Electrochemical formation and phase control of Mg-Li alloys

The electrochemical formation of Mg-Li alloys was investigated in a molten LiCl-KCl(58-42 mol%)eutectic melt at 723 K. The cyclic voltammogram for a Mo electrode showed that the electroreduction of Li~ proceeds in a single step and the deposition potential of Li metal was -2.40 V(vs.Ag/AgCl).For Mg electrode,the electroreduction of Li~ takes place at less cathodic potential than that at the Mo electrode which was caused by the formation of Mg-Li alloys.Phase of the deposited Mg-Li alloys could be controlled by the electrolysis potential,and the samples were characterized by X-ray diffraction and scanning electron microscopy. The results showed thatα-Mg andβ-Li phases were obtained at -2.35 and -2.55 V,respectively.     

High-performance liquid chromatography–tandem mass spectrometry in the identification and determination of phase I and phase II drug metabolites

Applications of tandem mass spectrometry (MS/MS) techniques coupled with high-performance liquid chromatography (HPLC) in the identification and determination of phase I and phase II drug metabolites are reviewed with an emphasis on recent papers published predominantly within the last 6 years (2002–2007) reporting the employment of atmospheric pressure ionization techniques as the most promising approach for a sensitive detection, positive identification and quantitation of metabolites in complex biological matrices. This review is devoted to in vitro and in vivo drug biotransformation in humans and animals. The first step preceding an HPLC-MS bioanalysis consists in the choice of suitable sample preparation procedures (biomatrix sampling, homogenization, internal standard addition, deproteination, centrifugation, extraction). The subsequent step is the right optimization of chromatographic conditions providing the required separation selectivity, analysis time and also good compatibility with the MS detection. This is usually not accessible without the employment of the parent drug and synthesized or isolated chemical standards of expected phase I and sometimes also phase II metabolites. The incorporation of additional detectors (photodiode-array UV, fluorescence, polarimetric and others) between the HPLC and MS instruments can result in valuable analytical information supplementing MS results. The relation among the structural changes caused by metabolic reactions and corresponding shifts in the retention behavior in reversed-phase systems is discussed as supporting information for identification of the metabolite. The first and basic step in the interpretation of mass spectra is always the molecular weight (MW) determination based on the presence of protonated molecules [M+H]⁺ and sometimes adducts with ammonium or alkali-metal ions, observed in the positive-ion full-scan mass spectra. The MW determination can be confirmed by the [M-H]^- ion for metabolites providing a signal in negative-ion mass spectra. MS/MS is a worthy tool for further structural characterization because of the occurrence of characteristic fragment ions, either MS ⁿ analysis for studying the fragmentation patterns using trap-based analyzers or high mass accuracy measurements for elemental composition determination using time of flight based or Fourier transform mass analyzers. The correlation between typical functional groups found in phase I and phase II drug metabolites and corresponding neutral losses is generalized and illustrated for selected examples. The choice of a suitable ionization technique and polarity mode in relation to the metabolite structure is discussed as well.     

Amplitude and phase fluctuation modes in the smectic Cα* phase of an antiferroelectric compound

Dielectric measurements have been carried out on the chiral smectic C_α (SmC_α*) phase of a MHPOBC analogous compound. Two relaxation modes have been observed in this phase for planar orientation of the molecules. One process has been observed at frequency lower than that of the soft mode of the chiral smectic A (SmA*) phase. This relaxation process is connected with the helicity of the SmC_α* phase. In the high‐frequency region, another relaxation process has been observed in the SmC_α* phase for which bias field dependence is similar to that of the soft mode at the SmA*–SmC* phase transition. The experimental observations are in agreement with a recently proposed dielectric theory for the SmC_α* phase and theoretical dielectric results obtained by numerical simulations. Thus, we report here experimental verification of two theoretically predicted dielectric modes in the SmC_α* phase.     

Direct and indirect photoinduced gas–liquid phase transitions

The condensation of supersaturated vapors of various substances in air under UV irradiation in a cloud chamber has been studied. The irradiation and subsequent photodissociation greatly facilitate the condensation of vapors in comparison with unirradiated mixtures, wherein both a vapor that directly absorbs radiation (direct photoinduced phase transition) and, for example, water vapor in the presence of photodissociating impurities (indirect photoinduced transition) can be condensed.     

Vapor phase composition and radical polymerization—how the gas phase influences the kinetics of heterophase polymerization

The outcome of radical styrene heterophase polymerization depends strongly on the composition of the gas phase. Data of a comprehensive experimental study show that the effect of the gas phase is quite a complex one and strongly influenced by the nature of the gas, the homogeneity or heterogeneity of the polymerization system, and the kind of initiator. Evidence is presented that the influence of air goes beyond the simple action of oxygen which can cause deceleration or acceleration of the reaction. The experimental results show that the optimum polymerization conditions are obtained in the absence of any foreign gas.     

The rotation and the phase transition in solid C60

The interaction between C60's in solid C60 has been calculated by (exp-6-1) potential, and the cause and the controlled factor of the high rapid rotations of C60 's were discussed. In order to describe the disordered degree of C60 rotation, an equivalent M is introduced. The phase transitions at the ~260 K and at the ~90 K are studied from the viewpoint of C60 rotation. The potential barriers of the ordered rotation below the ~260 K and the disordered rotation above the ~260 K have been given, and the effect of the external pressure on the temperature of phase transition has also been given.     

Cure reaction and phase behavior of liquid crystalline epoxides-anhydride systems

A series of novel liquid crystalline epoxides with lateral substituents were cured with anhydrides and the cure kinetics was investigated by non-isothermal DSC technique. The results showed that the lengths of lateral substituents have great effect on the value of Ea. The curing reaction became less active, when the liquid crystalline epoxides have long lateral substituents and were controlled by diffusion at the late stage of cure. A nematic structure was observed by POM and XRD.     

Synthesis and thermal properties of NiSbS–As doped phase

The substitution of Sb with As in the NiSbS intermetallic compound was studied in the framework of evaluating a possible increase of the thermoelectric properties. Different NiSb_1?xAs_xS samples were synthesized with increasing amounts of As (0 < x < 0.66) employing a simple synthetic route using a muffle furnace. Scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy was used to investigate the microstructure. X-ray powder diffraction techniques were employed in order to study the possible existence of a solid solution between NiSbS and NiAsS compounds, as well as to identify the crystal structure and determine the lattice parameters. All compounds were found to crystallise with the NiSbS prototype (cP12-P2₁3), with lattice parameters varying from a = 0.59341(7) nm (x = 0) to a = 0.56849(6) nm (x = 1). Good agreement with Vegard’s law was evidenced. Thermal measurements on NiSb_1?xAs_xS samples were carried out using DTA instruments to evaluate the thermal stability and the melting temperatures.     

Diffusion and phase equilibria of binary fluids in mesopores

The formation of adsorption hysteresis in mesoporous material with random pore structure may be interrelated with different distributions of the fluid density attained along different paths of the system preparation. To access microscopic details of these distributions, in addition to the main sorptive liquid, distribution of which along the pore space of Vycor porous glass was of interest, a small amount of a probe liquid with a substantially lower vapor pressure has been added. Molecular diffusivities of both liquids then have been traced using pulsed field gradient NMR. Due to different vapor pressures, the two molecular species explore different spaces occupied by the capillary-condensed (accessible for both species) and gaseous (accessible only for the molecules of the main sorptive) phases. Comparative analysis of the diffusion properties obtained at different states along the adsorption isotherm revealed further insight into peculiarities of the fluid distribution and mass transfer of binary fluids in pores.     

Enantiomeric separation of α-phenylethylamine and its analogs by mixed chiral and achiral stationary phase

A mixed stationary phase of modified β-cyclodextrin, 2,6-di-O-butyl-3-O-butyryl-β-cyclodextrin (phase A), and SE-54 (phase B) was used for enantiomeric separation of α-phenylethylami-ne, o,m,p-methyl and o,m,p-methoxy-substituted analogs. The composition of mixed phase was selected by comparison of each calculated amin(= (γm,i+1)/(γm,i))> the relative retention values of the most adjacent peaks, and γm,last, the relative retention values of the last eluting peak at each preselected ratio. Values of γm,i,α calculated by derived equations were in good agreement with the experimental results obtained with two specified mixed phases. All solutes investigated were almost baseline separated at a predicted composition of phase A and phase B in a single run within 18 minutes.     

Competition between crystallization and phase separation in polymer blends I. Diffusion controlled supermolecular structures and phase morphologies in poly(ɛ-caprolactone)/polystyrene blends

The type of supermolecular structure and the morphology in binary polymer blends with one crystallizable component and with a miscibility gap are strongly influenced by the relative rate of crystallization and demixing. Depending on the composition of the blend and on the relative position of the crystallization curve and the miscibility gap in the phase diagram, demixing-induced crystallization as well as crystallization-induced demixing can occur. Both these approaches lead to new and interesting structures. Additionally, the interaction of the two mentioned kinds of phase transition can under circumstances affect the growth rates of adjacent spherulites. This results in anisotropic concentration distribution or phase-separation morphology around their surfaces.Dedicated to Prof. Dr. W. Pechhold on the occasion of his 60th birthday.Presented at the Frühjahrstagung des FA Polymerphysik der DPG, Bad Nauheim, FRG, April 1990.     

Solid and liquid phase equilibria and solid-hydrate formation in binary mixtures of water with amines

Solid and liquid phase diagrams have been constructed for {water+triethylamine,or+N,N-dimethylformamide(DMF) or+N,N-dimethlacetamide (DMA)} Solid-hydrates form with the empirical formulae N(C2H5)3 3H2O,DMF 3H2O,DMF 2H2O,DMA 3H2O and (DMA)2 3H2O.All are congruently melting except the first which melts incongruently.The solid-hydrate formation is attributed to hydrogen bond.The results are compared with the references     

Characteristics of retention and enthalpies of sorption from the gas phase of esters of trimethylolpropane and С2–С5 acids on DB-1 stationary phase

Characteristics of retention and their temperature dependences, along with the thermodynamic characteristics of sorption on DB-1 nonpolar phase, are determined in the temperature range of 220–280°C for 21 mono-, di-, and trisubstituted esters of trimethylolpropane and monobasic acids with a variety of structures containing from 2 to 6 carbon atoms.

     

Orbital phase control of the conformations of α- and β-substituted enamines and vinyl ethers

The conformational stabilities of the α- and β-substituted enamines and vinyl ethers were predicted by orbital phase theory and confirmed by ab initio molecular orbital calculations. Cyclic interaction significantly occurs among the nonbonding orbital n _Y for the lone pair on the hetero atom Y (N in the enamines or O in the ethers), the π and π* orbitals of the CC bond, and the σ_C-H or σ*_C-X orbitals on the substituent CH₂X. The cyclic -n _Y-π-σ_C-H-π*- interaction is favored by the orbital phase continuity in the α-substituted molecules, while the cyclic -n _Y-π-σ*_C-X-π*- interaction is favored in the β-substituted molecules. The most stable conformation was then predicted to be synperiplanar or (pseudo)equatorial in the α-substituted molecules and anticlinical or (pseudo)axial in the β-substituted molecules. Received: 8 May 1998 / Accepted: 30 July 1998 / Published online: 16 November 1998     

QCM gas phase detection with ceramic materials—VOCs and oil vapors

Titanate sol–gel layers imprinted with carbonic acids were used as sensitive layers on quartz crystal microbalance. These functionalized ceramics enable us detection of volatile organic compounds such as ethanol, n-propanol, n-butanol, n-hexane, n-heptane, n-/iso-octane, and n-decane. Variation of the precursors (i.e., tetrabutoxy titanium, tetrapropoxy titanium, tetraethoxy titanium) allows us to tune the sensitivity of the material by a factor of 7. Sensitivity as a function of precursors leads to selective inclusion of n-butanol vapors down to 1 ppm. The selectivity of materials is optimized to differentiate between isomers, e.g., n- and iso-octane. The results can be rationalized by correlating the sensor effects of hydrocarbons with the Wiener index. A mass-sensitive sensor based on titanate layer was also developed for monitoring emanation of degraded engine oil. Heating the sensor by a meander avoids vapor condensation. Thus, a continuously working oil quality sensor was designed.     

Crystalline phase content and ionic conductivity correlation in LATP glass–ceramic

Li₂O–Al₂O₃–TiO₂–P₂O₅ (LATP) glass was fabricated by conventional melt quenching route. Glass transition temperature (T _g = 296 °C) and crystallization temperatures (T _C1,2) were obtained from thermal analysis. LATP glass was converted to glass–ceramic by heat treatment in the range 550–950 °C for 6 h. X-ray diffraction analysis revealed LiTi₂(PO₄)₃ as a major phase. Ionic conductivity increased monotonically with concentration, reaching a maximum of ~10⁻⁴ S/cm. AlPO₄ phase was detected in samples heat-treated above 850 °C. Its presence decreased the conductivity, suggesting LiTi₂(PO₄)₃ phase as main contributor to high ionic conductivity. NMR spectra confirmed the presence of mobile ⁷Li ions in the entire sample series and also gave some information on the structure and dynamics of conductivity.     

Thermodynamics of the solvation and phase distributions of 2,2′-dipyridyl in acetonitrile-DMSO-hexane and methanol-DMSO-hexane systems

The Gibbs energies of 2,2′-dipyridyl when transferred from dimethyl sulfoxide to its mixtures with acetonitrile and methanol are determined from the distribution of substance between immiscible phases. It is found that moving from dimethyl sulfoxide to acetonitrile and methanol weakens the solvation of 2,2′-dipyridyl due to a change in the solvation of amino groups and the hydrocarbon substituent, which is reflected in a reduction in the entropy component of the Gibbs energy.     

Hydrogen absorption and phase transitions in rapidly quenched LaNi alloys

Several LaNi binary alloys were rapidly quenched by melt spinning. A metastable phase and an uniform Laves phase were obtained. Differences in behaviour were observed between hydrogenation of quenched materials and of as-cast materials whose compositions were identical. The quenched materials, in contrast to the as-cast phases, had a tendency to form amorphous LaNiH alloys. The amorphous alloy was stable, in particular when the ratio La:Ni was 1:2.     

Studies on the phase behavior and solubilization of the microemulsion formed by surfactant-like ionic liquids with ɛ–β-fish-like phase diagram

The phase behavior and the solubilization of the microemulsion systems surfactant-like ionic liquids 1-hexadecyl-3-methylimidazolium bromide (C₁₆mimBr), 1-tetradecyl-3-methylimidazolium bromide (C₁₄mimBr), or 1-dodecyl-3-methylimidazolium bromide (C₁₂mimBr)/alcohol/alkane/brine have been studied with ɛ–β-fish-like phase diagram method at 40 °C and an oil-to-water mass ratio of 1:1. From the ɛ–β-fish-like phase diagram, the physicochemical parameters, such as the mass fraction of alcohol in the hydrophile–lipophile-balanced interfacial layer (A ^S), and the solubilities of ionic liquid (S ^O) and alcohol (A ^O) in alkane phase, were calculated. The solubilization of the microemulsion system has been discussed based on the ɛ–β-fish-like phase diagram. The smaller the oil molecule, the longer the alcohol chain length, and the larger the NaCl concentration in water, the larger the solubilization of the microemulsion system. In this paper, the solubilization of the microemulsion stabilized by both C₁₂mimBr and sodium dodecyl sulfonate (sodium dodecyl sulfate) was also investigated with the ɛ–β-fish-like phase diagram. The unequimolar composite of anionic and cationic surfactants can avoid the sedimentation aroused by the strong electrostatic attraction, and an obvious synergism effect in solubilization was obtained.