Following the crystallisation of Bi2Mo2O9 catalyst by combined XRD/QuEXAFS

The formation ofβ-phase Bi₂Mo₂O₉ catalyst from a precursor precipitate has been studied using thein situ combined XRD/QuEXAFS technique and DSC during calcination. Accordingly the precursor was observed to undergo a number of changes in both the molybdenum (VI) coordination and long-range ordering during this heating. Initially the two other forms of bismuth molybdate (α-andγ-phases) were observed to form from the poorly crystalline precursor at about 230°C, however, theβ-phase eventually crystallised after prolonged heating at 560°C. Dedicated to Professor C N R Rao on his 70th birthday     

Electrochemical characteristics of La0.6Sr0.4CoO3-δ, Pr0.6Sr0.4CoO3-δ and Gd0.6Sr0.4CoO3-δ on Ce0.85Sm0.15O1.925 electrolyte

Cyclic voltammetry, chronoamperometry and electro-chemical impedance have been used for the analysis of the following medium temperature half-cells: Ce_0.85Sm_0.15O_1.925| La_0.6Sr_0.4CoO_3-δ, Ce_0.85Sm_0.15O_1.925| Pr_0.6Sr_0.4CoO_3-δ and Ce_0.85Sm_0.15O_1.925| Gd_0.6Sr_0.4CoO_3-δ. The influence of the atomic mass of the A–site cation in the perovskite cathode on the oxygen reduction kinetics has been discussed. The total polarisation resistance, obtained from the Z′′, Z′-plots, increases with the rise of atomic mass of the cation in the A-site position. Two different time constants have been obtained for the oxygen electroreduction process, and the replacement of La³⁺ by Gd³⁺ in the cathode material decreases somewhat the surface catalytic activity, but the noticeably higher low-frequency series resistance, i.e. mainly diffusion-like mass transfer resistance, values have been obtained. However, the mainly diffusion-limited process at T≤773 K for Gd_0.6Sr_0.4CoO_3-δ and the kinetically mixed process (diffusion + charge transfer) for Pr_0.6Sr_0.4CoO_3-δ and La_0.6Sr_0.4CoO_3-δ have been established. At higher temperature (T≥993 K) and more negative potentials, the O₂ reduction process is limited mainly by the heterogeneous charge transfer step. Presented at the fourth Baltic Conference on Electrochemistry, Greifswald, March 13–16, 2005.     

The Polymorphism of Glycine. Thermochemical and structural aspects

X-ray, DSC and solution calorimetric investigations were carried out for α-, β- and γ-modifications of glycine. Particular attention was paid to kinetic and thermochemical aspects of γ- → α-phase transition. The temperature of this phase transition turned out to be sensitive to a) conditions under which the crystals of the γ-modification were grown, b) tempering of crystals c) form (geometry) of crystals. Kinetics of this phase transition of single crystals of γ-phase in rhomboedric form can be described by the equation for two-dimension nuclei growth, whereas for crystals of triangle geometry the equation for three dimension growth is valid. On the basis of energy parameters describing growth of α-form in γ- →α-phase transition, the kind of structure defects, which are responsible for this phase transition, was estimated. Taking into account the Δ_sol H _m, the absolute values of the lattice energies of the investigated polymorphs indescending order are follows: γ->α->β-modification. The obtained results are discussed with respect to the peculiarity of the crystal lattice structures, particularly the network of hydrogen bonds. The β-modification of glycine is monotropically related to the other forms, whereas γ-and α-polymorphs are enantiotropically-related phases. This revised version was published online in July 2006 with corrections to the Cover Date.     

New polyhydroxysteroids and steroid glycosides from the far east starfishCeramaster patagonicus

Two new polyhydroxysteroids and five new glycosides were isolated from the starfishCeramaster patagonicus and their structures were elucidated: 5α-cholestane-3β,6α,15β,16β,26-pentol, (22E)-5α-cholest-22-ene-3β,6α,8,15α,24-pentol, (22E)-28-O-[O-(2-O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-galactofuranosyl]-24-hydroxymethyl-5α-cholest-22-ene-3β,4β, 6α,8,15β,16β,28-heptol (ceramasteroside C₁), (22E)-28-O-[O-(2,4-di-O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-galactofuranosyl]-24-hydroxymethyl-5α-cholest-22-ene-3β, 6α,8,15β,16β,28-hexol (ceramasteroside C₂), (22E)-28-O-[O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-galactofuranosyl]-24-hydroxymethyl-5α-cholest-22-ene-3β,6α,8,15β,16β 28-hexol (eramasteroside C₃), (22E)-28-O-[O-(2-O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-galactofuranosyl]-24-methyl-5α-cholest-22-ene-3β,4β,6α,8, 15β, 26-hexol (ceramasteroside C₄), and (22E)-28-O-[O-(2-O-methyl-β-d-xylopyranosyl)-(1→2)-β-d-xylopyranosyl]-5α-cholest-22-ene-3β,6α,8,15β,24-pentol (ceramasteroside C₅)). Three known polyhydroxysteroids (24-methylene-5α-cholestane-3β,6α,8,15β,16β,26-hexol, 5α-cholestane-3β,6α,8,15β,16β,26-hexol, and 5α-cholestane-3β,6β,15α,16β,26-pentol) were also isolated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 190–195, January, 1997.     

Synthesis of aminoethyl glycoside of the oligosaccharide chain of ganglioside Fuc-GM1

2-Aminoethyl glycoside of the hexasaccharide chain of ganglioside Fuc-GM₁ was synthesized by a [3+3] synthetic scheme. At the key step of the synthetic route, glycosylation of the only hydroxyl group at C(4) of the galactose residue in an α-(N-acetylneuraminyl)-(2→3)-β-D-galactopyranosyl-(1→4)-β-D-glucopyranoside derivative with a peracetylated thioglycoside of α-L-fucopyranosyl-(1→2)-β-D-galactopyranosyl-(1→3)-2-trichloroacetamido-2-deoxy-β-D-galactopyranose gave a protected hexasaccharide in high yield. Subsequent removal of the protecting groups gave the target 2-aminoethyl glycoside of the oligosaccharide chain of gan-glioside Fuc-GM₁. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 148–153, January, 2006.     

Synthesis and characterization of gallium-based perovskitetype dense membrane with oxygen semipermeability

La0.15Sr0.85Ga0.3Fe0.7O3-δ(LSGFO) and La0.15Sr0.85Co0.3Fe0.7O3-δ(LSCFO) mixed oxygen-ion and electron conducting oxides were synthesized by using a combined EDTA and citrate complexing method, and the corresponding dense membranes were fabricated. The properties of the oxide powders and membranes were characterized with combined SEM, XRD, H2-TPR, O2-TPD techniques, mechanical strength and oxygen permeation measurement. The results showed that LSGFO had much higher thermochemical stability than LSCFO due to the higher valence stability of Ga3+. After the temperature-programmed reduction by 5% H2 in Ar from 20℃to 1020℃, the basic perovskite structure of LSGFO was successfully preserved. LSGFO also favors the oxygen vacancy formation better than LSCFO. Oxygen permeation measurement demonstrated that LSGFO had higher oxygen permeation flux than LSCFO, but they had similar activation energy for oxygen transportation, with a value of 110 and 117 kJ ?mol~(-1), respectively. The difference in oxygen permeation f     

Structural and spectroscopic characterization of Al2−x Cr x O3 powders obtained by polymeric precursor method

Al₂O₃ and Al_2−x Cr _x O₃ (x = 0.01, 0.02 and 0.04) powders have been synthesized by the polymeric precursors method. A study of the structural evolution of crystalline phases corresponding to the obtained powders was accomplished through X-Ray Diffraction and UV-vis spectroscopy (reflectance spectra and CIEL^*a^*b^* color data). The obtained results allow to identify the γ-Al₂O₃ to α-Al₂O₃ phase transition. The single-phase α-Al₂O₃ powder was obtained after heat treatment at 1050 °C for 2 h. The results show that the green to red color transition and ruby luminescence lines observed for the powders of Al_2−x Cr _x O₃ are related to the γ to α-Al₂O₃ phase transition and the temperature and time range for such transition depends on the chromium content.     

Oxygen permeability of mixed-conducting composite membranes: effects of phase interaction

Composite ceramic membranes, based on selected combinations of ionic conductors ((La_0.9Sr_0.1)_0.98Ga_0.8Mg_0.2O_3-δ—LSGM or Ce_0.8Gd_0.2O_2-δ—CGO) and electronic/mixed conductors (La₂Ni_0.8Cu_0.2O_4+δ—LNC, La_0.8Sr_0.2Fe_0.8Co_0.2O_3-δ—LSFC, La_0.7Sr_0.3MnO_3-δ—LSM, and SrCoO_3-δ – Sr₂Fe₃O_6.5±δ—SCSF), were processed and characterized aiming at the identification of key features to be considered in the design and optimization of materials performance as mixed conductors. Although after almost complete reaction between constituents, the best permeability was observed for the LSGM/LSFC combination processed under moderate firing conditions. Ceria-based composites, while preserving a typical composite microstructure, and suffering small compositional changes due to interaction between constituents, behaved always below the result of an ideal combination of the best characteristics of the individual components. Materials interaction, from modest compositional changes to formation of new phases, with deep changes in nominal composition, can be understood both as a challenge requiring proper identification of ideal processing conditions for phase preservation, but also as an opportunity for the development of entirely new composites and materials with compositional heterogeneities at grain size level.     

Phase Relations in The V2O5–MoO3–α-Sb2O4 System in The Solid State in Air Atmosphere

The phase equilibria established in the V₂O₅–MoO₃–α-Sb₂O₄ system in the solid state in an air atmosphere were examined by using XRD and DTA methods. The obtained results allowed us to find that in this system a novel compound is formed involving three oxides. Its formula can be written as Sb₃V₂Mo₃O₂₁. The synthesis of this compound requires picking up the atmospheric oxygen. X-ray characteristics of this compound were determined and it was found that it melted incongruently at 740°C. The results obtained until now allow us to divide the investigated V₂O₅–MoO₃–α-Sb₂O₄ system into five partial subsystems. This revised version was published online in July 2006 with corrections to the Cover Date.     

Phase stability and ionic conductivity in substituted La2W2O9

Different substitutions, i.e. Sr²⁺, Ba²⁺, K⁺, Nb⁵⁺ and V⁵⁺, have been performed in the triclinic α-La₂W₂O₉ structure in order to stabilise the high temperature and better ionic conductor cubic β-phase. This approach has been used to try to obtain a new series of ionic conductors with LAMOX-type structure without molybdenum and presumably better redox stability compared to β-La₂Mo₂O₉. Nanocrystalline materials obtained by a freeze-drying precursor method at 600 °C exhibit mainly the β-La₂W₂O₉ structure, however, the triclinic α-form is stabilised as the firing temperature increases and the crystallite size grows. Only high levels of Ba²⁺ and V⁵⁺ substitutions retained the cubic form at room temperature after firing above 1100 °C. However, these phases are metastable above 700 °C, exhibiting an irreversible transformation to the low temperature triclinic α-phase. The synthesis, structure, phase stability, kinetic of phase transformation and electrical conductivity of these materials have been studied in the present report.     

Influence of iron oxide support preparation method on the properties of Ru/Fe2O3 catalysts for water-gas shift reaction

Studies were undertaken of phase transitions of iron oxide obtained from iron oxide-hydroxides of type α-, β-, γ- and δ-FeOOH, and used as a support of ruthenium catalysts Ru/Fe₂O₃, employed in the water-gas shift reaction. In asprepared pure supports and ruthenium catalysts the main phase was α-Fe₂O₃. After use in the water-gas shift reaction, the support showed the presence of different phases of iron oxide. The most active Ru/Fe₂O₃ catalysts prepared on the basis of α- and δ-FeOOH, after use in the water-gas shift reaction, revealed the presence of Fe₃O₄ or a mixture of phases Fe₃O₄ and γ-Fe₂O₃. The least active catalysts, prepared on the basis of β- and γ-FeOOH, contained a solid solution of Fe₃O₄-γ-Fe₂O₃ with traces of α-Fe₂O₃.     

Sol–gel synthesis and transport property of nanocrystalline La<Subscript>2</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript> thin films

La₂Mo₂O₉ films were successfully synthesized on silicon (100) and poly-alumina substrates via modified sol–gel method with inorganic salts of La(NO₃)₃ and (NH₄)₆Mo₇O₂₄ as precursors. Pure La₂Mo₂O₉ phase was confirmed by XRD if the annealing temperature was higher than 500 °C. Energy dispersive spectrometry (EDS) of TEM revealed that the molar ratio of La to Mo was nearly 1:1. Field-emission SEM characterization showed that the films were dense, crack-free and uniform. The grain size of the films ranged from 30 to 400 nm depending upon the calcination temperature and duration time. The roughness calculated from AFM topography varied in the range between 10 and 35 nm. The thickness of the films was more than 200 nm for single-layered films. The electrical conductivity of the films reaches 0.06 S/cm at 600 °C that was almost more than one order of magnitude higher than that of the corresponding bulk material.     

Mixed-conducting perovskite-type SrxBi1-xFeO3-δ oxygen-permeating membranes

Sr_xBi_1-xFeO_3-δ (SBF) series mixed conductors were synthesized using standard ceramic method. The properties of such materials were characterized by XRD, O₂-TPD techniques. Abnormal crystal phenomena were found and explained and correlated with the oxygen permeation results. By analysis of the critical radius (r_c), the degree of openness of the lattice (F_v) and the average metal-oxygen bonding energy of the perovskite lattice (ABE), it was proposed that the oxygen permeation flux is determined mainly by the oxygen diffusion rate in bulk when 1-x⩽0.5, and by the concentration of oxygen vacancy when 1-x ⩾ 0.5. The stability of Sr_0.5Bi_0.5FeO_3-δ was also investigated, and the high stability of it was attributed to the stable BO₆ octahedra.     

Triterpene glycosides of Hedera taurica VI. Structures of hederosides G,H1, H2, and I from the berries of Crimean ivy

We have isolated from Crimean ivy berries in addition previously known triterpene glycosides — 3-O-α-L-arabinopyranosyl-28-O-[O-α-L-rhamnopyranosyl-(1 → 4)-O-β-D-glycopyranosyl-(1 → 6)-β-D-glucopyranosyl]hederagenin, 3-O-[O-α-L-rhamnopyranosyl-(1 → 2)-α-L-arabinopyranosyl]-28-O-[O-α-L-rhamnopyranosyl-(1 → 4)-O-β-D-glucopyranosyl-(1 → 6)-β-D-glycopyranosyl]hederagenin, the new triterpene glycosides hederoside H₂-3-O-[O-β-D-glycopyranosyl-(1 → 2)-β-D-glycopyranosyl-(1 → 2)-β-D-glucopyranosyl]-28-O-[O-β-D-glucopyranosyl-(1 → 6)-β-D-glucopyranosyl]oleanolic acid- and hederoside I-3-O-[O-β-D-glucopyranosyl-(1 → 2)-β-D-glucopyranosyl]-28-O-[O-β-D-glucopyranosyl-(1 → 6)-β-D-glucopyranosyl]hederagenin. Details of their¹³C NMR spectra are given. M. V. Frunze Simferopol' State University. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 779–783, November–December, 1990.     

Dehydrogenation of Isobutane Over V2O5/γ-Al2O3 Catalyst

The effect of the type of the support and the amount of V₂O₅ loading on the activity of V₂O₅/γ-Al₂O₃ catalyst for the dehydrogenation of isobutane have been investigated. Based on the experimental results of TPR, XRD and ESR spectroscopy, it is suggested that there are strong interactions between vanadia and carrier and that the V⁴⁺ species on the surface is the active site of V₂O₅/γ-Al₂O₃ for this reaction. This revised version was published online in June 2006 with corrections to the Cover Date.     

The effect of phase composition on the transport properties of composites La0.8Sr0.2Fe0.7Ni0.3O3 ? δ-Ce0.9Gd0.1O1.95

Full conductivity, diffusion and oxygen exchange processes in composites (100 − x)La_0.8Sr_0.2Fe_0.7Ni_0.3O_{3 − δ}−xCe_0.9Gd_0.1O_1.95 (x is the volume fraction, 0 ≤ x ≤ 71.1%) at 700°C over the oxygen partial pressure range from 0.2 to 3 × 10⁻³ atm are studied by the electrical conductivity relaxation method. The composites’ conductivity was shown to decrease monotonically with the increasing of Ce_0.9Gd_0.1O_1.95 fraction, while the oxygen chemical diffusion coefficient increased. The oxygen exchange constant is higher for the composites than for the individual phases of La_0.8Sr_0.2Fe_0.7Ni_0.3O_{3 − δ} and Ce_0.9Gd_0.1O_1.95. Possible reason of the dependence of the parameters D _chem and k _chem on the temperature, oxygen pressure, and the composite composition is the effect of the interface on the oxygen transfer processes. Most effective oxygen transfer occurs in the composites whose composition approaches La_0.8Sr_0.2Fe_0.7Ni_0.3O_{3 − δ}-Ce_0.9Gd_0.1O_1.95 (x = 71%).     

Synthesis and characterization of La2Mo2O9 obtained from freeze-dried precursors

La₂Mo₂O₉ ceramics have been prepared from freeze-dried precursors and their properties compared to those of lantanum molybdate obtained by conventional solid state (SS) reaction. All materials have been characterized by X-ray diffraction, scanning electron microscopy and thermal analysis (TGA/DTA/DSC and dilatometry) to characterize the phase formation and phase transition. When the freeze-dried method was applied, the synthesis temperature required to obtain dense samples was much lower than that for powders obtained by SS reaction. The morphology and structure of the oxide particle are significantly dependent on the synthesis method. The grain size is smaller, whereas the density of sintered pellets is higher for the freeze-dried precursor powder when compared with the SS reaction method. Impedance spectroscopy was used to measure the electrical conductivity of La₂Mo₂O₉ from 548 to 1123 K, in air, and to characterize the blocking effects of grain boundaries.     

Compatibility evaluation between La2Mo2O9 fast oxide-ion conductor and Ni-based materials

The chemical reactivity of La₂NiO_4+δ and nickel metal or nickel oxide with fast oxide-ion conductor La₂Mo₂O₉ is investigated in the annealing temperature range between 600 and 1000 °C, using room temperature X-ray powder diffraction. Within the La₂NiO_4+δ/La₂Mo₂O₉ system, subsequent reaction is evidenced at relatively low annealing temperature (600 °C), with formation of La₂MoO₆ and NiO. The reaction is complete at 1000 °C. At reverse, no reaction occurs between Ni or NiO and La₂Mo₂O₉ up to 1000 °C. Together with a previous work [G. Corbel, S. Mestiri, P. Lacorre, Solid State Sci. 7 (2005) 1216], the current study shows that Ni-CGO cermets might be chemically and mechanically compatible anode materials to work with LAMOX electrolytes in solid oxide fuel cells.     

Comprehensive survey of Nd substitution In La2Mo2O9 oxide-ion conductor

Differential thermal analysis coupled to temperature-controlled diffraction have given evidence of a topological metastability phenomenon in an extended compositional range of the La_2−xNd_xMo₂O₉ solid solution. A metastable-stable phase diagram is proposed for this series of LAMOX-type fast oxide-ion conductors. In the Nd range 0<x?0.35, a freezing of the oxygen/vacancy disorder of the β-phase at ambient temperature can be achieved through a splat-quenching to water-ice mixture or/and shaping/sintering into pellet. In the intermediate 0.4?x?1.2 range, the amount of β-metastable phase grows upon substitution for powders. The negative impact of β-metastable to α phase transition on conductivity tends to disappear through the partial stabilization of the β phase by shaping/sintering.     

A new furostanol glycoside with fatty acid synthase inhibitory activity from <Emphasis Type="Italic">Ophiopogon japonicusa</Emphasis>

A new furostanol glycoside, named ophiopogonin J (1), was isolated from the fibrous root of Ophiopogon japonicas. The structure of the compound was established as (25R)-26-[(O-β-D-glucopyranosyl-(1 → 2)-β-D-glucopyranosyl)]-20α -hydroxyfurost-5, 22-diene-3-O-α-L-rhamnopyranosyl-(1 → 2)-[β-D-xylopyranosyl(1 → 4)]-β-D-glucopyranoside on the basis of spectroscopic methods, including HR-ESI-MS and 1D and 2D NMR experiments.