Reactions of vanadium(V) with alkali sulphate or thiocyanate. Evidence for the formation of oxodiperoxovanadate(V) complexes containing ionic sulphate

Vanadium pentoxide (1 mol) reacts with alkali sulphate (2 mol) or alkali thiocyanate (2 mol) and an excess of hydrogen peroxide at pH 7-8, maintained by the addition of the corresponding alkali hydroxide, to produce yellow oxodiperoxovanadate(V) complexes containing sulphate. The compounds were characterised by elemental analyses, molar conductance measurements, and i.r. and laser Raman spectroscopic studies. The compounds are formulated as M[VO(O2)2] . M2SO4 (M=alkali metal). The peroxide has been shown to be bonded to the vanadium(V) centre in a triangular bidentate (C 2v) manner

Direct synthesis of hexafluoroferrates(III) and reaction of thiocyanate and fluoride with iron(III) and hydrogen peroxide as an access to fluoro(sulfato)ferrates(III)

The reaction of iron(II1) hydroxide with alkali-metal or ammonium fluoride and 48% hydrofluoric acid in the presence of hydrogen peroxide, followed by the addition of ethanol, directly gives alkali-metal or ammonium hexafluoroferrates(III), A3FeF6 (A = Na, K, or NH4), in very high yields. An investigation of the reaction of ammonium or potassium thiocyanate and 48% HF with iron(II1) hydroxide in the presence of hydrogen peroxide has been carried out. Sulfate has been obtained as the oxidation product of SCN-, without involving reduction of iron(II1) and providing an access to fluoro(sulfato)ferrates(III) of the types (NH4)2[Fe(SO4)F3J and K3[Fe(SO4)F4]. Similar reactions with sulfates in lieu of thiocyanates, either in the presence of or in the absence of H202, do not afford fluoro(sulfato)ferrates(III), however. IR spectroscopy and laser Raman spectroscopy provide evidence for a chelated sulfate in each of the fluoro(sulfato)ferrates(III)

Optimum Conditions for Hydrogen Peroxide Oxidation of Thiocyanate to Sulphate

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Newer manifestations of reactivity of coordinated peroxide at metal and non-metal centres

Newer reactions of coordinated peroxide at metal and non-metal centres are described. Reactions of peroxo-metal complexes with SO2(g), NO2(g), and CO2(g) have been carried out in aqueous medium. Typically, reactions of a highly peroxygenated metal complex, A[V(O2)3].3H2O (A=Na,K), follow an unprecedented sequence. The deep blue ESR-silent solution of A[V(O2)3].3H2O reacts to produce a yellow, ESR-inactive solution that on further reaction with the chosen substrate affords a green-blue ESR-active (cf. VO2+) solution. The reaction proceeds through distinct steps such that, first, one of the coordinated peroxides undergoes a two-electron irreversible cleavage of the O-O bond leading to a diperoxy-mono(sulphato)vanadate(V) intermediate, [(O2)2V-O-SO3]-, that readily undergoes hydrolysis to produce H2SO4 and an aquaoxo-diperoxovanadate(V) complex, [VO(O2)2H2O]-. The latter complex reacts with more SO2(g) causing reduction of vanadium (V) to vanadium (IV) and conversion of coordinated peroxide to coordinated sulphate producing the bis(sulphato)vanadyl complex, [VO(SO2)2(H2O)2]2-. Further, the reaction of A[V(O2)3].3H2O with SO2(g) in the presence of AF, yielding a ternary fluoro(sulphato)oxovanadate (IV) complex A4[VO(SO4)2F2(H2O)].2H2O, serves as a paradigm for the synthesis of ternary complexes of vanadyl, VO2+. It is also evidentinteralia that the [V(O2)3]- species offers potential as a novel synthon. Some recent developments in the peroxo-chemistry of B, C, P and As are highlighted. Heretofore unreported salts of peroxo phosphoric acid, viz. (NH4)3[PO3(O2)].3H2O and Na3[PO3(O2)].3H2O, have been synthesized and their potential as oxidants explored. Their role in oxidising organic substances is highlighted, especially as a substitute for the alkaline-H2O2 reagent

Complex fluoroberyllates. Synthesis and physicochemical characterization of mixed-fluoro complexes of beryllium Containing hydrogenoxalate (HC<SUB>2</SUB>O<SUB>4</SUB><SUP>-</SUP>), glycinate, and dihydrogenphosphate (H<SUB>2</SUB>PO<SUB>4</SUB><SUP>-</SUP>) as co-ligands

Synthesis of novel mixed complex fluoroberyllates of the types M2[BeF3(HC2O4)].H2O (M = NH4 or Na), K2[BeF3(HC2O4)], M2[BeF3(NH2CH2COO)].H2O (M = NH4 or Na), and M2[BeF2(H2PO4)2] (M = NH4 or K) has been achieved from the reaction of Be(OH)2 with MF and the corresponding co-ligands viz., oxalic acid, glycine, and orthophosphoric acid, at pH ca. 2. Vibrational spectroscopic evidences have been provided in respect of co-ordinated F- and the ligands HC2O4-, NH2CH2COO-, or H2PO4-. IR spectra of ammonium salt of the complexes demonstrate the presence of hydrogen bonding

Reactivity of µ-Peroxo-Bridged Dimeric Vanadate in Bromoperoxidation

Diglycyl triperoxodivanadate [V2O2(O2)3(Gly H)2(H2O)2], a synthetic compound with μ-peroxo-bridge derived from H2O2and vanadate, oxidized bromide to a bromination-competent intermediate in phosphate buffer and physiological pH. This is in contrast to the requirement of acid medium with H2O2as the oxidant. Addition of its solid to bromide solution instantly produced a 262-nm-absorbing compound that converted phenol red (a trap) to its 592-nm-absorbing bromo-derivative. The high bromination activity was lost on dissolving this compound in water and the solution showed the presence of peroxovanadates (mono and di) and vanadates (V1and oligomeric V10) in51V-NMR spectrum. Of these, diperoxovanadate and vanadate together supported slow bromination activity by a second set of reactions including bromide-assisted reductive formation of vanadyl. Bromination activity dependent on vanadyl was sensitive to oxidation by excess H2O2and to complexation by EDTA, whereas that of triperoxodivanadate was relatively insensitive. Vanadyl and diperoxovanadate are capable of forming a μ-peroxo-bridged complex that is essentially similar to the synthetic vanadate dimer used in the present experiments. It appears that a μ-peroxo-intermediate is the proximal oxidant of bromide in vanadium-catalyzed bromoperoxidation

Reactivity of coordinated peroxide at a highly peroxygenated vanadium(V) center in an aqueous medium

Reactions of a highly peroxygenated metal complex, A[V(02)3.3H20 (A = Na, K), with S02(g) follow an unprecedented sequence. The deep blue ESR-silent aqueous solution of A[V(02)].3H20 readily reacts with S02(g) to produce a yellow, ESR-inactive solution that on further reaction with SO2(g) affords a green-blue ESR-active (cf. V02+) solution. The reaction involving K[V(02)3].3H20 enabled isolation of the yellow intermediate characterized as K[V0(02)2(H20)]. The product obtained from the ultimate green-blue solution has been identified as an oxo(sulfato)vanadate(IV) species, A2[VO(S04)2(H20)3].H20(A = Na, K). At the stages of its yellow and green-blue coloration, the reaction medium pH values were recorded to be ca. 6 and ca. 2, respectively. Similarly, reactions of A[V(02)+3H20 with S02(g) in the presence of AF yielded ternary oxofluoro(su1fato)vanadate( 1V) compounds, A4[VO(S04)2F2(H20)].2H2O(A= Na, K). The compounds have been characterized from the results of elemental analyses, chemical determinations of oxidation states of the metals, magnetic susceptibility and ESR measurements, and IR and laser Raman spectroscopic studies. Sulfate is coordinated to the V02+ center in a unidentate manner

Synthesis and characterization of novel catalase resistant monoperoxo divanadate(V) compounds

2003-2009Oxo-bridged monoperoxo-divanadium(V) compounds in mixed-ligand environment, Na6[V2O3(O2)(NTAMSO4)(H2O)].2H2O (1) and Na2[V2O3(O2)(gly-gly)2(SO4)(H2O)].2H2O (2), have been synthesized by devising an unusual synthetic methodology based on the redox reaction of sodium salt of diperoxovanadate with vanadyl sulphate in presence of respective co-ligands (NTA= nitrilotriacetic acid, gly-gly= glycylglycine) at pH ca.7.0 (compound 1) or ca. 9.0 (compound2). Magnetic susceptibility measurement, ESR and electronic spectral data reveal that V(IV) of vanadyl is completely oxidised to V(V) during the reactions. The presence of side-on bound peroxo group, terminal as well as bridging oxo groups and un identate sulphate in the compounds are exhibited by their IR spectra. The ligands NT A in compound 1 and glyl-gly in compound 2 occur in their anionic form occupying three co-ordination positions around each of the oxo-bridged V(V) centres. The distinctive features of the compounds include their high stability towards decomposition in solution and remarkable ability to resist the action of the enzyme catalase. The compounds have been found to be inactive in the oxidation of NADH (nicotinamide adenine dinucleotide) or bromide. The dinuclear complex species appear to correspond to the inhibitor complexes formed in solution responsible for ligand induced inhibition of redox activity of a mixture of diperoxovanadate and vanadyl

Synthesis, characterisation and physicochemical properties of peroxo-vanadium(v) complexes with glycine as the hetero-ligand

The first glycine---peroxo complexes of vanadium- (V), NH4[VO(O2)2GlyH].H2O (1), K[VO(O2)2- GlyH].H2O (2)and [V2O2(O2)3(GlyH)2(H2O)2] (3) have been synthesised from the reaction of V2O5 with hydrogen peroxide and glycine (GlyH) at pH 3-4 (1 and 2) and pH 2 (3), respectively. The compounds have been characterised by elemental analysis, magnetic susceptibility and ESR, UV---Vis and IR spectroscopy. While glycine, occurring in its zwitterionic form, is coordinated to the V(V) centre in a monodentate fashion through its carboxylic oxygen, the peroxides in 1 and 2 occur as terminal bidentate ones. In compound 3 one of the peroxide ligands is present as a &#956;-peroxo group. Typically, an aqueous solution of 2 exhibits peroxo---V(V) LMCT bands at 328 and in the 200-190 nm region, whereas complex 3 shows only one broad LMCT band at 310-330 nm

Growth arrest of lung carcinoma cells (A549) by polyacrylate-anchored peroxovanadate by activating Rac1-NADPH oxidase signalling axis

Hydrogen peroxide is often required in sublethal, millimolar concentrations to show its oxidant effects on cells in culture as it is easily destroyed by cellular catalase. Previously, we had shown that diperoxovanadate, a physiologically stable peroxovanadium compound, can substitute H2O2 effectively in peroxidation reactions. We report here that peroxovanadate when anchored to polyacrylic acid (PAPV) becomes a highly potent inhibitor of growth of lung carcinoma cells (A549). The early events associated with PAPV treatment included cytoskeletal modifications, increase in GTPase activity of Rac1, accumulation of the reactive oxygen species, and also increase in phosphorylation of H2AX (gamma H2AX), a marker of DNA damage. These effects persisted even at 24 h after removal of the compound and culminated in increased levels of p53 and p21 together with growth arrest. The PAPV-mediated growth arrest was significantly abrogated in cells pre-treated with the N-acetylcysteine, Rac1 knocked down by siRNA and DPI an inhibitor of NADPH oxidase. In conclusion, our results show that polyacrylate derivative of peroxovanadate efficiently arrests growth of A549 cancerous cells by activating the axis of Rac1-NADPH oxidase leading to oxidative stress and DNA damage