scholarly journals FTIR-SPECTROSCOPIC INVESTIGATION OF SODIUM TUNGSTATE AND SODIUM MOLYBDATE SOLUTIONS IN WIDE RANGE OF рH

2017 ◽  
Vol 60 (1) ◽  
pp. 56
Author(s):  
Yulya V. Matveichuk
Keyword(s):  
Ir Spectroscopy ◽  
Spectroscopic Investigation ◽  
Sodium Tungstate ◽  
Sodium Molybdate ◽  
Tungsten Particle ◽  
Complex Frequency ◽  
Selective Electrode ◽  
Wide Range ◽  
Tungstate Solution ◽  
Stretching Vibrations

For citation:Matveichuk Yu.V. FTIR-spectroscopic investigation of sodium tungstate and sodium molybdate solutions in wide range of рH. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 1. P. 56-63. A FTIR spectroscopic study of aqueous solutions of sodium tungstate and molybdate (solution concentration was 0.1 mol/l) over a wide pH range (factor (level) of acidity Z, Z = C (H+)/C (WO42-) or Z = C (H+)/C(MoO42-)) was carried out. In solutions of sodium tungstate complex frequency band at 885-865 cm-1 correspoding to the stretching vibrations ν(W-O-W) was fixed. The frequency bands of 1720-1700 cm-1, 990, 985 and 1025 cm-1 corresponding to bending vibrations δ(W-OH) were fixed that indicates a significant change in composition of the solution as a result of hydrolytic and polycondensation processes. The sodium molybdate solution has not bands corresponding to the stretching vibrations v(Mo-O-Mo). Only the characteristic bands of the deformation vibrations δ(Mo-OH) were recorded. The low intensity complex band in the area of 885-865 cm-1 corresponding to the stretching vibrations ν(W-O-W) even for freshly prepared 0.1 mol/l sodium tungstate solution was appeared as well as the band at 1720-1700 cm-1 attributed to deformation vibrations δ(W-OH) that indicates a fast change in the solution composition. For solutions of sodium molybdate bands of stretching vibrations v(Mo-O-Mo) are fixed at a pH less than 6 after standing for several days. With Hydra/Medusa program diagrams of distribution of molybdate and tungsten particle depending on the pH were calculated. In relatively dilute solutions, the diagrams received with Hydra/Medusa program showed the only protonated (monomeric) form of molybdate ions, where as in the sodium tungstate solution until pH of 9 W6O216- and HW6O215- particles exist that agrees with the results of IR spectroscopy. The results of IR spectroscopy and modeling with Hydra/Medusa program will be used to support the pH operating range for molybdate and tungstate-selective electrodes, since they are an important feature of any analytical ion-selective electrodes. For tungstate-selective electrode it is necessary to maintain the pH less than 9, for molybdate-selective electrode - less than 8 (with dilute ammonia). Considering the changes in the composition of sodium molybdate and tungstate solutions, for the design of molybdate and tungstate-selective electrodes the freshly prepared solutions have to be only used, rather than stored for more than two days.

Oxoanions stimulate in vitro ovulation and signal transduction pathways in goldfish (Carassius auratus) follicles

1992 ◽  
Vol 263 (5) ◽  
pp. E943-E949 ◽  
Author(s):  
S. Y. Hsu ◽  
F. W. Goetz
Keyword(s):  
Signal Transduction ◽  
Carassius Auratus ◽  
Sodium Tungstate ◽  
Sodium Molybdate ◽  
Vanadyl Sulfate ◽  
Signal Transduction Pathways ◽  
Sodium Selenate ◽  
Sodium Chromate ◽  
Goldfish Carassius Auratus

The present study investigated the effects of a number of oxoanion compounds on in vitro ovulation of goldfish follicles and ovarian second messenger activities. Significant levels of ovulation were induced by 0.1 mM sodium chromate, 0.1 mM sodium metavanadate, 10 mM sodium molybdate, 0.1 mM sodium orthovanadate, 5 mM sodium selenate, 0.5 mM sodium tungstate, and 0.1 mM vanadyl sulfate. At levels that significantly stimulated ovulation, metavanadate, molybdate, orthovanadate, tungstate, and vanadyl sulfate also stimulated follicular phosphatidylinositol cycling and inhibited ovarian alkaline phosphatase activity. Moreover, the ovulation induced by these oxoanions was not inhibited by indomethacin (10 micrograms/ml), while ovulation induced by selenate and chromate was. In contrast, only vanadium-containing compounds significantly stimulated prostaglandin (PG) synthesis, and, in fact, selenate significantly inhibited PG production. Finally, only sodium molybdate- and vanadium-containing compounds appeared to increase follicular adenosine 3',5'-cyclic monophosphate content. While all oxoanions stimulated in vitro ovulation, they had differential effects on certain signal transduction pathways when tested at concentrations that stimulated in vitro ovulation. From the results, two basic groups could be delineated, one containing tungstate-, molybdate-, and vanadium-containing compounds and the other selenate and chromate. Thus the mechanism by which ovulation is induced by chromate and selenate may be different from that of vanadium-containing compounds, molybdate, and tungstate.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals The Stability of Incremental Analysis Update

2018 ◽  
Vol 146 (10) ◽  
pp. 3259-3275 ◽  
Author(s):  
Lawrence L. Takacs ◽  
Max J. Suárez ◽  
Ricardo Todling
Keyword(s):  
Digital Filter ◽  
General Circulation ◽  
Circulation Model ◽  
Stability Diagram ◽  
Recent Attempt ◽  
Complex Frequency ◽  
Incremental Analysis ◽  
Wide Range ◽  
The Stability ◽  
Background Fields

Abstract A recent attempt to downscale the 50-km MERRA-2 analyses to 7 km revealed an instability associated with the incremental analysis update (IAU) procedure that has thus far gone unnoticed. A theoretical study based on a simple damped harmonic oscillator with complex frequency provides the framework to diagnose the problem and suggests means to avoid it. Three possible approaches to avoid the instability are to (i) choose an “ideal” ratio of the lengths of the predictor and corrector steps of IAU based on a theoretical stability diagram, (ii) time average the background fields used to construct the IAU tendencies with given frequency, or (iii) apply a digital filter modulation to the IAU tendencies. All these are shown to control the instability for a wide range of resolutions when doing up- or downscaling, experiments with the NASA GMAO atmospheric general circulation model. Furthermore, it is found that combining IAU with the ensemble recentering step typical of hybrid ensemble–variational approaches also results in an instability based on the same mechanisms in the members of the ensemble. An example of such occurrence arises in an experiment performed with the GMAO 12.8-km hybrid 4D-EnVar system. Modulation of the ensemble IAU tendencies with a digital filter is shown to avoid the instability. In addition, the stability of certain 4D incremental analysis update (4DIAU) implementations is analyzed and a suggestion is made to improve its results, though a complete study of this subject is postponed to a follow-up work.

Vibrational and structural properties in the dihydrate sodium tungstate and in the dihydrate sodium molybdate crystals

2013 ◽  
Vol 1033 ◽  
pp. 154-161 ◽  
Author(s):  
G.D. Saraiva ◽  
C. Luz-Lima ◽  
P.T.C. Freire ◽  
A.J. Ramiro de Castro ◽  
G.P. de Sousa ◽  
...  
Keyword(s):  
Structural Properties ◽  
Sodium Tungstate ◽  
Sodium Molybdate

scholarly journals Probing Brønsted Acidity of Protonic Zeolites with Variable-Temperature Infrared Spectroscopy

2018 ◽  
Vol 63 (6) ◽  
pp. 538 ◽  
Author(s):  
C. O. Areán
Keyword(s):  
Ir Spectroscopy ◽  
Variable Temperature ◽  
Bathochromic Shift ◽  
Industrial Applications ◽  
Acid Strength ◽  
Hydroxyl Groups ◽  
Weak Base ◽  
Brønsted Acidity ◽  
Brönsted Acidity ◽  
Wide Range

Most industrial applications of zeolites as solid-acid catalysts rely on their high Brønsted acidity, which affects both catalytic activity and selectivity, and hence the convenience to find an accurate experimental technique for measuring the acid strength. The enthalpy change, ΔH0, involved in the hydrogen bonding interaction between a weak base (such as carbon monoxide) and the Brønsted acid [Si(OH)Al] hydroxyl groups should correlate directly with the zeolite acid strength. However, on account of simplicity, the bathochromic shift of the O–H stretching frequency, Δv(OH), is usually measured by IR spectroscopy at a (fixed) low temperature in-stead of ΔH0 and correlated with the acid strength for ranking the zeolite acidity. Herein, the use of variable-temperature IR spectroscopy to determine simultaneously ΔH0 and Δv(OH) is demonstrated, followed by a review of recent experimental results showing that the practice of ranking the acid strength by the corresponding O–H frequency shift probed by a weak base could be misleading; and that can be so much the case of zeolites showing a wide range of structure types.

scholarly journals Direct Observation of Peptide Hydrogel Self-Assembly

2021 ◽  
Author(s):  
Zoë Adams ◽  
Erika Olson ◽  
Zhengwen Lian ◽  
Audrey Kim ◽  
Matthew Holcomb ◽  
...  
Keyword(s):  
Ir Spectroscopy ◽  
Rapid Change ◽  
Stopped Flow ◽  
Side Chains ◽  
Ir Absorption ◽  
Hydrophobic Region ◽  
Site Specific ◽  
Self Assembling ◽  
Wide Range ◽  
Peptide Hydrogel

The characterization of self-assembling molecules presents significant experimental challenges, especially when associated with phase separation or precipitation. Transparent window infrared (IR) spectroscopy leverages site-specific probes that absorb in the “transparent window” region of the biomolecular IR spectrum. Carbon-deuterium (C-D) bonds are especially compelling transparent window probes since they are non-perturbative, can be readily introduced site selectively into peptides and proteins, and their stretch frequencies are sensitive to changes in the local molecular environment. Importantly, IR spectroscopy can be applied to a wide range of molecular samples regardless of solubility or physical state, making it an ideal technique for addressing the solubility challenges presented by self-assembling molecules. Here, we present the first continuous observation of transparent window probes following stopped-flow initiation. To demonstrate utility in a self-assembling system, we selected the MAX1 peptide hydrogel, a biocompatible material that has significant promise for use in tissue regeneration and drug delivery. C-D labeled valine was synthetically introduced into five distinct positions of the twenty-residue MAX1 β-hairpin peptide. Consistent with current structural models, steady-state IR absorption frequencies and linewidths of C-D bonds at all labeled positions indicate that these side chains occupy a hydrophobic region of the hydrogel and that the motion of side chains located in the middle of the hairpin is more restricted than those located on the hairpin ends. Following a rapid change in ionic strength to initiate gelation, the peptide absorption spectra were monitored as function of time, allowing determination of site-specific time constants. We find that within the experimental resolution, MAX1 gelation occurs as a cooperative process. These studies suggest that stopped-flow transparent window FTIR can be extended to other time-resolved applications, such as protein folding and enzyme kinetics.

Nuclear Magnetic Resonance and Quadrupole Coupling in Hydrous and Anhydrous Sodium Molybdate and Sodium Tungstate Spinel

1972 ◽  
Vol 50 (6) ◽  
pp. 567-572 ◽  
Author(s):  
G. F. Lynch ◽  
S. L. Segel
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Sodium Tungstate ◽  
Sodium Molybdate ◽  
Tone Burst ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Order Effects ◽  
Nuclear Magnetic

The nuclear magnetic resonance of 23Na in powder samples of hydrous and anhydrous sodium molybdate and sodium tungstate has been investigated. The anhydrous compounds crystallize in the cubic spinel of type H11, Fd3m presumably with ionic charges of 1 + and 6 + on the metals. The 23Na quadrupole couplings are the largest yet observed for this nucleus and have values of 2.62 and 2.48 MHz in the molybdate and tungstate respectively, as determined from both first- and second-order effects on the magnetic resonance spectrum. These couplings have negligible temperature dependences. Using charges of 1 + and 6 + for the metal ions, assuming that the oxygens are in their ideal positions in the spinel structure and neglecting any contributions from oxygen dipoles and quadrupoles, the electric field gradient was calculated to be 12 × 1013 e.s.u./cm3, in good agreement with the experimental gradient of 7.5 × 1013 e.s.u./cm3. Preliminary measurements of the sodium spin–lattice relaxation time, using tone-burst techniques, indicated a value between 30–60 s. The 95.97Mo nuclear resonances were also observed in the molybdate and these resonances showed no quadrupole effects.

TEM INVESTIGATIONS ON CNT-ADDED HEXAGONAL WO3 FILMS FOR SENSING APPLICATIONS

NANO ◽  
2008 ◽  
Vol 03 (04) ◽  
pp. 223-227 ◽  
Author(s):  
KATARÍNA SEDLÁCKOVÁ ◽  
RADU IONESCU ◽  
CSABA BALÁZSI
Keyword(s):  
Carbon Nanotubes ◽  
Tungsten Oxide ◽  
Sodium Tungstate ◽  
Acidic Precipitation ◽  
Temperature Range ◽  
Sensing Applications ◽  
Hexagonal Tungsten Oxide ◽  
Tungstate Solution ◽  
Average Size ◽  
Hazardous Gas

In this work, nanocrystalline hexagonal tungsten oxide was prepared by acidic precipitation from sodium tungstate solution. TEM studies of nanopowders showed that the average size of the hexagonal nanoparticles is 30–50 nm. Novel nanocomposites were prepared by embedding a low amount of gold-decorated carbon nanotubes into the hex- WO 3 matrix. The addition of MWCNTs lowered the temperature range of sensitivity of hex- WO 3 nanocomposites to NO 2 hazardous gas. The sensitivity of hex- WO 3 with Au -decorated MWCNTs to NO 2 is at the temperature range between 25°C and 250°C.

Darstellung und Strukturuntersuchung von Polywolframaten Ein Beitrag zur Aufklärung des Parawolframations A / Preparation and Structure Investigation of Polytungstates A Contribution to the Paratungstate A Problem

1979 ◽  
Vol 34 (3) ◽  
pp. 412-422 ◽  
Author(s):  
Joachim Fuchs ◽  
Ernst-Peter Flindt
Keyword(s):  
Liquid Ammonia ◽  
Sodium Tungstate ◽  
Structure Investigation ◽  
Absorption Bands ◽  
Experimental Conditions ◽  
X Ray ◽  
Predominant Species ◽  
Structure Determinations ◽  
Tungstate Solution ◽  
Ray Methods

Abstract Polytungstates are obtained by the reaction of hydrated tungsten (VI) oxide with bases or salts after occasional addition of organic solvents. With liquid ammonia the as yet unknown ditungstate, (NH4)2W2O7, is produced. Its IR spectrum has few absorption bands suggesting a very simple constitution. Piperidine yields 5 compounds according to varied experimental conditions, which all exhibit approximately paratungstate compositions but different crystal habits, lattice parameters, solubility and IR spectra. Structure determinations indicate that two of these compounds are heptatungstates, the anion of which, W7O246-, has the same structure as the heptamolybdate ion, Mo7O246-. From a comparison of their Raman spectra with the spectrum of a freshly acidified sodium tungstate solution (designated as Paratungstate A) it may be concluded that the heptatungstate ion is the predominant species in such a solution. The anion structure of the previously described tributylammonium(5:24):tungstate [(C4H9)3NH]5H3W12O40 was elucidated by X-ray methods. Here the tungsten atoms show the same arrangement as in the α-dodecatungstatophosphate ion (Keggin structure).

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