Molybdic Acid Research Articles

A label-free electrochemical biosensor for microRNA detection based on catalytic hairpin assembly and in situ formation of molybdophosphate

A label-free electrochemical biosensor for sensitive detection of miRNA-155 was presented by coupling enzyme-catalyzed in situ generation of electronic mediator for signal introduction with catalytic hairpin assembly (CHA) induced target recycling amplification strategy. In this work, alkaline phosphatase (ALP) was adopted to hydrolyze inactive substrate 1-naphthyl phosphate (NPP) to produce phosphate ion (PO43−), which could further react with acidic molybdate to form abundant molybdophosphate anion (PMo12O403−) on the surface of electrode. The produced PMo12O403− could directly generate a strong and stable electrochemical signal for quantitative detection of targets. In addition, CHA induced the cyclic reuse of the target was also employed as an effective strategy for improving the sensitivity of biosensor. This electrochemical method for miRNA-155 detection had achieved a good linear relationship ranging from 10fM to 1nM with a detection limit of 1.64fM. With this assay successfully applied in tumor cell lysates, it holds great potential for early cancer diagnosis by employing miRNA as the effective biomarker.

Catalyst and Process Design for the Continuous Manufacture of Rare Sugar Alcohols by Epimerization-Hydrogenation of Aldoses.

Sugar alcohols are applied in the food, pharmaceutical, polymer, and fuel industries and are commonly obtained by reduction of the corresponding saccharides. In view of the rarity of some sugar substrates, epimerization of a readily available monosaccharide has been proposed as a solution, but an efficient catalytic system has not yet been identified. Herein, a molybdenum heteropolyacid-based catalyst is developed to transform glucose, arabinose, and xylose into less-abundant mannose, ribose, and lyxose, respectively. Adsorption of molybdic acid onto activated carbon followed by ion exchange to the cesium form limits leaching of the active phase, which greatly improves the catalyst stability over 24 h on stream. The hydrogenation of mixtures of epimers is studied over ruthenium catalysts, and it is found that the precursor to the desired polyol is advantageously converted with faster kinetics. This is explained by density functional theory on the basis of its more favorable adsorption on the metal surface and the lower energy barrier for the addition of a hydrogen atom to the primary carbon atom. Finally, different designs for a continuous process for the conversion of glucose into mannitol are studied, and it is uncovered that two reactors in series with one containing the epimerization catalyst and the other containing a mixture of the epimerization and hydrogenation catalysts increases the mannitol/sorbitol ratio to 1.5 from 1 for a single mixed-bed reactor. This opens a prospective route to the efficient valorization of renewables to added-value chemicals.

Preparation of NO-doped β-MoO3 and its methanol oxidation property

The major drawback of the industrial iron molybdate catalysts which is their deactivation problem has driven the study of alternative catalysts for formaldehyde production from methanol. In this paper, NO-doped β-MoO3 was successfully synthesized from the commercial molybdic acid powder (H2MoO4) and characterized by differential thermal analysis (DTA), X-ray Diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Results obtained from XRD and Raman spectroscopy indicated that the synthesized sample has all features of the well-known β-MoO3 except for the presence of a new small peak. The curve-fitting of XPS spectra revealed that nitrogen-containing species may be present in the form of negatively charged nitrogen oxide in the prepared sample. Due to its metastable nature, NO-doped β-MoO3 may be transformed into the thermally stable α-MoO3 at temperature higher than 400 °C as pointed out by DTA study. However, when the reaction temperature was as low as 300 °C, the catalyst was stable for partial methanol oxidation with no significant change in activity during 30 h of catalytic study. Methanol conversion and formaldehyde selectivity were maintained at about 98% and 99%, respectively.

ChemInform Abstract: Silica‐Supported Molybdic Acid: Preparation, Characterization, and Its Catalytic Application in Synthesis of Pyranocoumarins.

AbstractSilica‐supported molybdic acid appears to be a novel, recyclable and safe catalyst for the three‐component condensation of 4‐hydroxycoumarin with aldehydes and malononitrile furnishing pyranocoumarins (IV) (14 examples) in high yield.

Removal of Phosphate Using Red Mud: An Environmentally Hazardous Waste By-Product of Alumina Industry

The industrial waste, bauxite residue generated in the Bayer chemical process of alumina production, commonly known as red mud (RM) has been used as the adsorbent for selective removal of phosphate in aqueous solutions. RM collected from the storage area of alumina industry was characterized by chemical analysis and physical methods such as BET surface area, Scanning Electron Microscopy (SEM), particle size analysis, and X-ray diffraction (XRD) methods. Among the various red mud samples (0.2–200 μ) studied, the samples treated with 1 M HCl for 2 h were found better for the selective adsorption of phosphate in comparison with untreated and heat treated RM samples. The presence of phosphate in the aqueous samples collected after adsorption studies with red mud was determined by standard spectrophotometric procedure using ammonium molybdate and ascorbic acid in nitrate medium at λmax 880 nm. The studies reported significant adsorption of phosphate on acid treated red mud in comparison with adsorption of phosphate on untreated and heat treated red mud, respectively. The adsorption of phosphate on raw red mud and activated red mud was further investigated with respect to stirring time, pH of the solution, dose of adsorbent, and varying phosphate concentration. Acid treated RM is observed as an efficient and cost-effective adsorbent for selective removal of phosphate in aqueous solutions.

NaGd(MoO4)2 nanocrystals with diverse morphologies: controlled synthesis, growth mechanism, photoluminescence and thermometric properties.

Pure tetragonal phase, uniform and well-crystallized sodium gadolinium molybdate (NaGd(MoO4)2) nanocrystals with diverse morphologies, e.g. nanocylinders, nanocubes and square nanoplates have been selectively synthesized via oleic acid-mediated hydrothermal method. The phase, structure, morphology and composition of the as-synthesized products are studied. Contents of both sodium molybdate and oleic acid of the precursor solutions are found to affect the morphologies of the products significantly, and oleic acid plays a key role in the morphology-controlled synthesis of NaGd(MoO4)2 nanocrystals with diverse morphologies. Growth mechanism of NaGd(MoO4)2 nanocrystals is proposed based on time-dependent morphology evolution and X-ray diffraction analysis. Morphology-dependent down-shifting photoluminescence properties of NaGd(MoO4)2: Eu3+ nanocrystals, and upconversion photoluminescence properties of NaGd(MoO4)2: Yb3+/Er3+ and Yb3+/Tm3+ nanoplates are investigated in detail. Charge transfer band in the down-shifting excitation spectra shows a slight blue-shift, and the luminescence intensities and lifetimes of Eu3+ are decreased gradually with the morphology of the nanocrystals varying from nanocubes to thin square nanoplates. Upconversion energy transfer mechanisms of NaGd(MoO4)2: Yb3+/Er3+, Yb3+/Tm3+ nanoplates are proposed based on the energy level scheme and power dependence of upconversion emissions. Thermometric properties of NaGd(MoO4)2: Yb3+/Er3+ nanoplates are investigated, and the maximum sensitivity is determined to be 0.01333 K−1 at 285 K.

Thermal stability and photoluminescence property of hexagonal MoO3·0.55H2O microrods

ABSTRACTThe metastable phase of well-faceted, hexagonal, prism-like molybdenum oxide hydrate (MoO3·0.55H2O) was successfully synthesized by evaporating molybdic acid solution prepared through cation membrane electrolysis of Na2MoO4·2H2O aqueous solution. The obtained crystals were characterized by X-ray diffraction (XRD), thermogravimetric (TG), scanning electronic microscopy (SEM) and photoluminescence (PL) spectrophotometry. The as-prepared MoO3·0.55H2O rods were of 2–4 μm in width and 5–12 μm in length. The MoO3·0.55H2O microrods displayed photoluminescence properties at room temperature and were transformed into stable orthorhombic α-MoO3 after air annealing at 380 °C. Moreover, the influence of temperature factor on the phase transformation process, morphology and photoluminescence properties of MoO3·0.55H2O was investigated in detail.

Tribological Behaviors of Molybdic Acid–Modified Phenolic/Polyfluo Wax Composite Coating

ABSTRACTPhenolic resin (PF) and molybdic acid–modified phenolic (Mo-PF) have been synthesized and developed and combined with polyfluo wax (PFW) to fabricate PF-PFW and Mo-PF-PFW composite coatings. The effects of applied load and sliding speed on the tribological properties of the phenolic composite coating were evaluated using a block-on-ring wear tester. Compared to the PF composite coating, the Mo-PF displayed a lower friction coefficient and a higher wear life under all tested conditions. Scanning electron microscope (SEM) investigation showed that the Mo-PF composite coating had a smooth worn surface after the friction test, and a continuous and uniform transfer film was formed on the surface of the counterpart ring. The improved tribological properties of Mo-PF composite coating resulted from its enhanced thermal properties.

Nano-structured β-MgMoO4 : Synthesis, Characterization and Catalytic Efficiency in the 3- Nitrophenol Reduction

A monoclinic magnesium molybdate, MgMoO 4 , was synthesized via the thermal decomposition at 500 °C of an oxalate precursor that was prepared by grinding and heating at 160 °C a solid state mixture of magnesium nitrate, ammonium molybdate and oxalic acid. The precursor was characterized by thermal gravimetric analysis (TGA), and the final obtained powders were studied by X-ray diffraction (XRD), N 2 adsorption desorption (BET), and Transmission Electron Microscopy (TEM). The results are consistent with the formation of β-MgMoO 4 agglomerated spherical nanoparticles, with an average crystallite size of 40 nm, 36 nm and 76 nm obtained from TEM, XRD and BET, respectively. The β-MgMoO 4 nanoparticles were applied as catalysts in the reduction of 3-Nitrophenol to 3-Aminophenol and the rate constant of the reaction was subsequently determined as 3.1x 10 -2 min -1

Hybrid Fabric/Molybdic Acid-Modified Phenolic Resin Composites with Improved Antiwear Properties

ABSTRACTMolybdic acid–modified phenolic resin (Mo-PF) had been synthesized and was used to prepare fabric composites. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) indicated that the thermal properties were improved when the phenolic resin was modified by molybdic acid. The tribological properties of the fabric composites were evaluated by a pin-on-disk tribometer. Compared to the unmodified ones, the result showed that the fabric composites made by Mo-PF displayed a lower wear rate under all tested conditions. The optimal content of molybdic acid to modify the phenolic resin was obtained, as the correspondingly produced fabric composite displayed improved tribological properties. The effect of applied load, sliding speed, and environment temperature on tribological properties of the fabric composites and the related mechanisms were also discussed.

The Influence of Sodium Molybdate on the Rate of Corrosion of Aluminum in Phosphoric(V) Acid

Corrosion rates of aluminum in phosphoric (V) acid solutions were determined gravimetrically in a presence of sodium molybdate which acts as an inhibitor. Inhibition efficiencies were calculated. The most effective corrosion inhibition was observed for 0.5 M H3PO4 and 100 mM of Na2MoO4. Since insoluble corrosion products precipitated onto specimens and influenced the determined corrosion rates, an analysis of a morphology of the specimens was performed by using a scanning electron microscope. The corrosion products are composed of Mo, P, Al and O. An Mo/P atomic ratio varied between 0.8 and 1.6 depending on the concentrations of phosphoric (V) acid and sodium molybdate. For three concentrations of H3PO4, the concentration ranges of sodium molybdate, where the gravimetric method may be applied were determined.

Synthesis and X-ray diffraction data for dibromo-dioxo-(1,10-phenanthroline-N,N′)-molybdenum(VI) (C12H8N2MoBr2O2)

The dibromo-dioxo-(1,10-phenanthroline-N,N′)-molybdenum(VI) complex (C12H8N2MoBr2O2) was prepared from molybdic acid and 1,10-phenanthroline using hydrobromic acid as solvent. The molybdenum complex solid was separated by filtration and washed with ethyl ether. The X-ray powder diffraction pattern for the title compound was analyzed and found to crystallizes in monoclinic system, space group P21/c (No14) with refined unit-cell parameters a = 12.036 (1), b = 9.819 (1), c = 12.671 (2) Å, and β = 110.44° (1). The volume of the unit cell is V = 1403.2 (3) Å3.

Comparison of Urinary Total Proteins by Four Different Methods

The total proteins in human urine have been compared by sulfosalicylic acid, sulfosalicylic acid with sodium sulphate and trichloroacetic acid methods with pyrogallol red molybdate method as there are no studies found quantifying imprecision and bias components. Fresh urine of 36 patients was analyzed by four methods. Imprecision and inaccuracy were determined by repeated analysis and method comparison studies using correlation plots, Bland and Altman, and Passing and Bablok regression analyses respectively. The coefficient of variation was 5.07% for pyrogallol red molybdate; 6.84% for sulfosalicylic acid; 3.97% for sulfosalicylic acid with sodium sulphate and 5.93% for trichloroacetic acid methods. Bland and Altman analysis showed a bias of 5.8, 1.7 and -5.4 for pyrogallol red molybdate versus sulfosalicylic acid, sulfosalicylic acid with sodium sulphate and trichloroacetic acid methods respectively. Passing and Bablok regression revealed a constant bias for pyrogallol red molybdate versus all turbidimetric methods but a proportional bias only with trichloroacetic acid method. Sulfosalicylic acid with sodium sulphate method is preferred to sulfosalicylic acid and trichloroacetic acid methods.

ChemInform Abstract: Synthesis and Characterization of Novel Nanosilica Molybdic Acid and Its First Catalytic Application in the Synthesis of New and Known Pyranocoumarins.

AbstractA novel nanosilica molybdic acid composition catalyzes the one‐pot three‐component condensation of 4‐hydroxycoumarin, malonitrile and various aldehydes to form pyrano[2,3‐c]chromenes.

A novel octanuclear nickel(II)-molybdenum(VI) heterometallic cluster based on the salicylhydroxamate ligand.

Salicylhydroxamic acid (H3shi) is known for its strong coordination ability and multiple coordination modes, and can easily coordinate to metal cations to form compounds with five- or six-membered rings, as well as mono-, di- and multinuclear compounds with interesting structures having potential applications in organic chemistry, coordination chemistry, and the materials and biological sciences. A novel octanuclear nickel(II)-molybdenum(VI) heterometallic cluster based on the salicylhydroxamate ligand, namely di-μ3-acetato-di-μ2-acetato-di-μ3-hydroxido-di-μ3-oxido-tetraoxidooctakis(pyridine-κN)bis(μ5-salicylhydroxamato)hexanickel(II)dimolybdenum(VI) monohydrate, [Mo2Ni6(C7H4NO3)2(C2H3O2)4O5(OH)2(C5H5N)8]·H2O, (I), was synthesized by the reaction of sodium molybdate, nickel acetate and salicylhydroxamic acid in a dimethylformamide/pyridine/methanol solution at room temperature. The salicylhydroxamate(3-) (shi(3-)), acetate and oxide ligands adopt complicated coordination modes and link six Ni(II) and two Mo(VI) cations into the octanuclear heterometallic cluster. All of the metal cations exhibit octahedral coordination geometries and are connected to each other through the sharing of corners, edges or planes. The heterometallic clusters are further connected to form two-dimensional supramolecular layers through weak C-H...O hydrogen bonds. Studies of the magnetic properties of the title compound reveal antiferromagnetic interactions between the Ni(II) cations.

Kinetics of Catalytic Oxidation of Petroleum Sulfoxides by Hydrogen Peroxide

The kinetic mechanisms of petroleum sulfoxide oxidation by hydrogen peroxide in the presence of molybdic and tungstic acid catalysts are studied. The reaction orders with respect to the reagents in the kinetic equation are determined. A scheme of catalytic peroxide oxidation of petroleum sulfoxides that explains the obtained experimental results is presented in a generalized form. Based on the kinetic data, it is shown that peroxy acids act as sulfoxide oxidants and the intermediate reaction products are most probably complexes of sulfoxide with peroxy acids present in the reverse emulsion shell.

Mefenamic Acid Selective Membranes Sensor and Its Application to pharmaceutical Analysis

PVC membrane sensor for the selective determination of Mefenamic acid (MFA) was constructed. The sensor is based on ion association of MFA with Dodecaphospho molybdic acid (PMA) and Dodeca–Tungstophosphoric acid(PTA) as ion pairs. Nitro benzene (NB) and di-butyl phthalate (DBPH) were used as plasticizing agents in PVC matrix membranes. The specification of sensor based on PMA showed a linear response of a concentration range 1.0 × 10–2 –1.0 × 10–5 M, Nernstian slopes of 17.1-18.86 mV/ decade, detection limit of 7 × 10-5 -9.5 × 10 -7M, pH range 3 – 8 , with correlation coefficients lying between 0.9992 and 0.9976, respectively. By using the ionphore based on PTA gives a concentration range of 1.0 × 10–4 –1.0 × 10–5 M, Nernstian slope of 17.18-18.4 mV/ decade, limit of detection 8.0 × 10–6-9.3 × 10-5M,pH range 3 – 8 and correlation coefficients range between 0.9984 and 0.9891, respectively. The measurement interferences in the presence of Li+, Na+, Mg2+ Ca2+, Fe3+and Al3+ were studied using separate and match potential methods for selectivity coefficient determination. The method was applied for the determination of Mefenamic Acid in pharmaceutical preparations

Molybdenum Solubility in Aluminium Nitrate Solutions

For over 60 years, research reactors (RR or RTR for research testing reactors) have been used as neutron sources for research, radioisotope production (99Mo/99mTc), nuclear medicine, materials characterization, etc… Currently, over 240 of these reactors are in operation in 56 countries. They are simpler than power reactors and operate at lower temperature (cooled to below 100°C). The fuel assemblies are typically plates or cylinders of uranium alloy and aluminium (U-Al) coated with pure aluminium. These fuels can be processed in AREVA La Hague plant after batch dissolution in concentrated nitric acid and mixing with UOX fuel streams. The aim of this study is to accurately measure the solubility of molybdenum in nitric acid solution containing high concentrations of aluminium. The higher the molybdenum solubility is, the more flexible reprocessing operations are, especially when the spent fuels contain high amounts of molybdenum. To be most representative of the dissolution process, uranium-molybdenum alloy and molybdenum metal powder were dissolved in solutions of aluminium nitrate at the nominal dissolution temperature. The experiments showed complete dissolution of metallic elements after 30minutes stirring, even if molybdenum metal was added in excess. After an induction period, a slow precipitation of molybdic acid occurs for about 15hours. The data obtained show the molybdenum solubility decreases with increasing aluminium concentration. The solubility law follows an exponential relation around 40g/L of aluminium with a high determination coefficient. Molybdenum solubility is not impacted by the presence of gadolinium, or by an increasing concentration of uranium.

The effect of a thiol-containing organic molecule on molybdenum adsorption onto pyrite

The effect of a small thiol-containing organic molecule on the adsorption of Mo to pyrite was investigated through the use of equilibration experiments with molybdate (MoO42−), tetrathiomolybdate (MoS42−), and 2-mercaptopropionic acid (2MPA). MoO42−, MoS42−, and 2MPA individually adsorb to pyrite through the formation of specific interactions with the mineral surface. In select combination experiments, 2MPA effectively out-competes MoO42− for pyrite surface sites, which is indicative of the relatively weaker MoO42−-pyrite interactions. Results suggest that the presence of 2MPA on the pyrite surface would inhibit MoO42− access to catalytic mineral surface sites for the transformation of MoO42− to MoS42−. In contrast, thiols are not expected to be an obstacle to Mo uptake once the “switch point”, or the critical H2S concentration required for the formation of MoS42−, has been surpassed. This is due to the stronger adsorption of MoS42− to the pyrite surface. EXAFS results support weak specific interactions with little change to the MoO42− environment upon adsorption to pyrite. In contrast, larger changes to the Mo–S internuclear distances during MoS42− adsorption to pyrite support a more substantial structural change upon adsorption. MoS42− is able to bind to both the pyrite surface and a thiol-containing organic molecule to form a ternary structure on the pyrite surface, and may provide for a molecular-level connection between Mo and thiol-containing organic molecules. Mo(VI) is reduced to Mo(IV) during MoS42− adsorption to pyrite as a result of ligand-induced reduction, thereby confirming that the thiolated form of Mo is necessary for Mo reduction.

Rapid microwave-assisted hydrothermal synthesis of one-dimensional MoO3 nanobelts

MoO3 nanobelts with good crystallinity were synthesized from molybdic acid, hydrogen peroxide and nitric acid through a microwave-assisted hydrothermal process. The synthesis method was simple, rapid, low-cost, safe, and also suitable for large-scale fabrication. The morphology, structure and chemical state of the product were characterized by SEM, TEM, XRD, XPS and FT-IR, respectively. Furthermore, a possible growth mechanism of the nanobelts was presented based on the experimental observations.