Tuning the electrocatalytic hydrogen evolution reaction promoted by [Mo2O2S2]-based molybdenum cycles in aqueous medium

A new series of bioactive Mo(V)2O2S2-based thiosemicarbazone complexes: Solution and DFT studies, and antifungal and antioxidant activities

This paper deals with the synthesis, characterization, and studies of biological properties of a series of 5 coordination compounds based on binuclear core [Mo(V)2O2S2]2+ with thiosemicarbazones ligands bearing different substituents on the R1 position of the ligand. The complexes are first studied using MALDI-TOF mass spectrometry and NMR spectroscopy to determine their structures in solution in relation to single-crystal X-Ray diffraction data. In a second part, the antifungal and antioxidative activities are explored and the high potential of these coordination compounds compared to the uncoordinated ligands is demonstrated for these properties. Finally, DFT calculation provides important support to the solution studies by identifying the most stable isomers in each [Mo2O2S2]2+/Ligand system, while the determination of HUMO and LUMO levels is performed to explain the antioxidative properties of these systems.

Tuning the nuclearity of [Mo2O2S2]2+-based assemblies by playing with the degree of flexibility of bis-thiosemicarbazone ligands

[MoV2O₂S₂]²⁺-based thiosemicarbazone complexes appear as very promising molecules for biological applications due to the intrinsic properties of their components. This paper deals with the synthesis and characterization of six coordination complexes obtained by the reaction of [MoV2O₂S₂]²⁺ clusters with bis-thiosemicarbazone ligands that contain flexible or rigid spacers between the two thiosemicarbazone units. Interestingly, structural characterization by single-crystal X-ray diffraction, MALDI-TOF MS technique and NMR spectroscopy revealed that the nuclearity of the complex is controlled by the nature of the spacer between the thiosemicarbazone units. Binuclear complexes, namely [MoV2O₂S₂(L^1-3)], are isolated with flexible spacers while tetranuclear complexes [(MoV2O₂S₂)₂(L^4-6)₂] are formed when the bis-thiosemicarbazone ligands are built on rigid spacers.

Screening of biological properties of MoV2O2S2- and MoV2O4-based coordination complexes: Investigation of antibacterial, antifungal, antioxidative and antitumoral activities versus growing of Spirulina platensis biomass

This paper deals with the biological potential of coordination compounds based on binuclear core [Mo^V₂O₂E₂]²⁺ (E = O or S) coordinated with commercially available ligands such as oxalates (Ox^2-), L-cysteine (L-cys^2-), L-histidine (L-his^-), Iminodiacetate (IDA^2-), Nitrilotriacetate (HNTA^2- or NTA^3-) or ethylenediamine tetraacetate (EDTA^4-) by means of various in vitro assays in a screening approach. Results suggest that the obtained complexes show weak antibacterial and antifungal properties while not being cytotoxic on cancerous and mammalian cells. In contrast, [Mo₂O₂E₂(L-cys)₂]^2- complexes stand out as powerful antioxidant, whereas [Mo₂O₂E₂(EDTA)]^2- associating tetraphenylphosphonium counter-cations display strong antibiotic activity. Finally, some complexes have evidenced a positive activity towards the growing of spirulina platensis together with a modification of the proportions of biological components inside the cells. These findings reveal promising bioactivity of the bridged binuclear Mo^(+V) cores inside complexes and encourage further research for new highly active yet non-toxic molecules for biological and biomedical applications.

Water-Soluble α-Amino Acid Complexes of Molybdenum as Potential Antidotes for Cyanide Poisoning: Synthesis and Catalytic Studies of Threonine, Methionine, Serine, and Leucine Complexes

Water-soluble complexes are desirable for the aqueous detoxification of cyanide. Molybdenum complexes with α-amino acid and disulfide ligands with the formula K[(L)Mo₂O₂(μ-S)₂(S₂)] (L = leu (1), met (2), thr (3), and ser (4)) were synthesized in a reaction of [(DMF)₃MoO(μ-S)₂(S₂)] with deprotonated α-amino acids; leu, met, thr, and ser are the carboxylate anions of l-leucine, l-methionine, l-threonine, and l-serine, respectively. Potassium salts of α-amino acids (leu (1a), met (2a), thr (3a), and ser (4a)) were prepared as precursors for complexes 1-4, respectively, by employing a nonaqueous synthesis route. The ligand exchange reaction of [Mo₂O₂(μ-S)₂(DMF)₆](I)₂ with deprotonated α-amino acids afforded bis-α-amino acid complexes, [(L)₂Mo₂O₂(μ-S)₂] (6-8). A tris-α-amino acid complex, [(leu)₂Mo₂O₂(μ-S)₂(μ-leu + H)] (5; leu + H is the carboxylate anion of l-leucine with the amine protonated), formed in the reaction with leucine. 5 crystallized from methanol with a third weakly bonded leucine as a bridging bidentate carboxylate. An adduct of 8 with SCN^- coordinated, 9, crystallized and was structurally characterized. Complexes 1-4 are air stable and highly water-soluble chiral molecules. Cytotoxicity studies in the A549 cell line gave IC₅₀ values that range from 80 to 400 μM. Cyclic voltammetry traces of 1-8 show solvent-dependent irreversible electrochemical behavior. Complexes 1-4 demonstrated the ability to catalyze the reaction of thiosulfate and cyanide in vitro to exhaustively transform cyanide to thiocyanate in less than 1 h.

Enhancing Selective Adsorption in a Robust Pillared-Layer Metal-Organic Framework via Channel Methylation for the Recovery of C2-C3 from Natural Gas

Here, we reported a strategy for channel methylation to construct a robust ultramicroporous metal-organic framework (MOF) Ni(TMBDC)(DABCO)_0.5 through hydrothermal synthesis method and investigated its adsorption performance for recovering ethane (C₂) and propane (C₃) from natural gas. The as-synthesized Ni(TMBDC)(DABCO)_0.5 featured ultramicroporosity with a uniform pore size of 0.5 nm. The resulting sample showed a strong adsorption interaction with C₃H₈ and C₂H₆, and its C₃H₈ adsorption capacity at a low pressure of 1 kPa was up to 2.80 mmol/g and its C₂H₆ adsorption capacity at a low pressure of 10 kPa reached as high as 2.93 mmol/g, exhibiting strong binding affinity for ethane and propane. The enhanced adsorption can be attributed to the presence of the dense and accessible methyl and methylene groups in the channels of the sample. Grand Canonical Monte Carlo (GCMC) simulations also confirmed that the methylene groups from the DABCO pillar and the methyl groups from the TMBDC ligand play an important role in enhancing the adsorption of ethane and propane. Its ideal adsorbed solution theory (IAST)-predicted selectivity of C₂H₆/CH₄ reached unprecedentedly 29, much higher than most of the reported data for MOFs. The stability test confirmed that the crystal structure of Ni(TMBDC)(DABCO)_0.5 still remained intact after it was exposed to moist air with a relative humidity of 100% for days. The breakthrough experiment demonstrated that the CH₄/C₂H₆/C₃H₈ ternary mixture was completely separated using a fixed bed of Ni(TMBDC)(DABCO)_0.5 at ambient temperature, showing a great potential for recovering the low content of ethane and propane from natural gas.

Electrochemical properties of the [SiW10O36(M2O2E2)]6− polyoxometalate series (M = Mo(v) or W(v); E = S or O)

New insights about the electrochemical properties of S-containing polyoxometalates. Electrochemical properties of the compounds γ-[SiW₁₀O₃₆(M₂O₂E₂)]⁶⁻ (M = Mo(v) or W(v); E = O²⁻ or S²⁻) in DMF.

Chemical Diversity of Metal Sulfide Minerals and Its Implications for the Origin of Life

Prebiotic organic synthesis catalyzed by Earth-abundant metal sulfides is a key process for understanding the evolution of biochemistry from inorganic molecules, yet the catalytic functions of sulfides have remained poorly explored in the context of the origin of life. Past studies on prebiotic chemistry have mostly focused on a few types of metal sulfide catalysts, such as FeS or NiS, which form limited types of products with inferior activity and selectivity. To explore the potential of metal sulfides on catalyzing prebiotic chemical reactions, here, the chemical diversity (variations in chemical composition and phase structure) of 304 natural metal sulfide minerals in a mineralogy database was surveyed. Approaches to rationally predict the catalytic functions of metal sulfides are discussed based on advanced theories and analytical tools of electrocatalysis such as proton-coupled electron transfer, structural comparisons between enzymes and minerals, and in situ spectroscopy. To this end, we introduce a model of geoelectrochemistry driven prebiotic synthesis for chemical evolution, as it helps us to predict kinetics and selectivity of targeted prebiotic chemistry under “chemically messy conditions”. We expect that combining the data-mining of mineral databases with experimental methods, theories, and machine-learning approaches developed in the field of electrocatalysis will facilitate the prediction and verification of catalytic performance under a wide range of pH and Eh conditions, and will aid in the rational screening of mineral catalysts involved in the origin of life.

Construction of a new binding manner in carboxylic acid-functionalized phosphomolybdates

A new binding manner of C–N–Mo bonds was constructed in carboxylic acid-functionalized phosphomolybdates, and the polyanion was present as a hexamer.

A [Mo2O2S2]-based ring system incorporating tartrate as the bridging ligand: synthesis, structure and catalytic activity of Cs4[Mo2O2(μ-S)2]2(μ4-tart)2 (tart=[C4H2O6]4−)

Treatment of [Mo2S2O2(H2O)6]2+ with racemic tartaric acid (tartH4) in the presence of sodium hydroxide and cesium chloride in aqueous solution led to the isolation of a new tetra-molybdenum ring cluster Cs4[Mo2O2(μ-S)2]2(μ4-tart)2. The cyclic cluster polyanion consists of two dinuclear [Mo2O2(μ-S)2]2+ moieties and two bridging tart4− ligands. The cyclic polyoxothiomolybdate cluster, supported on the mesoporous silica SBA-15, was tested for heterogenerous catalysis in thiophene hydrodesulfurization.

Syntheses, structural diversities and characterization of a series of coordination polymers with two isomeric oxadiazol-pyridine ligands

In this work two positional-isomeric oxadiazol-pyridine ligands 3-(5-methyl-1,3,4-oxadiazol-2-yl)pyridine (L₁) and 4-(5-methyl-1,3,4-oxadiazol-2-yl)pyridine (L₂) have been designed and synthesized.

Toward the Rational Benchmarking of Homogeneous H2-Evolving Catalysts

Molecular electrocatalysts for H₂ evolution are usually studied under various conditions (solvent, proton sources) that prevent direct comparison of their performances. We provide here a rational method for such a benchmark based on (i) the recent analysis of the current-potential response for two-electron-two-step mechanisms and (ii) the derivation of catalytic Tafel plots reflecting the interdependency of turnover frequency and overpotential based on the intrinsic properties of the catalyst, independently of contingent factors such as the cell characteristics. Such a methodology is exemplified on a series of molecular catalysts among the most efficient in recent literature.