Raman studies on species in aqueous solutions. Part I. The vanadates

Griffith, William P.; Wickins, T. D.

doi:10.1039/j19660001087

Cited by 106 publications

(85 citation statements)

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“…34,35 This is in contrast to Griffith and Wickins, who observed only Raman bands typical of the hexaniobate ion in a 12 M KOH solution. 36 The presence of the hexaniobate ion at high KOH concentrations (6.7 and 15 M) was also observed in this study, as confirmed by Raman spectroscopy. In addition, as detailed below, the absence of the monomer in 6.7 and 15 M KOH solutions at room temperature was also confirmed by solution 93 Nb NMR spectroscopy.…”

Section: A Hexaniobate Ionsupporting

confidence: 66%

Hydrothermal synthesis of KNbO₃ and NaNbO₃ powders

et al. 2003

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Orthorhombic KNbO 3 and NaNbO 3 powders were hydrothermally synthesized in KOH and NaOH solutions (6.7-15 M) at 150 and 200°C. An intermediate hexaniobate species formed first before eventually converting to the perovskite phase. For synthesis in KOH solutions, the stability of the intermediate hexaniobate ion increased with decreasing KOH concentrations and temperatures. This led to significant variations in the induction periods and accounted for the large disparity in the mass of recovered powder for different processing parameters. It is also believed that protons were incorporated in the lattice of the as-synthesized KNbO 3 powders as water molecules and hydroxyl ions.

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Section: A Hexaniobate Ionsupporting

confidence: 66%

Hydrothermal synthesis of KNbO₃ and NaNbO₃ powders

et al. 2003

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“…The tetrahedral vanadate ion has the capacity either to exchange ligands or to accept a fifth ligand (as in crystalline metavanadates) to form a trigonal bipyramidal complex (13), which resembles the transition state for phosphoryl transfer (2,24,25). Although there is no evidence of a five-coordinate V1 species in free solution (13,(26)(27)(28), such a complex might be stabilized at the myosin active site. Because ADP is required for Vi incorporation, it is further possible that Vi incorporation involves the formation of a binary transition-state analog at the active site (24,29).…”

Section: Resultsmentioning

confidence: 95%

Inhibition of myosin ATPase by vanadate ion.

Goodno¹

1979

Proc. Natl. Acad. Sci. U.S.A.

274

218

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Inhibition of the myosin ATPase by vanadate ion (V1) has been studied in 90 mM NaCl/5 mM MgCl2/20 mM Tris HCI, pH 8.5, at 250C. Although the onset of inhibition during the assay is slow and dependent upon Vi concentration (kap -t 0.3 M-1 s-'), the final level of inhibition approaches iOO4o, provided the V; concentration is in slight excess over the concentration of ATPase sites. Inhibition is not reversible by dialysis or the addition of reducing agents. The source of this irreversible inhibition consists of the formation of a stable, inactive complex with the composition MADP-V1 (where M represents a single myosin active site). The complex has been isolated, and its mechanism of formation from M, ADP, and Vi has been studied. Omission of ATP increases the rate of formation by about 35-fold (kapp 11 M-1 s-'), yet this rate is still low in comparison with the rates of simple protein-ligand association reactions. This slowness is interpreted in terms of a rate-limiting isomerization step that follows the association of M, ADP, and V1: M*ADP*V1 _ Mt.ADP.V1 (t indicates the inactive product of the isomerization). (9) and Weeds and Taylor (10), respectively. The HMM fraction that precipitated between 45 and 60% saturated ammonium sulfate was dialyzed free of ammonium sulfate, centrifuged 30 min at 40,000 X g, and used within 10 days. The concentration of HMM was expressed in terms of the ATPase-site concentration, which was determined spectrophotometrically by using a value of A2801% = 6.47 (11), assuming a molecular weight of 340,000 and two ATPase sites per molecule.ATPase assays were carried out in buffer A (0.09 M NaCl/5 mM MgCl2/20 mM Tris-HCI, pH 8.5) at 250C by the addition of MgATP (final concentration, 1 mM) to HMM at 1-7 AM sites.Assay times ranged from 0.1 to 5 hr. The reaction was stopped in aliquots (1 ml) of the assay solution with 1 ml of 10% trichloroacetic acid. The aliquots were then clarified by centrifugation and half of each was analyzed for Pi by the procedure of Taussky and Shorr (12). V1 concentrations below 10 mM caused less than 1% interference.Vanadium Analysis. Stock solutions of V1 were prepared from either Na3VO4 (adjusted to pH 10 with 6 M HCl) or V205 (adjusted to pH 10 with 10 M NaOH) and then boiled to destroy yellow polymeric species such as V100286-(13). Standard solutions were prepared by volumetric dilution. In order to minimize the pH-dependent polymerization of Vi, all studies were carried out under the alkaline conditions used for the ATPase assays (buffer A). UV-visible spectra of Vi standard solutions were obtained by using a Cary 14 spectrophotometer, and the extinction coefficient was determined: Xrnax = 265 nm, C265 = 2925 M-1 cm-1. The Vi concentration was determined spectrophotometrically wherever possible.Where this was unfeasible (e.g., in the presence of protein), vanadium was determined by a modification of the colorimetric procedure of Pribil (14), using the metallochromic dye PAR.To a 1-ml sample in buffer A was added 100 Al of 1 M imidazole (pH 6.0) and ...

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“…This is especially surprising taking into account the experimental evidence that V-O-V vibrations are not located above 900 cm -1 in solid compounds as well as in solutions. 46, 49 We will discuss here the pros and cons of the alternative assignments, without making a definite conclusion. Future characterization studies, together with detailed theoretical calculations on realistic molecular models, hopefully will make one of these assignments unambiguous.…”

Section: Structural Model For a Vo 4 Species On Anmentioning

confidence: 99%

“…Second, Griffith et al showed that the V-O-V stretch vibration lies below 850 cm -1 for polymeric and dimeric vanadium oxide species. 49 The spectrum of aqueous V 10 61 for which polymeric species are never observed. 12,60 Although SiO 2 exhibits a band at 970 cm -1 , there is no band from silica observable near 920 cm -1 .…”

Section: Structural Model For a Vo 4 Species On Anmentioning

confidence: 99%

ΛO₄ Upside Down: A New Molecular Structure for Supported VO₄ Catalysts

et al. 2005

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Vanadium oxide (1 wt %) supported on γ-Al 2 O 3 was used to investigate the interface between the catalytically active species and the support oxide. Raman, UV-vis-NIR DRS, ESR, XANES, and EXAFS were used to characterize the sample in great detail. All techniques showed that an isolated VO 4 species was present at the catalyst surface, which implies that no V-O-V moiety is present. Surprisingly, a Raman band was present at 900 cm -1 , which is commonly assigned to a V-O-V vibration. This observation contradicts the current literature assignment. To further elucidate on potential other Raman assignments, the exact molecular structure of the VO 4 entity (1 VdO bond of 1.58 Å and 3 V-O bonds of 1.72 Å) together with its position relative to the support O anions and Al cation of the Al 2 O 3 support has been investigated with EXAFS. In combination with a structural model of the alumina surface, the arrangement of the support atoms in the proximity of the VO 4 entity could be clarified, leading to a new molecular structure of the interface between VO 4 and Al 2 O 3 . It was found that VO 4 is anchored to the support oxide surface, with only one V-O support bond instead of three, which is commonly accepted in the literature. The structural model suggested in this paper leaves three possible assignments for the 900 cm -1 band: a V-O-Al vibration, a V-O-H vibration, and a V-(O-O) vibration. The pros and cons of these different options will be discussed.

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Raman studies on species in aqueous solutions. Part I. The vanadates

Cited by 106 publications

References 0 publications

Hydrothermal synthesis of KNbO₃ and NaNbO₃ powders

Hydrothermal synthesis of KNbO₃ and NaNbO₃ powders

Inhibition of myosin ATPase by vanadate ion.

ΛO₄ Upside Down: A New Molecular Structure for Supported VO₄ Catalysts

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Raman studies on species in aqueous solutions. Part I. The vanadates

Cited by 106 publications

References 0 publications

Hydrothermal synthesis of KNbO3 and NaNbO3 powders

Hydrothermal synthesis of KNbO3 and NaNbO3 powders

Inhibition of myosin ATPase by vanadate ion.

ΛO4 Upside Down: A New Molecular Structure for Supported VO4 Catalysts

Contact Info

Product

Resources

About

Hydrothermal synthesis of KNbO₃ and NaNbO₃ powders

Hydrothermal synthesis of KNbO₃ and NaNbO₃ powders

ΛO₄ Upside Down: A New Molecular Structure for Supported VO₄ Catalysts