent materials and sensitizers of singlet oxygen, O₂(¹Δ_g). The compound exhibits a red-NIR luminescence in the solid state and in solution (e.g., quantum yield of 0.76 in tetrahydrofuran) upon excitation by UV–vis light. The luminescence originating from the excited triplet states is quenched by molecular oxygen to produce O₂(¹Δ_g) with a high quantum yield. Irradiation of the compound by X-rays generated a radioluminescence with the same emission spectrum as that obtained by UV–vis excitation. It proves the formation of the same excited triplet states regardless of the excitation source. By virtue of the described behavior, the compound is suggested as an efficient sensitizer of O₂(¹Δ_g) upon X-ray excitation. The luminescence and radioluminescence properties were maintained upon embedding the compound in polystyrene films. In addition, polystyrene induced an enhancement of the radioluminescence intensity via energy transfer from the scintillating polymeric matrix. Sulfonated polystyrene nanofibers were used for the preparation of nanoparticles which form stable dispersions in water, while keeping intact the luminescence properties of the embedded compound over a long time period. Due to their small size and high oxygen diffusivity, these nanoparticles are suitable carriers of sensitizers of O₂(¹Δ_g). The presented results define a new class of nanoscintillators with promising properties for X-ray inducible photodynamic therapy

A Cell Membrane Targeting Molybdenum-Iodine Nanocluster: Rational Ligand Design toward Enhanced Photodynamic Activity

The development of singlet oxygen photosensitizers, which target specific cellular organelles, constitutes a pertinent endeavor to optimize the efficiency of photodynamic therapy. Targeting of the cell membrane eliminates the need for endocytosis of drugs that can lead to toxicity, intracellular degradation, or drug resistance. In this context, we utilized copper-free click chemistry to prepare a singlet oxygen photosensitizing complex, made of a molybdenum-iodine nanocluster stabilized by triazolate apical ligands. In phosphate-buffered saline, the complex formed nanoaggregates with a positive surface charge due to the protonatable amine function of the apical ligands. These nanoaggregates targeted cell membranes and caused an eminent blue-light phototoxic effect against HeLa cells at nanomolar concentrations, inducing apoptotic cell death, while having no dark toxicity at physiologically relevant concentrations. The properties of this complex were compared to those of a negatively charged parent complex to highlight the dominant effect of the nature of apical ligands on biological properties of the nanocluster. These two complexes also exerted (photo)­antibacterial effects on several pathogenic strains in the form of planktonic cultures and biofilms. Overall, we demonstrated that the rational design of apical ligands toward cell membrane targeting leads to enhanced photodynamic efficiency

Polymeric Membranes Containing Iodine-Loaded UiO-66 Nanoparticles as Water-Responsive Antibacterial and Antiviral Surfaces

The fight against pathogenic bacteria and viruses represents a challenging task requiring the development of innovative materials. The design of water-responsive disinfecting surfaces constitutes a pertinent endeavor to limit the spread of infectious pathogens that strive in wet environments and are often carried by the droplets or aerosols of biological fluids. In this context, we designed a polymeric nanostructured membrane which, when in contact with water, was able to release elemental iodine, a potent antimicrobial agent. The membrane was based on poly­(vinylidene fluoride-co-hexafluoropropylene) electrospun nanofibers containing nanoparticles of an archetypal metal–organic framework (MOF), UiO-66. The gas adsorption capacity of the MOF container was preserved upon incorporation into the polymeric nanofibers, which also exerted a protective effect against the fast structural collapse of UiO-66 in phosphate-buffered saline, a model for biological fluids. The membrane loaded high amounts of iodine via gas diffusion and its release was (mostly) triggered by contact with the aqueous medium. The antibacterial activity of the membrane was tested against the Escherichia coli strain DH5α and revealed prompt and robust disinfecting properties. The membrane also efficiently inhibited the infectivity of viral model vesicular stomatitis virus glycoprotein pseudotyped HIV-1 particles in HEK-293 cells in a short time. The observed synergistic effects between the MOF container and the polymeric support material constitute attractive features for the development of MOF-based materials for biological applications

PEGylated Molybdenum–Iodine Nanocluster as a Promising Radiodynamic Agent against Prostatic Adenocarcinoma

The combination of photodynamic therapy and radiotherapy has given rise to a modality called radiodynamic therapy (RDT), based on reactive oxygen species-producing radiosensitizers. The production of singlet oxygen, O2(1Δg), by octahedral molybdenum (Mo6) clusters upon X-ray irradiation allows for simplification of the architecture of radiosensitizing systems. In this context, we prepared a radiosensitizing system using copper-free click chemistry between a Mo6 cluster bearing azido ligands and the homo-bifunctional linker bis-dPEG11-DBCO. The resulting compound formed nanoparticles, which featured production of O2(1Δg) and efficient cellular uptake, leading to remarkable photo- and radiotoxic effects against the prostatic adenocarcinoma TRAMP-C2 cell line. Spheroids of TRAMP-C2 cells were also used for evaluation of toxicity and phototoxicity. In vivo experiments on a mouse model demonstrated that subcutaneous injection of the nanoparticles is a safe administration mode at a dose of up to 0.08 g kg–1. The reported results confirm the relevancy of Mo6-based radiosensitizing nanosystems for RDT

Gas Phase Reactivity of [Mo₆X₁₄]^2– Dianions (X = Cl – I)

We investigate collision-induced dissociation (CID) of [Mo6X14]2– (X = Cl, Br, I) and the reactivity of fragment ions of these precursors with background gases. Ion mobility measurements and theoretical calculations provide structural information for some of the observed ions. Sequential losses of MoX2 units dominate the dissociation pathways of [Mo6Cl14]2–. Meanwhile, loss of X radicals is the main channel for X = Br and I. Ion mobility measurements and computational investigations indicate minor structural changes in the octahedral Mo6 unit for [Mo6Im]− (m = 6–13) fragments. We observe that mass spectra obtained using CID substantially vary among mass spectrometers: Specifically, ions with molecular formula [Mo6Xm(O2)n]− (X = Br and I) are observed as dominant species produced through reactions with O2 in several mass spectrometers, but also adduct free fragment ions were observed in other instruments, depending on the background conditions. Ion-trap fragmentation combined with theoretical investigations indicates that spontaneous losses of X radicals occur upon binding of O2 to [Mo6Im]− fragments (m ≤ 12). Theoretical investigations indicate that both oxygen atoms are bound to the vacant sites of the Mo6 units. This study opens up a new vista to generate and study a large variety of hexanuclear Mo6Xm(O2)n anions