Analysis of the structure of very large bacterial aggregates by small-angle multiple light scattering and confocal image analysis

This work aims at developing a more accurate measurement of the physical parameters of fractal dimension and the size distribution of large fractal aggregates by small-angle light scattering. The theory of multiple scattering has been of particular interest in the case of fractal aggregates for which Rayleigh theory is no longer valid. The introduction of multiple scattering theory into the interpretation of scattering by large bacterial aggregates has been used to calculate the fractal dimension and size distribution. The fractal dimension is calculated from the form factor F(q) at large scattering angles. At large angles the fractal dimension can also be computed by considering only the influence of the very local environment on the optical contrast around a subunit. The fractal dimensions of E. coli strains flocculated with two different cationic polymers have been computed by two techniques: static light scattering and confocal image analysis. The fractal dimensions calculated with both techniques at different flocculation times are very similar: between 1.90 and 2.19. The comparison between two completely independent techniques confirms the theoretical approach of multiple scattering of large flocs using the Mie theory. Size distributions have been calculated from light-scattering data taking into account the linear independence of the structure factor S(q) relative to each size class and using the fractal dimension measured from F(q) in the large-angle range or from confocal image analysis. The results are very different from calculations made using hard-sphere particle models. The size distribution is displaced toward the larger sizes when multiple scattering is considered. Using this new approach to the analysis of very large fractal aggregates by static light multiple scattering, the fractal dimension and size distribution can be calculated using two independent parts of the scattering curve.     

Etude de la cristallinite de derives n-octadecyliques de l'alcool polyvinylique obtenus par greffage chimique

Differential scanning calorimetry has been used to study the heats of fusion and melting transitions of n-octadecyl derivatives of polyvinyl alcohol. These derivatives were obtained by grafting paraffinic chains on polyvinyl alcohol, at various proportions. The melting transitions are independent of the degree of substitution; the heats of fusion are proportional to the fraction of crystallizable units. Using Flory's equilibrium crystallization theory, it is possible to interpret these results assuming, as demonstrated previously, that the chemical grafting is sequential with two unreacted hydroxyl groups between two adjacent paraffinic side-chains.     

Chromatographie par complexe de transfert de charge. Application à l'analyse d'hydroliquéfiats du charbon par HPLC

Résumé L'analyse de coupes lourdes (huile de distillation sous vide et huile issue du séparateur à chaud) provenant de l'hydroliquéfaction catalytique du charbon a été réalisée par mise en ouvre de différentes techniques chromatographiques. L'identification des principales structures résulte de l'application de la chromatographie par couplage de transfert de charge en mode HPLC et des spectroscopies UV et de masse.

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Donotor-acceptor complex chromatography —Application to analysis of coal liquefaction products by HPLC

Summary A Vacuum gas oil and the corresponding residue of a coal liquefaction product were investigated by means of HPLC and MS. Nearly a complete identification was performed by chromatographic, UV-spectroscopic methods and MS.

     

Influence of extra-framework cations on the adsorption properties of X-faujasite systems: microcalorimetry and molecular simulations

Isotherms and differential enthalpies of adsorption are obtained for nitrogen at ambient temperature on monovalent (Li(+), Na(+), K(+)) and divalent (Ca(2+), Ba(2+), Sr(2+), Mn(2+)) substituted X-faujasite systems by microcalorimetry measurements. These experimental data are compared with those obtained by combining grand canonical Monte Carlo simulations and newly derived force fields for describing the interactions between the extra-framework cations and the adsorbates obtained from a simple model based only on the intrinsic properties of the cations. It is the first time that such good qualitative agreement is reported between experiment and simulation for a series of both monovalent and divalent cations.     

Laser-Induced fluorescence detection in conventional-size liquid chromatography with a frequency-doubled argon-ion laser

Laser-induced fluorescence (LIF) detection in conventional-size column liquid chromatography is achieved at 257 nm with a frequency-doubled argon-ion laser. Short-wavelength excitation offers two important advantages: firstly, a wide variety of analytes can be excited, and secondly, the Raman scatter of the eluent does not interfere with the fluorescence of the analytes. A standard mixture of polynuclear aromatic hydrocarbons was studied, both with LIF detection and with a commercially available sensitive conventional fluorescence detector. The improvement in the detection limits ranges from about a factory of 4 to 30; the LIF detection limits are typically at the 50 ng l^?1 level, which corresponds to an injected amount of 0.5 pg.     

Recent improvements of the ion analyzer and typical examples of applications

Improvements of a CAMECA IMS 300 ion microanalyzer are described: ion source, resolution, ion detector and counting system. Comparison with the performances of an electron microprobe is presented. Examples of application are given.     

Loss of metallicity in metal rich lithium oxide clusters

Mixed lithium-lithium oxide aggregates are experimentally obtained from unimolecular evaporative cascades starting at metal rich Li _p ⁺ (Li₂O)_n species and ending with the stoichiometric limit Li⁺(Li₂O)_n, for several sizes of the oxide part (Li₂O)_n with 0 ≤ n ≤ 8. The results show evidence of the vanishing of the properties of the quantum metallic droplet i.e. shell closing and odd-even alternation, portrayed in the dissociation energy, with increasing size of the oxide component. The competition between monomer and dimer lithium evaporation from the heated metal rich Li _p ⁺ (Li₂O)_n species points out the influence of the perturbation induced by the oxide component on the mixed metal oxide clusters.     

Recherches en série diazépine-1,4 et triazépine-1,2,4. XI—etude en spectrométrie de masse des fragmentations de triazépines-1,2,4

The mass spectra of eleven 1,2,4-triazepines with oxo, thioxo, methoxy and methylmercapto groups in the 3 and 5 positions are reported and analysed. Each of the five structures of the triazepine ring present is characterized by a particular group of fragmentations.     

Automated determination of verapamil and norverapamil in human plasma with on-line coupling of dialysis to high-performance liquid chromatography and fluorometric detection

A fully automated method for the simultaneous determination of verapamil and its main metabolite norverapamil in human plasma is described. This method is based on on-line sample preparation using dialysis followed by clean-up and enrichment of the dialysate on a precolumn and subsequent HPLC analysis with fluorometric detection. All sample handling operations were performed automatically by a sample processor equipped with a robotic arm (ASTED system). The plasma samples were dialysed on a cellulose acetate membrane (cut-off: 15 kD) and the dialysate was purified and enriched on a short pre-column filled with cyanopropyl silica. Before starting dialysis, this trace enrichment column (TEC) was first conditioned with the HPLC mobile phase and then with pH 3.0 acetate buffer. 370 μl of plasma sample spiked with the internal standard (gallopamil) were dialysed in the static-pulsed mode. The solution at the donor side was pH 3.0 acetate buffer containing Triton X-100 while the acceptor solution was made of the same acetate buffer. When dialysis was discontinued, the analytes were desorbed from the TEC by the HPLC mobile phase and transferred to the C₁₈ analytical column by means of a switching valve. This mobile phase consisted of a mixture of acetonitrile, pH 3.0 acetate buffer and 2-aminoheptane. The influence of different parameters of the dialysis process on the recovery of verapamil and norverapamil has been studied. The effect of the volume, the aspirating and dispensing flow-rates of the dialysis solution has been investigated. The recoveries of verapamil and norverapamil in plasma were close to 75% and the limits of quantification were 5 ng/ml for both analytes. The method was found to be linear in the concentration range from 5 to 500 ng/ml (r²: 0.9996 for both analytes). The intra-day and inter-day reproducibilities at a concentration of 100 ng/ml were 2.3% and 5.6% for verapamil and 1.7% and 5.1% for norverapamil, respectively.     

Determination of weak (2.0–2.5) dissociation constants of non-UV absorbing solutes by capillary electrophoresis

Summary Capillary electrophoresis (CE) has proved to be a fast and convenient method for the determination of the dissociation constants of non-UV absorbing solutes in the acidic pK _A range (2.0–2.5). The electroosmotic flow was reversed by washing the capillary with 0.2% polybren aqueous solution. A series of background electrolytes was prepared with phenylphosphonic acid (pK _A=1.29) and β-alanine (pK _A=3.55) with the same ionic strength and a high buffer capacity in order to improve the repeatability (0.1–0.2 %) of the electrophoretic mobility and to determine the values of pK _A accurately. This procedure was applied to the determination of the dissociation constants of several alkyl-alkylphosphonic acids whose pK _A values have not yet been published in the literature. In this work, their dissociation constants have been found to vary between 1.91 and 2.34 for alkyl-methylphosphonic acids and between 2.10 and 2.38 for alkyl-ethylphosphonic acids.