Is vanadium a more versatile target in the activity of primordial life forms than hitherto anticipated?

The two predominant forms of vanadium occurring in the geo-, aqua- and biosphere, soluble vanadate(V) and insoluble oxovanadium(IV) (vanadyl), are subject to bacterial activity and transformation. Bacteria belonging to genera such as Shewanella, Pseudomonas and Geobacter can use vanadate as a primary electron acceptor in dissimilation or respiration, an important issue in the context of biomineralisation and soil detoxification. Azotobacter, which can employ vanadium as an essential element in nitrogen fixation, secretes a vanadophore which enables the uptake of vanadium(V). Siderophores secreted by other bacteria competitively (to ferric iron) take up vanadyl and thus interfere with iron supply, resulting in bacteriostasis. The halo-alkaliphilic Thioalkalivibrio nitratireducens possibly uses vanadium as a constituent of an alternative, molybdopterin-free nitrate reductase. Marine macro-algae can generate a variety of halogenated organic compounds by use of vanadate-dependent haloperoxidases, and a molecular vanadium compound, amavadin, from Amanita mushrooms has turned out to be an efficient catalyst in oxidation reactions. The present account is a focused and critical review of the current knowledge of the interplay of bacteria and other primitive forms of life (cyanobacteria, algae, fungi and lichens) with vanadium, with the aim to provide perspectives for applications and further investigations.     

Bioanorganische Chemie des Vanadiums. Leben ohne Vanadium?

Vanadium is used by microorganisms as an electron acceptor in respiration, and as an essential transition metal in enzymatic reactions. An example for the employment in respiratory function is the soil bacterium Shewanella, which reduces vanadate(V) to oxidovanadium(IV). Examples for enzymatic reactions are the nitrogen fixation (by the proteobacterium Azotobacter and the cyanobacterium Anabaena), and the two‐electron oxidation of halide X^– to a species {X⁺} by marine macro‐algae, fungi and lichen. In vanadium nitrogenase, vanadium is constituent of a {Fe₇VS₉} cluster, in vanadate‐dependent haloperoxidases it is present in the form of H₂VO₄^– bound to a histidyl residue of the protein matrix. Mushrooms of the genus Amanita store vanadium in the form of amavadin, a “bare” (non‐oxo) vanadium(IV) complex. Several sea squirts and fan worms accumulate vanadium from sea water and store it as an aqua complex of vanadium(III). “Tailored” vanadium complexes with organic ligands have been shown to be active as insulin‐mimics in vivo and in vitro: They are able to stimulate the cellular uptake of glucose and to inhibit the degradation of lipids. These functions are related to the phosphate‐vanadate antagonism.     

Flow injection electrogenerated chemiluminescence determination of vanadium and its application to environmental water sample

A selective flow injection electrogenerated chemiluminescence(CL) method for the determination of vanadium is described in this paper. It was based on the chemiluminescence reaction of luminol with vanadium(II), which was on-line electrogenerated from vanadate using a flow-through carbon electrolytic cell. Under the optimal conditions, the CL intensity was linear to the concentration of vanadium in the range of 5.0x10(-10)-1.0x10(-7) gml(-1) with a detection limit of 2x10(-10) gml(-1) vanadium. The relative standard deviation was 4% for 5.0x10(-8) gml(-1) vanadium in 11 repeated measurements. The method has been successfully applied to the determination of vanadium in environmental water samples.     

Speciation analysis of vanadium in natural water samples by electrothermal vaporization inductively coupled plasma optical emission spectrometry after separation/preconcentration with thenoyltrifluoroacetone immobilized on microcrystalline naphthalene

A sensitive and simple method for low temperature electrothermal vaporization inductively coupled plasma optical emission spectrometry (ETV-ICP-OES) determination of V(IV) and V(V) after separation/preconcentration by a micro-column packed with immobilized thenoyltrifluoroacetone (TTA) on microcrystalline naphthalene has been developed. Thenoyltrifluoroacetone was used as both a chelating agent for micro-column separation/preconcentration and a chemical modifier for ETV-ICP-OES determination of vanadium. Both vanadium species could be trapped by micro-column at pH 4.0, and the vanadate (VO₂⁺) ion could be collected selectively at pH 2.4. Solid material loaded with analyte in the micro-column was dissolved with 100 μL of acetone containing 2.0 mmol L⁻¹ TTA and the vanadium was determined subsequently by ETV-ICP-OES. The concentration of vanadyl (VO²⁺) ion was calculated by subtracting the vanadate concentration from the total concentration of vanadium. Under the optimized experimental conditions, the detection limit (3σ) for the preconcentration of 5 mL of aqueous solution is 0.068 μg L⁻¹ for both species and the relative standard deviations were 4.3% for vanadium(V) and 4.8% for vanadium(IV) (c=10 μg L⁻¹, n=7), respectively. The method was applied successfully to the determination of vanadium(IV) and vanadium(V) in natural water samples.     

Formation and structure of 1:1 complexes between aryl hydroxamic acids and vanadate at neutral pH

Although aryl hydroxamic acids are well-known to form coordination complexes with vanadate (V(V)), the nature of these complexes at neutral pH and submillimolar concentrations, the conditions under which such complexes inhibit various serine amidohydrolases, is not well established. A series of qualitative and quantitative experiments, involving UV/vis, (1)H NMR, and (51)V NMR spectroscopies, established that both 1:1 and 1:2 vanadate/hydroxamate complexes form at pH 7.5, with the former dominating at submillimolar concentrations. Formation constants for the complexes of several aryl and alkyl hydroxamic acids were determined; for example, for benzohydroxamic acid, the stepwise formation constants of the 1:1 and 1:2 complexes were 3000 and 400 M(-1), respectively. The (51)V chemical shift of the 1:1 4-nitrobenzohydroxamic acid complex was -497 ppm, and that of its unsubstituted analogue was -498 ppm. A (1)H-(15)N HSQC spectrum of the 4-nitrobenzo-(15)N-hydroxamic acid/vanadate complex indicated the presence of an N-H group with (15)N and (1)H chemical shifts of 115 and 5.83 ppm, respectively. A (13)C NMR spectrum of the complex of 4-nitrobenzo-(13)C-hydroxamic acid with vanadate displayed a resonance at 170.1 ppm and thus a coordination-induced shift (CIS) of +3.8 ppm. In contrast, the CIS value of an established 1:2 complex, thought to contain chelated hydroxamic acid ligands, was +11.9 ppm. These spectral data led to the following structural picture of 1:1 complexes of vanadate and aryl hydroxamic acids. They contain penta- or hexa-coordinated vanadium. The ligand is in the hydroxamate rather than hydroximate form. The ligand is presumably bound to vanadium through the hydroxamic hydroxyl oxygen, but the hydroxamic acid carbonyl oxygen interacts weakly with vanadium. These species are the most likely candidates for the inhibitors of serine amidohydrolases found in vanadate/hydroxamic acid mixtures.     

Spectrophotometric determination of vanadium with 1,10-phenanthroline

A simple and sensitive spectrophotometric method for the determination of vanadium based upon the reaction of vanadate with 1,10-phenanthroline in the presence of sodium dithionite in ammoniacal solution is described. The absorbance of the complex measured at 645 nm follows Beer's law for solutions containing 30-400 microg of vanadium in 100 ml of solution. A 10-fold excess of molybdenum, tungsten, phosphorus or chromium does not interfere. The molar absorptivity is 8.0 x 10(3) 1 mole(-1) cm(-1). The complex is shown to be tris-1,10-phenanthroline vanadium(II). The method has been applied successfully to the determination of vanadium in bauxite.     

Vanadium in Italian waters: monitoring and speciation of V(IV) and V(V)

In this work, a highly sensitive method was developed to separate vanadium (IV) from vanadium (V), which are both contained in water at trace levels. A suitable strong anionic exchange column (SAX) loaded with disodium ethylendiaminetetraacetic acid (Na₂EDTA) was used to trap both vanadium species dissolved in 10–100 ml of water at pH 3. The vanadyl ion was selectively eluted by means of 15 ml of an aqueous solution containing Na₂EDTA, tetrabutylammonium hydroxide (TBA⁺OH⁻), and isopropanol (ⁱPr-OH) and was subsequently determined by atomic absorption spectroscopy with electrothermal atomization. The concentration of vanadate ion was calculated by subtracting the vanadyl concentration from the total concentration of vanadium. The optimal conditions for a selective elution were evaluated. The recovery of vanadium (IV) was 95% or better. The proposed method provides a simple procedure for the speciation of vanadium in aqueous matrices. The collection of the two forms could easily be carried out at the sampling site. Therefore, the risk of changing the concentration ratio between vanadium species was widely reduced. The detection limits were 1 μg/l for both species, when a 10-ml sample was eluted through the column. The method was applied successfully to vanadium speciation on different kinds of Italian volcanic water: Mount Etna (Sicily), Lake Bracciano and Castelli Romani (Latium).     

The First Vanadium Oxide Nanotubes Containing an Aromatic Amine as Template

A new vanadate has been prepared in high yield by reacting vanadium(V) triisopropoxide and 3‐phenylpropylamine in solution, followed by hydrolysis and hydrothermal treatment of the intermediate product. For the first time, an aromatic amine has successfully been applied as structure‐directing template for the synthesis of vanadium oxide nanotubes. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images demonstrate the tubular morphology of the phenylpropylamine vanadium oxide nanotubes obtained. The size and structure are similar to that of vanadium oxide nanotubes formed with aliphatic amines. The tube walls comprise layers of vanadium oxide with the organic template intercalated in between. The interlayer distance is ca. 2.1 nm, and the structure of the VO_x layers can be described by a square lattice with a≈0.61 nm. Furthermore, the TEM investigation has revealed the presence of many defects in the wall structure.     

Optical Properties of Sol-Gel Derived Vanadium Oxide Films

Vanadium oxide gels can be made from vanadate aqueous solutions or from vanadium alkoxides. The condensation of vanadic acid gives long ribbon-like oxide particles which macroscopically orient in the same direction in aqueous sols when their concentration is larger than 0.12 mol·l⁻¹. These anisotropic sols and gels should be considered as lyotropic nematic liquid crystals. Thick films in which ribbons align along the same direction can be deposited. These oriented coatings exhibit improved electrochemical properties as reversible cathodes for lithium batteries. Amorphous oxo-polymers are formed via the controlled hydrolysis of vanadium alkoxides. They allow the deposition of optically transparent thin films that exhibit interesting electrochromic properties and turn reversibly from yellow to green upon electrochemical reduction. Moreover these alkoxide derived films can be easily reduced into vanadium dioxide. These VO₂ thin films exhibit thermochromic properties and could be used as optical switches in the infrared. The transition temperature of these VO₂ films can be modified by doping the vanadium oxide with other cations.     

Vanadium speciation by ion chromatography

An ion-chromatographic method, using a carbonate-buffered (1,2-cyclohexylenedinitrilo)tetraacetic acid (CDTA) eluant, is described for the simultaneous determination of vanadium(IV) and vanadium(V). Vanadium(IV) was, after pre-column complexation with CDTA, separated from vanadium(V) (as vanadate) by anion-exchange chromatography. The analytical range is 0.5 to 20 g/ml and 0.25 to 10 g/ml for vanadium(IV) and vanadium(V), respectively. Detection limits are estimated to be 145 and 70 ng/ml for vanadium(IV) and vanadium(V), respectively.     

Indirect determination of vanadium by atomic absorption spectrometry

An indirect method for the determination of vanadium as vanadate by atomic absorption spectrometry is described. In neutral medium, vanadate forms a stable ion-association complex with copper (II) and biguanide, which is extractable into butanol with an efficiency higher than 99%. The copper content in the extract (and hence indirectly VO^?₃) is determined by aspirating it directly into an acetylene flame. The calibration graph is linear up to 3.4 μg ml^?1 of VO^?₃. The limit of detection is 16 ng ml^?1. Only chromium interferes.     

Studies in qualitative inorganic analysis. part XXXIX

Summary A virtually specific test for vanadium(V) is described which, in particular, permits the detection of vanadate in the presence of chromate and molybdate. The behaviour of vanadate in the anion separation scheme of the MAQA scheme of qualitative analysis has been investigated.

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Zusammenfassung Ein praktisch spezifischer Nachweis von Vanadin(V) wurde beschrieben, womit vor allem Vanadat in Gegenwart von Chromat und Molybdat nachgewiesen werden kann. Das Verhalten von Vanadat im Anionentrennungsgang der MAQA¹ wurde untersucht.

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Part XXXVIII, Mikrochim. Acta [Wien]1969, 1097.     

V2O5/TiO2催化剂表面结构FT-IR发射光谱研究(II)

用傅里哀变换红外发射光谱原位考察了V_2O_5/TiO_2催化剂在制备焙烧过程中担载偏钒酸铵的热分解步骤及其形成的表面活性相结构。偏钒酸铵在200 ℃左右分解, 在300 ℃之前完全转化为晶相V_2O_5。担载于TiO_2上的偏钒酸铵在100 ℃左右与TiO_2已产生强的化学作用, 在200 ℃之前已完全分解。对于10%(质量分数)V_2O_5/TiO_2催化剂其担载偏钒酸分解后在1020 cm~(-1)附近出现晶相V_2O_5的特征峰。但在500 ℃进一步焙烧后晶相V_5O_5的峰减弱并在1025—900 cm~(-1)区出现宽峰, 表明部分晶相V_2O_5可能转化为二维高分散的VO_x物种。2%(质量分数)V_2O_5/TiO_2催化剂在焙烧过程中也显示晶相V_2O_5的弱峰, 但同时也观察到属于VO_x物种的宽峰。进一步降低钒担载量, V_2O_5晶相特征峰逐渐消失, 而在1025—900 cm~(-1)区出现二维VO_x物种的宽峰。结果还表明傅里哀变换红外发射光谱是表征氧化物催化剂表面相结构的一种有力的方法。     

Complexation between vanadium(V) and citrate: spectroscopic and structural characterization of a dinuclear vanadium(V) complex

Investigation of the aqueous coordination chemistry for citrate and vanadium(V) resulted in the isolation and characterization of a dinuclear vanadium(V) citrato complex (1) Na₂K₂[VO2(Hcit)]₂ · 9H₂O. Complex (1) is an intermediate between the fully deprotonated and diprotonated citrate vanadate. It may represent an early mobilized precursor in the biosynthesis of FeV-co, as well as a relevant model in the proton transport relay process between P-cluster pair to M-cluster pair. The complex has been characterized by elemental analyses and i.r. spectroscopy. Its i.r. spectra are consistent with a oxo-bridged dinuclear structure as revealed by a single crystal X-ray diffraction study.     

Kinetic fluorimetric determination of traces of vanadium(V) by means of a catalysed autoxidation process

A kinetic method for determination of traces of vanadium(V) (0.04-0.5 ppm) is described. It is based on the catalytic action of vanadate in the autoxidation of sodium 4,8-diamino-1,5-dihydroxyanthraquinone-2,6-disulphonate, giving rise to kinetic curves characterized by an induction period before the appearance of a product exhibiting an intense red fluorescence in acidic solution. This product has been investigated and the experimental variables and interferences have been studied.     

NMR investigation of the interaction of vanadate with carbasilatranes in aqueous solutions

Reaction of vanadate with carbasilatranes [methoxy{N,N',N' '-2,2',3-[bis(1-methylethanolato)(propyl)]amino}silane (1), methoxy{N,N',N' '-2,2',3-[bis(1-ethanolethanolato)(propyl)]amino}silane (2), and {N,N',N' '-2,2',2-[bis(ethanolato)(glycolpropyl ether)]amino}silane (3)] in aqueous solution results in the formation of vanadosilicates and five-coordinated chelate vanadium(V) complexes as evidenced by 51V, 1H, and 13C NMR spectroscopy. Chiral carbasilatrane S,S-1 was characterized in the solid state by X-ray diffraction, revealing a trigonal bipyramidal geometry around the metal ion, with one unidentate methoxy group and one atrane nitrogen atom at the axial positions and one carbon and two atrane oxygen atoms at the equatorial plane of the bipyramid. Crystal data (Mo Kalpha; 100(2) K) are as follows: orthorhombic space group P2(1)2(1)2(1); a = 8.8751(6), b = 9.7031(7), c = 14.2263(12) A; Z = 4. The complexation of vanadium either with 1 or 2 is stereoselective yielding approximately 94% of the complex containing ligand in the S,R-configuration. The lower ability of the S,S- and R,R-diastereoisomers of 1 and 2 to ligate vanadate was attributed to stereochemical factors, dictating a square pyramidal geometry for the chelated complexes. A dynamic process between the vanadium chelate complexes and the respective carbasilatranes was evaluated by 2D {1H} EXSY NMR spectroscopy. These spectra show that the vanadate complexes with the open carbasilatranes exchange more slowly with the free ligand compared to the respective alcohol aminate complexes.     

钒与糖代谢及糖尿病

微量元素钒作为生物体内必需元素，经证实有很重要的生理学功能，与机体糖代谢有十分密切的关系，且能降低糖尿病动物模型的高血糖，极有可能被开发为治疗糖尿病的药物。     

In Process Citation

In studies of the reactivity of oxygen heterocycles, it has been found that khelline gives a molar reacting ratio of 1:16 with vanadate in 2.5M sulphuric acid, the products being vanadium(IV), 2.3 furan dicarboxylic acid, formic acid, acetic acid and carbon dioxide. This reaction can be used for determination of khelline and also for preparation of 2,3-furan dicarboxylic acid.     

Sarcoplasmic reticulum calcium ATPase is inhibited by organic vanadium coordination compounds: pyridine-2,6-dicarboxylatodioxovanadium(V), BMOV, and an amavadine analogue

The general affinity of the sarcoplasmic reticulum (SR) Ca (2+)-ATPase was examined for three different classes of vanadium coordination complexes including a vanadium(V) compound, pyridine-2,6-dicarboxylatodioxovanadium(V) (PDC-V(V)), and two vanadium(IV) compounds, bis(maltolato)oxovanadium(IV) (BMOV), and an analogue of amavadine, bis( N-hydroxylamidoiminodiacetato)vanadium(IV) (HAIDA-V(IV)). The ability of vanadate to act either as a phosphate analogue or as a transition-state analogue with enzymes' catalysis phosphoryl group transfer suggests that vanadium coordination compounds may reveal mechanistic preferences in these classes of enzymes. Two of these compounds investigated, PDC-V(V) and BMOV, were hydrolytically and oxidatively reactive at neutral pH, and one, HAIDA-V(IV), does not hydrolyze, oxidize, or otherwise decompose to a measurable extent during the enzyme assay. The SR Ca (2+)-ATPase was inhibited by all three of these complexes. The relative order of inhibition was PDC-V(V) > BMOV > vanadate > HAIDA-V(IV), and the IC 50 values were 25, 40, 80, and 325 microM, respectively. Because the observed inhibition is more potent for PDC-V(V) and BMOV than that of oxovanadates, the inhibition cannot be explained by oxovanadate formation during enzyme assays. Furthermore, the hydrolytically and redox stable amavadine analogue HAIDA-V(IV) inhibited the Ca (2+)-ATPase less than oxovanadates. To gauge the importance of the lipid environment, studies of oxidized BMOV in microemulsions were performed and showed that this system remained in the aqueous pool even though PDC-V(V) is able to penetrate lipid interfaces. These findings suggest that the hydrolytic properties of these complexes may be important in the inhibition of the calcium pump. Our results show that two simple coordination complexes with known insulin enhancing effects can invoke a response in calcium homeostasis and the regulation of muscle contraction through the SR Ca (2+)-ATPase.     

Atomic absorption spectrometry of vanadium with a tungsten electrothermal atomizer

A detailed study of the atomic absorption characteristics of vanadium with a tungsten micro-tube atomizer is presented. The absolute sensitivities (1% absorption) were 2 × lO^-10 and 4 × 10^-11 g of vanadium for ammonium vanadate and the vanadium N-benzoyl-N-phenylhydroxylamine complex, respectively. Diverse elements and acids have pronounced depressive effects, but vanadium may be determined in rocks after selective extraction of the above complex into chloroform.