Showing papers on "Vanadate published in 1994"
TL;DR: In this article, the vanadium coordination was investigated by UV-visible, near infrared, Raman, 51V NMR, and ESR spectroscopies, respectively after drying, calcination and catalytic oxidative dehydrogenation of propane in the 300-450°C temperature range.
196 citations
TL;DR: In this article, the authors used the citrate method to prepare catalysts with the Mg/V atomic ratio varying from 1/4 to 9/1, and found that alpha-Mg2V2O7 (pyrovanadate) was the most selective, while MgV 2O6 (metavanadate), the worst one.
164 citations
TL;DR: The use of digitonin to permeabilize the plasma membrane of Trypanosoma brucei procyclic and bloodstream trypomastigotes allowed the identification of a non-mitochondrial nigericin-sensitive Ca2+ compartment, which is tentatively named the acidocalcisome.
Abstract: The use of digitonin to permeabilize the plasma membrane of Trypanosoma brucei procyclic and bloodstream trypomastigotes allowed the identification of a non-mitochondrial nigericin-sensitive Ca2+ compartment. The proton ionophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) was able to cause Ca2+ release from this compartment, which was also sensitive to sodium orthovanadate. Preincubation of the cells with the vacuolar H(+)-ATPase inhibitor bafilomycin A1 greatly reduced the nigericin-sensitive Ca2+ compartment. Bafilomycin A1 inhibited the initial rate of ATP-dependent non-mitochondrial Ca2+ uptake and stimulated the initial rate of nigericin-induced Ca2+ release by permeabilized procyclic trypomastigotes. ATP-dependent and bafilomycin A1- and 7-chloro-4-nitrobenz-2-oxa-1,3-diazole (NBD-Cl)-sensitive Acridine Orange uptake was demonstrated in permeabilized cells. Under these conditions Acridine Orange was concentrated in abundant cytoplasmic round vacuoles by a process inhibited by bafilomycin A1, NBD-Cl, nigericin, and Ca2+. Vanadate or EGTA significantly increased Acridine Orange uptake, while Ca2+ released Acridine Orange from these preparations, thus suggesting that the dye and Ca2+ were being accumulated in the same acidic vacuole. Acridine Orange uptake was reversed by nigericin, bafilomycin A1 and NH4Cl. The results are consistent with the presence of a Ca2+/H(+)-ATPase system pumping Ca2+ into an acidic vacuole, that we tentatively named the acidocalcisome.
157 citations
TL;DR: The three-dimensional structures of complexes of recombinant rat prostatic acid phosphatase with the transition-state analogs vanadate and molybdate with 0.3-nm resolution were determined using protein crystallographic methods.
Abstract: The three-dimensional structures of complexes of recombinant rat prostatic acid phosphatase with the transition-state analogs vanadate and molybdate were determined to 0.3-nm resolution using protein crystallographic methods. The overall structure of the enzyme remains unchanged upon binding of the metal oxyanions; only local conformational differences in the positions of some side chains at the active site were found. The metal oxyanions bind in an identical fashion at the active site with trigonal bipyramidal coordination geometry. The metal ion is within coordination distance of the His 12 side chain which is located at one of the axial positions. The three equatorial oxygen atoms interact with the conserved residues Arg11, Arg15, Arg79 and His257, Within hydrogen-bonding distance of the axial oxygen atom is the side chain of the conserved residue Asp258. The implications of these results for the catalytic mechanism of acid phosphatase are discussed.
130 citations
TL;DR: In this paper, the synthesis and characterization of polyoxovanadate-intercalated MgAl hydrotalcite-like layered double hydroxides (LDH) is described.
Abstract: The synthesis and characterization of polyoxovanadate-intercalated MgAl hydrotalcite-like layered double hydroxides (LDH) is described. Seven different methods have been used to intercalate the vanadate anion. These include exchange of the initial carbonate or terephthalate anions, as well as reconstruction of the layered structure from the carbonate form previously calcined at 550 o C-the reconstruction being either directly to the vanadate or indirectly via a terephthalate intermediate. Preswelling with glycerol was also used in some cases
120 citations
TL;DR: The aqueous chemistry of vanadate (vanadium(V)) is very complex since many protonation equilibrium and oligomerization equilibria are occurring simultaneously as mentioned in this paper.
Abstract: The aqueous chemistry of vanadate (vanadium(V)) is very complex since many protonation equilibria and oligomerization equilibria are occurring simultaneously. Vanadate monomer (V1), dimer (V2), tetramer (V4) and pentamer (V5) are exchanging with each other on a millisecond time scale so that none of these species can be isolated for aqueous biological studies. Measuring the effects of each anion on an enzyme must be carried out in an equilibrium mixture containing the other vanadate oligomers. Defining conditions to measure the effects of oxovanadates is non-trivial, since vanadate interacts with buffers and other assay components. Information concerning the simple aqueous chemistry of vanadate with various ligands is thus necessary to ensure that the vanadate is free to interact with an enzyme or a protein. Experimental approaches, which take into account the aqueous chemistry of labile oxovanadates, to biological studies are described here. For this purpose, the interactions of oxovanadates wit...
113 citations
TL;DR: Shisheva et al. as discussed by the authors showed that vanadium effects on protein tyrosine kinases are preserved after cell disintegration, suggesting that vanadate effect is secondary to inhibiting protein phosphotyrosine phosphatases.
86 citations
TL;DR: It is demonstrated that the ATPase of Acetobacterium woodii is a Na+-translocating F1FO-type ATPase, indicating that the enzyme is of the F1 FO type.
Abstract: The ATPase of Acetobacterium woodii was purified after solubilization of membranes with Triton X-100 by poly(ethylene glycol) precipitation and gel filtration. The enzyme consists of at least six subunits of apparent molecular masses of 57, 52, 35, 19, 15 and 4.8 kDa, as determined by SDS/PAGE. The 52-kDa band is immunologically related to the F1F0-ATPase beta subunit of Escherichia coli. The enzyme is not inhibited by vanadate but is inhibited by nitrate, azide and N,N'-dicyclohexylcarbodiimide; the 4.8-kDa subunit specifically reacts with N,N'-dicyclohexyl[14C]carbodiimide, indicating that the enzyme is of the F1F0 type. The enzyme activity is dependent on MgATP (Km = 0.4), has a pH optimum of pH 7-9 and is stimulated by sulfite. ATP hydrolysis is strictly dependent on sodium ions with a Km for Na+ of 0.4 mM. The purified enzyme was reconstituted into liposomes. Upon addition of ATP, primary and electrogenic 22Na+ transport into the lumen of the proteoliposomes was determined. These experiments demonstrate that the ATPase of Acetobacterium woodii is a Na(+)-translocating F1F0-type ATPase.
84 citations
TL;DR: The glucose-lowering effect of vanadate in STZ-induced diabetic rats can be explained by its inhibition of feeding, and its hypophagic action does not appear to involve inhibition of NPYergic pathways in the hypothalamus.
Abstract: Vanadate treatment can lower glycemia in diabetic rats. This action is generally attributed to vanadate's insulinomimetic properties, but vanadate also inhibits feeding, which could lower blood glucose. We therefore assessed the contribution of hypophagia to vanadate's antihyperglycemic action in a 3-week study of streptozocin-induced (STZ) diabetic rats. Untreated diabetic rats ( n = 8) ate 54% more food than nondiabetic control rats ( P 0.05 vs. vanadate-treated diabetic rats). Vanadate treatment did not affect plasma insulin concentrations in diabetic rats. In nondiabetic rats ( n = 8), vanadate treatment significantly reduced food intake ( P < 0.05) and also lowered plasma insulin concentrations ( P < 0.05) without significantly affecting glycemia. To investigate the mechanism of vanadate's hypophagic effect, we also measured regional hypothalamic levels of neuropeptide Y (NPY), a potent central appetite stimulant that is thought to drive hyperphagia in STZ-induced diabetes. Hypothalamic NPY concentrations rise markedly in diabetes and are normalized by insulin replacement. Unlike insulin, vanadate treatment did not normalize regional hypothalamic NPY concentrations in diabetic rats. Vanadate does not therefore appear to exert an insulin-like action at the hypothalamic level; its hypophagic action does not appear to involve inhibition of NPYergic pathways in the hypothalamus. We conclude that the glucose-lowering effect of vanadate in STZ-induced diabetic rats can be explained by its inhibition of feeding. Although vanadate has certain insulinomimetic effects in vitro and in vivo, the role of these effects in vanadate's antidiabetic actions must be critically reexamined.
79 citations
01 Jan 1994
TL;DR: It is demonstrated that vanadium effects on protein tyrosine kinases are preserved after cell disintegration, supporting a working hypothesis implicating the intracellular vanadyl pool in modulating CytPTK activity.
Abstract: substrate concentrations. Preincubation of adipocytes with vanadyl(0.4 mM), and staurosporine (which arrests the cytosolic enzyme) sub- stantially inhibited insulin-stimulated lipogenesis. Va- nadyl is readily oxidized to vanadate by hydrogen per- oxide. In contrast, CytPTKs were poorly inhibited by vana- dyl, and vanadate stimulated several CytPTKs 2-6-fold. CytPTK derived from rat adipocytes, liver and brain were activated, and CytPTK from
78 citations
TL;DR: Vanadate tetramer, V4 has been identified as the species responsible for the specific UV-light induced photocleavage of the active site of myosin and possibly adenylate kinase.
Abstract: Aqueous solutions of vanadate contain several labile oxovanadates; each interacts differently with enzymes and other proteins. Vanadate monomer, V1 can act as a ground state or transition state analog of phosphate. Vanadate dimer, V2 inhibits a series of enzymes including dehydrogenases, one aldolase and a phosphatase. V2 can also activate enzymes, and this activation has been observed with a mutase and dehydrogenase. Vanadate tetramer, V4 (often referred to as “metavanadate”), inhibits a large number of enzymes including dehydrogenases, isomerases, and one aldolase. V4 also binds to a series of enzymes including superoxide dismutase, myosin and possibly adenylate kinase. V4 has been identified as the species responsible for the specific UV-light induced photocleavage of the active site of myosin and possibly adenylate kinase. Redox chemistry between V1 and V4 and proteins has been reported. Vanadate pentamer, V5 has not yet shown high affinity for proteins, and studies with related oxomolybdates...
TL;DR: In this paper, the IR and Raman spectra of Mg orthovanadate Mg3(VO4)2, Mg pyrovanadate mg2V2O7 and Mg metavanadate nv2O6 powders are reported, described and discussed on the basis of the crystal structures of these phases and of the optical activity of the fundamental vibrational modes predicted with the use of the correlation method.
Abstract: The IR and Raman spectra of Mg orthovanadate Mg3(VO4)2, Mg pyrovanadate Mg2V2O7 and Mg metavanadate MgV2O6 powders are reported, described and discussed on the basis of the crystal structures of these phases and of the optical activity of the fundamental vibrational modes predicted with the use of the correlation method. The IR-active combinations are also discussed. The structural and vibrational features of these compounds are discussed in relation to those of other V-based oxidic catalytic materials.
TL;DR: In this paper, three vanadate phases, i.e., MgV2O6 (metavanadate), α-Mg2V 2O7 (pyrovana-date), and Mgs V2O8 (orthovanadate) have been successfully prepared with high purity by the citrate method at a relatively low temperature (550°C).
Abstract: Three magnesium vanadate phases, i.e., MgV2O6 (metavanadate), α-Mg2V2O7 (pyrovana-date) and Mgs V2O8 (orthovanadate), have been successfully prepared with high purity by the citrate method at a relatively low temperature (550°C). FT-IR, LRS, XRD and SEM techniques have been used to characterize these vanadate phases. The effect of calcination temperature has also been investigated. It was found that the particle size and morphology of the MgV2O6 phase, which is a function of calcination temperature, appear to have a strong effect on the infrared spectra. Furthermore, the catalytic properties of the three phases were examined in the oxidative dehydrogenation of propane. The propene selectivity follows the order: α-Mg2V2O7 > Mg3 Vg2O8 > MgV2O6, which is consistent with their redox properties. This fact suggests that there is some correlation between the catalytic and redox properties of these magnesium vanadate phases.
TL;DR: In this article, the adsorption and coadsorption of nitrogen dioxide and ammonia on an anatase-supported vanadia catalyst prepared by ion exchange from an acidic aqueous solution of ammonium vanadate are investigated by IR spectroscopy and ESR.
TL;DR: It is found that the V-type H+ pump in isolated rat liver endosomes is sensitive to 100 microM SCH and OME to a similar degree, and this finding indicates the importance of using low concentrations (< 10 microM) of OME and SCH in studies of H(+)-K(+-ATPase in nongastric tissues to avoid misinterpretation of the data due to nonspecific inhibition of V- type H( +)-ATPases.
Abstract: Adenosinetriphosphatase (ATPase) activity stimulated by K+ and inhibited by Sch-28080 (SCH), omeprazole (OME), and vanadate has been measured in microsomes from mammalian renal medulla and attributed to a kidney isoform of the H(+)-K(+)-ATPase. To determine whether the H(+)-K(+)-ATPase inhibitors could also inhibit the vacuolar (V)-type H(+)-adenosinetriphosphatase (H(+)-ATPase, i.e., H+ pump) in mammalian intracellular vesicles, we examined their effects on bafilomycin-sensitive acidification in renal cortical vesicles (CEV) and medullary endocytic vesicles (MEV). Rats were injected with fluorescein isothiocyanate-labeled dextran, and labeled endosomes were enriched from kidney tissue homogenates by differential and Percoll density gradient centrifugation. In the CEV, the V-type H+ pump was inhibited 25% by SCH and 30% by OME (100 microM each). Whereas the inhibition by OME was concentration and time dependent, the inhibition by SCH was only concentration dependent. Inhibition by these compounds was similar in the presence of 50 mM K+ (in = out) and in the complete absence of K+, thus ruling out a significant involvement of H(+)-K(+)-ATPase-mediated acidification. Inhibition, however, was not observed with 10 microM SCH and OME. The sensitivity of the V-type H+ pump to 100 microM SCH and OME in CEV was confirmed by the comparable inhibitions of intravesicular acidification observed in acridine orange fluorescence quench studies and by inhibition of Pi liberation in an ATPase assay. We also found that the V-type H+ pump in isolated rat liver endosomes is sensitive to 100 microM SCH and OME to a similar degree. In the MEV, acidification was only weakly affected by 100 microM SCH and OME, thus suggesting that H(+)-ATPases in endosomes from cortical and medullary tubules are different, possibly due to a previously described selective expression of subunit isoforms. Our finding indicates the importance of using low concentrations (< 10 microM) of OME and SCH in studies of H(+)-K(+)-ATPase in nongastric tissues to avoid misinterpretation of the data due to nonspecific inhibition of V-type H(+)-ATPases.
Journal Article•
TL;DR: A model proposing that K+ channels play a dominant role in high-K+ (113 mmol l-1) bathing medium and a K+/Na+/2Cl- cotransporter may gain in importance in 51 mmol l -1 [K+]bl was proposed.
Abstract: In the presence of 6 mmol l-1 Ba2+, known to block the K+ channels in the basal membrane, a rise in bath [K+] ([K+]bl) induced an increase in intracellular K+ concentration ([K+]i) similar in amount and in time course to that obtained in the absence of Ba2+. The presence of active and passive (other than through K+ channels) K+ uptake mechanisms across the basal membrane was investigated in different bath K+ concentrations. Dihydro-ouabain (10(-3) mol l-1), a blocker of the Na+/K(+)-ATPase, tested in low bath [K+], and Sch28080 (10(-4) mol l-1), a K+/H(+)-ATPase inhibitor, were without effect on fluid secretion. Dihydro-ouabain was also without effect on electrical potential differences either in the absence or in the presence of Ba2+. Vanadate (10(-3) mol l-1), in contrast, strongly reduced fluid secretion not only in control solution but also in high-K+, Na(+)-free medium and reduced the transepithelial and the apical membrane potential differences but not the basal membrane potential difference of [K+]i. Omitting Na+ from the bathing medium, replacing Cl- by Br- or applying bumetanide (10(-5) mol l-1) inhibited fluid secretion only in a low-K+ (10 mmol l-1) medium. In 51 mmol l-1 [K+]bl, omitting Na+ was without effect and 10(-4) mol l-1 bumetanide was needed to inhibit secretion. Replacing Cl- by Br- stimulated fluid secretion at this K+ concentration. Bumetanide (10(-4) mol l-1) had no effect in 113 mmol l-1 [K+]bl. Bumetanide (10(-4) mol l-1) in 51 mmol l-1 [K+]bl did not affect membrane potentials, did not lower [K+]i and did not affect the rise in [K+]i observed on an increase in [K+]bl. The results were summarized in a model proposing that K+ channels play a dominant role in high-K+ (113 mmol l-1) bathing medium. A K+/Cl- cotransporter may become more important in 51 mmol l-1 [K+]bl and a K+/Na+/2Cl- cotransporter may gain in importance in 10 mmol l-1 [K+]bl. Active mechanisms for K+ uptake across the basal membrane seem to play no detectable role in sustaining fluid secretion. The response to vanadate might be due to an effect on the apical electrogenic H+ pump.
TL;DR: It is concluded that vanadate prolongs insulin action at insulin concentrations that do not maximally activate the IRK by augmenting IRK activity and activation of receptor above that required for a maximum biological response results in prolongation of action.
Abstract: Vanadate, a protein tyrosine phosphatase inhibitor, preserves insulin-stimulated lipogenesis after removal of insulin. To investigate the mechanism of this action of vanadate, lipogenesis was studied in isolated rat adipocytes exposed to vanadate for 60 min followed by insulin for 15 min at 37°C. Vanadate (10–50 μM) prolonged insulin-stimulated lipogenesis. The half-time (t½) of the decay in insulin (0.34 nM)-stimulated lipogenesis after removal of insulin by washing in pH 7.0 followed by pH 7.6 buffer was 21 min in the absence and 59 min in the presence of vanadate. During these conditions, vanadate did not alter insulin binding nor the removal of insulin by the series of washes. In contrast to lipogenesis, the t½ of the decay in insulin receptor tyrosine kinase (IRK) activity, assayed with the artificial substrate Poly\[Glu:Tyr\] (4:1), was not significantly prolonged by vanadate (6 vs. 6.8 min). However, insulin-stimulated IRK activity was markedly augmented by vanadate to 319 ± 19% of insulin alone, associated with a similar augmentation of phosphotyrosine incorporation into the insulin receptor beta-subunit determined by Western blotting with antiphosphotyrosine antibodies. To determine the relationship between prolongation of lipogenesis and the increase in IRK, adipocytes were exposed to 17.2 nM insulin to activate the IRK to the same extent as insulin (0.34 nM) plus vanadate (maximum activation). During these two conditions, the decay of lipogenesis was similar and after stimulation with 17.2 nM insulin was not prolonged by vanadate. We conclude that vanadate prolongs insulin action at insulin concentrations that do not maximally activate the IRK by augmenting IRK activity.The data suggest that the amplitude of the insulin signal, the IRK, is transduced into duration of response, lipogenesis. Thus activation of receptor above that required for a maximum biological response results in prolongation of action.
TL;DR: It is proposed that the mechanism for vanadium-dependent toxicity and antineoplastic action is due to DNA cleavage by hydroxyl radicals generated in living systems.
Abstract: Vanadium ion is toxic to animals. However, vanadium is also an agent used for chemoprotection against cancers in animals. To understand both the toxic and beneficial effects we studied vanadium distribution in rats. Accumulation of vanadium in the liver nuclei of rats given low doses of compounds in the +4 or +5 oxidation state was greater than in the liver nuclei of rats given high doses of vanadium compounds or the vanadate (+5 oxidation state) compound. Vanadium was incorporated exclusively in the vanadyl (+4 oxidation state) form. We also investigated the reactions of vanadyl ion and found that incubation of DNA with vanadyl ion and hydrogen peroxide (H2O2) led to intense DNA cleavage. ESR spin trapping demonstrated that hydroxyl radicals are generated during the reactions of vanadyl ion and H2O2. Thus, we propose that the mechanism for vanadium-dependent toxicity and antineoplastic action is due to DNA cleavage by hydroxyl radicals generated in living systems.
TL;DR: The resulting reactive species generated byVanadium(IV) from H2O2 and lipid hydroperoxide via a Fenton-like reaction may play a significant role in the mechanism of vanadium(V)-induced cellular injury.
TL;DR: Gel filtration shows that the ATPase activity is mainly associated with a 68 kDa protein that is extracted with the p33/p35 annexins and cross-reacts with antibodies to these proteins.
Abstract: An ATPase activity is associated with maize (Zea mays) annexins. It has a pH optimum of 6.0, shows Michaelis-Menten kinetics and is not stimulated by Ca2+, Mg2+, EDTA or KCl; it is not inhibited by vanadate, molybdate, nitrate or azide, but N-ethylmaleimide inhibits by approximately 30% at 1-2 mM. These properties indicate that the activity is unlike other ATPases, although it has many features in common with the myosin ATPase. Gel filtration shows that the ATPase activity is mainly associated with a 68 kDa protein that is extracted with the p33/p35 annexins and cross-reacts with antibodies to these proteins.
TL;DR: This study demonstrates that different forms of vanadium are direct inhibitors of ALP activity, dependent on the enzymatic activity investigated and on the origin of the ALP.
Abstract: The direct effect of different vanadium compounds upon alkaline phosphatase (ALP) activity was investigated. Vanadate and vanadyl inhibited both the soluble and particulate ALP activity from UMR.106 cells and from bovine intestinal ALP. We have also shown the inhibition of ALP activity in the soluble fraction of osteoblasts by peroxo and hydroperoxo vanadium compounds. ALP activity in the particulate fraction was not inhibited by these species; nor was the bovine intestinal ALP. Using inhibitors of Tyr-phosphatase (PTPases), the soluble ALP was partially characterized as a PTPase. The major activity in the particulate fraction represents the bone-specific ALP-activity. This study demonstrates that different forms of vanadium are direct inhibitors of ALP activity. This effect is dependent on the enzymatic activity investigated and on the origin of the ALP.
TL;DR: Upon addition of sarcoplasmic reticulum (SR), the line width of tetrameric vanadate signal of 51V-NMR spectra narrowed in the presence of ATP and Ca2+, whereas monomericVanadate line widths were broadened.
TL;DR: High-affinity Ca2+ uptake was found to be completely inhibited by low concentrations of vanadate, but not by thapsigargin, suggesting that the activity is mediated by a Ca(2+)-ATPase distinct from sarco(endo)plasmic reticulum type of higher animal cells.
TL;DR: It is shown that a protein tyrosine phosphatase inhibitor, sodium orthovanadate, induces rat pheochromocytoma cells to express neurites, a prominent morphological marker of neuronal phenotype, and that vanadate-induced neurite outgrowth responses in phechromocyToma and SH-SY5Y cells can be induced by the inhibition of tyrosin phosphatases.
TL;DR: The results suggest that blood hypertension in rats exposed to vanadate depends on specific mechanisms of renal toxicity related to the levels of exposure.
Abstract: The effects of 1, 10, or 40 micrograms/ml of vanadium, given for six or seven months as sodium metavanadate in drinking water on cardiovascular and biochemical variables and the electrolyte metabolism of male Sprague-Dawley rats were investigated. At the end of the exposure period, all animals exposed to vanadate had increased systolic and diastolic blood pressure. This effect was not dose dependent and heart rate and cardiac inotropism were not affected. The role of defective renal function and electrolyte metabolism in such effects was supported, in the rats exposed to 10 and 40 ppm of vanadium, by the following changes: (a) decreased Na, + K(+)-ATPase activity in the distal tubules of nephrons; (b) increased urinary excretion of potassium; (c) increase in plasma renin activity and urinary kallikrein, kininase I, and kininase II activities; (d) increased plasma aldosterone (only in the rats treated with 10 ppm of vanadium). The alterations in the rats exposed to 1 ppm of vanadium were: (a) reduced urinary calcium excretion; (b) reduced urinary kallikrein activity; (c) reduced plasma aldosterone. These results suggest that blood hypertension in rats exposed to vanadate depends on specific mechanisms of renal toxicity related to the levels of exposure.
TL;DR: It is concluded that helical tubes are composed of the Ca(2+)-free, dephosphorylated conformation (E), and the nucleotide-bound conformation(E-ATP) is also tolerated, in contrast, multilamellar crystals are compose of theCa(2-)-bound con formation (E.Ca2) and do not tolerate nucleotide binding.
TL;DR: It is concluded that MgATP stimulation of Na-Ca exchange is proportional to the levels of phosphorylation that result from the balance of the activity of a kinase and a phosphatase activity.
Abstract: We have proposed that in squid axons MgATP stimulation of Na-Ca exchange involves a phosphorylation-dephosphorylation process catalyzed by a kinase-phosphatase system. In the present work, we used ...
TL;DR: In this article, it was shown that oxyanions, such as vanadate (V) or vanadyl (IV), cause insulin-like effects on rats by stimulating the insulin receptor tyrosine kinase.
TL;DR: The acid-base properties of V 2 O 5 /γ-Al 2 O 3 catalysts were characterized by ammonia, pyridine and sulphur dioxide adsorptions using microcalorimetry and diffuse reflectance Fourier transform Ir spectroscopy (DRIFT).
Abstract: The acid-base properties of V 2 O 5 /γ-Al 2 O 3 catalysts were characterized by ammonia, pyridine and sulphur dioxide adsorptions using microcalorimetry and diffuse reflectance Fourier transform Ir spectroscopy (DRIFT) For vanadium content less than 10 wt-% V 2 O 3 (49 μmol(V 2 O 5 ) m −2 ), the vanadium cations were found to be well spread as vanadate compounds over alumina Such vanadate species developed Bronsted and Lewis-type acidity as shown by a DRIFT spectroscopy study of pyridine adsorption, but did not exhibit a basic character Sulphur dioxide adsorption allowed to differentiate a vanadate layer from free alumina Ammonia and sulphur dioxide adsorptions also showed that at low vanadium coverage, a large part of the vanadate layer was bound to acid-base pairs of alumina Vanadium pentoxide crystallites were detected at less than complete monolayer coverage with vanadate compounds, but did not contribute to the development of the acidic surface character At low vanadium coverage, ( 2 O 5 , 12 μmol(V 2 O 5 ) m −2 ), the acidic character of the V 2 O 5 /γ-Al 2 O 3 catalysts is ascribed to vanadium-free alumina, whereas it is largely attributed to vanadate compounds at higher vanadium coverage