Study of the Ternary Systems M(II)(NO3)2–LiNO3–H2O (M(II) 5 Mg, Ca, Sr, Ba) at 25°C

Summary.  The isothermal solubility diagrams of four aqueous systems containing lithium nitrate and nitrates of group IIA metals – magnesium, calcium, strontium, and barium – were studied at 25°C. No double salt formation was observed. The results were compared with similar nitrate and chloride systems. Some trends in the shape of the phase diagrams were observed. Hydration analysis was applied to the solubility branches, rendering information about ionic processes in saturated solutions. Further, the ratio of activity coefficients of the saturating solid phase in ternary and binary solutions (γ/γ₀) was obtained. Received April 13, 2001. Accepted June 15, 2001     

Low‐temperature preparation of bismuth ferrite microcrystals by a sol‐gel‐hydrothermal method

Well‐crystallized pure perovskite bismuth ferrite (BiFeO₃) powders with various morphologies have been synthesized by a novel sol‐gel‐hydrothermal route for the first time, which combined the conventional sol‐gel process and the hydrothermal method. The as‐prepared samples were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA) and ferroelectric test system. The results revealed that the compositions, morphological and dimensional changes in bismuth ferrite samples synthesized by sol–gel–hydrothermal method strongly depend on the concentrations of mineralizer. Ferroelectric hysteresis loops are displayed in the BiFeO₃ samples. The bismuth ferrites were hydrothermally synthesized at as low a temperature as 180 °C, which is comparatively lower than that synthesized by the normal sol–gel route. The formation mechanism of the bismuth ferrite crystalline was also discussed. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Polarographic Determination of Bismuth Sensitization in the Presence of Nioxime

Abstract

Nioxime sensitizes the differential pulse polarographic determination of B1(III) in alkaline medium and in the presence of tart rate and citrate; detection limits of 8 and 12 ppb are obtained. Characterization of the electroactive process included an examination of the degree of reversibility and the effect on the peak current of pH, buffer composition, nioxime and bismuth concentrations and the presence of other metal ions.     

Thiothenoyltrifluoroacetone as the Extracting and Colorimetric Reagent for Bismuth

Abstract

Thiothenoyltrifluoracetone (STTA) was used for the simultaneous extraction and direct spectrophotometric determination of bismuth at microgram concentration. About 98.5 μg of bismuth was extracted as the orange-red colored complex with 10 ml of 0.001 M STTA in carbontetrachloride. The extraction was quantitative at pH 6. The system conformed to Beer's Law in the concentration range of 2.5 to 30 μg/ml of bismuth at 460 nm. The method is both sensitive and selective.

The molar absorptivity was 5.6 × 10³ and sensitivity was 0.037 μg/cm². The method is selective as it is possible to accomplish extraction and colorimetrically determination of bismuth in the presence of 1:50 of several ions. Only ions such as cadmium, tin, iron, titanium and nickel interfere seriously. The overall process of extraction and determination takes hardly 30 minutes. The method is reproducible.     

Automated Determination of Arsenic,Selenium, Antimony,Bismuth and Tin by Atomic Absorption Utilizing Sodium Borohydride Reduction

Abstract

An automated system for the determination of arsenic, selenium, antimony, bismuth and tin is described. These elements and their compounds are reduced with sodium borohydride to the corresponding hydride. Sensitivity of the automated system is comparable and in most cases better than the manual technique. The automated method was found superior to the manual with respect to reproducibility and ease of operation.     

Spectrophotometric Evidence for the Formation of a Mixed Bismuth-Phosphorus Heteropoly Acid

Abstract

Spectrophotometric evidence is presented to show that bismuth interacts with phosphate and molybdate in acid solution to form a mixed bismuth-phosphorus heteropoly acid. The complex is similar to 12-molybdophosphoric acid by virtue of its degree of dissociation in both concentrated and dilute acid solutions. The complex is more stable than 12-molybdophosphoric acid because it is formed when bismuth is added to a solution of 12-molybdophosphoric acid. The proposed bismuth-phosphorus compound is reduced much more readily to a heteropoly blue than is 12-molybdophosphoric acid, a fact that has contributed to a false belief that the bismuth may have been acting catalytically in the reduction of 12-molybdophosphoric acid.     

DFT analysis of the active site in catalytic metabolic redox reactions of mononuclear molybdenum enzymes

Abstract

Model complexes [Mo^VIO₂(S₂C₂Me₂)SMe]^? (A, derived from the X-ray crystal structure of native sulfite oxidase (SO)) and [Mo^VIO₂(mnt)₂]^2? (B, coordination mode similar to the active site of selenate reductase (SeR)) were computed at the COSMO-B3LYP/SDDp//B3LYP/Lanl2DZ(p) energy level of Density Functional Theory in order to study their behavior in oxidation of selenite (Se^IV) and sulfite (S^IV) to selenate (Se^VI) and sulfate (S^VI), respectively. For the oxidation of sulfite, computational model A, which resembles the SO active site, is clearly the best choice (lowest barrier, minor exothermicity). For the reduction of selenate, a smaller activation is computed for model A; however, the reaction is less exothermic with model B, which resembles the SeR active site.     

Stability Constants for Dimercaptosuccinic Acid with Bismuth(III), Zinc(II), and Lead(II)

Abstract

Stability constants for the complexation of zinc(II), lead(II), and bismuth(III) by the vicinal dithiolate chelating agent meso-dimercaptosuccinic acid (DMSA) have been determined by a combination of potentiometric titration and spectrophotometric competition at 25°C and 0.1 M ionic strength. The spectrophotometric studies use the shifts in the ultraviolet bands of the thiol groups to quantitate metal binding to DMSA in the presence of competitive aminocarboxylic acids. Bismuth(III) forms a bis(DMSA) chelate with an exceptionally high stability constant of 10^43,87. This complex undergoes a series of protonations over the pH range 10 to 2, but there appears to be no measurable dissociation of ligand over this pH range. The zinc-DMSA system is dominated by a Zn₂(DMSA)₂ dimer, which has a protonation constant of 10⁶ and dissociates completely at lower pH. No more than 20% of total zinc exists as a monomeric complex at any pH. Lead forms a 1:1 complex with a stability constant of 10^17,4. Insoluble protonated lead complexes precipitate at pH < 6.5. Speciation calculations have been used to evaluate the potential competition from serum zinc to the binding of Pb²⁺ and Bi³⁺ by DMSA. The results indicate that DMSA should be relatively effective for the in vivo chelation of both Bi³⁺ and Pb^{2 +}.     

INTERACTIONS OF COBALT(II) TETRASULFOPHTHALOCYANINE WITH NITRITE IN THE PRESENCE OF NITRATE AND PERCHLORATE IONS

Abstract

Spectroscopic changes observed on addition of nitrite to solutions of cobalt(II) tetra-sulfophthalocyanine ([Co(II)TSPc]^4-) in the presence of N^? ₃ or ClO^? ₄ are reported. There is spectroscopic evidence for the oxidation of [Co(II)TSPc]^4- to a [Co(III)TSPc]^3- species in the presence of nitrite ions. Equilibrium and kinetic studies for the interaction between [Co(II)TSPc]^4- and NO^? ₂ are reported. The rate was found to be first order in both [Co(II)TSPc]^4- and NO^? ₂. The rate constant for the forward reaction, k _f=1.6 × 10^?4 dm³mol^?1s^?1 was determined at 20°C for the interaction between nitrite ions and [Co(II)TSPc]^4- in the presence of NO₃ ^? or ClO₄ ^? ions.