Anions vanadate

Calcium seems to have a significant effect on the accumulation and transport of the vanadate anion. Morrell et al. (1983) found that low levels of Ca in the nutrient solution resulted in less vanadate accumulation in the root and proportionally more of it being transported to the shoot. These results agree with the hypothesis of Cannon (1963) who suggested that V was immobilised in the root as the sparingly soluble calcium vanadate. 

From a chemical point of view, the setting for the encounter between tunicate and vanadium at the sea water interface is fairly simple to visualize. In the oxygenated, mildly alkaline, highly dilute conditions of the external sea water environment vanadium is present as monomeric vanadate anion. It is there predominantly as the free ion the low concentrations of organic chelators in sea water favor complex dissociation rather than formation (Cf. p. 141)8. ... 

Occupation of the triangles of the uranophane anion topology results in the formation of the uranophane-type sheet (Fig. 7b). Layered compounds containing uranyl vanadate anionic sheets of this type have recently been obtained with diamines, piperazine and l,4-diazabicyclo[2,2,2]octane dabco), as counter cations in the interlayer space (Fig. 7c) [31]. 

Thilo (25) classified oxo acids of various elements into three groups on the basis of the stability of the oxo acid in aqueous solutions, as shown in Table I. Although Thilo placed the elements in order of their ionic radii, covalent radii of the elements are used in Table I. The most stable phosphate in aqueous solutions is the monomer, orthophosphate. However, isopoly acid anions of phosphorus, i.e., condensed phosphates, are generally stable in an approximately neutral aqueous solution at room temperature. The rate of hydrolysis of the condensed phosphates is very low under these conditions. On the other hand, polysulfates and polyarsenates are very rapidly hydrolyzed into their monomers in aqueous solutions. In an alkaline solution, vanadate anions are present as monomer, i.e., orthovanadate. When the pH of the solution is de- creased, the orthovanadate anions are successively polymerized to form polymers with medium degrees of polymerization. Although silicate anions behave similarly, a highly polymerized form of silicate anions,... 

Speciation of vanadium(IV) ions was achieved. In acidic solution, vanadium(V) exists as the vanadyl ion (VO ), and vanadium(V) is present as V02 as well as the vanadate anion (V03 ). Cationic peaks were obtained. 

La, Lu, and Y do not show any UV absorption when used as host cations in rare earth orthovanadate phosphors. Of the usual host cations only gadolinium has absorption and emission bands in the UV region. The rare earth orthovana-dates are exceptional phosphor host materials in that the vanadate anion can be excited by both long and short UV radiation (fig. 121). The excitation of YVO4 in the 320 nm region occurs via the Aj T2 allowed transition of VO4 (Burrus and Paulusz, 1969). The excitation at shorter wavelengths (250 nm) involves... 

The phosphate-binding site consists of several residues His-40, His-92, Glu-58, Arg-77 (all located in the major )8 sheet), and Asn-98. These residues exhibit extensive H-bonding interactions with phosphate groups, whether from the backbone of RNA, the phosphate group(s) of nucleotides, inorganic phosphate (HPO4 ), or its analog tetrahedral vanadate anion. 

It is extensively used industrially as a catalyst, notably in the oxidation of sulphur dioxide to the trioxide in sulphuric acid manufacture. It is an essentially acidic oxide, dissolving in alkalis to give vanadates however, addition of acid converts the anionic vanadate species to cationic species, by processes which are very complex, but which overall amount to the following ... 

The chemistry of vanadium compounds is related to the oxidation state of the vanadium. Thus, V20 is acidic and weaMy basic, VO2 is basic and weaMy acidic, and V2O2 and VO are basic. Vanadium in an aqueous solution of vanadate salt occurs as the anion, eg, (VO ) or (V O ) , but in strongly acid solution, the cation (V02) prevails. Vanadium(IV) forms both oxyanions ((V O ) and oxycations (VCompounds of vanadium(III) and (II) in solution contain the hydrated ions [V(H20)g] and [V(H20)g], respectively. 

The polarographic method is applicable to the determination of inorganic anions such as bromate, iodate, dichromate, vanadate, etc. Hydrogen ions are involved in many of these reduction processes, and the supporting electrolyte must therefore be adequately buffered. 

Jordan P, H Vilter (1991) Extraction of proteins from material rich in anionic mucilages partition and fractionation of vanadate-dependent bromoperoxidases from the brown algae Laminaria digitata and L. saccharina in aqueous polymer two-phase systems. Biochim Biophys Acta 1073 98-106. 

Abbreviations. a-M, a-mannosidase AP, acid phosphatase as-ni-ATPase, anion-stimulated, nitrate-inhibitable ATPase CCR, NAD(P)H-dependent cytochrome oreduc-tase cs-vi-ATPase, cation-stimulated, vanadate-inhibitable ATPase, CAT, catalase GS 1/11, glucan synthase 1 or 11 IDPase, inosine diphosphatase cs-PPase, cation-stimulated pyrophosphatase RNA polymerase, DNA-dependent RNA polymerase TP-25, 25 kDa tonoplast integral protein. 

L — maltolate the coordination environment of the vanadium in K[V02(malt)2] H2O is approximately octahedral, the two 0x0 ligands being in cis positions. [K(H20)e] units link adjacent vanadium(V) complex anions to give a chain structure 166). The main products of aerobic oxidation of [V O(dmpp)2l in aqueous solution are [V02(dmpp)] and [VOo(dmpp)2]. High pH favors these V products, whereas at low pH V species predominate 171). Vanadium(V) also forms a VO(OR)(malt)2 series, readily prepared from ammonium vanadate, maltol, and the appropriate alcohol in a water-alcohol-dichloromethane medium 172), and 3-hydroxy-4-pyridinonate analogues V0(0R)L2 on oxidation of their oxovanadium(IV) precursors in solution in the appropriate alcohol ROH 168). 

The vanadate equilibria are given in Table 7.7. The V02(0H)2 and V03(0H) anions are sorbed on positively charged sites on oxides and silicates at low pH, but sorption decreases with pH as the surface positive charge decreases. Consequently V is quite soluble at high pH and less soluble at low pH. 

Reports have appeared claiming that triperoxo vanadates behave as nucleophilic oxidants. In particular, triperoxo vanadium complexes, A[V(02)3]3H20 (A=Na or K), are proposed as efficient oxidants of a,-unsaturated ketones to the corresponding epoxide, benzonitrile to benzamide and benzil to benzoic acid, reactions which are usually carried out with alkaline hydrogen peroxide. Subsequent studies concerning the oxidation of cyclobutanone to 4-hydroxybutanoic acid, carried out with the above-cited triperoxo vanadium compound, in alcohol/water mixtures, clearly indicated that such a complex does not act as nucleophilic oxidant, but only as a source of HOO anion. 

The vanadate(V) anions give rise to numerous salts. Among the most common are the orthovanadates (V04 ), metavanadates and... 

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