Molybdic Acid Research Articles

Developing a colorimetric assay for Fe(II)/2-oxoglutarate-dependent dioxygenase

The Fe(II)/2-oxoglutarate-dependent dioxygenases (2-OGDs) catalyze the oxidation of substrates ranging from small molecules to large biomolecules with concomitant oxidation of co-substrate (2-oxoglutarate) into succinate. In the present study, we reported a coupled colorimetric assay that can be generally applied to measure the activities of all members of 2-OGDs family. Succinyl-CoA synthetase is employed as the coupling enzyme to transform succinate produced from 2-OGDs catalysis to form succinyl-CoA with concomitant hydrolysis of ATP to form ADP and orthophosphate. Orthophosphate can be quantitated by reacting it with molybdic acid forming a blue pigment. As a proof of concept, kinetic parameters of ectoine hydroxylase obtained using this method are compared to a traditional time- and labor-consuming HPLC based method. As 2-OGDs family enzymes are important drug targets due to their impressive versatility in catalyzing numerous oxidative reactions that are still very challenging using synthetic chemistry, colorimetric method detailed in the manuscript has the potential to enable the practice of high throughput drug screening for 2-OGDs.

Characterization of santalene synthases using an inorganic pyrophosphatase coupled colorimetric assay

We developed a colorimetric assay using yeast inorganic pyrophosphatase (IPP1) as a coupling enzyme to measure the activities of terpene synthases. IPP1 hydrolyzes pyrophosphate, the byproduct of terpene synthase catalyzed reactions, into orthophosphate, which can then be quantitated by reacting with molybdic acid to form a blue color compound. As a proof of concept, this method was used to quantitatively characterize three santalene synthases, SaSSy and SspiSSy involved in sandalwood oil biosynthesis, and a phylogenetically distant SanSyn from Clausena lansium. Our study provided the kinetic parameters of all three santalene synthases and demonstrated the validity of the enzyme couple colorimetric assay by the comparison of this assay with the existing GC-MS (Gas Chromatography-Mass Spectrometry) method. [Display omitted]

Structure evolution of mononuclear tungsten and molybdenum species in the protonation process: Insight from FPMD and DFT calculations

In this work, we apply static density functional theory (DFT) calculations, as well as classical and first-principles molecular dynamics (FPMD) simulations, using the free-energy perturbation method to study the protonation ability, active site and structures of W(VI) and Mo(VI) in acidic aqueous solution. Using FPMD simulations, utilizing the pKa's calculation technique, we concluded that the octahedral WO2(OH)2(H2O)2 is the true formula for tungstic acid (H2WO4), and the hydroxyl ligands are the acidic site. This aqueous structure of H2WO4 is analogous to the previously reported structure of molybdic acid (H2MoO4). The FPMD trajectories of the tungstic acid deprotonation show that the mono-protonated monotungstate ion (HWO4−) may partially exist as a five-coordinated WO3(OH)(H2O)− species except for the four-coordinated WO3(OH)− species. This result is supported by DFT calculations, with an isoenergetic point (ΔE = 1.9 kcal·mol−1) for the WO3(OH)(H2O)− and WO3(OH)− species, when explicit solvent molecules are taken into account. In contrast, for the H2MoO4 acid, FPMD trajectories during the deprotonation process show that two H2O ligands immediately escape from the first coordinated sphere of Mo(VI) to form the four-coordinated MoO3(OH)− species. This difference indicates that structural expansion of W(VI) began in the first protonated step, while that of Mo(VI) only occurs in the second step. In addition, our calculated first and second acid constants for tungstic acid are higher than previously reported values for molybdic acid. This result suggests that WO42− is more easily protonated than the MoO42− anion in the same acidic solution, which is further confirmed by DFT calculations of hydrated oxoanions and its protonated species, based upon the hydration energy.

Inverse Opal-like Porous MoSex Films for Hydrogen Evolution Catalysis: Overpotential-Pore Size Dependence.

Transition metal dichalcogenides (TMDs) are prized as electrocatalysts for hydrogen evolution reaction (HER). Common TMD syntheses entail conditions of high temperatures and reagents that are detrimental to the environment. The electrochemical synthesis of TMDs is advocated as a viable alternative to the conventional synthetic procedures in terms of simplicity, ecological sustainability, and versatility of deposition on various surfaces at room temperature. In this work, we demonstrate the successful fabrication of electrocatalytic inverse opal porous MoSex films, where 2 ≤ x ≤ 3, via solid template-assisted electrodeposition from the simultaneous electroreduction of molybdic acid and selenium dioxide as the respective metal and chalcogen precursors in an aqueous electrolyte. The electrosynthesized porous MoSex films contain pores with diameters of 0.1, 0.3, 0.6, or 1.0 μm, depending on the size of the polystyrene bead template used. The investigation reveals that porous MoSex films with a pore size of 0.1 μm, which prevailed over the other pore sizes, are endowed with the lowest HER overpotential of 0.57 V at -30 mA cm-2 and a Tafel slope of 118 mV dec-1, alluding to the adsorption step as rate limiting. Across all pore sizes, the Volmer adsorption step limits the HER mechanism. Nevertheless, the pore size dictates the catalytic activity of the porous MoSex films apropos of HER overpotential such that the HER performance of smaller pore sizes of 0.1 and 0.3 μm surpasses those with wider pore sizes of 0.6 and 1.0 μm. The observed trends in their HER behavior may be rationalized by the tunable surface wettability as pore sizes vary. These fundamental findings offer a glimpse into the efficacy of electrodeposited porous TMDs as electrocatalysts and exemplify the feasibility of the electrosynthesis method in altering the morphological structure of the TMDs.

CFIA-Turbidimetric and Photometric Determination of Vitamin B9 (Folic acid) Using LEDs as a Source of Irradiation and Two Solar Cells as an Energy Transducer

A specific, sensitive and simple method was used for the determination of: vitamin B9 (Folic acid) in pure and pharmaceutical formulations using continuous flow injection analysis. The method is based on formation of ion pair compound between folic acid and ammonium molybdate in an aqueous medium to obtain a gray precipitate complex, using homemade; Ayah-6SX1-ST-2D solar cell CFI Analyzer. Optimum parameters was studied to increase the sensitivity for developed method. The linear range for the calibration graph was 0.01-0.6 mMol.L-1 of vitamin B9 and LOD was 131.994 ng/sample with correlation coefficient ( r ) of 0.9810, RSD% was lower than 0.1%, (n=9) for the determination of vitamin B9 at concentration (0.07and 0.5) mMol.L-1 respectively. The developed method was applied successfully for the determination of vitamin B9 in pharmaceutical tablets. A comparison was made between two methods: developed method and the classical UV spectrophotometric method at ?max=255 nm, by using the standard addition method via the use of paired t-test. It showed that there was no significant difference between the developed method and the classical method for determination vitamin B9 at 95% confidence level.

Facile Nanostructured Composite Synthesis of Selenium and Molybdenum Chalcogenides/Carbon Nanotubes for Li‐Ion Batteries

For lithium‐ion batteries (LIBs), MoS2, which has conversion reaction pathways that can accommodate lithium ions during charge, is a very special inorganic material that has a two‐dimensional planar structure similar to graphite. For reliable performance of high‐energy LIBs, Se–molybdenum chalcogenides with sulfide and selenide (Se–MC) were prepared via the incorporation of a carbon nanotube (CNT) conducting matrix to solve the crucial limitations of MoS2, which include poor electronic conductivity and severe volume changes during cycling. For the preparation of Se–MC/CNT, a facile, one‐pot synthetic method using molybdic acid, selenium dioxide, and thioacetamide, which are the precursors for molybdenum, selenide, and sulfide, respectively, and CNT was developed. A detailed investigation of the surfaces and crystal structures of the prepared samples was conducted using transmission electron microscopy and X‐ray photoelectron spectroscopy analyses. Furthermore, LIBs containing the Se–MC/CNT exhibited a significantly extended cycle life and an improved rate capability that revealed the synergetic effect of the CNTs and selenide for controlling the morphology.

Exploiting an automated microfluidic hydrodynamic sequential injection system for determination of phosphate

A microfluidic hydrodynamic sequential injection (μHSI) spectrophotometric system was designed and fabricated. The system was built by laser engraving a manifold pattern on an acrylic block and sealing with another flat acrylic plate to form a microfluidic channel platform. The platform was incorporated with small solenoid valves to obtain a portable setup for programmable control of the liquid flow into the channel according to the HSI principle. The system was demonstrated for the determination of phosphate using a molybdenum blue method. An ascorbic acid, standard or sample, and acidic molybdate solutions were sequentially aspirated to fill the channel forming a stack zone before flowing to the detector. Under the optimum condition, a linear calibration graph in the range of 0.1–6mg P L−1 was obtained. The detection limit was 0.1mgL−1. The system is compact (5.0mm thick, 80mm wide × 140mm long), durable, portable, cost-effective, and consumes little amount of chemicals (83μL each of molybdate and ascorbic acid, 133μL of the sample solution and 1.7mL of water carrier/run). It was applied for the determination of phosphate content in extracted soil samples. The percent recoveries of the analysis were obtained in the range of 91.2–107.3. The results obtained agreed well with those of the batch spectrophotometric method.

Sol–Gel Synthesis of Bismuth Molybdate Catalysts for the Selective Oxidation of Propylene to Acrolein: Influence of pH Value and Theoretical Molar Atomic Ratio

Different bismuth molybdate catalysts for the selective oxidation of propylene to acrolein were prepared by the sol–gel method, starting from bismuth nitrate, ammonium molybdate, and citric acid. The influence of pH value and theoretical molar Bi/Mo atomic ratio on the complexation and gelation is surveyed using IR spectroscopy, X‐ray diffraction, and BET. Their catalytic activities for the conversion propylene to acrolein are examined.

Synthesis, characterization, Hirshfeld surface and theoretical properties of $$(\hbox {C}_{7}\hbox {H}_{10}\hbox {N})_{4} [\hbox {H}_{2}\hbox {P}_{2}\hbox {Mo}_{5}\hbox {O}_{23}]\cdot \hbox {H}_{2}\hbox {O}$$ ( C 7 H 10 N ) 4 [ H 2 P 2 Mo 5 O 23 ] · H 2 O

The reaction of molybdic acid, phosphoric acid and copper(II) sulfate pentahydrate with m-toluidine in aqueous solution at room temperature furnished a new diphosphopentamolybdate ( $$\hbox {C}_{7}\hbox {H}_{10}\hbox {N})_{4}[\hbox {H}_{2}\hbox {P}_{2}\hbox {Mo}_{5}\hbox {O}_{23}]\cdot \hbox {H}_{2}\hbox {O}$$ (1). A single-crystal X-ray diffraction study showed that the compound crystallizes in the triclinic crystal system with space group $$P-1$$ and unit cell constants, $$a~=~12.833$$ (3) Å, $$b~=~13.9855$$ (4) Å, $$c=14.9446$$ (4) Å, $$\alpha =64.607$$ (3) $${^{\circ }}$$ , $$\beta ~=~70.578$$ (2) $${^{\circ }}$$ , $$\gamma $$ = 65.713 (3) $${^{\circ }}$$ . The sample was also analyzed by energy dispersive spectroscopy (EDS), infrared spectroscopy (IR) and UV-visible spectroscopy. Using the refined atomic structure, Hirshfeld surface analysis and Semi-empirical calculations were performed to study the intermolecular interactions and calculate theoretical properties of 1. SYNOPSIS The title compound ( $$\hbox {C}_{7}\hbox {H}_{10}\hbox {N})_{4}[\hbox {H}_{2}\hbox {P}_{2}\hbox {Mo}_{5}\hbox {O}_{23}]\cdot \hbox {H}_{2}\hbox {O}$$ was synthesized and characterized by IR and UV spectroscopy, and its structure was solved by single crystal X-ray diffraction. The presence of the Mo, P, O, C and N atoms was confirmed by EDS analysis. The Hirshfeld surface analysis was performed to elucidate non-bonding interactions and theoretical properties were calculated.

Nanosilica Molybdic Acid as a Reusable Catalyst for Chemoselective Synthesis of Novel 4-Dihydropyrano[2,3-c]pyrazoles

Nanosilica Molybdic Acid as a Reusable Catalyst for Chemoselective Synthesis of Novel 4-Dihydropyrano[2,3-c]pyrazoles

Direct liquefaction of lignin and lignin rich biomasses by heterogenic catalytic hydrogenolysis

As part of an ongoing project at Karlsruhe Institute of Technology (KIT), Germany, this work examines the liquefaction of varying feedstocks under conditions of the Bergius process of direct coal liquefaction by high pressure heterogeneous catalytic hydrogenolysis. Applying this process onto renewable resources like lignin and lignin-rich biomass has the potential to produce aromatic components for chemical industry.The performed experiments investigate the chemical conversion of different lignin types alongside samples of beech bark and beech wood fiber residues from pulp and paper industry using different heterogeneous catalysts and catalyst preparations. Reaction conditions such as catalyst concentration, temperature and concentration of sulfur were varied in order to optimize the conditions of liquefaction for the chosen setup.It will be shown that lignin and lignin-rich biomass can be liquefied under conditions of direct coal liquefaction using molybdic acid and sulfidic iron catalysts. The liquid oil product can be obtained in good yields up to 60% mass fraction of the input feedstock, consisting of alkylated phenols and alkyl benzenes while removing the majority of hetero atomic functional groups. This can be achieved while producing only a minimal amount of solid residue, reaction water and a valuable gas byproduct.

Solubility of MoO3 in acid solutions and vapor-liquid distribution of molybdic acid

This study reports the measurements of the solubility of crystalline molybdenum trioxide, MoO3, in acid (HClO4, HCl) aqueous solutions at 563, 573, 593, and 623 K, mostly at pressures close to the saturated water vapor pressure. The solubility data can be explained by the two dissolution reactions: a). MoO3(cr) + OH− = HMoO4−, with log10Ko values equal to (7.08 ± 0.20), (7.09 ± 0.20), (7.43 ± 0.20) at 563, 573, and 593 K, and b). MoO3(cr) + H2O(l) = H2MoO4(aq), with log10Ko equal to –(2.40 ± 0.20), –(2.22 ± 0.20), –(2.41 ± 0.20), –(1.95 ± 0.20) at 563, 573, 593, and 623 K, respectively. Combining these results with the literature data on the thermodynamics of H2MoO4 in the ideal gas state, we evaluated Henry's constants of this form at investigated temperatures, which turned out to be close to those of Si(OH)4, just as one would expect on the basis of chemical similarity. Reasonable estimates of the fugacity coefficients of H2MoO4 in steam allowed the calculation of the vapor-liquid distribution constant, KD=limx→0y/x, for this species, where y and x stand for the mole fractions of a solute in coexisting vapor and liquid phases, respectively. The value of the Krichevskii parameter, which governs the variation of KD in the investigated range of temperatures, is equal to –(228 ± 33) MPa for H2MoO4, being close to that of Si(OH)4, –(190 ± 10) MPa.

Rare Examples of Biomimicking Molybdenum(VI) Catalysed Peroxidative Bromination of the Organic Substrates that Coordinate to the Oxido‐Diperoxido Mo(VI) Centre

AbstractThe two novel oxido‐diperoxido molybdate(VI) complexes [MoO(O2)2{BHPPM]. PPh4 (1) [BHPPM=5‐bromo‐2‐hydroxyphenyl(phenyl)methanone] and [MoO(O2)2 {DBHPPM}]. PPh4 (2) [DBHPPM=3,5‐dibromo‐2‐hydroxyphenyl(phenyl)methanone] with 2‐hydroxyphenyl(phenyl)methanone and 2‐hydroxyphenyl(phenyl)methanoneoximato ligands have been synthesized by adding methanolic solution of the ligand to the pale yellow solution obtained by dissolving molybdic acid in hydrogen peroxide and precipitating the complexes using tetraphenylphosphonium bromide. The complexes were characterized by IR, UV‐vis, Mass, CHN, molar conductance, magnetic moment, mass and 1H NMR spectro‐ scopic methods. Molecular structure of oxido‐diperoxidomolybdate(VI) (1) and (2) were established by X‐ray crystallography. The ligand first coordinates to the molybdenum(VI) in presence of hydrogen peroxide, thereafter, molybdate(VI) catalysed peroxidative bromination of the ligand takes place during the synthesis of the oxido‐diperoxidomolybdate(VI) complexes with the above in situ generated brominated ligands.

Comparison of the Mechanical Performance between Nano Clay and Molybdic Acid Filled Banana (Empty Fruit Bunch) Fiber Reinforced Polyester Composites

The objective of present work is to prepare composites by incorporating banana empty fruit bunch(EFB) fiber extracting from agriculture biomass into a polyester matrix and the mechanical properties of the resulting composites are investigated with and without the addition of nano clay and molybdic acid. The composites are formulated up to a maximum fiber volume of about 38% and the effects of nano clay and molybdic acid on the mechanical properties of composites were investigated by varying its percentage of addition(0-2-4-6-%)

A simple method for the estimation of phosphorus in urine

32P is preferentially eliminated from the body in urine and is estimated by in situ precipitation of ammonium molybdophosphate (AMP) in the urine followed by gross beta counting. The amount of AMP formed depends on the amount of stable phosphorus (P) present in the urine. Hence, the present study was undertaken to estimate daily urinary excretion of P by the spectrophotometry method. P forms a colorless complex (phosphomolybdate) with molybdic acid, which on reduction produces deep-blue-colored complex called molybdenum blue. The intensity of this blue color is directly proportional to the amount of P present in the sample. 24 h urine samples collected from radiation workers were analyzed for stable P, and its range was observed to be between 0.4 and 1.4 g/day. This information was valuable in finalizing volume of the urine sample required for analysis of 32P in bioassay sample by gross beta counting technique.

Freestanding MoO2/Mo2C imbedded carbon fibers for Li-ion batteries

Flexible and freestanding MoO2/Mo2C imbedded carbon fibers (MoO2/Mo2C ICFs) have been successfully synthesized via an integrated procedure including electrospinning, thermo-plastication in air and reduction/carbonization at high temperature. A series of techniques such as SEM, TEM, N2 adsorption-desorption analysis, XRD, TGA, IR and XPS have been employed to systemically characterize the MoO2/Mo2C ICFs. In particular, it is observed that the MoO2/Mo2C ICFs derived from phosphomolybdic acid have more highly porous structures than those derived from molybdic acid. Most impressively, the obtained MoO2/Mo2C ICFs are directly used as binder- and current collector-free anode materials for LIBs, which exhibit desirable rate capability and satisfactory cycling performance. The electrochemical investigations illustrated that the MoO2/Mo2C ICFs could deliver an initial discharging capacity of 1422.0 mA h g-1 with an original coulombic efficiency of 63.3%, and the subsequent reversible capacity could reach as high as 1103.6 mA h g-1 even after 70 cycles at a current density of 0.1 A g-1. Such a capacity is larger than the theoretical capacity of MoO2 (838 mA h g-1) and pure carbon fibers (460.5 mA h g-1). More importantly, the MoO2/Mo2C ICFs exhibited an excellent rate performance with a capacity of 445.4 mA h g-1 even at a charging current density of 1.6 A g-1. The remarkable enhancement in rate capability and long cycling performance resulted from a synergistic effect between the MoO2 nanoparticles and porous carbon fiber matrix. This methodology can be widely extended to fabricate other metal oxide/carbon composites for significant energy storage and conversion applications.

Synthesis and characterization of molybdic acid immobilized on modified magnetic nanoparticles as a new and recyclable catalyst for the synthesis of chromeno[4,3-b]chromenes

Synthesis and characterization of molybdic acid immobilized on modified magnetic nanoparticles as a new catalyst is reported.

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

Nanosilica molybdic acid: synthesis, characterization and application as a green and reusable catalyst for the Pechmann condensation

Nanosilica molybdic acid (SMA NPs) was founded as an efficient and recyclable nanocatalyst for the synthesis of coumarin derivatives in excellent yields with good purity. Nano-SMA as a new solid acid was characterized by X-ray fluorescence, X-ray diffraction, energy-dispersive X-ray analyzer, transmission electron microscopy and Fourier transform infrared spectroscopy. Coumarin derivatives were obtained via the Pechmann condensation reaction of phenols and β-ketoesters at 80 °C under solvent-free conditions. The main advantages of the present procedure are high yields, shorter reaction time and green chemistry procedure, simple work-up and inexpensive and reusability of the catalyst.

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.