Etude par resonance quadripolaire des noyaux 63-Cu et 75-As de complexes tetrameres de la triethylarsine avec des halogenures de cuivre(I)

63-Cu and 75-As quadrupole resonance results have been obtained for the tetrameric triethylarsine copper(I) halides (Cl, Br and I). Unusual behaviours of the temperature dependence of the 63-Cu and 75-As quadrupole resonance lines have been observed simultaneously. Between 77 and 300 K, the chlorine derivative undergoes two structural phase changes at 93 and 173 K, while phase transformations occur at 152 and 86 K respectively for the bromine and iodine derivatives.     

High Temperature Phase Transitions in Na_xCoO_2 Materials

1 INTRODUCTION In recent years, much attention has been focused on the NaxCoO2 system due to its notable properties and potential technologic applications as a cathode material in high-energy density, reversible solid state battery systems[1, 2]. Recently, large thermoelectric power[3～6] in NaxCoO2 and superconductivity (～4 K) in hydrated NaxCoO2yH2O (x = 0.35, y = 1.33) ma- terial have been observed[7]. This hydrated layered phase is the first 3d-transition metal oxide with superco…     

Determination de la structure d'halogenotriazoles-1,2,4 par spectrometrie de masse

The mass spectra of a substituted halo-1,2,4-triazoles series have been studied. The main fragmentation pathways have been determined and the utility in structure determinations of isomeric compounds is demonstrated.     

Etude en Spectrometrie de Masses des Fragmentations de Derives de la Triazine-1,2,4

The mass spectra of 49 1,2,4-triazines with oxo, thioxo, methoxy and methylmercapto groups in the 3 and 5 positions are reported and analysed. Five distinct patterns have been observed upon electron impact but an initial loss of N₂ has not been identified. A tautomeric equilibrium has been shown to occur in the vapour phase from some fragmentation pathways.     

Evolution des tenseurs de dilatation thermique en fonction de la temperature. II. Etude calorimetrique et cristallographique de la transition de phase ordre-desordre du thiophene chrome tricarbonyle C4H4SCr(CO)3

Benzenechromium tricarbonyl C₆H₆Cr(CO)₃ and thiophenechromium tricarbonyl C₄H₄SCr(CO)₃ are isomorphous at room temperature. We have measured, in the range 77–295°K, the variations of specific heat and of the tensor of thermal expansion for these two molecular compounds. The first one exhibits quite normal behavior; on the other hand, the second one exhibits a first order phase transition, monoclinic ? triclinic at T = 185°K, associated with an order-disorder phase transition. Structural evolution of thiophene-chromium tricarbonyl, during phase transition, has been explained from the variation of its tensor of thermal expansion.     

Étude par analyse thermique différentielle des transformations ordre-désordre dans des alliages dentaires á base d'or et de cuivre

Two phase transformations have been detected by differential thermal analysis of two dental gold alloys between 25 and 500°C. The upper temperature transformations has been identified as an order-disorder change by means of hardness measurements. The thermal effect is proportional to the copper content of the alloy.     

SmCP-networked films obtained by in situ photopolymerization of neat reactive banana-shaped liquid crystals

The synthesis and characterization of reactive banana-shaped compounds have been carried out, and their ability to be photopolymerized in their SmCP mesophase has been assessed. The presence of a SmCP liquid crystalline phase in these compounds has been confirmed by X-ray studies. The polymerization of these molecules has been demonstrated by calorimetric techniques as well as by the preparation and characterization of SmCP-ordered free films that are mechanically stable at room temperature. Furthermore, polymerized films exhibit second harmonic generation activity at room temperature in the absence of an electric field.     

Production of α-terpineol fromEscherichia coli cells expressing thermostable limonene hydratase

The genes encoding a thermostable limonene hydratase have been located on a cloned fragment inEscherichia coli conferring growth on limonene and production of the monoterpenes perillyl alcohol and α-terpineol. Whole cell bioconversion studies at elevated temperature employing both an aqueous phase and neat limonene phase demonstrated significant production of α-terpineol with additional production of carvone.     

Intensified Saturation of Iron with Nitrogen by the Method of Thermogasocyclic Nitriding

Here, we describe the thermogasocyclic-nitriding method, which consists in multiple alternation of process stages with high and low nitrogen potential conducted at temperatures lower and higher, respectively, than the temperature of the eutectoid transformation in the Fe–N system. The phase composition of the nitrided layer after various operation modes and kinetics of the growth of its individual regions have been studied. The possibilities of intensifying the nitriding process and regulating the phase composition of the layer by an appropriate choice of process parameters, namely, the number of half cycles and their duration, have been demonstrated.     

Etude radiocristallographique et calorimetrique des transitions de phase de Ag8GeTe6

Powder and single crystals of the Ag₈GeTe₆ phase have been prepared by direct synthesis and chemical vapor transport reaction (iodine), respectively. The low-temperature phase of this material has been investigated by differential scanning calorimetry analysis and X-ray diffraction. The phase transitions are interpreted as a result of low-temperature ordering of the Ag⁺ ions.     

Spectrometrie de masse d'heterocycles azotes. IV—comportement sous l'impact electronique d'iodures de pyrazoliniums-2

The behaviour of 2-pyrazolinium iodides in mass spectroscopy has been investigated. The simultaneous fragmentation of four neutral molecules has been observed, which have been formed by substitution reactions of the iodide anion on the N-1 substituents. Thus, these reactions which have been shown to occur in protic solvents, also occur in the gaseous phase and under electron-impact.     

Calorimètre pour la mesure des chaleurs de mélange des liquides

A calorimeter has been designed for measuring the heat of mixing of liquid systems, which eliminates the need to correct for changes in the composition of the vapour phase on mixing. Improved accuracy has been obtained. It permits the measurements of thermic effects of the order of 0.005 joule, corresponding to temperature differences of 10^?4 of a degree. Heats of mixing have been measured for the system hexadecane-hexane, the results of which are highly satisfactory.     

Influence de la tacticite du polychlorure de vinyle sur son comportement physique en fonction de la temperature

Three PVC samples, having syndiotacticity contents between 55 and 68%, have been prepared and characterized by previously described methods. Their thermal behaviour has been studied using three techniques, viz. inverse chromatography. ATD and Rheovibron. The results make clear the influence of tacticity on both the number and the intensity of transitions. These results are accounted for on the basis of a possible influence of TG conformations on the behaviour of the amorphous phase.     

Preparation de membranes echangeuses de cations par photogreffage d'ethers allyliques du poly (alcool vinylique). Etude de certaines de leurs proprietes—II: Photogreffage des poly (alcools vinyliques) allyles

Poly(vinyl alcohols) partially allylated have been grafted with sulphonic acid. The influence of experimental parameters (vinyl sulphonic acid concentration, swelling before grafting, photoinitiator concentration, grafting temperature and duration of the irradiation) have been studied in detail.     

Representation T-V-x des systemes binaires a tension de vapeur non negligeable

The effect of the variableV/m on the appearance of DTA endotherms has been used to obtain quantitative data on theT-V-x representation of the NdAs-As system. The peritectic reaction is NdAs₂ (solid)+vapour ? NdAs (solid)+liquid at 1185 K. At this temperature, the four phases set up a quadrangle in theV/m-x plane. The sides of this quadrangle have been defined by experiment: the vapour phase is composed of 87 mol% As and itsV/m value is 12.2 mm³ mg^?1. The peritectic liquid is composed of 87 mol% As. The eutectic equilibrium at 1080 K appears to be NdAs (solid)+As (solid)+vapour ← liquid It sets up a triangle, inside which the liquid phase is placed. The vapour phase is composed of 100 mol% As, and itsV/m value is 10 mm³ mg^?1. The eutectic liquid is composed of 90 mol% As. Three polythermal sections of the NdAs-As binary system are described for a constant volume.     

Structure and photocatalytic properties of materials based on titanium dioxide and silver nanoparticles

Phase composition and structure of mesostructured materials, titanium dioxide and titanium dioxide modified with silver nanoparticles, have been studied by X-ray diffraction analysis. Introduction of Ag(I) ions into the initial composition and variation of the annealing temperature over the 500–950°C range allows controlling the anatase to rutile crystal phase ratio in the samples. The photocatalytic activity of TiO₂ and TiO₂/Ag samples has been demonstrated using the methyl orange degradation reaction. The catalytic properties of the materials have been found to depend on the anatase to rutile phase ratio and on the presence of silver nanoparticles.     

Etude thermoanalytique et lyodisponibilite de dispersions solides du tolbutamide

We have established the phase diagram tolbutamide (TBM)-PEG 6000 and determined the eutectic composition 1/9 (w/w) in tolbutamide and melting temperature 56.2°C±0.3; no solid solution has been found. Negative mixing enthalpies of physical mixture (?2.5 J·g^?1) and solid dispersions coprecipitate (?3.9 J·g^?1) melt (?9.9 J·g^?1) for eutectic composition involve the existence of interactions between drug and carrier. We have determined the dissolution kinetics: amount % dissolved (10 min) 65.87±0.55 (physical mixture), 78.02±0.02 (coprecipitate), 99.90±0.10 (melt). We have observed a good agreement between dissolution kinetics and mixing enthalpies data.     

Liquid-vapor and liquid-liquid phase equilibria of the Brodholt-Sampoli-Vallauri polarizable water model

Liquid-vapor and liquid-liquid phase equilibria of the polarizable Brodholt-Sampoli-Vallauri water model have been investigated by Gibbs ensemble Monte Carlo computer simulations. The coexisting liquid and vapor densities and energy of vaporization of the model is found to be in a reasonable agreement with experimental data in the entire temperature range of liquid-vapor coexistence. The critical temperature and density of the model are found to be 615 K and 0.278 gcm(3), respectively, close to the experimental values of 647.1 K and 0.322 gcm(3). In the supercooled state two distinct liquid-liquid coexistence regions are observed. The existence of liquid-liquid phase separation of a polarizable water model is demonstrated for the first time.     

Tribute to Prof. Roy Edward Bruns,Universidade Estadual de Campinas

Abstract

Arrhythmic patients treated with quinidine have been found to ingest caffeine from various sources. Caffeine interferes with the quantitation of quinidine in plasma samples. This method for determination of quinidine in plasma is based on high performance isocratic liquid chromatography with the use of a C-18 bonded reverse phase column at room temperature. Unlike some liquid chromatographic procedures for quinidine, caffeine does not interfere. Quinidine is extracted from alkalinized plasma into benzene. The benzene layer is removed and evaporated to dryness under nitrogen at 50 C. The residue is reconstituted with methanol and injected into the column. The mobile phase is 30/70 (v/v) mixture of methanol/0.4% glacial acetic acid. Analysis can be completed within 10 minutes. The procedure is sensitive (0.5mg/L) and is well reproducible (CV= 3.5% for a 2 mg/L concentration in plasma).     

Spectres infrarouges et raman du complexe solide MgBr22Et2O: Changement de phase et isomérie de rotation des molécules d'éther coordonnées

Infrared and Raman spectra of solid magnesium bromide dietherate MgBr₂2Et₂O have been studied at different temperatures between 300 and 90 °K in the 4000 to 30 cm^? range. Infrared spectra of this compound at various pressures up to 10 kbar have also been investigated. The MgBr₂2Et₂O crystal has two phases and there is a reversible transition between them. This phase transition concerns primarily the conformational change of (C₂Hg₅)₂O molecules and much less the arrangement of the ligands around the central magnesium atom. At room temperature or low pressure the GG conformation appears to be predominant while at low temperature or high pressure there is only TG (or TT) conformation of ether molecules. The enthalpy difference and transition temperature between the phases have been determined calorimetrically. An assignment of the spectra of both phases is given. The analysis of intramolecular vibrations gives information about the relative contribution of conformational change and coordination effect to the frequency shifts of (C₂H₅)₂O vibrations. The assignment of magnesium-ligand vibrations on the other hand allows us to estimate the Mg-Br and Mg-O force constants.