Lacunary Polyoxotungstate Research Articles

Selective Hydrolysis of Ovalbumin by Zr-Based Lacunary Polyoxotungstate in Surfactant Solutions.

This study aims to design an artificial metalloprotease based on a Zr-containing polyoxometalate Na8[Zr(W5O18)2] [Zr(W5)2] for the hydrolysis of ovalbumin (OVA) in the presence of different surfactants, which can be used in many areas of the biological and medical sciences, particularly for targeted proteolytic drug design. For this reason, parameters, including the free energy of binding, the chemical nature of amino acid residues, secondary structures, and electrostatic potentials, of Zr(W5)2-OVA and Zr(W5)2-OVA-surfactant were analyzed by molecular docking simulations. The investigations showed that the presence of surfactants decreases the binding affinity of Zr(W5)2 for OVA amino acids, and hydrogen bonds and van der Waals interactions are formed between Zr(W5)2 and OVA amino acids. Additionally, GROMACS further illustrated the significance of SDS and CTAB surfactants in influencing the conformational changes of the OVA that lead to selective protein hydrolysis. In agreement with molecular dynamics simulation results, the experimental analysis showed more protein hydrolysis for the Zr(W5)2-OVA-surfactant systems. For instance, circular dichroism spectroscopy indicated that Zr(W5)2-OVA-CTAB and Zr(W5)2-OVA-TX-100 were more hydrolytically efficient due to the increased level of β-structures rather than α-chains, which showed that surfactants can facilitate the accessibility of Zr(W5)2 to the cleavage sites by inducing partial unfolding of the OVA structure.

Porphyrin-Polyoxotungstate Molecular Hybrid as a Highly Efficient, Durable, Visible-Light-Responsive Photocatalyst for Aerobic Oxidation Reactions.

Organic-polyoxometalate (POM) hybrids have recently attracted considerable interest because of their distinctive properties and wide-ranging applications. For the construction of organic-POM hybrids, porphyrins are promising building units owing to their optical properties and reactivity, including strong visible-light absorption and subsequent singlet-oxygen (1O2*) generation. However, the practical utilization of porphyrins as photocatalysts and photosensitizers is often hindered by their own degradation by 1O2*. Therefore, there is a substantial demand for the development of porphyrin-derived photocatalysts with both high efficiency and durability. Herein, we present a porphyrin-polyoxotungstate molecular hybrid featuring a face-to-face stacked porphyrin dimer (I) fastened by four lacunary polyoxotungstates. Hybrid I exhibited remarkable efficiency and durability in photocatalytic aerobic oxidation reactions, and the selective oxidation of various dienes, alkenes, sulfides, and amines proceeded using just 0.003 mol % of the catalyst. Mechanistic investigations suggested that the high activity of I stems from the efficient generation of 1O2*, resulting from the heavy-atom effect of POMs. Furthermore, despite its high efficiency in 1O2* generation compared to free porphyrins, I exhibited superior durability against 1O2*-induced degradation under photoirradiation.

Computation of 31P NMR chemical shifts in Keggin-based lacunary polyoxotungstates.

Density Functional Theory (DFT) calculations were employed to systematically study the accuracy of various exchange-correlation functionals in reproducing experimental 31P NMR chemical shifts, δExp(31P) for Keggin, [PW12O40]3- and corresponding lacunary clusters: [PW11O39]7-, [A-PW9O34]9-, and [B-PW9O34]9-. Initially, computed chemical shifts, δCalc(31P) were obtained with without neutralising their charge in which associated error, δError(31P), decreased as a function of Hartree-Fock (HF) exchange, attributed to constriction of the P-O tetrahedron. By comparison, δCalc(31P) performed with explicitly located counterions to render the system charge neutral, reduced discrepancies, δError(31P) by 1-2 ppm. However, uncertainties in δCalc(31P) remain, particularly for [B-PW9O34]9- anions attributed to direct electrostatic interactions between the counterions and the central tetrahedron. Optimal results were achieved using the PBE/TZP//PBE0/TZP method, achieving a mean absolute error (MAE) and a mean squared error (MSE) of 4.03 ppm. Our results emphasize that understanding the nature of the electrolyte and solvent environment is essential to obtaining reasonable agreement between theoretical and experimental results.

Synergistic effect of lacunary polyoxotungstates and carbon nanotubes for extraction of organophosphorus pesticides

In this work, for the first time, a nanocomposite composed of carbon nanotubes and lacunary polyoxotungstates (LPOT/CNT) was synthesized. The nanocomposites were used as a sorbent for the dispersive micro solid-phase extraction (D-µSPE) of five organophosphorus pesticides (OPPs) (i.e. fenthion, diazinon, fenitrothion, profenofos, and phosalone) from water and fruit juice samples. The extracted OPPs were quantified via gas chromatography-flame ionization detector (GC–FID). The main factors affecting the D-µSPE of the OPPs, such as the desorption conditions, amount of sorbent, and extraction time, were investigated, in detail. The LPOT/CNT nanocomposite shows a synergistic effect and its extraction efficiency is higher than intact CNTs and LPOTs. Under the optimized conditions, the D-µSPE-GC-FID method showed linearity from 0.02 to 200 ng mL−1, limits of detection in the range of 0.007–0.02 ng mL−1. The precision expressed as relative standard deviations (RSD%) ranged from 3.3 to 4.7%. The D-µSPE-GC-FID based on LPOT/CNT sorbent was used for the extraction of OPPs in fruit juices (apple juice and peach juice) and real water samples (wastewater and river water) and with relative recovery values of 94.2–99.6%.

A new 2-D layer-like organic-inorganic hybrid tungstobismuthate constructed from [Bi2W20O70]14− units and dimeric [Cu2(dien)2]24+ complex cations

The reaction of the lacunary polyoxotungstate [B-α-BiW9O33]9− with Cu(Ac)2·H2O in the presence of diethylenetriamine under hydrothermal conditions generating a new 2-D layer-like organic-inorganic hybrid tungstobismuthate [Cu(dien)(H2O)]2[Cu2(dien)2]2H2[Bi2W20O70]·15H2O (1) (dien = diethylenetriamine). 1 has been carefully characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis (TGA), X-ray single-crystal diffraction. 1 crystallizes in the orthorhombic Pbca space group with a = 21.077(2) Å, b = 21.788(2) Å, c = 22.821(2) Å, V = 10480.1(17) Å3, Z = 4, GOOF = 1.043, R1 = 0.0454, wR2 = 0.0710. Structural analyses show that 1 exhibits an organic-inorganic hybrid 2-D layer-like architecture constructed by [Bi2W20O70]14− polyanions by means of the [Cu2(dien)2]4+ bridges. Notably, the dien ligand presents two kinds of coordination modes in 1, which has been rarely observed in previously reported polyoxometalates. The magnetic study of 1 demonstrates the existence of ferromagnetic coupling interactions between Cu2+ ions in dimeric [Cu2(dien)2]4+ groups.

High-Nuclearity Heterometallic tert-Butylethynide Clusters Assembled with tert-Butylphosphonate.

tert-Butylphosphonic acid and lanthanide precursors were employed to construct two high-nuclearity hybrid silver(I)-ytterbium(III) phosphonate clusters: compound 1 consists of a Ag16 ethynide cluster fused with a trinuclear hydroxoytterbium phosphonate cluster, whereas compound 2 is composed of two Ag16 ethynide clusters bridged by a hexanuclear oxo/hydroxoytterbium phosphonate cluster. Using transition-metal-substituted lacunary polyoxotungstates in place of the lanthanide reactant, new phosphonate-functionalized silver(I)-copper(II) ethynide clusters [Ag34 Cu6 (3) and Ag37 Cu6 (4)] and silver(I) ethynide clusters [Ag51 (5) and Ag72 (6)] were obtained. The structures of complexes 3-6 feature core-shell arrangements, in which silver(I)-copper(II) or silver(I) ethynide cluster shells stabilized by peripheral phosphonate ligands enclose different kinds of tungstate core templates.

Construction of polyoxometalates from dynamic lacunary polyoxotungstate building blocks and lanthanide linkers.

A series of polynuclear metal-oxo clusters have been constructed from the dynamic polyoxometalate (POM) building block {B-α-Sb(III)W9O33} and lanthanide (Ln) linkers via a stepwise synthetic strategy with the molecular formulas of [Ln2(H2O)4{WO2(pic)}2(SbW8O30)2](10-) (Na4Li6[La-1]·28H2O, Na3Li7[Pr-2]·30H2O) and [{Ln(H2O)}{Ln(pic)}(Sb3O4)(SbW8O31)(SbW10O35)]2(24-) (K2Na6Li16[Tb-3]·63H2O, Na9Li15[Dy-4]·61H2O, Na7Li17[Ho-5]·53H2O) (Hpic = picolinic acid). The five compounds have been characterized by FT-IR, elemental analysis, TG, powder X-ray diffraction (PXRD) and single crystal X-ray diffraction. In compounds 1-5, various POM moieties, such as {B-β-SbW8O30}, {B-α-SbW8O31} and {B-α-SbW10O35}, were formed through a series of disassembling and re-assembling processes of the dynamic {B-α-SbW9O33} precursor with specific pH, reaction temperature and time. Furthermore, the use of oxytropic Ln(3+) ions as linkers, together with auxiliary organic pic ligands and/or inorganic Sb(3+) ions, led to diverse connection modes between the POM building blocks and Ln linkers and the assembly of new polynuclear metal-oxo clusters. The polyoxoanions of La-1 and Pr-2 possess the same structural feature, which can be viewed as a sandwich-type cluster composed of two {B-β-SbW8O30} units connected by two {WO2(pic)} fragments and two hydrated Ln ions. These sandwich-type polyoxoanions are further linked by the hydrated Ln ions to form a 1-D helical chain. The polyoxoanions of Tb-3, Dy-4 and Ho-5 display the same structural features, although they contain different counter-cations and lattice water molecules. In the polyoxoanions of 3-5, one {B-α-SbW8O31} POM moiety and one {B-α-SbW10O35} POM unit are connected by one {Sb3O4} fragment and one {Ln(pic)} linker, forming an asymmetric sandwich-type metal-oxo cluster. Two of these sandwich-type clusters are further fused together by extra two hydrated Ln ions, leading to an isolated polynuclear metal-oxo cluster with a size of 16.4 × 28.5 Å. The photoluminescence properties of Tb-3 and Dy-4 were investigated. Both compounds exhibit characteristic Tb(3+) and Dy(3+) luminescence. The relationship between the luminescence properties and the crystal structure of the polyoxoanion was discussed.

Synthesis of Keggin-type lacunary 11-tungstophosphates encapsulated into mesoporous silica pillared in clay interlayer galleries and their catalytic performance in oxidative desulfurization

Keggin-type lacunary polyoxotungstates [PW11O39(H2O)]7− (PW11) and metal-modified [PW11O39(H2O)M]5− (M=Ni2+ or Co2+) were incorporated into the mesoporous silica pillared clays (MSPC) by a hydrothermal sol–gel method. The resulting materials retain the layered structure of the clay precursor and possess a mesoporous structure. The catalytic performance of the materials was tested using oxidative desulfurization of dibenzothiophene-containing model oil as a probe reaction. The results indicated that PW11-MSPC possess an excellent catalytic performance.

Solvothermal Synthesis and Structure of a New Indium-Substituted Polyoxotungstate: [(CH3)2NH2]4[In3(H2O)3(NO3)(A-α-H3PW9O34)2]·H2O

A rare In-substituted polyoxotungstate [(CH3)2NH2]4[In3(H2O)3(NO3)(A-α-H3PW9O34)2]·H2O (1) was synthesized by solvothermal method and structurally characterized by single-crystal X-ray diffraction, IR, and PXRD. Crystal data for 1: Orthorhombic, Pna2 1 , a = 30.4630(3) A, b = 17.1079(14) A, c = 21.1629(17) A, V = 11029.4(16) A3, Z = 4. Compound 1 is constructed from two trilacunary Keggin [A-α-H3PW9O34]6− polyoxoanions linked together by a triangular trinuclear [In3(H2O)3(NO3)]8+ indium cluster, resulting in a novel tri-indium-substituted sandwich-type polyoxotungstate. A rare indium-substituted polyoxotungstate has been synthesized by solvothermal assembly of lacunary polyoxotungstate precursor with p-block metal indium, which represents the first {A-α-PW9O34}-based indium-substituted polyoxotungstate.

On the mechanisms of the reaction of dodecatungstophosphate with alkyl radicals in aqueous solutions

The reduced lacunary polyoxotungstate, [PW 11O 39] 8−, reacts with the .CH 2CH(OH)CH 3 and .CH 2C(CH 3) 2OH radicals via a mechanism involving β-hydroxide elimination to yield propene and 2-methyl propene respectively, and [PW 11O 39] 7−. [PW 11O 39] 8− is also oxidized by methyl radicals in a reaction which yields methane as the major product. It is proposed that the reactions proceed via the formation of short lived transients with W–C σ bonds.

ChemInform Abstract: Highly Selective Oxidation of Organosilanes to Silanols with Hydrogen Peroxide Catalyzed by a Lacunary Polyoxotungstate.

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Highly Selective Oxidation of Organosilanes to Silanols with Hydrogen Peroxide Catalyzed by a Lacunary Polyoxotungstate

Highly Selective Oxidation of Organosilanes to Silanols with Hydrogen Peroxide Catalyzed by a Lacunary Polyoxotungstate

Highly Selective Oxidation of Organosilanes to Silanols with Hydrogen Peroxide Catalyzed by a Lacunary Polyoxotungstate

Highly Selective Oxidation of Organosilanes to Silanols with Hydrogen Peroxide Catalyzed by a Lacunary Polyoxotungstate

Synthesis and structures of dinuclear ZrIV and HfIV hydroxo complexes with the monolacunar Keggin and Dawson anions

The reactions of the tetranuclear hydroxo complexes [M4(fu2-OH)8(H20)16]8+ (M = Zr or Hf) with monolacunar Keggin-type [α-PW11O39]7- and Dawson-type [α2-P2W17O61] phosphotungstates afford the polyoxoanions [(H2O)HT(fu2-OH)(PW11O39)2]8- and [(H2O)M(fu2-OH)(P2W17O61)2]14- (M = Zr or Hf), respectively, in which the 1: 1 heterometal lacunary polyoxotungstate complexes are linked into dimers through two hydroxo bridges coordinated to the heterometal atoms. The structures of these compounds were established by single-crystal X-ray diffraction and confirmed by 31P NMR spectroscopy in solution.

Self-Assembly of Yttrium-Containing Lacunary Polyoxotungstate Macroanions in Solution with Controllable Supramolecular Structure Size by pH or Solvent Content

The self-assembly and the formation of "Blackberry" type supramolecular structures for a type of Yttrium-containing polyoxometalate (K 15Na 6(H 3O) 9[(PY 2W 10O 38) 4(W 3O 14)].9H 2O, or {P 4Y 8W 43}) macroanions is characterized by using static and dynamic light scattering techniques. {P 4Y 8W 43} macroions are found to form hollow, spherical, single-layer "blackberry" structures in water and water-acetone mixed solvents. Very interestingly, the blackberry size can be accurately controlled by either changing acetone content in water-acetone mixed solvents, or by changing solution pH in aqueous solution. The blackberry size increases with decreasing pH (lower charge density) or higher acetone content in the mixed solvent (lower dielectric constant) and the blackberry size can change in responding to the change of external conditions. This indicates that the {P 4Y 8W 43} macroanions possess the properties of both "strong electrolyte type" and "weak electrolyte type" macroions, as we outlined previously. This is due to the special chemical feature of such clusters, which can be treated as Na 2HPO 4-type electrolytes in solution. The kinetics of the blackberry formation can be controlled by temperature.

Fe2 and Fe4 Clusters Encapsulated in Vacant Polyoxotungstates: Hydrothermal Synthesis, Magnetic and Electrochemical Properties, and DFT Calculations

While the reaction of [PW(11)O(39)](7-) with first row transition-metal ions M(n+) under usual bench conditions only leads to monosubstituted {PW(11)O(39)M(H(2)O)} anions, we have shown that the use of this precursor under hydrothermal conditions allows the isolation of a family of novel polynuclear discrete magnetic polyoxometalates (POMs). The hybrid asymmetric [Fe(II)(bpy)(3)][PW(11)O(39)Fe(2) (III)(OH)(bpy)(2)]12 H(2)O (bpy=bipyridine) complex (1) contains the dinuclear {Fe(micro-O(W))(micro-OH)Fe} core in which one iron atom is coordinated to a monovacant POM, while the other is coordinated to two bipyridine ligands. Magnetic measurements indicate that the Fe(III) centers in complex 1 are weakly antiferromagnetically coupled (J=-11.2 cm(-1), H=-JS(1)S(2)) compared to other {Fe(micro-O)(micro-OH)Fe} systems. This is due to the long distances between the iron center embedded in the POM and the oxygen atom of the POM bridging the two magnetic centers, but also, as shown by DFT calculations, to the important mixing of bridging oxygen orbitals with orbitals of the POM tungsten atoms. The complexes [Hdmbpy](2)[Fe(II)(dmbpy)(3)](2)[(PW(11)O(39))(2)Fe(4) (III)O(2)(dmbpy)(4)]14 H(2)O (2) (dmbpy=5,5'-dimethyl-2,2'-bipyridine) and H(2)[Fe(II)(dmbpy)(3)](2)[(PW(11)O(39))(2)Fe(4) (III)O(2)(dmbpy)(4)]10 H(2)O (3) represent the first butterfly-like POM complexes. In these species, a tetranuclear Fe(III) complex is sandwiched between two lacunary polyoxotungstates that are pentacoordinated to two Fe(III) cations, the remaining paramagnetic centers each being coordinated to two dmbpy ligands. The best fit of the chi(M)T=f(T) curve leads to J(wb)=-59.6 cm(-1) and J(bb)=-10.2 cm(-1) (H=-J(wb)(S(1)S(2)+S(1)S(2*)+S(1*)S(2)+S(1*)S(2*))-J(bb)(S(2)S(2*))). While the J(bb) value is within the range of related exchange parameters previously reported for non-POM butterfly systems, the J(wb) constant is significantly lower. As for complex 1, this can be justified considering Fe(w)--O distances. Finally, in the absence of a coordinating ligand, the dimeric complex [N(CH(3))(4)](10)[(PW(11)O(39)Fe(III))(2)O]12 H(2)O (4) has been isolated. In this complex, the two single oxo-bridged Fe(III) centers are very strongly antiferromagnetically coupled (J=-211.7 cm(-1), H=-JS(1)S(2)). The electrochemical behavior of compound 1 both in dimethyl sulfoxide (DMSO) and in the solid state is also presented, while the electrochemical properties of complex 2, which is insoluble in common solvents, have been studied in the solid state.

Phenylimido Functionalization of α-[PW12O40]3-

A synthetic route of potentially wide scope is reported herein for the organoimido functionalization of polyoxotungstates. This report focuses on the reaction between the monovacant lacunary polyoxotungstate, alpha-((n-C4H9)4N)4H3[PW11O39], and W(NC6H5)Cl4 in anhydrous acetonitrile. Evidence from 1H, 31P, 183W, and 1H-183W HMQC NMR spectroscopy, as well as cyclic voltammetry, electronic absorption, and elemental analysis, is presented for the formation of alpha-[PW12O39(NC6H5)]3- (2) of Cs symmetry, which is structurally related to Td alpha-[PW12O40]3- (3) by formal oxide substitution. The electronic structure of 2 is significantly perturbed from 3 with significant arylimido-->tungsten charge transfer, primarily localized to the W(NC6H5) fragment with secondary charge delocalization onto the remaining W and corner-shared bridging O atoms. This is consistent with the approximately 800 ppm downfield 183W NMR shift for the phenylimido-tungsten, modest cathodic shifts in reversible redox potentials, electronic and IR spectra, and density functional theory calculations.

Hybrid Polyoxotungstates as Second-Generation POM-Based Catalysts for Microwave-Assisted H2O2 Activation

[structure: see text] Organic-inorganic hybrids synthesized from lacunary polyoxotungstates (POMs) have been screened as oxidation catalysts with H2O2 under MW irradiation. Yields up to 99% have been obtained in 25-50 min depending both on the POM structure and on the organic moiety. The reaction scope, optimized with the best performing catalyst [gamma-SiW10O36(PhPO)2]4-, includes epoxidation of terminal and internal double bonds, alcohol oxidation, and sulfoxidation, as well as oxygen transfer to electron-deficient substrates as chalcone, ketones, and sulfoxides.

Polyoxometalate catalysts: toward the development of green H2O2‐based epoxidation systems

This paper describes the development of green, efficient H(2)O(2)-based epoxidation systems with three kinds of polyoxometalates: (i) a dinuclear peroxotungstate [W(2)O(3)(O(2))(4)(H(2)O)(2)](2-) (I), (ii) a divacant lacunary polyoxotungstate [gamma-SiW(10)O(34)(H(2)O)(2)]4 (II), (iii) and a divanadium-substituted polyoxotungstate [gamma-1,2-H(2)SiV(2)W(10)O(40)](4-) (III). The highly chemo-, regio-, and diastereoselective epoxidation of various allylic alcohols with only 1 equiv H(2)O(2) in water can be efficiently catalyzed by potassium salt of I (K-I). The catalyst K-I can be recycled with the retention of the catalytic performance. Protonation of a divacant lacunary polyoxotungstate [gamma-SiW(10)O(36)](8-) gives [gamma-SiW(10)O(34)(H(2)O)(2)](4-) (II) with two aquo ligands. The tetra-n-butylammonium salt of II (TBA-II) catalyzes epoxidation of common olefins including propylene with >or=99% selectivity to epoxide and >or=99% efficiency of H(2)O(2) utilization. The bis(mu-hydroxo)bridged dioxovanadium site in [gamma-1,2-H(2)SiV(2)W(10)O(40)](4-) (III) can also efficiently catalyze epoxidation of a variety of olefins with 1 equiv H(2)O(2). Notably, the system with III shows unique stereospecificity, diastereoselectivity, and regioselectivity for the epoxidation of cis/trans olefins, 3-substituted cyclohexenes, and nonconjugated dienes, respectively, which are quite different from those reported for epoxidation systems up to now. Furthermore, the heterogenization of the mentioned polyoxometalates can be achieved by using ionic liquid-modified SiO(2) as a support without loss of catalytic performance.

Synthesis and Structure of the Pentacopper(II) Substituted Tungstosilicate [Cu5(OH)4(H2O)2 (A‐α‐SiW9O33)2]10‐.

AbstractFor Abstract see ChemInform Abstract in Full Text.