Vanadyl formate VO(HCOO)2·H2O as a precursor for preparing nanoscale vanadium sesquioxide V2O3

Vanadyl formate monohydrate VO(HCOO)₂·H₂O has been synthesized by a facile two-stage method. The chemical and structural identity of the synthesized compound has been confirmed by X-ray diffraction, thermogravimetry, vibrational and absorption spectroscopy. It was established that during heating in water and ethylene glycol, VO(HCOO)₂·H₂O leads to vanadyl hydroxide VO(OH)₂ and vanadyl glycolate VO(OCH₂CH₂O) being formed. When heated in air or in helium at 300 °C and higher, VO(HCOO)₂·H₂O transforms into vanadium pentoxide or sesquioxide, respectively. VO(HCOO)₂·H₂O was used as a precursor for the synthesis of nanoscale vanadium sesquioxide (with an average particle size of 50 nm), which is stable under the normal conditions and is characterized by a lower metal-insulator transition temperature than the microsized (bulk) compound. The effect of transition temperature reduction for nanoscale vanadium sesquioxide agrees with the lower value of its unit cell volume (V = 296.74 Å³) as compared with that for bulk V₂O₃ (297.7 Å³). The main factor affecting the V₂O₃ particle size is the annealing temperature of precursor in inert atmosphere.     

Vanadium incorporated high surface area MCM-41 catalysts

High surface area MCM-41 (1452 m²/g) and V-MCM-41 materials were synthesized by a direct hydrothermal synthesis method. Characteristic XRD patterns, SEM and AFM photographs indicated no significant change in the morphology of MCM-41 by incorporation of vanadium. XPS and EDS results proved that incorporation of vanadium into the MCM-41 structure was successfully achieved when vanadyl sulfate hydrate was used as the vanadium source. However, use of ammonium vanadate as the vanadium source was not equally successful.     

Methanol Adsorption on V2O3(0001)

Well ordered V₂O₃(0001) layers may be grown on Au(111) surfaces. These films are terminated by a layer of vanadyl groups which may be removed by irradiation with electrons, leading to a surface terminated by vanadium atoms. We present a study of methanol adsorption on vanadyl terminated and vanadium terminated surfaces as well as on weakly reduced surfaces with a limited density of vanadyl oxygen vacancies produced by electron irradiation. Different experimental methods and density functional theory are employed. For vanadyl terminated V₂O₃(0001) only molecular methanol adsorption was found to occur whereas methanol reacts to form formaldehyde, methane, and water on vanadium terminated and on weakly reduced V₂O₃(0001). In both cases a methoxy intermediate was detected on the surface. For weakly reduced surfaces it could be shown that the density of methoxy groups formed after methanol adsorption at low temperature is twice as high as the density of electron induced vanadyl oxygen vacancies on the surface which we attribute to the formation of additional vacancies via the reaction of hydroxy groups to form water which desorbs below room temperature. Density functional theory confirms this picture and identifies a methanol mediated hydrogen transfer path as being responsible for the formation of surface hydroxy groups and water. At higher temperature the methoxy groups react to form methane, formaldehyde, and some more water. The methane formation reaction consumes hydrogen atoms split off from methoxy groups in the course of the formaldehyde production process as well as hydrogen atoms still being on the surface after being produced at low temperature in the course of the methanol ?? methoxy + H reaction.     

Oxidative dehydrogenation of isobutyric acid: Characterization and modeling of vanadium containing polyoxometalate catalysts

The catalyzed oxidative dehydrogenation of isobutyric acid by H₄[PMo₁₁VO₄₀] and VOH[PMo₁₂O₄₀] was studied at 593 K. Thermal evolution of H₄[PMo₁₁VO₄₀] at 593 K leads to a complex mixture of different species with or without vanadium inside the Keggin structure. After reaction, the one and only heteropolyanion is partly reduced [PMo₁₂O₄₀]^3– and vanadium is present as vanadyl cations. Vanadyl cations are bound to the oxygen atoms of the heteropolyanion at 593 K and enhance the selectivity to methacrylic acid with respect to acetone. On the other hand, copper cations improve the reoxidation of the catalyst and increase the IBA conversion. Synergism between copper and vanadyl cations was observed.     

Synthesis of polyethers by oxovanadium-catalyzed oxidative coupling polymerization of di(1-naphthoxy) compounds

Poly(dinaphthylene ether)s (4) were prepared by oxovanadium-catalyzed oxidative coupling polymerizations of di(1-naphthoxy) compounds (3). Polymerizations were conducted in nitrobenzene in the presence of vanadyl acetylacetonate, trifluoromethane sulfonic acid and trifluoroacetic anhydride under an oxygen atmosphere at room temperature and produced poly[1,5-di(1-naphthoxy) pentane] (4a) having weight-average molecular weights up to 50,000. Vanadyl acetylacetonate acted as an oxidant and the polymerization was conducted using only 5% vanadyl acetylacetonate based on the monomer. The structure of polymer 4a was characterized by ¹³C-NMR spectroscopy, and selective coupling was found to occur at the C-4 position of the 1-substituted naphthalene ring due to the high electron density at this carbon.     

Chemistry of organosulphur compound types occurring in heavy oil sands: 3. Reaction of thiophene and tetrahydrothiophene with vanadyl and nickel salts

As part of a study of the chemistry of the steam-stimulated recovery of heavy oils, the hydrolysis and subsequent desulphurization of tetrahydrothiophene and thiophene by aqueous solutions of vanadyl and nickel salts was investigated. Vanadyl sulphate and vanadyl chloride were shown to behave very differently, emphasizing that these salts have different molecular species in aqueous solutions.     

The effect of vanadium sources on the synthesis and catalytic activity of VMCM-41

Mesoporous VMCM-41 was synthesized hydrothermally using various vanadium sources, viz, tetravalent vanadium such as vanadyl sulfate and vanadyl acetylacetonate, as well as pentavalent vanadium like sodium vanadate and ammonium vanadate. The influence of different vanadium sources on the framework substitution of vanadium, as well as their catalytic activity for the oxidation of cyclohexane, was investigated. Among the different vanadium stocks, the tetravalent vanadium sources showed maximum vanadium incorporation in the silicate framework of MCM-41. As a consequence, these catalysts gave much higher substrate conversion and excellent product selectivity. On the other hand, the catalysts prepared from pentavalent vanadium sources showed lower activity owing to the smaller amounts of vanadium in the matrix. Although the activity of the catalyst slightly decreased after first recycle as due to leaching of small amounts of active vanadium species, it however remained nearly the same even after several recycles. This was further confirmed by washing experiments wherein non-framework vanadium ions were removed upon ammonium acetate treatment; the washed catalysts showed a similar activity to those of the recycled catalysts. Thus, recycled/washed VMCM-41 behaves truly as heterogeneous catalyst. Furthermore, the influence of pore size of the catalyst was tested for the oxidation of bulkier substrate, viz, cyclododecane.     

MCFA alleviate H2O2-induced oxidative stress in AML12 cells via the ERK1/2/Nrf2 pathway

Oxidative stress is an important factor in the occurrence and development of liver disease. Medium-chain fatty acids (MCFAs) have potential antioxidant function, whereas the exact underlying mechanism of MCFA in oxidative injury of hepatocytes remains unclear. In our present study, three different MCFAs, 8-carbon octanoic acid (OA), 10-carbon capric acid (CA), and 12-carbon lauric acid (LA), have been performed to observe their protective action for hepatocyte under the H₂O₂ challenge. The result showed that MCFA treatment significantly increased the cell viability, T-AOC, and expression of antioxidant-related genes in AML12 cells under oxidative stress condition, and reduced reactive oxygen species (ROS) production. Moreover, MCFA treatment significantly increased the protein expression of Nrf2 and the phosphorylation level of ERK1/2; LA treatment significantly promoted the Nrf2 nuclear translocation. With a further test, the rescue ability of MCFA was blocked by treating with the ERK inhibitor U0126. Overall, our data suggested that MCFA treatment has positive impact on protecting AML12 cells against oxidative stress through ERK1/2/Nrf2 pathway.     

C60 Fullerene Reduces 3-Nitropropionic Acid-Induced Oxidative Stress Disorders and Mitochondrial Dysfunction in Rats by Modulation of p53, Bcl-2 and Nrf2 Targeted Proteins

C₆₀ fullerene as a potent free radical scavenger and antioxidant could be a beneficial means for neurodegenerative disease prevention or cure. The aim of the study was to define the effects of C₆₀ administration on mitochondrial dysfunction and oxidative stress disorders in a 3-nitropropionic acid (3-NPA)-induced rat model of Huntington’s disease. Animals received 3-NPA (30 mg/kg i.p.) once a day for 3 consecutive days. C₆₀ was applied at a dose of 0.5 mg/kg of body weight, i.p. daily over 5 days before (C₆₀ pre-treatment) and after 3-NPA exposure (C₆₀ post-treatment). Oxidative stress biomarkers, the activity of respiratory chain enzymes, the level of antioxidant defense, and pro- and antiapoptotic markers were analyzed in the brain and skeletal muscle mitochondria. The nuclear and cytosol Nrf2 protein expression, protein level of MnSOD, γ-glutamate-cysteine ligase (γ-GCLC), and glutathione-S-transferase (GSTP) as Nrf2 targets were evaluated. Our results indicated that C₆₀ can prevent 3-NPA-induced mitochondrial dysfunction through the restoring of mitochondrial complexes’ enzyme activity, ROS scavenging, modulating of pro/antioxidant balance and GSH/GSSG ratio, as well as inhibition of mitochondria-dependent apoptosis through the limitation of p53 mitochondrial translocation and increase in Bcl-2 protein expression. C₆₀ improved mitochondrial protection by strengthening the endogenous glutathione system via glutathione biosynthesis by up-regulating Nrf2 nuclear accumulation as well as GCLC and GSTP protein level.     

Selective oxidation of n-pentane on 12-molybdovanadophosphoric acids

The selective oxidation of n-pentane on 12-molybdovanadophosporic acids with 0, 1, 2, and 3 vanadium atoms was studied and compared with the behaviour of vanadyl pyrophosphate. Catalysts were characterized before and after the catalytic test by electron spin resonance, Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, krypton BET surface area and visible diffuse reflectance spectroscopy. The activity in the n-pentane conversion process increases linearly with increasing number of vanadium atoms, except for the H₆PMo₉V₃O₄₀ sample, for which physico-chemical characterization suggests partial surface degradation during the catalytic tests. A turnover frequency of about 5·10⁻⁴ molecules of n-pentane transformed per atom of vanadium and per second for both 12-molybdovanadophosporic acids and vanadyl pyrophosphate was calculated. Oxidation of n-pentane on heteropoly compounds formed only maleic anhydride and the selectivity increased linearly with increasing number of vanadium atoms present in the Keggin unit. In contrast, under the same reaction conditions both maleic and phthalic anhydride are formed on vanadyl pyrophosphate.     

Soy-Derived Equol Induces Antioxidant Activity in Zebrafish in an Nrf2-Independent Manner

Antioxidant effects of soy-derived isoflavones are predicted to be mediated by the Keap1-Nrf2 pathway. Recently, we constructed an assay system to evaluate the antioxidant effects of dietary phytochemicals in zebrafish and revealed a relationship between these effects and the Keap1-Nrf2 pathway. In this study, we used this system to examine the antioxidant effects of seven isoflavones. Among those seven, equol showed strong antioxidant effects when arsenite was used as an oxidative stressor. The antioxidant effect of equol was also shown in Nrf2-mutant zebrafish nfe2l2a^fh318, suggesting that this effect was not mediated by the Keap1-Nrf2 pathway. To elucidate this unidentified mechanism, the gene expression profiles of equol-treated larvae were analyzed using RNA-seq and qRT-PCR, while no noticeable changes were detected in the expression of genes related to antioxidant effects, except weak induction of Nrf2 target genes. Because nfe2l2a^fh318 is an amino acid-substitution mutant (Arg485Lue), we considered that the antioxidant effect of equol in this mutant might be due to residual Nrf2 activity. To examine this possibility, we generated an Nrf2-knockout zebrafish nfe2l2a^it321 using CRISPR-Cas9 and analyzed the antioxidant effect of equol. As a result, equol showed strong antioxidant effects even in Nrf2-knockout larvae, suggesting that equol indeed upregulates antioxidant activity in zebrafish in an Nrf2-independent manner.     

Synthesis,characterization and sulfide oxidation activity of vanadyl Schiff base complexes anchored on MCM-41

Vanadyl Schiff base complexes covalently attached on the surface of MCM-41 have been synthesized by anchoring Schiff base and subsequent reaction with VO(acac)₂. XRD, nitrogen adsorption and desorption, UV-visible spectroscopy and FT-IR show that vanadyl Schiff base complexes were successfully anchored on the surface of MCM-41 and the mesopore ordering decreased after the anchoring. The so-prepared heterogeneous catalysts have showed high activity for sulfide oxidation.     

Distribution of vanadyl porphyrins in a Mexican offshore heavy crude oil

The present work entails a study made regarding vanadyl porphyrins distribution of Mexican heavy crude oil from Sonda de Campeche offshore field (drilling range 4350–4371 m) in the southeast of Gulf of México. Furthermore, according to planning request about future trends of refining schemes the distribution of vanadyl porphyrins was investigated in the total heavy crude oil and their distilled residue, free of the asphaltene fraction. Vanadyl-metaloporphyrins were extracted and separated by means of adsorption chromatographic schemes using adsorbents and solvents of increasing polarities. Vanadyl porphyrins were identified and characterized by ultraviolet and visible (UV-vis) spectrophotometry, high-performance liquid chromatography (HPLC) and mass spectrometry (MS). Results show that vanadyl porphyrins are present in the total crude oil and within the deasphalted residue, namely five homologues series DPEP, ETIO, THBD, BD and B with the ETIO series predominating in deasphalted residue. On the whole, data related to the distribution of vanadyl porphyrins indicates the convenience of using procedures that eliminate asphaltenes in order to remove vanadyl porphyrins and improve the efficiency of catalysts used in different catalytic refining processes.     

Novel Method for Synthesis of Well-Crystallized Vanadyl(2+) Hydrogen Phosphate Hemihydrate: Crystallization in Organic Media Containing a Small Amount of Water

Vanadyl(2+) hydrogen phosphate hemihydrate (VOHPO₄0.5H₂O, VHP) that had high crystallinity and showed a strong (001) peak in its X-ray diffractometry (XRD) pattern was synthesized via thermal treatment of a mixture of vanadyl(2+) acetylacetonate and triethyl phosphate at 200°C in organic solvents that contained a small amount of water. Scanning electron microscopy observations revealed that the product consisted of thin plates (2-4 µm wide and <0.5 µm thick). When the reaction was conducted at 250°C, a VHP sample was formed that exhibited stronger XRD peaks and had a plate width of >20 µm. The present VHP sample was topotactically transformed to divanadyl(2+) pyrophosphate, which showed a strong (020) XRD peak, via thermal treatment in a nitrogen atmosphere at 500°C.