High pressure elastic and plastic deformations of silica: In situ diamond anvil cell Raman experiments

Normal silica glass is usually referred to as low density amorphous silica as it can be converted to high density amorphous silica by a hydrostatic pressure (polyamorphic transition). In this work in situ Raman experiments are performed in a diamond anvil cell up to 18 GPa. The pressure effects on the structure of silica after successive compression decompression experiments are analyzed. The mode Grüneisen parameters corresponding to the elastic compression of high density amorphous silica are obtained and compared with those of normal silica. A reorganization of the high density amorphous silica below 3 GPa is evidenced.     

Assessment of the retention properties of poly(vinyl alcohol) stationary phase for lipid class profiling in liquid chromatography

Potentialities of polymerized vinyl alcohol on silica gel were assessed for class separation of simple lipids, sphingolipids, glyceroglycolipids and phospholipids by high-performance liquid chromatography. A screening of pure solvents in binary gradient elution and a chemometric approach was used to define a rugged two segment linear gradient formed from four solvents for total lipid class separation. Triethylamine and formic acid were added in all mobile phase components for acidic phospholipid separation and evaporative light scattering response enhancement. Simple analytical procedures are described for the analysis of complex lipid materials.     

Factors controlling the regioselectivity of additions to α-enones—III: Reactions of 3-aryl α-enones with phosphorylated anions

Reaction of phosphonoester 2 and phosphononitrile 3 with chalcone and p-methoxychaleone in THF-t-BuOK at room temperature gives only the product resulting from CC double bond attack. The same reagents with benzalacetone lead to mixture of products resulting from CC double bond and carbonyl attack, though phosphine oxide 4 gives only the products of CC attack. Dypnone gives products of carbonyl attack with 3 and does not react with 2.These results are discussed in terms of perturbation theory: C₄ attack increases with delocalization of the reagent's negative charge and lowering of the α-enone LUMO level.     

Determination of alpidem and its metabolites in human plasma by high-performance liquid chromatography and fluorimetric detection

A high-performance liquid chromatographic method has been developed for the simultaneous determination of alpidem and its metabolites in human plasma. The method involved a single extraction of the parent drug and metabolites into diethyl ether from alkalinized plasma, evaporation of the organic solution and chromatography of the extracts on a C18 column coupled to a fluorimetric detector. An internal standard was used for the quantitative determination of the compounds. The method was selective for alpidem and three of its metabolites and has a limit of detection of less than 1 ng ml-1 for all the compounds. Since the chromatographic run took more than 20 min, the chromatographic process was fully automated and performed overnight.     

Low-temperature solubility of copper in iron: experimental study using thermoelectric power,small angle X-ray scattering and tomographic atom probe

Measuring the solubility limit of copper in iron at temperature lower than 700°C is problematic because copper diffusion is too slow in this temperature range. To overcome this difficulty, fine precipitation of copper is studied. The solubility limit of copper is measured after complete precipitation using two complementary techniques: thermoelectric power and small angle X-ray scattering. Values obtained are confirmed by tomographic atom probe and give results much higher than what is usually extrapolated from high-temperature experiments.     

Analysis of the dispersion spectrum of fluid-loaded anisotropic plates: leaky-wave branches

The supersonic complex-velocity versus real-frequency dispersion spectrum of the leaky waves in fluid-loaded anisotropic plates is discussed. Utilizing the sextic plate formalism provides approximate solutions for leaky-wave velocity in a form that reveals their basic features, such as the unique correspondence of the signs of its imaginary part and of the free-plate group velocity, the relation between the leakage and the rate of frequency dispersion, and the principal trends at low, high and near-cutoff frequencies in arbitrary anisotropic plates. A particular thrust of the study is the derivation of closed-form asymptotics for the fundamental leaky-wave velocity branch(es) at low frequency and for the continuum of leaky-wave branches near the fluid-coupled and fluid-uncoupled thickness resonances. Conditions for the asymptotics accuracy are analysed, and a comparison between an analytical approximation and exact numerical curves is presented for various cases.     

Cooling overall spin temperature: protein NMR experiments optimized for longitudinal relaxation effects

In experiments performed on protonated proteins at high fields, 80% of the NMR spectrometer time is spent waiting for the ¹H atoms to recover their polarization after recording the free induction decay. Selective excitation of a fraction of the protons in a large molecule has previously been shown to lead to faster longitudinal relaxation for the selected protons [K. Pervushin, B. Vögeli, A. Eletsky, Longitudinal ¹H relaxation optimization in TROSY NMR spectroscopy, J. Am. Chem. Soc. 124 (2002) 12898–12902; P. Schanda, B. Brutscher, Very fast two-dimensional NMR spectroscopy for real-time investigation of dynamic events in proteins on the time scale of seconds, J. Am. Chem. Soc. 127 (2005) 8014–8015; H.S. Attreya, T. Szyperski, G-matrix Fourier transform NMR spectroscopy for complete protein resonance assignment, Proc. Natl. Acad. Sci. USA 101 (2004) 9642–9647]. The pool of non-selected protons acts as a “thermal bath” and spin-diffusion processes (“flip-flop” transitions) channel the excess energy from the excited pool to the non-selected protons in regions of the molecule where other relaxation processes can dissipate the excess energy. We present here a sensitivity enhanced HSQC sequence (COST-HSQC), based on one selective E-BURP pulse, which can be used on protonated ¹⁵N enriched proteins (with or without ¹³C isotopic enrichment). This experiment is compared to a gradient sensitivity enhanced HSQC with a water flip-back pulse (the water flip-back pulse quenches the spin diffusion between ¹H^N and ¹H^α spins). This experiment is shown to have significant advantages in some circumstances. Some observed limitations, namely sample overheating with short recovery delays and complex longitudinal relaxation behaviour are discussed and analysed.     

Three-dimensional through-bond homonuclear-heteronuclear correlation experiments for quadrupolar nuclei in solid-state NMR applied to (27)Al-O-(31)P-O-(27)Al networks

We present here the first 3D homonuclear/heteronuclear correlation experiment applied to quadrupolar nuclei and making use of the sole scalar J-coupling. This experiment, based on the 2D-Homonuclear-Heteronuclear Single Quantum Correlation (H-HSQC) experiment, uses a relayed transfer from the (27)Al central transition to neighbouring (31)P spins and to the central transition of a second (27)Al. It confirms the correlation map characterizing the two (27)Al and the (31)P NMR signatures of (27)Al-O-(31)P-O-(27)Al chemically bonded molecular motifs.     

In situ synchrotron radiation topography of NaCI during high temperature creep

High temperature plastic deformation is associated with large changes in the microstructure of single crystals. To observe this microstructure during the creep test, we have performed X-ray reflection topography, taking advantage of the high intensity of the synchrotron radiation. A special creep machine was designed which permits in situ observation.

Creep tests and microstructural observations were performed on NaCl single crystals compressed along <100> at about 600°C. As soon as the deformation started, subgrains appeared within the crystal, independent of the initial microstructure. Migration of the subboundaries during transient creep is followed by stabilization during steady state creep where a well developed subgrain structure keeps constant while new appearing subboundaries migrate. Misorientation between sub-grains increases progressively although more slowly in the steady state creep. A correlation between the microstructure evolution and the changes in the creep curves has been attempted.     

Spectral editing in solid-state MAS NMR of quadrupolar nuclei using selective satellite inversion

A sensitivity enhancement method based on selective adiabatic inversion of a satellite transition has been employed in a (pi/2)CT-(pi)ST1-(pi/2)CT spectral editing sequence to both enhance and resolve multisite NMR spectra of quadrupolar nuclei. In addition to a total enhancement of 2.5 times for spin 3/2 nuclei, enhancements up to 2.0 times is reported for the edited sites in a mixture of rubidium salts.