Showing papers by "Enrique J. Baran published in 1988"

Vibrational Spectra of Arsenates and Phosphates of the Type Kcaln(XO4)2

Abstract: The infrared and Raman spectra of polycrystal-line samples of different compounds of the types KCaLn(AsO4)2 and KCaLn(PO4)2, belonging to the hexagonal LaPO4, structural modification, were recorded and discussed. A complete vibrational assignment, based on a factor group analysis, is proposed. The influence of the different lanthanide cations on the internal vibrations of the XO4 groups is briefly discussed and some comparisons with related compounds are also made. It is well known that simple lanthanide arsenates, phosphates, vanadates and cnromates (V) of the type LnXO4 belong to two different structural types.

The inhibitory effect of vanadium oxoanions on the activity of copper-zinc superoxide dismutase

Abstract: The inhibitory effect of vanadate species on the enzymatic activity of bovine copper-zinc superoxide dismutase has been investigated at different pH values and vanadium concentrations. A definite inhibitory effect, clearly related to the main negative charge of each of the vanadate solutions, has been found. The results suggest that the origin of the inhibitory effect may be similar to that found for the phosphate ion, i.e., a diminution of the effectiveness of the substrate electronic guidance mechanism by partial neutralization of the charges close to the active site. Under physiological conditions, the inhibitory effect of vanadate is somewhat smaller than the phosphate.

Infrared spectra and thermal behaviour of salts of the bis(malonato) oxovanadium(IV) anion

Abstract: Infrared spectra of a series of anhydrous (Rb, Cs) and hydrated (Na, K, Ca, Sr, Ba, Pb, Ag, Tl) salts of the complex anion VO(C3H2O4)2]2− were recorded and briefly discussed. The thermal behaviour of these compounds, as well as that of the corresponding diprotonated ethylenediamine cation, were investigated by TG- and DTA-methods in N2-atmosphere and complemented with studies carried out in crucible furnaces in air. Pyrolysis intermediates and residues were characterized by IR spectroscopy and overall stoichiometries for the degradation processes were proposed. In most cases orthovanadate/VO2 mixtures were obtained as final residues in N2, whereas the corresponding divanadates were produced in air.

Spektroskopisches und thermisches Verhalten vom VOSeO3 · 3 H2O und VOSeO3

Abstract: Die IR-Spektren des aus Losung Gefallten VOSeO3 · 3 H2O sowie der polymeren, durch Festkorperreaktion erhaltenen VOSeO3-Phase wurden aufgenommen und besprochen. Die Untersuchung des thermischen Abbaus von VOSeO3 · 3 H2O bewies, das es unmoglich ist, ein einfaches wasserfreies Vanadyl(IV)-selenit zu erhalten. Nach der Wasserabgabe und bei Temperaturen um 400°C, beobachtet man einen Abbau von SeO2. Diese Ergebnisse lassen die Existenz von Vse-Oxoverbindungen im Zusammensetzungsbereich SeO2/VO2 < 1 Vermuten. Spectroscopic and Thermal Properties os VOSeO3 · 3. H2O and VOSeO3 The infrared spectra of VOSeO3 · 3 H2O, obtained by precipitation from aqueous solutions, and of the polymeric phase VOSeO3, prepared by solid state reaction, were recorded and discussed. The investigation of the thermal behaviour of VOSeO3 · 3 H2O shows that it is impossible to obtain a simple anhydrous vanadyl(IV) selenite. At temperatures around 400°C, and after the release of water, a loose of SeO2 was observed. The results suggest the possible existence of VSe oxocompounds in the composition range SeO2/VO2 < 1.