Direct extraction of nickel from model sulfate solution with hydrazide of versatic <Emphasis Type="Italic">tert</Emphasis>-Carboxylic acids

Possibility of direct extraction of 0.66 g L–1 Ni(II), 0.048 g L^–1 Co(II), and 0.024 g L^–1 Zn(II) in the presence of the nine commonly accompanying elements from a model solution for underground sulfuric acid leaching of an oxidized Ni ore with a 0.4–0.6 M solution of a hydrazide of Versatic C₁₅–C₁₉ acids in kerosene was considered. The optimal conditions of extraction, extract washing to remove impurities, and re-extraction of Ni and Co were determined. It was found that the direct extraction of up to 90% of nickel, cobalt, and zinc is possible with an at least fivefold concentration in the extraction stage. The separation of Ni from Co and co-extracted Fe, Zn, and Mn is possible in the re-extraction stage by washing of the organic phase with a 0.5 M HCl solution.     

Phase transitions in double molybdates K<Subscript>2</Subscript>M<Stack><Subscript>2</Subscript><Superscript>II</Superscript></Stack>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> with M = Mg or Co

Phase transitions and cation mobility in double molybdates K₂M ₂ ^II (MoO₄)₃ with M = Mg or Co and the products of their heterovalent doping with scandium(III) and vanadium(V) have been studied. The transition from low to high conductivity in K₂M ₂ ^II (MoO₄)₃ is the result of a two-stage phase transition, whose occurrence is significantly extended in time. Heterovalent substitutions noticeably decrease the heat of the phase transition. The transition to the low-temperature phase is not achieved even after long-term exposure.     

Recognition of Artificial Nucleobases by E. coli Purine Nucleoside Phosphorylase versus its Ser90Ala Mutant in the Synthesis of Base‐Modified Nucleosides

A wide range of natural purine analogues was used as probe to assess the mechanism of recognition by the wild‐type (WT) E. coli purine nucleoside phosphorylase (PNP) versus its Ser90Ala mutant. The results were analyzed from viewpoint of the role of the Ser90 residue and the structural features of the bases. It was found that the Ser90 residue of the PNP 1) plays an important role in the binding and activation of 8‐aza‐7‐deazapurines in the synthesis of their nucleosides, 2) participates in the binding of α‐D ‐pentofuranose‐1‐phosphates at the catalytic site of the PNP, and 3) catalyzes the dephosphorylation of intermediary formed 2‐deoxy‐α‐D ‐ribofuranose‐1‐phosphate in the trans‐2‐deoxyribosylation reaction. 5‐Aza‐7‐deazaguanine manifested excellent substrate activity for both enzymes, 8‐amino‐7‐thiaguanine and 2‐aminobenzothiazole showed no substrate activity for both enzymes. On the contrary, the 2‐amino derivatives of benzimidazole and benzoxazole are substrates and are converted into the N1‐ and unusual N2‐glycosides, respectively. 9‐Deaza‐5‐iodoxanthine showed moderate inhibitory activity of the WT E. coli PNP, whereas 9‐deazaxanthine and its 2′‐deoxyriboside are weak inhibitors.     

Flow of viscous liquid in porous model medium with fractal structure

The flow of viscous liquid in a porous model medium with a fractal structure is considered. The hydrodynamic permeability of a medium is calculated according to the Happel and Brenner cell method using Brinkman equations. An analysis is carried out for boundary conditions on the cell surfaces of four types corresponding to the Happel, Kuwabara, Kvashnin, and Cunningham models. Situations that correspond to the flow of viscous liquid in a porous medium formed by fractal aggregates and the uniform flow of viscous liquid around the single composite particle are analyzed.     

Synthesis and properties of oxide ion conductor Pr2Mo2O9 with La2Mo2O9 structure

Polycrystalline Pr₂Mo₂O₉ samples have been prepared by solid-state synthesis and single crystals of this compound have been grown. Pr₂Mo₂O₉ is unstable in the temperature range 700–900°C and partially decomposes with the formation of Pr₂Mo₃O₁₂ at these temperatures, but upon further heating to 1000–1050°C, Pr₂Mo₂O₉ is recovered. At room temperature, the structure, polymorphism, and physical properties of Pr₂Mo₂O₉ are similar to those of the known oxide ion conductor La₂Mo₂O₉. Pr₂Mo₂O₉ exhibits a reversible first-order phase transition to the cubic phase in the temperature range 520–540°C. The electric conductivity of Pr₂Mo₂O₉ is close to that of La₂Mo₂O₉ and amounts to 3.5 × 10⁻² S/cm at 700°C. The conductivity of Pr₂Mo₂O₉ is described by the Arrhenius law in the low-temperature phase and by the Vogel-Fulcher-Tammann equation in the high-temperature phase.     

Synthesis and electrical properties of Aurivillius phases in the Bi<Subscript>2</Subscript>MoO<Subscript>6</Subscript>-Bi<Subscript>2</Subscript>VO<Subscript>5.5</Subscript> system

To search for new oxygen conductive phases, a series of Bi₂V_{1 ? x} Mo_xO_{5.5 + x/2} ceramic samples have been synthesized in which the extreme compositions Bi₂VO_5.5 (x = 0) and Bi₂MoO₆ (x = 1) are single-layer Aurivillius phases having ferroelectric properties and high ionic oxide conductivity. It is established that single-layer Aurivillius phases exist in the composition ranges 0 ≤ x ≤ 0.1 and 0.9 ≤ x ≤ 1. Additional phases with BiVO₄ and Bi₆Mo₂O₁₅ structures are found in the range 0.2 ≤ x ≤ 0.8. The presence of molybdenum stabilizes the orthorhombic β-Bi₂VO_5.5 phase at room temperature. The conductivity of solid solutions based on Bi₂VO_5.5 differs only slightly from that of pure bismuth vanadate. Conductivity of solid solutions based on Bi₂MoO₆ is half an order of magnitude higher than that of pure bismuth molybdate.     

Reaction of 3,4-diiodo-2,5-dimethyl-1H-pyrrole with thioamides

3,4-Diiodo-2,5-dimethyl-1H-pyrrole reacted with thioacetamide in polar solvents or under solvent-free conditions to give 2,4,6-trimethyl-5H-pyrrolo[3,4-d][1,3]thiazole. The major product in the reaction of the title compound with thiobenzamide was 3,5-diphenyl-1,2,4-thiadiazole.     

Calculation of intraband electronic and interband hole luminescence spectra of various alkali halide crystals under pulsed excitation by intense electron and laser beams in the nanosecond and picosecond regimes

We perform a theoretical analysis of the spectra of two rather new kinds of fundamental luminescence in dielectrics: intraband electronic and interband hole emissions. The primary photon emitters are radiative transition of ionization-passive conduction-band electrons and valence-band holes. These types of luminescence have been observed and studied experimentally by the use of two powerful nanosecond and picosecond radiation sources: strong electronic accelerators and lasers with ultraviolet harmonic generators. Good agreement is obtained between the calculated spectra and the ones measured experimentally. Comparison of the results with the experimental data makes it possible to determine certain important parameters of the electron spectrum, in particular the upper boundary of the passive region for ionization of the conduction band in crystalline CsI. Institute for Ultraprecise Electronics, Siberian Division, Russian Academy of Sciences. Polytekhnic University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 103–115, December, 1995.