Preyssler Anion Research Articles

Revealing the three-dimensional murine brain microstructure by contrast-enhanced computed tomography.

To improve our understanding of the brain microstructure, high-resolution 3D imaging is used to complement classical 2D histological assessment techniques. X-ray computed tomography allows high-resolution 3D imaging, but requires methods for enhancing contrast of soft tissues. Applying contrast-enhancing staining agents (CESAs) ameliorates the X-ray attenuating properties of soft tissue constituents and is referred to as contrast-enhanced computed tomography (CECT). Despite the large number of chemical compounds that have successfully been applied as CESAs for imaging brain, they are often toxic for the researcher, destructive for the tissue and without proper characterization of affinity mechanisms. We evaluated two sets of chemically related CESAs (organic, iodinated: Hexabrix and CA4+ and inorganic polyoxometalates: 1:2 hafnium-substituted Wells-Dawson phosphotungstate and Preyssler anion), for CECT imaging of healthy murine hemispheres. We then selected the CESA (Hexabrix) that provided the highest contrast between gray and white matter and applied it to a cuprizone-induced demyelination model. Differences in the penetration rate, effect on tissue integrity and affinity for tissue constituents have been observed for the evaluated CESAs. Cuprizone-induced demyelination could be visualized and quantified after Hexabrix staining. Four new non-toxic and non-destructive CESAs to the field of brain CECT imaging were introduced. The added value of CECT was shown by successfully applying it to a cuprizone-induced demyelination model. This research will prove to be crucial for further development of CESAs for ex vivo brain CECT and 3D histopathology.

PEG-Infiltrated Polyoxometalate Frameworks with Flexible Form-Factors.

We present the synthesis of metal oxide frameworks composed of the Preyssler anion, [NaP5W30O110]14–, bridged with transition-metal cations and infiltrated with polyethylene glycol. The frameworks can be dissolved in water to form freestanding rigid or flexible films or gels. Powder X-ray diffraction shows that all form-factors maintain the short-range order of the original crystals. Raman spectroscopy reveals that, similar to hydrogels, the macroscopic mechanical properties of these composites are dependent on the water content and the extent of hydrogen-bonding within the water network. The understanding gained from these studies facilitates solution-phase processing of polyoxometalate frameworks into flexible form factors.

Macrocyclic Polyoxometalates: Selective Polyanion Binding and Ultrahigh Proton Conduction.

The rational development of an anion templation strategy for the construction of macrocycles has been historically limited to small anions, but large polyoxoanions can offer unmatched structural diversity and ample binding sites. Here we report the formation of a {Mo22 Fe8 } macrocycle by using the Preyssler anion, [NaP5 W30 O110 ]14- ({P5 W30 }), as a supramolecular template. The {Mo22 Fe8 } macrocycle displays selective anion binding behavior in solution. In the solid state, the 1 : 2 host-guest complex, {P5 W30 }2 ⊂{Mo22 Fe8 }, transports protons more effectively, through an extended hydrogen-bonding network, than a related 1 : 1 complex where the guest is completely encapsulated. The results highlight the great potential this anion templation approach has in producing macrocyclic systems for selective anion recognition and proton conduction purposes.

Macrocyclic Polyoxometalates: Selective Polyanion Binding and Ultrahigh Proton Conduction

The rational development of an anion templation strategy for the construction of macrocycles has been historically limited to small anions, but large polyoxoanions can offer unmatched structural diversity and ample binding sites. Here we report the formation of a {Mo22Fe8} macrocycle by using the Preyssler anion, [NaP5W30O110]14− ({P5W30}), as a supramolecular template. The {Mo22Fe8} macrocycle displays selective anion binding behavior in solution. In the solid state, the 1 : 2 host–guest complex, {P5W30}2⊂{Mo22Fe8}, transports protons more effectively, through an extended hydrogen-bonding network, than a related 1 : 1 complex where the guest is completely encapsulated. The results highlight the great potential this anion templation approach has in producing macrocyclic systems for selective anion recognition and proton conduction purposes.

Polyoxometalate‐Derived Ultrasmall Pt2W/WO3 Heterostructure Outperforms Platinum for Large‐Current‐Density H2 Evolution

AbstractPlatinum (Pt)‐based catalysts with high Pt utilization efficiency for efficient H2 evolution are attracting extensive attention to meet the issues of energy exhaustion and environmental pollution. Herein, a one‐step electrochemical method is demonstrated to construct ultrafine heterostructure Pt2W/WO3 on reduced graphene oxide (RGO) by injecting multielectrons into the Preyssler anion [NaP5W30O110]14− to codeposit with anodic deliquescent Pt cations. The resulting Pt2W/WO3/RGO shows much higher performance than that of commercial Pt catalysts for large‐current‐density H2 evolution, which can deliver a large current density of 500 mA cm−2 with an overpotential of only 394 mV, much lower than that of 20% Pt/C (578 mV). Comparisons with control experiments and density functional theory (DFT) calculations both suggest that the much enhanced activity can be mainly attributed to the synergistic cooperation of different components to drive fast and continuous hydrogen desorption on Pt2W/WO3/RGO, while it could not run normally for 20% Pt/C under similar conditions due to the formation of huge bubbles on the electrode surface. The effective integration of high catalytic activity and hydrogen desorption ability into a single material can yield advanced materials for large‐current‐density H2 evolution with remarkable stability.

Co2+-Linked [NaP5W30O110]14-: A Redox-Active Metal Oxide Framework with High Electron Density.

A new metal oxide framework based on the redox-active Preyssler anion linked with Co(H2O)42+ bridging units is presented. The framework can be photochemically reduced, allowing thestorage of multiple electrons under mild conditions. Titrations with molecular redox species show that this reduction is reversible and can accommodate up to 10 electrons per Preyssler cluster (corresponding to an electron density on the order of1021 cm-3) without changing the crystal structure. This addition of delocalized electrons is accompanied by a 1000-fold increase in the conductivity. These results demonstrate that the ability to add delocalized electrons to polyoxometalate clusters can be incorporated into self-assembled extended solids, enabling the development and tuning of metal oxide materials with emergent or complementary properties.

A potassium-encapsulated Preyssler-based structure modified by binuclear cyclic copper(II) clusters: photocatalytic and electrochemical properties

Through the use of a flexible ligand 1,1′-bis(3,5-dimethyl-1H-pyrazolate)methane (H2bdpm), a K-encapsulated Preyssler-based complex, [Cu4(H2bdpm)4(H2O)10(H6KP5W30O110)]·2(H2bdpm)·14H2O, has been synthesized under hydrothermal conditions. Single crystal X-ray diffraction analysis shows that the complex contains rare K-encapsulated Preyssler anions, which are linked by binuclear cyclic clusters [Cu2(H2bdpm)2]4+ to form a 1D chain. Adjacent chains are further connected by abundant intermolecular forces to construct a 2D supramolecular framework. The photocatalytic and electrochemical properties of the complex have been investigated. (1) The Preyssler-based POM-TMCs are rarely reported. (2) The K-encapsulated Preyssler anion is uncommonly observed in Preyssler-based compound. (3) Preyssler anions are linked by binuclear CuII clusters to form a 1D chain. (4) Compound 1 exhibits photocatalytic and electrochemical properties.

SYNTHESIS OF CARBON NANOTUBES VIA CATALYTIC CHEMICAL VAPOR DEPOSITION METHOD AND THEIR MODIFICATION WITH PREYSSLER ANION, [NaP5W30O110]14-

Multiwalled carbon nanotubes (MWCNTs) were synthesized by catalytic chemical vapor deposition method using Fe/Co catalyst over CaCO3 support and acetylene gas as a carbon precursor in the temperature range of 650–800°C, and were modified with Preyssler anion nanostructures via impregnation method. The existence of nanoheteropolyacid [NaP5W30O110]14- inside the MWCNTs was confirmed by infrared spectroscopy and transmission electron microscopy.

Cover Picture: Electronic Properties and Molecular Simulations of Polyoxometalates (Isr. J. Chem. 2/2011)

Polyoxometalates (POMs) are molecular metal-oxide clusters that often feature highly symmetrical structures. A classical example is the Preyssler anion [NaP5W30O180]14− pictured on the cover. This D5h-symmetry cluster is presented as a ball-and-stick structure, with the tungsten atoms, W, in turquuoise, linked together by oxygen atoms in red, and the P atoms of its five encapsulated phosphate units in plum. The framework is surrounded by a set of points defining a surface, which serves to computationally simulate the effects of the solvent and counter ions. Further details can be found in the article by C. Bo and J. M. Poblet, on page 228 of this issue.

Catalytic synthesis of warfarin acetals by using different heteropolyacid catalysts

Catalytic synthesis of warfarin acetals by using different heteropolyacid catalysts In this research, we report on the synthesis of warfarin acetals by using Preyssler's anion, [NaP5W30O110]-14 and heteropolyacids (HPAs) catalysts. This reaction was performed using methanol and ethanol at reflux temperature conditions. Under these conditions we have excellent yields and high selectivity. Preyssler heteropolyacid catalyst were easily recycled recovery and reused without the loss of its catalytic activities. The synthesis of warfarin acetals has been achieved using the catalytic amounts of green, inexpensive and eco-friendly Keggin types heteropolyacids. The products were obtained in high yields.

Acylation of aromatic compounds by acid anhydrides using Preyssler's anion [NaP5W30O110]14- and heteropolyacids as green catalysts

Acylation of aromatic compounds by acid anhydrides using Preyssler's anion [NaP5W30O110]14- and heteropolyacids as green catalysts The Preyssler, Wells-Dowson and Keggin heteropolyacids are efficient and eco-friendly solid acid catalysts for the acylation of electron-rich aromatic compounds with acid anhydrides. The performance of different forms of heteropolyacids was compared. In all the cases, the best results were obtained using the Preyssler heteropolyacid as the catalyst. In the presence of 25 mol% (with respect to H+ equivalency) Preyssler catalyst, highly para-selective acetylation of anisole occurs using two equivalents of acetic anhydride, in 15 min at room temperature. The isolated yield of the p-methoxyacetophenone product is 98%.

Inhibition of amyloid-β protein fibrillization upon interaction with polyoxometalates nanoclusters

In this paper, two representative polyoxometalates (POMs), the wheel-shaped Preyssler anion [NaP 5W 30O 110] 14− (P5W30) and the Keggin-type anion [H 2W 12O 40] 6− (H2W12) are shown to interact with Aβ1-40 and to inhibit its fibrillization. Circular Dichroism (CD) shows that addition of both POMs dramatically altered the evolution towards the final β-sheet secondary structure. Atomic force microscopy (AFM) imaging and dynamic light scattering (DLS) experiments converge to indicate very different shapes and dimensions for the complexes formed in the absence and in the presence of the POMs. Finally, isothermal titration calorimetry (ITC) showed that both POMs showed a purely exothermic (Δ H < 0) interaction process.

Synthesis and Characterization of Two Novel Organic-Inorganic Compounds Based on Tetrahexyl and Tetraheptyl Ammonium Ions and the Preyssler Anion and Their Catalytic Activities in the Synthesis of 4-Aminopyrazolo[3,4-d]- Pyrimidines

Two novel organic–inorganic compounds based on tetrahexylammonium (THA) and tetraheptylammonium (THPA) ions and the Preyssler anion, [NaP5W30O110]14-, were synthesized and formulated as (THA)7.7H6.3 [NaP5W30O110] (A) and (THPA)7.5 H6.5[N aP5W30O110] (B). The synthesized compounds were characterized by IR, UV, and TGA and used for the catalytic synthesis of 4-aminopyrazolo[3,4,-d]pyrimidine derivatives 2a-2d. Our findings showed efficient catalytic activities for A and B.

Preyssler Anion as a Green and Eco-friendly Catalyst for Photocatalytic Oxidation of Aromatic Aldehydes

Photocatalytic oxidation of aromatic aldehydes to related carboxylic acids was investigated with molecular oxygen in the presence of Preyssler anion, with formula [NaP5W30O110]14 −. It was observed that H14[NaP5W30O110] could catalyze the oxidation of aromatic aldehydes by molecular oxygen under homogeneous conditions as well as supported on silica in heterogeneous conditions. Also, for further studies, we have investigated the application of Preyssler catalyst in the presence of hydrogen peroxide as oxidizing agent. Our findings showed that this catalyst is very active in the presence of hydrogen peroxide and UV light. The effects of catalyst concentration, time and loading percentage have been studied.

A 1-D ladder-like aggregate constructed from Preyssler anion and transition metal linkers

A 1-D ladder-like aggregate, K2Na6[Na(H2O)Fe2(H2O)8(P5W30O110)] · 23.5H2O (1; K2Na6[1a] · 23.5H2O) has been obtained by conventional aqueous solution reaction. X-ray diffraction analysis reveals that 1 crystallizes in the monoclinic system, space group P 2 1 /m, a = 16.938(3) Å, b = 21.396(4) Å, c = 17.520(4) Å, β = 98.14(3)°, V = 6285(2) Å3, and Z = 2. Polyoxoanion 1a shows a 1-D ladder-like chain, built up of Preyssler anion and Fe3+ linkers, which represents the first extended structure based on Preyssler anion and transition metal linkers. The 1-D chains in 1 are further connected into a 3-D open framework by potassium and sodium cations. Compound 1 displays electrocatalytic activity towards the reduction of nitrite.

Dehydration of Oximes to Nitriles Catalyzed by a Green Heteropolyacid Catalyst: Preyssler's Anion, [NaP5W30O110]14−

AbstractA mild, simple and high yielding procedure for the direct conversion of oximes to nitriles has been developed using heteropolyacid in acetic acid. Aromatic and aliphatic aldoximes were converted to the corresponding nitriles in the presence of Preyssler type heteropolyacid, which could be reused several times without any appreciable loss of activity.

Novel catalytic synthesis of 6,7-dimethoxyisatin with the use of heteropolyacids (HPAs) as acid solid catalyst

Novel catalytic synthesis of 6,7-dimethoxyisatin with the use of heteropolyacids (HPAs) as acid solid catalyst An efficient method for the preparation of 6,7-dimethoxyisatin and its derivatives was developed with good yield by using Preyssler-type heteropolyacid (HPA) as acid catalyst under green conditions. The comparison between Keggin type heteropolyacids, H3[PW12O40], H4[SiW12O40] and H4[SiMo12O40], H3[PMo12O40] and mineral acids with Preyssler's anion shows that the latter possess better catalytical activity than the other heteropolyacids and no degradation of the structure was observed.

Acetylation of p-Aminophenol by Preyssler's anion [NaP5W30O110]14-, [NaP5 W29MoO110]14- with green condition at room temperature

Acetylation of p-Aminophenol by Preyssler's anion [NaP5W30O110]14-, [NaP5 W29MoO110]14- with green condition at room temperature Synthesis of acetaminophen at green condition and room temperature in the presence of the Preyssler type heteropolyacids has been investigated in order to contribute toward clean technology, which is the most important need of the society. All of the catalysts are recyclable and reusable.

In situ measurement of the Preyssler polyoxometalate morphology upon electrochemical reduction: A redox system with Born electrostatic ion solvation behavior

SAXS (small-angle X-ray scattering) and controlled-potential bulk electrolysis were combined to probe the radius of gyration ( R g) of the molecular polyoxometalate (POM) cluster known as the Preyssler anion, [YP 5W 30O 110] n− dissolved in an aqueous mineral acid electrolyte, as a function of its charge, n−. The experimentally-determined R g for the oxidized anion ( n = 12) and its 2-, 4- and 10-electron reduced forms following the course of exhaustive electrolyses with a reticulated vitreous carbon electrode polarized at −0.145, −0.255, and −0.555 V vs. Ag/AgCl, respectively, is independent of reduction (and charge) under the solution conditions employed here. Within the limits of resolution and precision of our in situ measurements and analyses, ±0.2 Å, we have found that the R g is 5.8–6.0 Å, which is in agreement with R gs calculated from the atomic coordinates of previously reported crystallographic structures for the solid-state salts of the fully-oxidized cluster, [Y 3+P 5W 30O 110] 12− (abbreviated [YPA] 12−). The equivalence indicates that any modification of the P-W-O structure that may arise upon reduction of the Preyssler anion is too small to affect the R g. Moreover, the identical, experimentally-determined R gs (5.9 ± 0.1 Å) for the oxidized solution anions of [La 3+PA] 12−, [Ca 2+PA] 13−, [Sr 2+PA] 13−, and [Na +PA] 14− further demonstrate that the size of metal-ion-exchanged Preyssler anions, [M n+PA] n −15, is independent of the charge, n, on M and, hence, the overall cluster charge, n−15. This provides an ideal scenario with which to test the Born model of electrostatic ion solvation, wherein the electrochemical potential difference, Δ E 1 o , between the first reduction couples of [M n+PA] n −15 anions that differ by a unit charge (for M n+ Na +, Ca 2+, Sr 2+, Y 3+, La 3+, Th 4+) was used in a derivation of the original Born equation to calculate their Born radius, r. The result, 6.0(2) Å, is equivalent to the effective radius calculated for a charged ellipsoid in a dielectric medium ( r eff = 5.9 Å), thereby providing validation of the Born model.

Stabilization of Plutonium(III) in the Preyssler Polyoxometalate

The Na(+) ion encapsulated within the Preyssler heteropolyoxoanion, [NaP5W30O110](14-), was exchanged with Pu(III) under hydrothermal conditions to obtain [Pu(III)P5W30O110](12-) (abbreviated [PuPA](12-)) with hybrid electrochemical properties resulting from the combination of the key redox behaviors of the Pu cation and the P-W-O anion. The electroanalytical chemistry of this two-center, multielectron redox system in a 1 M HCl electrolyte shows that Pu(III) is oxidized to Pu(IV) at the half-wave potential, E(1/2), of +0.960 V versus Ag/AgCl, which is 0.197 V more positive than the corresponding electrode potential for the Pu(III) aqua ion also in 1 M HCl, indicating the stabilization of the trivalent Pu cation by its encapsulation in the Preyssler polyoxometalate (POM). This effect is uncommon in actinide-POM chemistry, wherein electrode potential shifts of the opposite nature (to more negative values), leading to the stabilization of the tetravalent ions by complexation, are renowned. Moreover, in cyclic voltammetry measurements of the Pu(III) aqua ion and [PuPA](12-), the peak currents, i(p), for the one-electron Pu(III)/Pu(IV) processes show different dependencies with the scan rate, nu. The former shows proportionality with nu(1/2), indicating freely diffusing species, whereas the latter shows proportionality with nu, indicating a surface-confined one. The first of the five successive two-electron, W-centered reduction processes in [PuPA](12-) occurs at E(1/2) = -0.117 V versus Ag/AgCl, which is 1.077 V less than the E(1/2) for the Pu(III)/Pu(IV) oxidation, thereby providing an experimental, electrochemical measure of the highest occupied molecular orbital/lowest unoccupied molecular orbital energy gap, which compares well with values previously obtained by density-functional theory, complete active space-self consistent field, and post-Hartree-Fock calculations for a series of M(n+)-exchanged systems, [MPA](n-15) for 1 < or = n < or = 4 (Fernandez, J. A.; Lopez, X.; Bo, C.; de Graff, C.; Baerends, E. J.; Poblet, J. M. J. Am Chem. Soc. 2007, 129, 12244-12253). It was not possible to prepare the Np-exchanged Preyssler anion in the manner of [PuPA](12-), because of the instability of tri- and tetravalent Np to oxidation and the formation of the neptunyl(V) ion, which also could not be exchanged for Na(+).