Study of the silver selenide—silver telluride system

The system Ag₂TeAg₂Se was investigated by DTA, X-ray diffraction and microstructural analysis within the composition interval from 0 to 100% Ag₂Te. Samples obtained after heating at 500°C for 720 h were studied.The high-temperature polymorphs form a continuous solid solution with a minimum at 35% Ag₂ Te and 835°C. At low temperatures solid-phase transformations take place. The break-down of the solid solution proceeds eutectoidally at about 110°C on the Ag₂Te side peritectoidally at about 150°C on the Ag₂Se side. The system Ag₂TeAg₂Se is rather complex.     

Fuel Combustion Reactions and Catalysts: XXI. Synthesis and Characterization of Modified Mn–Al–O Catalysts for High-Temperature Oxidation

The phase composition of supported Mn–Al–O catalysts and their activity in the reaction of methane oxidation were studied depending on the composition of aluminum oxide supports (-Al₂O₃ with different -Al₂O₃ contents modified with individual Mg, La, and Ce oxides or Mg + La and Mg + Ce oxide mixtures) and calcination temperatures (500, 900, and 1300°C). It was found that the Mn–Al–O catalysts based on -alumina containing -Al₂O₃ and modified with Mg, La, or Ce additives are more active and thermally stable (up to 1300°C) than the samples based on pure -Al₂O₃. A conclusion was drawn that a higher degree of disorder of the structure of -Al₂O₃, compared to that of -Al₂O₃, is favorable for a deeper interaction of manganese and modifying additives with the support at the early stages of the synthesis and for the formation of Mn–Al compounds with complex composition (solid solutions and/or hexaaluminates) at 1300°C. These compounds are responsible for the stability and high activity of the catalysts in methane oxidation.     

Application of capillary electrochromatography using macroporous polyacrylamide columns for the analysis of lignans from seeds of Schisandra chinensis

Capillary electrochromatography (CEC) using polymer-based monolithic stationary phase has been developed as a promising method for the determination of lignans of Schisandra chinensis. The columns were prepared by in situ copolymerisation of acrylamide, N,N'-methylenebisacrylamide, vinylsulfonic acid and lauryl acrylate in presence of poly(ethylene glycol) as a porogenic agent. The columns [33 cm (24.5 cm effective length) x 75 microm I.D.] were successfully used to analyse and quantify the major lignans in extract of the seeds of Schisandra chinensis. Good separations were achieved in less than 35 min. The calibration graphs were linear in the range 0.025-1.0 mg/ml of given lignan with correlation coefficients between 0.9951 and 0.9996. The inter-day reproducibility of the peak area were below 3.9% and the inter-day reproducibility of the migration time were below 4.2%. The results of quantitative CEC analyses were compared with those obtained by reversed-phase HPLC, the levels of schizandrin, gomisin A, gomisin N and wuweizisu C determined by CEC were in a good agreement with those determined by HPLC.     

DNA-modified electrodes; part 4: optimization of covalent immobilization of DNA on self-assembled monolayers

The covalent immobilization of DNA onto self-assembled monolayer (SAM) modified gold electrodes (SAM/Au) was studied by X-ray photoelectron spectrometry and electrochemical method so as to optimize its covalent immobilization on SAMs. Three types of SAMs with hydroxyl, amino, and carboxyl terminal groups, respectively, were examined. Results obtained by both X-ray photoelectron spectrometry and cyclic voltammetry show that the largest covalent immobilization amount of dsDNA could be gained on hydroxyl-terminated SAM/Au. The ratio of amount of dsDNA immobilized on hydroxyl-terminated SAMs to that on carboxyl-terminated SAMs and to that on amino-terminated SAMs is (3-3.5): (1-1.5): 1. The dsDNA immobilized covalently on hydroxyl-terminated SAMs accounts for 82.8-87.6% of its total surface amount (including small amount of dsDNA adsorbed). So the hydroxyl-terminated SAM is a good substrate for the covalent immobilization of dsDNA on gold surfaces.     

Sensitive high-performance liquid chromatographic determination of famotidine in plasma. Application to pharmacokinetic study.

A sensitive high-performance liquid chromatographic (HPLC) method for the quantitation of famotidine in human plasma is described. Clopamide was used as the internal standard. Plasma samples were extracted with diethyl ether to eliminate endogenous interferences. Plasma samples were then extracted at alkaline pH with ethyl acetate. Famotidine and the internal standard were readily extracted into the organic solvent. After evaporation of ethyl acetate, the residue was analysed by HPLC. The chromatographic separation was accomplished with an isocratic mobile phase consisting of acetonitrile-water (12:88, v/v) containing 20 mM disodium hydrogenphosphate and 50 mM sodium dodecyl sulphate, adjusted to pH 3. The HPLC microbore column was packed with 5 microns ODS Hypersil. Using ultraviolet detection at 267 nm, the detection limit for plasma famotidine was 5 ng/ml. The calibration curve was linear over the concentration range 5-500 ng/ml. The inter- and intra-assay coefficients of variation were found to be less than 10%. Applicability of the method was demonstrated by a bioavailability/pharmacokinetic study in normal volunteers who received 80 mg famotidine orally.     

ANION AND SOLVENT EFFECTS ON THE RATE OF REDUCTION OF TRIPLET EXCITED THIAZINE DYES BY FERROUS IONS

Abstract— The lifetimes of the triplet excited states of thionine and methylene blue were measured in aqueous and 50 v/v% aqueous acetonitrile solutions acidified with 0.01 N sulfuric or trifluoromethyl-sulfonic acid. The rate constants for reaction of the triplet excited dyes with ferrous ions were measured in the same solutions. The triplet lifetimes in the absence of added quenchers were insensitive to a change in acid from trifluoromethylsulfonic to sulfuric or to a change in solvent from water to 50v/v% aqueous acetonitrile (τ for triplet thionine ˜7.5 μs, τ for triplet methylene blue ˜4.5 μs). In contrast, the rate constant for reaction of the triplet dyes with ferrous ions increased by nearly a factor of 10 with a change in acid from trifluoromethylsulfonic to sulfuric. In solutions containing sulfate ions this reaction rate constant increased with increasing sulfate concentration and with a change in solvent from water to 50 v/v% aqueous acetonitrile. The results are discussed in terms of the possibility of association of the positively charged reactive ions with sulfate anions. Quenching of the triplet excited dyes by ferric ions or by ground state dye molecules was shown to be negligible at the concentration used for the ferrous ion quenching study.     

Phytoecdysteroids of plants of the genusSilene. VII. Sileneoside D — ecdysterone 3-O-α-D-galactopyranoside fromSilene brahuica

A phytoecdysteroid, sileneoside D, has been isolated from the roots ofSilene brahuica Boiss. and it has been shown to be ecdysterone 3-O-α-D-galactopyranoside.     

Crystal structure of the stoichiometric compound Cs2W3O10 with a fractional number of atoms in the unit cell

The crystal structure of Cs₂W₃O₁₀ (a=16.103, c=10.169 Å, $I\bar 4$ , Z=120/11) was determined from three-dimensional X-ray diffraction data (CAD-4 automatic diffractometer, 1612 reflections, R=0.044). The structure has an AB₂O₆ defective pyrochlore motif in which some of the groups consisting of four WO₆ octahedra have been subtracted from the tungsten-oxygen framework and substituted by Cs⁺. The crystal has no vacancies in the substitution site (as confirmed by the occupancy refinement), and the composition of the crystal is strictly stoichiometric with a fractional number of atoms in the unit cell. A similar composition is suggested for the isostructural rubidium compound, which was earlier considered nonstoichiometric.     

Coumarins of three species of the genusHaplophyllum

The results are given of an investigation of three species of the genusHaplophyllum: H. villosum, H. kowalenskyi, andH. tenue, fromwhich five substances of coumarin nature have been isolated. Of them, two substances (I and II) have been identified as scopoletin and lomatin isovalerate, respectively, while suitable structures have been established for the new compounds tenuidin, villosin, and tenudiol. It has been shown that the coumarin composition of the plants changes with the growth site.     

Algorithms for high-level data processing in gas chromatography

Computer processing of gas chromatographic data is discussed, with special emphasis on the numerical operations needed. The CHADIC program is described. This program enables optimal separation conditions to be determined and isothermal gas chromatograms to be processed for qualitative and quantitative analysis.