Peroxovanadate Complexes Research Articles

A Simple and Novel Colorimetric Optimized Assay for Determination of Hydrogen Peroxide Concentration Under Oxidative Stress Conditions

Background: Reactive oxygen species are formed through the electron transfer reactions in the mitochondria and chloroplasts and rapidly converted to H2O2.Therefore, H2O2 as a more stable ROS can be considered as an indicator of cellular stress and it can be used in a steady state to monitor intracellular stress level. In this regard, the increasing use of various nanoparticles, most of which are associated with biological systems, are essential to be studied for their possible adverse effects. We measured the concentration of hydrogen peroxide in samples collected before and after the treatment with silver nanoparticles by a novel method and optimized this method for the living tissue. Methods: In this study, we evaluated the endogenous H2O2 production from Pyricularia oryzae tissue under normal and stress conditions (such as after treatment with nanoparticles) by spectrophotometric assay. The method used is based on instant reaction of hydrogen peroxide with vanadium pentoxide in sulfuric acid solution, forming a peroxovanadate complex that has a maximum absorption at 454 nm. This method was also compared with other methods. Results: The results of this method compared with other methods in the same tissue showed that the method is simple, inexpensive and more efficient, and the complex is stable for several hours and can be used for a variety of H2O2 concentrations. Also, the detection range of the mentioned method equals with high-sensitivity methods such as available commercial kits. Furthermore, this method can also measure higher values of H2O2. Conclusion: The optimized methods for measuring the H2O2 concentration with vanadium pentoxide in sulfuric acid solution by the colorimetric method are simple, efficient, rapid, accurate, cost-effective and do not have problems of other methods. The measurements using this method in Pyricularia oryzae under oxidative stress showed that the created oxidative stress caused by the use of silver nanoparticles increased H2O2 in fungal tissue. H2O2 is the SOD reaction product that is later decomposed by CAT. This method is able to measure H2O2 in different ranges and under normal and stress conditions which are indicative of antioxidant defense. Therefore, we recommend it to the researchers in similar conditions.

NMR and theoretical study on the coordination interactions between peroxovanadium(V) complex and bisubstituted pyridine ligands

To understand the substitution effects of pyridine ligands on coordination equilibrium, the coordination interactions between a series of bisubstituted pyridine ligands and peroxovanadium(V) [OV(O2)2(D2O)]−/[OV(O2)2(HOD)]− in solution have been investigated by multinuclear (1H, 13C, and 51V) magnetic resonance and HSQC. A series of new six-coordinate peroxovanadate complexes [OV(O2)2L] n − (L = 2, 3, 4, n = 1 or 3) have been observed, and the coordination ability of the bisubstituted pyridines to peroxovanadium(V) is 3,4-dimethylpyridine (2) > 3,5-dimethylpyridine (3) > pyridine-3,5-dicarboxylate (4) ≫ 2,3-dimethylpyridine (1). The coordination interactions among title system have been further studied by DFT (density functional theory) calculations, and the results indicate that solvent may play an important role in these coordination interactions.

A Novel Method for the Determination of Hydrogen Peroxide in Bleaching Effluents by Spectroscopy

A spectrophotometric method for the determination of hydrogen peroxide in pulp bleaching effluents is reported. The method is based on hydrogen peroxide instantly reacting with vanadium pentoxide in sulfuric acid solution, forming a peroxovanadate complex that has an absorption maximum at 454 nm. It was found that the optimum conditions were as follows: detection wavelength of 454 nm, a V2O5:H2O2 mole ratio of 2.2, and a sulfuric acid concentration of 0.5 mol/L. In order to eliminate the interference from dissolved lignin, fines, and suspended solids, the samples were acidified and centrifuged for spectroscopic quantification. The results showed that the method has an excellent measurement precision (RSD < 0.3%) and accuracy for the quantification of hydrogen peroxide content in pulp bleaching effluents. The present method is simple and accurate, making it suitable for applications in the pulp and paper industry.

Morphological and textural characterization of vanadium oxide supported on zirconia by ionic exchange

Zirconia-supported vanadium oxide samples containing vanadium up to 6.8 wt.% were prepared by ionic exchange using aqueous solution of peroxovanadate complexes and hydrous zirconium oxide. The samples, heated at 823 K for 5 h in air, were studied by several techniques, including X-ray diffraction, surface area determinations, diffuse reflectance spectroscopy (UV–vis), Raman spectroscopy, pore size distribution measurements and atomic force microscopy. The results showed that the preparation procedure applied leads to good vanadium dispersion. The interaction between the anchored surface species and the support affects some ZrO 2 properties, including texture and phase transition. Depending on the vanadium loading, several species formed. In the most diluted sample small polyvanadate entities predominate, whereas at increasing vanadium loading (up to about 6 V atoms nm −2) more condensed species formed yielding granular-type surface aggregates. At higher loading, granular-type particles and large flat structures, due to amorphous two- or three-dimensional polyvanadate species and ZrV 2O 7-like structures developed. Treatments with an ammonia solution specified that only a fraction of the vanadium species (in a polymeric form) interacts with the zirconia surface. Atomic force microscopy directly imaged the formation of vanadium aggregates (superimposed to the interacting species) at increasing vanadium content and their removal by the ammonia leaching.

Simple spectrophotometric method for the determination of sulfur dioxide by its decolorizing effect on the peroxovanadate complex

A simple, rapid, and economical spectrophotometric method is developed for the determination of sulfur dioxide in sugar and air samples. The developed method is based on a red-brown peroxovanadate complex (λmax = 470 nm) produced in 2 M sulfuric acid when ammonium metavanadate is treated with hydrogen peroxide. Under fixed concentrations of hydrogen peroxide and ammonium metavanadate, when sodium metabisulfite (Na2S2O5 = 2SO2) is added, it preferentially reacts with hydrogen peroxide producing sulfuric acid, and the unreacted hydrogen peroxide then reacts with ammonium metavanadate; therefore, the concentration of sulfur dioxide is directly proportional to a decrease in the concentration of the peroxovanadate complex. The stoichiometric ratio between hydrogen peroxide and ammonium metavanadate as well as the stability constant of the complex are determined by the modified Job’s method and the respective values are found to be 1: 1 and 2.5 × 104 mol−1 L, respectively. The system obeys Lambert-Beer’s law in the concentration range 3.57–64.26 ppm of sulfur dioxide. The molar absorptivity, correlation coefficient, and Sandell’s sensitivity values are found to be 0.649 × 103 L mol−1 cm−1, 0.9908, and 0.1972 μg cm−2, respectively. The method is applied to the determination of sulfur dioxide present in commercial sugars and air samples. The results obtained are reproducible with a standard deviation of 0.02–0.05. For method validation, sulfur dioxide is also determined separately following the AOAC method for an air sample and the ICUMSA method for commercial sugars. The results obtained by the developed and official methods are in good agreement.

A simple and rapid spectrophotometric method for the determination of nitrite by its decolorizing effect on peroxovanadate complex

A rapid, simple, and most economical spectrophotometric method was proposed for the determination of nitrite in various water samples, soil samples, and roots of leguminous plants. The method is based on decolorizing effect of nitrite on complex formed between hydrogen peroxide and vanadate in acidic medium. The decolorization of that complex by nitrite was exploited to monitor the reaction spectrophotometrically at 470 nm.The method was optimized for effect of concentrations of ammonium metavanadate, hydrogen peroxide, various acids, concentrations of sulphuric acid, order of reagents addition and color stability. The color of the complex was found to be stable for about 2 days, and the stability constant of the complex was also calculated by modified Job's method. The linearity range of the calibration graph was over 6.67–66.7 μg ml −1 of nitrite with molar absorptivity, 0.276 × 10 3 mol −1 l cm −1 and Sandell's sensitivity, 0.1667 μg cm −2. The method was applied successfully for the determination of nitrite in soil samples, various wastewater samples and roots of leguminous plants.

Inhibition of vanadium chloroperoxidase from the fungus Curvularia inaequalis by hydroxylamine, hydrazine and azide and inactivation by phosphate

The first detailed inhibition study of recombinant vanadium chloroperoxidase (rVCPO) using hydroxylamine, hydrazine and azide has been carried out. Hydroxylamine inhibits rVCPO both competitively and uncompetitively. The competitive inhibition constant K ic and the uncompetitive inhibition constant K iu are 40 and 80 μM, respectively. The kinetic data suggest that rVCPO may form a hydroxylamido complex, hydroxylamine also seems to react with the peroxovanadate complex during turnover. The kinetic data show that the type of inhibition for hydrazine and azide is uncompetitive with the uncompetitive inhibition constant K iu of 350 μM and 50 nM, respectively, showing that in particular azide is a very potent inhibitor of this enzyme. Substitution of vanadate in the active site by phosphate also leads to inactivation of vanadium chloroperoxidase. However, the presence of H 2O 2 clearly prevents the inactivation of the enzyme by phosphate. This shows that pervanadate is bound much more strongly to the enzyme than vanadate.

Synthesis and Spectroscopic Characterizations of an Insulinomimetic Peroxovanadate Complex in Aqueous Solution

AbstractThe reaction system of diperoxooxalatovanadate {K3[VO(O2)2‐(C2O4)]·H2O, bpV(Oxa)} and imidazole was studied in an aqueous solution by ID multinuclear (1H, 13C and 51V) NMR, 2D NMR diffusion ordered spectroscopy (DOSY), and variable temperature NMR techniques. It was shown that DOSY was a useful tool for the study of a mixture. All of the 1H and 13C NMR signals of the peroxovanadate (V) complexes were assigned. The NMR experimental results indicated that a new complex was formed through the coordination interactions between bpV(Oxa) and imidazole. The newly‐formed complex is stable under the experimental condition. Electrospray ionization mass spectrometry (ESI‐MS) provides positive evidence to support the conclusion.

Speciation in the aqueous H+/H2VO4−/H2O2/l-(+)-lactate system

A detailed study of the quaternary aqueous H+/H2VO4−/H2O2/L-(+)-lactate (Lac−) system has been performed at 25 °C in 0.150 M Na(Cl) medium, representing the ionic strength of human blood, using quantitative 51V NMR and potentiometric data (glass electrode). Data were evaluated with the computer program LAKE, which is able to treat combined EMF and NMR data. The pKa-value for lactic acid was determined as 3.653 ± 0.002. The error given is 3σ. In the ternary H+/H2VO4−/Lac− system, eight complexes were found in the pH region 1.1–10.9; only half of them are mononuclear. Owing to the fast reduction of vanadium(V) in acidic solutions and to the slow equilibria of the inorganic vanadates under certain conditions, the final model of this ternary system presented in the study is limited to pH > 3.1. Solutions, in which reduction occurred to any extent, were excluded from all calculations, hence the study is limited to vanadium(V). In the quaternary H+/H2VO4−/H2O2/Lac− system, seven complexes could be found in addition to all binary and ternary complexes over the pH region 2.1–10.0, only two of which were mononuclear. Equilibrium is fast, but significant decomposition of peroxide occurs in acidic solutions over very short time, limiting the final model to pH > 4. Chemical shifts, compositions and formation constants are given, and equilibrium conditions are illustrated in distribution diagrams as well as the fit of the model to the experimental data. Simple biological tests were carried out to check the resistance of different peroxovanadate complexes (including the ones with Lac−) against human catalase and the results are being presented here.

A Dinuclear Peroxo-Vanadium(V) Complex with Coordinated Tripeptide. Synthesis, Spectra and reactivity in Bromoperoxidation

Synthesis of a triglycine peroxo-vanadate complex, [V2O2(O2)3(Gly-Gly-Gly)2].H2O by the reaction of V2O5 with H2O2 and the tripetide at pH 2 is described; the peroxo-bridged complex is highly effective in generating a bromination competent intermediate at physiological pH.

Solvent effects on 51V NMR chemical shifts: characterization of vanadate and peroxovanadate complexes in mixed water/acetonitrile solvent

The majority of 51V NMR studies on V(V) complexes have been reported in water, which currently limits the usefulness of 51V NMR in identifying V(V) species in non-aqueous solvents. In this report, the 51V NMR spectra have been obtained for vanadate and peroxovanadate complexes that exist at pH ≤ 7 in solutions containing 2–90% water in acetonitrile. Millimolar vanadate and peroxovanadate solutions in acetonitrile containing as little as 2% water were prepared by diluting a conc. aq. solution of vanadate (Bu 4N + salt) with acetonitrile. As with simple oxovanadate oligomers and peroxovanadate complexes in aqueous solutions, the species present in acetonitrile solution are a function of vanadium, acid and peroxide concentrations. The 51V resonances for several species can be assigned by correlating changes in chemical shifts as a function of water concentration. Species definitively characterized include VO 2 +, H x VO 4 x−3 , HV 2O 7 3−, V 4O 12 4−, V 5O 15 5−, V 10O 28 6−, VO(O 2) +, VO(O 2) 2 − and V 2O 2(O 2) 3. While the chemical shift for every assigned species moves downfield as water concentration is decreased, the magnitude of the downfield shift is highly dependent on the vanadium species. The assignments provided herein from the foundation for establishing the reactivity patterns for peroxovanadate in non-aqueous media.

The chemistry of peroxovanadium compounds relevant to insulin mimesis.

The inorganic coordination chemistry of peroxovanadium compounds relevant to insulin mimesis is reviewed. The structure and kinetic reactivity of solutions of vanadate anion, vanadyl complexes and peroxovanadate complexes are briefly compared. Peroxovanadium compounds contain an oxo group, one or two peroxo ligands (O2(2-)) and an ancillary ligand which is usually bidentate. These compounds approximate a trigonal bipyramidal structure which can be divided conceptually into a polar 'oxo' half and a relatively non-polar organic half. This presents a number of interesting design variations which are discussed with respect to the development of a rudimentary structure-activity correlation of insulin mimetic ability.