Trofimov synthesis of betulin derivatives with 2,3-annelated pyrrole

Lupane-type triterpenoid derivatives containing a 2,3-annelated 1H-pyrrole or an N-vinylpyrrole moiety were synthesized by reaction of 28-OTr-lup-20(29)-en-3-one oxime and acetylene in KOH/DMSO superbase medium at atmospheric pressure.     

Antiradical activity of dioxolane derivatives

1,3-Benzodioxoles synthesized by condensation of 3,6-di-tert-butylbenzene-1,2-diol with carbonyl compounds showed antiradical activity due to their ability to undergo one-electron oxidation with formation of stable radical cations. On this basis, the antiknock effect of their structural analogs, 1,3-dioxolanes derived from vicinal diols, was interpreted in terms of oxidation of these compounds with active radicals generated from fuel hydrocarbons to produce more stable radical or radical ion species, depending on the fuel composition. The formation of radical species was detected in model oxidation reactions of 2,2-dimethyl-1,3-dioxolane and 2,2-dimethyl-1,3-dioxolan-4-ylmethanol with radicals generated by photolysis of iron(III) chloride and benzoyl peroxide.     

New complex ytterbium molybdophosphates M 2 I Yb(PO4)(MoO4) (MI = K, Na): Synthesis and structure solution

Complex rare-earth molybdophosphates of sodium and potassium (Na₂Yb(PO₄)(MoO₄) (I) and K₂Yb(PO₄)(MoO₄) (II) are synthesized by solid-phase reactions at 600°C (for I) and 750°C (for II). The molybdophosphates are characterized using powder X-ray diffraction, laser second harmonic generation (SHG), IR spectroscopy, and differential thermal analysis. Their structures are refined using the Rietveld technique. The compounds are isostructural and crystallize in an orthorhombic system (space group Ibca, Z = 8). The unit cell parameters are a = 18.0086(1) Å, b = 12.0266(1) Å, c = 6.7742(1) Å for compound I and a = 19.6646(1) Å, b = 12.0570(1) Å, c = 6.8029(1) Å for compound II. The structures are built of YbO₈ chains extended along axis c and linked into layers through PO₄ tetrahedra. The Na⁺ cations (CN = 6) and the K⁺ cations (CN = 8) reside in the interlayer spaces.     

Synthesis and crystal structure of the gallium-containing montebrasite analogue LiGa(OH)PO4

Gallium lithium hydroxyphosphate LiGa(OH)PO₄ was prepared under mild hydrothermal conditions (T = 160°C, τ = 48 h) and characterized (IR spectroscopy, chemical and thermal analysis). LiGa(OH)PO₄ was found to be structurally similar to the ambligonite family phases. The crystal structure was refined by the Rietveld method (space group $P\bar 1$ , Z = 2): a = 5.0853(1) Å, b = 5.2973(1) Å, c = 7.3006(1) Å, α = 67.830(1)°, β = 67.839(1)°, γ = 82.027(1)°, R _p = 0.0519, R _wp = 0.0765. A zero SHG signal confirmed a centrosymmetric structure of the compound. The structure is represented by a mixed {Ga(OH)[PO₄]} _3∞ ^? framework composed of the PO₄ tetrahedra and GaO₄(OH)₂ octahedra. The framework contains hexagonal channels running in the [100] and [010] directions. The basic element of the framework is a linear chain of GaO₄(OH)₂ octahedra sharing trans OH vertices. The Li⁺ ions reside in the framework voids.     

New form of scandium fluoride

Like its stoichiometric predecessors, tetragonal ScF_2.76 showed the tendency to undergo structural evolution under pressure. A new polymorph modification of scandium fluoride deficient in fluorine has been prepared after treatment at 40 kbar. The compound belongs in a cubic system, lattice parameter a=6.503 Å. The structural relationships with other forms of scandium fluoride and possible applications are discussed.     

Acoustical method for measuring the gas content in bottom sediments

Gas bubbles in the bottom of shallow-water seas and freshwater basins lead to a substantial decrease in the sound speed. The gas content in the bottom changes because of the variability of the biological activity and water contamination, therefore serving as an indicator of the environmental equilibrium in the basin. It is proposed to monitor the gas content in bottom sediments by measuring the frequency spectrum of the bottom reflection coefficient in a broad frequency band. The data of calculations are presented for the sound speed in gas-containing sediments and for the values of the bottom reflection coefficient. A method is proposed for monitoring the gas content by measuring the frequency and angular characteristics of the natural ambient noise.     

Ionic conductivity of double vanadate Ag3Sc2(VO4)3

Ionic conductivity of double vanadate Ag₃Sc₂(VO₄)₃ with the NASICON structure is studied by the method of impedance spectroscopy in the frequency range from 5 to 5 × 10⁵ Hz and in the temperature range of 300–827 K. The vanadate Ag₃Sc₂(VO₄)₃ is prepared in the form of fine crystalline powder by solid-state synthesis from V₂O₅, Sc₂O₃, and AgNO₃ at 1173 K. The conductivity of Ag₃Sc₂(VO₄)₃ ceramic samples σ = 8 × 10^?3 S/cm (at 563 K). The σ vs. T curve demonstrates an anomaly at 563–623 K which corresponds to thermal effects in this temperature range. The values of enthalpy of ion transport activation are ΔH = 0.40 ± 0.05 eV (T < 563 K) and ΔH = 0.30 ± 0.05 eV (T > 623 K). The ionic conductivity of Ag₃Sc₂(VO₄)₃ is due to Ag⁺ ions localized in channels of the framework structure of the NASICON type.     

Phase formation in the Ag3PO4-ScPO4 quasi-binary system

The phase formation in the subsolidus region of the Ag₃PO₄-ScPO₄ quasi-binary system was studied by X-ray powder diffraction and differential thermal analyses throughout the range of concentration ratios of the initial components at an interval of 10 mol % within the temperature range 20–1000°C in air at atmospheric pressure. A T-x section was constructed. The formation of the binary phosphate Ag₃Sc₂(PO₄)₃ melting incongruently at 1300 ± 5°C was detected. The composition of an eutectic (with the melting point 900 ± 5°C) is between those of the compounds Ag₃PO₄ and Ag₃Sc₂(PO₄)₃.     

Structural factors responsible for the activity of macromolecular phenolic antioxidants

Hybrid macromolecular antioxidants based on hydrophilic polymers with chemically grafted sterically hindered phenol fragments in aqueous solution exhibited considerably higher antiradical activity than that typical of compositions consisting of a polymer and low-molecular phenol analogs. The activity of the examined antioxidants is determined mainly by formation of supramolecular structures in solution, as well as by the position of the phenolic fragment inside or outside hydrate shell. An important structural factor is the size of the spacer connecting the redox-active phenol ring with the polymer.