Enhancement of photoactivity and cellular uptake of (Bu4N)2[Mo6I8(CH3COO)6] complex by loading on porous MCM-41 support. Photodynamic studies as an anticancer agent

The incorporation by ionic assembly of the hexanuclear molybdenum cluster (Bu4N)2[Mo6I8(CH3CO2)6] (1) in amino-decorated mesoporous silica nanoparticles MCM-41, has yielded the new molybdenum-based hybrid photosensitizer 1@MCM-41. The new photoactive material presents a high porosity, due to the intrinsic high specific surface area of MCM-41 nanoparticles (989 m2 g-1) which is responsible for the good dispersion of the hexamolybdenum clusters on the nanoparticles surface, as observed by STEM analysis. The hybrid photosensitizer can generate efficiently singlet oxygen, which was demonstrated by using the benchmark photooxygenation reaction of 9,10-anthracenediyl-bis(methylene)dimalonic acid (ABDA) in water. The photodynamic therapy activity has been tested using LED light as an irradiation source (λirr ~ 400-700 nm; 15.6 mW/cm2). The results show a good activity of the hybrid photosensitizer against human cervical cancer (HeLa) cells, reducing up to 70 % their viability after 20 min of irradiation, whereas low cytotoxicity is detected in the darkness. The main finding of this research is that the incorporation of molybdenum complexes at porous MCM-41 supports enhances their photoactivity and improves cellular uptake, compared to free clusters.Ministerio de Ciencia, Innovación y Universidades of Spain (grant RTI2018-101675-B-I00) is acknowledged. F.G. thanks Universitat Jaume I (grant UJI-B2021-51) for the financial support. R.M.-M. laboratory members thank the financial support from the Spanish Government (project RTI2018-100910-B-C41) and the Generalitat Valenciana (project PROMETEO 2018/024). The research was supported by the Ministry of Science and Higher Education of the Russian Federation (M.N.S.). C.T. acknowledges the Generalitat Valenciana for her postdoctoral fellowship (APOSTD/2019/121). R.G. thanks Universitat Jaume I for a postdoctoral fellowship (POSTDOC-B/2018/09). We would like to thank Prof. Iván Mora-Seró (INAM-UJI) for the singlet oxygen phosphorescence measurements. The help of Jean Colombari in the final phase of this work is also recognized. SCIC-UJI is acknowledged for the technical support

Photodynamic Inactivation of Staphylococcus aureus Biofilms Using a Hexanuclear Molybdenum Complex Embedded in Transparent polyHEMA Hydrogels

Three new photoactive polymeric materials embedding a hexanuclear molybdenum cluster (Bu4N)2[Mo6I8(CH3COO)6] (1) have been synthesized and characterized by means of Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and emission spectroscopy. The materials are obtained in the format of transparent and thin sheets, and the formulations used to synthesize them are comprised of 2-hydroxyethyl methacrylate (HEMA), as a polymerizable monomer, and ethylene glycol dimethacrylate (EGDMA) or poly(ethylene glycol)dimethacrylate (PEGDMA), as cross-linkers. All the polymeric hydrogels generate singlet oxygen (1O2) upon irradiation with visible light (400–700 nm), as demonstrated by the reactivity toward two chemical traps of this reactive species (9,10-dimethylanthracene and 1,5-dihydroxynaphthalene). Some differences have been detected between the photoactive materials, probably attributable to variations in the permeability to solvent and oxygen. Notably, one of the materials resisted up to 10 cycles of photocatalytic oxygenation reactions of 1,5-dihydroxynaphthalene. All three of the polyHEMA hydrogels doped with 1 are efficient against S. aureus biofilms when irradiated with blue light (460 nm). The material made with the composition of 90% HEMA and 10% PEGDMA (Mo6@polymer-III) is especially easy to handle, because of its flexibility, and it achieves a notable level of bacterial population reduction (3.0 log10 CFU/cm2). The embedding of 1 in cross-linked polyHEMA sheets affords a protective environment to the photosensitizer against aqueous degradation while preserving the photochemical and photobactericidal activity

Cycloaddition of alkynes to diimino Mo3S4 cubane-type clusters: a combined experimental and theoretical approach

A heterocyclic ligand 4,40-di-tert-butyl-2,20-bipyridine (dbbpy) has been coordinated to the Mo3S4 cluster unit affording the complex [Mo3S4Cl3(dbbpy)3]+ ([1]+) in a one-step ligand-exchange protocol from [Mo3S4(tu)8(H2O)]Cl4 4H2O (tu = thiourea). The new cluster was isolated as [1]PF6 and [1]Cl salts in high yields and the crystal structure of the latter determined by X-ray analysis. The synthetic procedure was extended to tungsten to afford [W3S4Cl3(dbbpy)3]+ ([2]+). Kinetic and NMR studies show that [1]+ reacts with several alkynes to form dithiolene species via concerted [3+2] cycloaddition reactions whereas [2]+ remains inert under similar conditions. The different rates for the reactions of [1]+ are rationalised by computational (DFT) calculations, which show that the more electron-withdrawing the substituents of the alkyne the faster the reaction. The inertness of [2]+ is due to the endergonicity of its reactions, which feature DGr values systematically 5–7 kcal mol 1 more positive than for those of [1]+

Kinetics Aspects of the Reversible Assembly of Copper in Heterometallic Mo3CuS4 Clusters with 4,4′-Di-tert-butyl-2,2′- bipyridine

Treatment of the triangular [Mo3S4Cl3(dbbpy)3]Cl cluster ([1]Cl) with CuCl produces a novel tetrametallic cuboidal cluster [Mo3(CuCl)S4Cl3(dbbpy)3][CuCl2] ([2][CuCl2]), whose crystal structure was determined by X-ray diffraction (dbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine). This species, which contains two distinct types of Cu(I), is the first example of a diimine-functionalized heterometallic M3M′S4 cluster. Kinetics studies on both the formation of the cubane from the parent trinuclear cluster and its dissociation after treatment with halides, supported by NMR, electrospray ionization mass spectrometry, cyclic voltammetry, and density functional theory calculations, are provided. On the one hand, the results indicate that addition of Cu(I) to [1]+ is so fast that its kinetics can be monitored only by cryo-stopped flow at −85 °C. On the other hand, the release of the CuCl unit in [2]+ is also a fast process, which is unexpectedly assisted by the CuCl2 − counteranion in a process triggered by halide (X−) anions. The whole set of results provide a detailed picture of the assembly−disassembly processes in this kind of cluster. Interconversion between trinuclear M3S4 clusters and their heterometallic M3M′S4 derivatives can be a fast process occurring readily under the conditions employed during reactivity and catalytic studies, so their occurrence is a possibility that must be taken into account in future studies

Water-Soluble Mo3S4 Clusters Bearing Hydroxypropyl Diphosphine Ligands: Synthesis, Crystal Structure, Aqueous Speciation, and Kinetics of Substitution Reactions

The [Mo3S4Cl3(dhprpe)3]+ (1+) cluster cation has been prepared by reaction between Mo3S4Cl4(PPh3)3 (solvent)2 and the watersoluble 1,2-bis(bis(hydroxypropyl)phosphino)ethane (dhprpe, L) ligand. The crystal structure of [1]2[Mo6Cl14] has been determined by X-ray diffraction methods and shows the typical incomplete cuboidal structure with a capping and three bridging sulfides. The octahedral coordination around each metal center is completed with a chlorine and two phosphorus atoms of the diphosphine ligand. Depending on the pH, the hydroxo group of the functionalized diphosphine can substitute the chloride ligands and coordinate to the cluster core to give new clusters with tridentate deprotonated dhprpe ligands of formula [Mo3S4(dhprpe-H)3]+ (2+). A detailed study based on stopped-flow, 31P{1H} NMR, and electrospray ionization mass spectrometry techniques has been carried out to understand the behavior of acid−base equilibria and the kinetics of interconversion between the 1+ and the 2+ forms. Both conversion of 1+ to 2+ and its reverse process occur in a single kinetic step, so that reactions proceed at the three metal centers with statistically controlled kinetics. The values of the rate constants under different conditions are used to discuss on the mechanisms of opening and closing of the chelate rings with coordination or dissociation of chloride

Clusters complexes de polyoxometallates (synthèse et études en solution et à l'état solide)

Ce travail de thèse décrit la synthèse et les caractérisations de nouveaux composés Polyoxo(thio)métallates. Dans ce manuscrit sont étudiés la réactivité de clusters dinucléaires de type [Re2CI8]2-, [Rh2(CH3COO)4(H2O)2] et [Mo2O2S2(H20)6]2+ avec des POMs vacants tels que BW11, PW11et P8W48. Dans ce cadre, plusieurs architectures nouvelles ont été obtenues et caractérisées par RX sur monocristaux et en solution par RMN. Dans cette partie, une attention particulière est portée au composé [P8W48(Mo4O4s4(OH)2(H20))2]36-. Dans une seconde partie du manuscrit, la réactivité du cation [Mo2O2S2(H20)6]2+ vis-à-vis de molybdate est abordée. Cette étude a permis d isoler 3 nouvelles espèces moléculaires spectaculaires de nucléarité Mo40, Mo63 et Mo132 suivant les conditions de synthèse. Les synthèses et les caractérisations de ces espèces sont présentées dans ce manuscrit et ces derniers résultats ouvrent de larges perspectives.This work describes the syntheses and the characterizations of some new Polyoxo(thio)metalates. In this manuscript are studied the reactivities of some dinuclear clusters as [Re2CI8]2-, [Rh2(CH3COO)4(H2O)2] and [Mo2O2S2(H20)6]2+ with vacant POMs like BW11, PW11et P8W48. Several new supramolecular architectures have been obtained and characterised by X-Ray diffraction in the solid state and by solution studies using Electronic spectroscopy and NMR. In this part, a particular attention was bring to the new compound [P8W48(Mo4O4s4(OH)2(H20))2]36-. The second part is devoted to the reactivity of the thiocation [Mo2O2S2(H20)6]2+ towards molybdates. This study allowed to isolate 3 new spectacular molecular architectures for which the nuclearity varies from Mo40 to Mo63 and Mo132 as a function of the synthesis conditions. The syntheses and the characterizations of these species are presented in this manuscript and these results open large interesting perspectives.VERSAILLES-BU Sciences et IUT (786462101) / SudocSudocFranceF

Nanostructured Hybrids Based on Tantalum Bromide Octahedral Clusters and Graphene Oxide for Photocatalytic Hydrogen Evolution

The generation of hydrogen (H2) using sunlight has become an essential energy alternative for decarbonization. The need for functional nanohybrid materials based on photo- and electroactive materials and accessible raw materials is high in the field of solar fuels. To reach this goal, single-step synthesis of {Ta6Bri12}@GO (GO = graphene oxide) nanohybrids was developed by immobilization of [{Ta6Bri12}Bra2(H2O)a4]·4H2O (i = inner and a = apical positions of the Ta6 octahedron) on GO nanosheets by taking the advantage of the easy ligand exchange of the apical cluster ligands with the oxygen functionalities of GO. The nanohybrids were characterized by spectroscopic, analytical, and morphological techniques. The hybrid formation enhances the yield of photocatalytic H2 from water with respect to their precursors and this is without the presence of precious metals. This enhancement is attributed to the optimal cluster loading onto the GO support and the crucial role of GO in the electron transfer from Ta6 clusters into GO sheets, thus suppressing the charge recombination. In view of the simplicity and versatility of the designed photocatalytic system, octahedral tantalum clusters are promising candidates to develop new and environmentally friendly photocatalysts for H2 evolution

A Series of Lanthanide Complexes with Keggin-Type Monolacunary Phosphotungstate: Synthesis and Structural Characterization

The coordination of rare-earth metal ions (Ln3+) to polyoxometalates (POM) is regarded as a way of modifying and controlling their properties, such as single-molecular magnetism or luminescent behavior. The half-sandwich complexes of Ln3+ with monolacunary Keggin POMs (Ln3+/POM = 1:1) are of particular interest, since the Ln3+ retains its ability to coordinate extra ligands. Thus, the knowledge of the exact structures of 1:1 Ln/POM complexes is important for the development of reliable synthetic protocols for hybrid complexes. In this work, we isolated three 1:1 Gd3+/POM complexes of the general formula Cat4Gd(PW11O39)·xH2O (Cat = K+ or Me4N+). Complex (Me4N)2K2[Gd(H2O)2PW11O39]·5H2O (1) is polymeric, revealing a layered structural motif via bridging Gd3+ and K+ ions. Complexes (Me4N)6K2[Gd(H2O)3PW11O39]2·20H2O (2) and (Me4N)7K[Gd(H2O)3PW11O39]2·12H2O (3) are classified as dimeric; the difference between them consists of the different crystal packing of the polyoxometalates, which is induced by a variation in the cationic composition. Isostructural complexes have also been characterized for praseodymium, europium, terbium and dysprosium. The coordination number of Ln3+ (8) persists in all the compounds, while the binding mode of the POM varies, giving rise to different architectures with two or three H2O co-ligands per Ln3+. However, whatever the particular structure and exact composition, the {Ln(PW11O39)} moieties are always involved in bonding with each other with the formation either of polymeric chains or dimeric units. In water, these aggregates can dissociate with the formation of [Ln(H2O)4PW11O39]4-. This behavior must be taken into account when choosing L for the design of hybrid {Ln(L)POM} complexes

Enhanced Photocatalytic Activity and Stability in Hydrogen Evolution of Mo6 Iodide Clusters Supported on Graphene Oxide

Catalytic properties of the cluster compound (TBA)2[Mo6Ii8(O2CCH3)a6] (TBA = tetrabutylammonium) and a new hybrid material (TBA)2Mo6Ii8@GO (GO = graphene oxide) in water photoreduction into molecular hydrogen were investigated. New hybrid material (TBA)2Mo6Ii8@GO was prepared by coordinative immobilization of the (TBA)2[Mo6Ii8(O2CCH3)a6] onto GO sheets and characterized by spectroscopic, analytical, and morphological techniques. Liquid and, for the first time, gas phase conditions were chosen for catalytic experiments under UV¿Vis irradiation. In liquid water, optimal H2 production yields were obtained after using (TBA)2[Mo6Ii8(O2CCH3)a6] and (TBA)2Mo6Ii8@GO) catalysts after 5 h of irradiation of liquid water. Despite these remarkable catalytic performances, ¿liquid-phase¿ catalytic systems have serious drawbacks: the cluster anion evolves to less active cluster species with partial hydrolytic decomposition, and the nanocomposite completely decays in the process. Vapor water photoreduction showed lower catalytic performance but offers more advantages in terms of cluster stability, even after longer radiation exposure times and recyclability of both catalysts. The turnover frequency (TOF) of (TBA)2Mo6Ii8@GO is three times higher than that of the microcrystalline (TBA)2[Mo6Ii8(O2CCH3)a6], in agreement with the better accessibility of catalytic cluster sites for water molecules in the gas phase. This bodes well for the possibility of creating {Mo6I8}4+-based materials as catalysts in hydrogen production technology from water vaporThis research was funded by the Severo Ochoa Program, grant number SEV-2016-0683, Ministerio de Ciencia e Innovación, grant number PGC2018-099744, Consejo Superior de Investigaciones Científicas, grant number I-Link1063, and Russian Foundation for Basic Research, grant number 18-33-20056