Isolation of isomangiferin from honeybush (Cyclopia subternata) using high-speed counter-current chromatography and high-performance liquid chromatography

Isomangiferin was isolated from Cyclopia subternata using a multi-step process including extraction, liquid–liquid partitioning, high-speed counter-current chromatography (HSCCC) and semi-preparative reversed-phase high-performance liquid chromatography (HPLC). Enrichment of phenolic compounds in a methanol extract of C. subternata leaves was conducted using liquid–liquid partitioning with ethyl acetate–methanol–water (1:1:2, v/v). The enriched fraction was further fractionated using HSCCC with a ternary solvent system consisting of tert-butyl methyl ether–n-butanol–acetonitrile–water (3:1:1:5, v/v). Isomangiferin was isolated by semi-preparative reversed-phase HPLC from a fraction containing mostly mangiferin and isomangiferin. The chemical structure of isomangiferin was confirmed by LC–high-resolution electrospray ionization MS, as well as one- and two-dimensional NMR spectroscopy.     

Dehalogenation of α -haloketones and vic-dibromides with nickel boride

α-Haloketones and $\text{vic}$-dibromides are converted to the corresponding ketones and alkenes respectively with nickel boride generated $\text{in situ}$ from sodium borohydride and nickel chloride.     

Understanding and improving the deposition conditions of SiO2 thin films obtained by ultrasonic sol-gel procedure

Sol-gel deposition of an ultrasonically atomized aerosol has been proven to be a convenient thin film deposition method. Flexibility of the ultrasonic process allows the use of a large range of source solutions. In this paper we describe and discuss the deposition conditions of SiO₂ films. The chemical parameters are contemplated and we discuss the influence of ultrasonic waves on the reliability of our process. Source solutions and SiO₂ film properties are studied by viscosimetry, Fourier Transform IR spectroscopy and spectroscopic ellipsometry.     

The synthesis and crystal structure of CaCu3Mn4O12: A new ferromagnetic-perovskite-like compound

Single crystals of CaCu₃Mn₄O₁₂, a new ferromagnetic perovskite-like compound (T_c ? 160°C), have been synthesized at 50 kbar and 1000°C. By X-ray analysis it was found to be cubic (a = 7.241Å), space groupIm3 with two molecules per unit cell. The two Ca²⁺ and six Cu²⁺ cations occupy theA sites of the ideal perovskite structure, while the eight Mn⁴⁺ cations occupy theB sites. In theIm3 space group the sites occupied by the calcium and copper cations have different point symmetry and therefore the 12-oxygen polyhedra have different distortions. The Ca cations are surrounded by slightly distorted icosahedra, the CaO distance is 2.562Å. The twelve oxygens around the copper cations are arranged as three mutually perpendicular rectangles of different size, the smallest and the largest of which are almost squares. The three sets of Cu0 distances are 1.942, 2.707, and 3.181Å, respectively. The octahedral Mn0 distance is 1.915Å. This arrangement is similar to that found in NaMn₃Mn₄O₁₂. A comparison between the two structures and a discussion of their thermal data are given.     

Structural stability and electronic properties of AgInS<Subscript>2</Subscript> under pressure

We employ state-of-the-art ab initio density functional theory techniques to investigatethe structural, dynamical, mechanical stability and electronic properties of the ternaryAgInS₂ compoundsunder pressure. Using cohesive energy and enthalpy, we found that from the six potentialphases explored, the chalcopyrite and the orthorhombic structures were very competitive aszero pressure phases. A pressure-induced phase transition occurs around 1.78 GPa from the low pressure chalcopyritephase to a rhombohedral RH-AgInS₂ phase. The pressure phase transition around 1.78 GPa isaccompanied by notable changes in the volume and bulk modulus. The calculations of thephonon dispersions and elastic constants at different pressures showed that thechalcopyrite and the orthorhombic structures remained stable at all the selected pressure(0, 1.78 and 2.5 GPa), where detailed calculations were performed, while the rhombohedralstructure is only stable from the transition pressure 1.78 GPa. Pressure effect on thebandgap is minimal due to the small range of pressure considered in this study. Themeta-GGA MBJ functional predicts bandgaps which are in good agreement with availableexperimental values.     

Sur de nouveaux borates mixtes des métaux de transition isotypes de la warwickite

The isomorphism of borates CaLn³⁺BO₄ where Ln³⁺ stands for a small rare earth cation of Y³⁺, with the mineral warwickite (Fe,Mg)₃Ti(BO₄)₂ is demonstrated. The octahedral sites of the warwickite structure seem thus to accommodate rather large cations, like trivalent Y³⁺ or Dy³⁺ and bivalent Ca²⁺. The synthesis of several new transition-metal borates with this structure is reported. From a survey of all the warwickite-type compounds one comes to the conclusion that the structure is only stable when the size of the divalent cation M²⁺ is larger than that one of the trivalent M³⁺.