Dosage du silicium par précipitation du complexe silicomolybdique jaune par la quinoléine

The authors have studied the conditions of precipitation of complex silicomolybdic yellow by quinoline from the point of view of the determination of silicon.Under the conditions that produce complete development of the complex, the precipitation is itself quantitative in the presence of an excess of quinoline, the role of which is to make the precipitate insoluble in its formation surroundings. The precipitation of free molybdate is prevented by adding the quantity of acid necessary for complexing it.The precipitate thus obtained filters without difficulty, and only needs to be dried for 1 hour at 150° in order to attain constant weight. It corresponds then exactly to the formula: SiO₂.12MoO₃.4(C₉H₇N).2H₂O.     

Etude du complexe par liaison hydrogène du carbazole à l'état fondamental par spectroscopie UV

The modifications of UV absorption spectra of carbazole show the hydrogen bonding complex in the ground state. The red shifts of carbazole absorption spectra in solvents able to form a complex are more important than those obtained in aprotic solvents, with high polarity. The solvents with OH groupment can interact with carbazole to form NH ⋯ O and OH ⋯ π type hydrogen bonds.     

Identification de modèles tribologiques par pendule

A model is developed to calculate the period and damping of a rigid pendulum's oscillations when submitted to friction. A theoretical investigation shows that the pendulum is a sensitive accurate tool for assessing friction phenomena of very low intensity. The process of measurement and analysis method is then used to identify a real pendulum.     

Ammonia-borane: the hydrogen source par excellence?

Ammonia-borane, H3NBH3, is an intriguing molecule for chemical hydrogen storage applications. With both protic N-H and hydridic B-H bonds, three H atoms per main group element, and a low molecular weight, H3NBH3 has the potential to meet the stringent gravimetric and volumetric hydrogen storage capacity targets needed for transportation applications. Furthermore, devising an energy-efficient chemical process to regenerate H3NBH3 from dehydrogenated BNHx material is an important step towards realization of a sustainable transportation fuel. In this perspective we discuss current progress in catalysis research to control the rate and extent of hydrogen release and preliminary efforts at regeneration of H3NBH3.     

Analyse élémentaire organique par diffusion de l'hydrogéne á travers la silice et par carbonisation

Résumé En mettant á profit les découvertes des savants français du début de ce siécle sur la perméabilité de la silice fondue pour l'hydrogéne, l'oxygéne et l'azote, nous avons montré que le dosage á l'échelle ultramicro de l'hydrogéne, de l'oxygéne par voie directe, du carbone et du squelette oxydo-carboné d'une molécule d'un même échantillon de substance contenant carbone, hydrogéne et oxygéne, était possible, avec des moyens extrêmement modestes.

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Summary By taking advantage of the discoveries made at the beginning of this century by French scientists with respect to the permeability of fused silica to hydrogen, oxygen, and nitrogen, we have shown that the determination on the ultramicro scale of hydrogen, oxygen by the direct way, and of carbon and of the oxydo-carbonaceous skeleton of a molecule is possible employing the same sample of a substance containing carbon, hydrogen, and oxygen, and by means of extremely modest equipment.

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Zusammenfassung Die zu Beginn dieses Jahrhunderts von französischen Autoren entdeckte Durchlässigkeit von Quarzglas für Wasserstoff, Sauerstoff und Stickstoff bei hohen Temperaturen bietet die Grundlage zur direkten ultramikroanalytischen Bestimmung von Wasserstoff und Sauerstoff. In der gleichen Einwaage einer aus C, H und O bestehenden Substanz lassen sich mit einfachen Mitteln auch der Kohlenstoffgehalt und der von Wasserstoff befreite Rest des Moleküls bestimmen.

     

Dosage indirect du potassium par complexométrie

An indirect complexometric method for the determination of potassium is described Potassium is precipitated is perchlorate, which is reduced to chloride Silver chloride is treated with tetracyano nickelate, nickel being titrated chelatometrically     

Microdétermination du zinc par chromatographie-colorimétrie

Résumé La détermination colorimétrique de zinc avec de la dithizone est une méthode excellente quand il s'agit de dissolutions pures de zinc; mais les résultats sont douteux en présence d'autres métaux, specialement de cuivre. Dans ce travail, nous proposons une méthode chromatographique sur papier pour la séparation totale du zinc, suivie de la dissolution de la tache et du dosage par colorimétrie avec la dithizone.

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Summary The dithizone colorimetric method for zinc is an excellent procedure when pure solutions of zinc are being used. However, the results are doubtful in the presence of other metals, particularly copper. In this study, a paper Chromatographic method is proposed for the complete separation of the zinc, followed by solution of the stain and colorimetric determination with dithizone.

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Zusammenfassung Die kolorimetrische Bestimmung des Zinks mit Dithizon bewährt sich ausgezeichnet, sofern es sich um reine Zinklösungen handelt; in Gegenwart anderer Metalle, besonders Kupfer, sind die Resultate aber unsicher. Daher wird eine vollständige papierchromatographische Abtrennung des Zinks vorgeschlagen, dessen Chromatogrammfleck gelöst und mit Dithizon kolorimetrisch bestimmt wird.

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Dédié à l'occasion du 100^me anniversaire de la naissance deFriedrich Emich.     

Étude par diffraction des rayons X,par résonance magnétique nucléaire 31P en phase solide et par spectrométrie infrarouge des hydroxyapatites mixtes cadmium–strontium

X-ray powder diffraction, solid-state ³¹P-MAS-NMR and IR spectroscopy of cadmium–strontium mixed hydroxyapatites. Strontium–cadmium hydroxyapatite solid solutions Cd_xSr_(10–x)(PO₄)₆(OH)₂ were prepared in aqueous medium. They were characterized by X-ray powder diffraction, ³¹P-MAS-NMR and IR spectroscopic analyses. The structural refinement, by X-ray powder pattern fitting (Rietveld method), indicates the limits of strontium–cadmium solid solutions (x≤4) and allows us to determine the cadmium repartition in the apatite cell. Through the progressive replacement of Sr²⁺ (r=1.32 Å) by the smaller cation Cd²⁺ (r=1.09 Å), all interatomic distances decrease according to the decrease of the cell parameters. However, contrary to what could be expected from the coordinance of the metallic sites S₁ (hexacoordination) and S₂ (heptacoordination) the small cadmium cation does not preferentially occupy the four sites S₁: it is almost statistically distributed over both sites, with a slight preference for S₂. The ³¹P- solid-state-NMR of the pure phases Sr₁₀(PO₄)₆(OH)₂ and Cd₁₀(PO₄)₆(OH)₂ reveals a moderate chemical shift anisotropy (≈20 ppm) corresponding to slight distortion of the phosphate tetrahedron. This observation holds also for the mixed species where the surrounding of the phosphate anion is expected to change significantly when substituting Cd for Sr. Through the progressive replacement of strontium by cadmium, the isotropic signal moves regularly to high frequency, according to the deshielding observed for Cd₁₀(PO₄)₆(OH)₂ (δ_iso=12.2 ppm) with respect to Sr₁₀(PO₄)₆(OH)₂ (δ_iso=2.9 ppm). Moreover the isotropic signal broadens considerably because of unresolved chemical shift distributions in the highly disordered material. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SAShydroxyapatite / Rietveld refinement / ³¹P-MAS-NMR / cadmium / strontium / phosphate     

Analyse cytologique de l'expression d'un épitope porté par les glycoprotéines excrétées par Candida albicans

The present study concerns an epitope identified by a monoclonal IgM, named 5B2, generated against the parasitic phase of Candida albicans. The epitope was previously shown to be carried by excreted C. albicans glycoproteins and to be present in the sera of patients suffering from systemic candidiasis. The cytological analysis of the epitope expression was investigated in 3 different yeast strains: the C. albicans strain from which 5B2 was generated (VW.32); a C. albicans mutant, deficient in cell wall mannans (KD.102); and a Sacchromyces cerevisiae strain. Immunofluorescence assays using IgM-5B2 showed discontinoous labelling with the VW.32 strain and no labelling with the 2 other yeast strains; however, the superficial structures of the 3 strains reacted homogeneously with ConA. Ultrastructural immunodetection experiments performed with the VW.32 cells, using gold-conjugated monoclonal antibody, revealed the presence of the epitope in the vacuolo-vesicular system, the periphery of the cytoplasm, the periplasmic space and the cell wall. Under the same conditions, cells from the KD.102 strain only exhibited weak cytoplasmic labelling whereas the presence of the epitope in S. cerevisiae blastoconidia was restricted to the vesicles. Competition and double labelling experiments with IgM and ConA showed that the epitope, distributed on the great majority of VW.32 glycoproteins, is shared by a lesser proportion of the KD.102 glycoproteins and only by some vesicular glycoproteins of S. cerevisiae. Inhibition of the N-glycosylation process of the VW.32 strain by tunicamycin resulted in the absence of cytokinesis and germ tube formation. In such cells, epitope 5B2 was no longer expressed on the bud surface. These cytological results concerning the C. albicans epitope are discussed in relation to recent, more general biochemical data on the yeast glycosylation process.     

Caractérisation des couches minces de Cd1–xZnxS préparées par dépôt chimique

Cd_1–xZn_xS is an important material that can be used to make n-type window-layers for thin film heterojunction solar cells. After a theoretical study of the solution chemistry of cadmium and zinc sulphates, ammonia and thiourea corresponding to sulphurs precipitation, we have been interested in the study of the effect of some parameters (temperature and zinc concentration) on the deposition process of Cd_1–xZn_xS on a glass substrate. X-ray diffraction studies showed that this latter compound crystallises in a hexagonal wurtzite crystalline structure. The AFM analysis showed that a homogenous deposited film was obtained for x = 0.1. The different values of gap energy are in the range 2,42–2,50 eV for x values between 0.08 and 0.28.     

Contrôle des jets par écoulement à contre-courant

The expansion of axisymmetric jets and their initial turbulence level are considerably enhanced by using a suction collar of sufficient length around the nozzle and by applying a counterflow near the jet exit. The observed phenomena seem to be due to recirculations generated by the suction in the collar chamber.     

Caractérisation mécanique par flexion,nano- et macro-indentation de revêtements de SiC par PACVD micro-onde sur acier

Various SiC coatings were deposited on a steel substrate in a micro-wave plasma activated CVD device, then tested by a depth-sensing indentation instrument for measurement of their hardness and of their Young's modulus. Tests by three-point bending and by Vickers and Rockwell C indentation yielded consistent results about their rupture and adherence properties. The mechanical origin of the damage patterns induced by indentation is discussed on the basis of a numerical simulation of the testing.     

Sur le microdosage des ions fluorures par alcalimétrie indirecte

Résumé Les auteurs ont mis au point une méthode spécifique de microdosage titrimétrique des ions F^– susceptible d'être associée à une minéralisation préalable d'un échantillon de substance organique fluorée en vue d'y doser le fluor, à l'échelle microanalytique.Le principe en est fondé sur la réaction globale probable: 6 F^– + 4 H⁺ + SiO₂ +n K+ - SiF₆ ² + 2 H₂O +n K⁺, qui donne lieu à la disparition de 4 ions H+ du milieu réactionnel pour 6 ions F^– initialement présents. Cette consommation d'ions hydrogènes est mesurée par alcalimétrie et permet ainsi de doser le fluor. La réaction précédente ne se produit qu'en milieu acide, et en présence d'ions K⁺ sans précipitation apparente de fluosilicate de potassium.Le résultat brut du dosage doit subir une correction additive fonction de la teneur apparente correspondante en fluor et du volume de la solution et dont la valeur peut être déterminée à l'aide d'un diagramme établi expérimentalement.

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Summary A specific micro determination is given for the titrimetric determination of fluoride ions that is susceptible of being associated with a preliminary mineralization of a sample of a fluorine-bearing organic compound with a view of determining in it the fluorine on the micro scale. The fundamental principle is the probable total reaction: 6 F^– + 4 H⁺ + SiO₂ +n K⁺ SiF₆ ^6–2 + 2 H₂O +n K⁺ which leads to the disappearance of 4 H⁺ ions from the reaction milieu for each 6 F^– ions originally present. This consumption of ions is measured alkalimetrically and the fluorine content can be calculated accordingly. The above reaction occurs only in an acid medium and in the presence of K⁺ ions without apparent precipitation of potassium fluosilicate. The gross result of the determination must be corrected by an additive function of the apparent content corresponding to the fluorine present and to the volume of the solution. The value of this correction factor may be determined with the aid of a diagram which has been constructed on the basis of trials set up for this purpose.

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Zusammenfassung Eine neue spezifische Methode zur Mikrobestimmung von Fluoridionen wird angegeben. Diese eignet sich für organische fluorhältige Substanzen nach deren Mineralisierung. Sie beruht auf der wahrscheinlichen Reaktion: 6 F^– + 4 H⁺ + SiO₂ +n K⁺ * SiF₆ ^2– + 2 H₂O +n K⁺, wonach für je 6 Fluoridionen 4 Wasserstoffionen gebunden werden. Dieser Verbrauch an H-Ionen wird alkalimetrisch gemessen und bietet damit die Grundlage zur Fluorbestimmung. Diese erwähnte Reaktion findet nur in saurem Milieu bei Gegenwart von Kaliumionen statt, ohne daß es zu einer erkennbaren Ausscheidung von Kaliumsilicofluorid kommt. Dem Bruttoergebnis der Bestimmung ist eine Korrektur zuzuzählen, die von dem jeweiligen scheinbaren Fluorgehalt und dem Lösungsmittelvolumen abhängig ist und deren Größe sich aus einem experimentell ermittelten Diagramm ergibt.

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Travail publié en. l'honneur du 70ème anniversaire de Monsieur le professeur Dr.Hans Lieb.     

Séparation des alcalino-terreux par chromatographie sur colonne de cellulose

A good separation of tracer amounts of. Ca- Sr- Ba- Ra could be obtained by chromatography on a cellulose powder column on using successively the following two eluants: 1. Methanol-ether-HCl 12N (v/v: 75-25-5) (Ca, Sr). 2. Methanol - HCI 12N (v/v: 100-5) (Ba, Ra). Eluant 1, which has already been proposed for the separation of Ba and Sr in tracer amounts. is well suited for the separation of Ca Sr (carrier free) A further test of this eluant for the separation of ⁸⁹Sr-¹⁴⁰Ba, obtained carrier-free, from an irradiated uranium nitrate sample, proved to be successful.Eluant 2, gives a satisfactory Ba- Ra separation (Ba either carries free or not) and may be used for a rapid preparation of mesothorium 1 -sources (²²⁸Ra), free from barium; it is also recommended for the purification of small quantities of radium.     

Spectres d'absorption détectés par effet photoacoustique en infrarouge par transformée de Fourier—applications à quelques médicaments

Photoacoustic detection in Fourier transform i.r. spectrometry has led to spectra obtained without sample preparation. This fact may be a very important advantage in biological applications, but these spectra are not directly in good agreement with transmission spectra. In the present work a simple mathematical correction treatment is presented which is in accord with the theory of the photoacoustic effect. This correction routine is applied to some drugs in view of a possible application to direct identification in pharmaceutical preparations.     

Ouverture régiosélective d'époxydes par Me3SiN3 catalysée par Ti[O.iPr]4

Ti[O-iPr]₄ catalyzes the ring opening reaction of functionnalized epoxides with Me₃SiN₃ in a highly regioselective manner.