Utilisation de l'antieatalyse dans la chimie analytique

Sans résumé     

Utilisation du borohydrure de sodium pour la reduction assistee de mesylates secondaires de diallylaminoglycosides ; nouvelle voie d'acces a la (=L)-daunosamine

Secondary mesylate in trans relationship with diallylamino group is reduced by means of a participation reaction affording deoxygenated aminoglycosides ; for one of them this reaction is a new pathway leading to (=L)-daunosamine.     

Utilisation d'ylides du phosphore en chimie des sucres XXIII Eliminations accompagnant certaines réactions de Wittig

Some reactions of 3-O-alkyl-6-deoxy-1,2-O-isopropylidene-α-D-xylo-hexofuranos-5-uloses (1 and 2) with Wittig reagents are described. These ketosugars react with methylenetriphenylphosphorane and benzylidenetriphenylphosphorane to give the expected unsaturated branched-chain sugars and dienes formed by elimination of H–C(4) and the 3-alkyloxy group. Structural studies on all these compounds have been effected using NMR. spectroscopy and particularly, when necessary, nuclear Overhauser Effect. One important by-product of these reactions is an unsaturated ketone 3,6-dideoxy-1,2-O-isopropylidene-α-D-glycero-hex-3-enofuranos-5-ulose (6). Compounds 1 and 2 do not react with cyanomethylenetriphenylphosphorane.     

Sur une nouvelle synthese du (±) norpatchoulenol

A new total synthesis of (±) norpatchoulenol is described with a ScN′ type reaction as the key step.     

Utilisation d'ylides du phosphore en chimie des sucres. XV. Synthèse de sucres à insaturation terminale

Treatment of 3-O-benzyl-1, 2-O-isopropylidene-3-O-methyl-α-D -xylo-pentodialdlo-1,4-furanose and 2,5-anhydro-3,4-O-isopropylidene-aldehydo-D -ribose with moderately stable and stable phosphonium ylides led to the corresponding terminal-unsaturated sugars obtained as a mixture of cis and trans isomers. The cis:trans ratios were determined by ¹H-NMR. and (or) GLC. They showed that steric factors play an important role in the control of the stereochemistry of these reactions.     

Utilisation du calcul des modes normaux de vibration pour la détermination de la conformation de la glycylglycine et de la triglycine en solution aqueuse

The valence force field of α-glycylglycine was applied to different G matrices calculated for several values of the dihedral angles ψ₁, φ₂ and ψ₂. The relations v_i = ?(ψ_i,φ_i) obtained for different isotopic species were compared with the experimental frequencies of the aqueous solution thereby giving the absolute value of the angles. A complementary study by means of depolarised light scattering led to the determination of their sign. These relations were then used in the conformational analysis of triglycine in aqueous solution. The conformation of glycylglycine differs strongly in aqueous solution from that in the solid state, especially concerning the relative positions of the peptide and carboxylic group (φ₂ = ?70° and ?160°). For triglycine, we showed the existence of a chelated ring “C₇” similar to that observed for the acetylated dipeptides.     

Determination non destructive du profil profond de repartition de traces de fluor. Application a l'email dentaire

A non-destructive method is proposed for the determination of fluorine in dental enamel. The detection of the prompt gamma-rays emitted by bombarding with 3 MeV protons lead to the solution of an equation system giving the average fluorine content in the successive layers of the sample. The mathematical treatment of this system is discussed as well as its improvement and generalization.      

Remarques sur les applications de la colorimétrie de précision au microdosage du fluor dans les composés organiques et au dosage de traces de fluor

Summary The authors compare briefly spectrophotocolorimetric assay of the F- ion by discoloration of the ferrisulfosalicylate complex and by formation of the fluor-alizarine complexon-cerium complex after combustion in Schöniger flasks (milligram analysis) and combustion in a Wickbold apparatus (trace assay). The alizarine complexon appears to be more suitable for analysing small amounts of substances in fluorine, and for analysing substances which are simultaneously substituted with fluorine and sulphur or fluorine and phosphorus.

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Zusammenfassung Zwei spektrophotometrische Verfahren zur Fluoridbestimmung wurden verglichen: die Entfärbung des Eisen-Sulfosalicylsäure-Komplexes und die Bildung des Fluor-Alizarin-Komplexon-Cer-Komplexes. Die organische Substanz wird entweder durch Verbrennung im Schöniger-Kolben (Milligramm-Einwaagen) oder nach Wickbold (Spurenbestimmung) mineralisiert. Das Alizarin-Komplexon-Verfahren eignet sich besser für die Bestimmung niedrigster Fluorgehalte sowie für die Fluorbestimmung in Gegenwart von Schwefel oder Phosphor.

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A Monsieur le professeur Hans Lieb, à l'occasion de son quatre vingt dixième anniversaire.     

Utilisation de l'ultracentrifugeuse pour la mesure des masses et pour l'etude de la polydispersite des polymeres de synthese

After a review of the two techniques based on sedimentation rate and equilibrium in binary medium, more recent methods involving the presence of a second non-macromolecular solute are described. Application of these methods to synthetic polymers is still rare but of increasing interest. The use of computers simplifies the exploitation of the measurements.     

Sur une methode simplifiee de dosage microbiologique du ms-inositol

A simplified microbiological assy for inositol involving the use of Schizuscicchurnmyces pombe Lindner is decscribted. The results are very reproducible and the method is simple to operate.     

Determination du fluor dans les milieux aqueux par activation au moyen de photons gamma

An apparatus ensuring identitical irradiation conditions for three samples and a standard of large volumes is reported. The interference caused by the protons originating from the¹⁶O(γ, p)¹⁵N reaction is determined. Results show that the secondary rection¹⁸O(p, n)¹⁸F induced by the protons of the former reaction gives an apparent fluorine content in natural waters of 0.015 μg/g for a maximum gamma photon beam energy of 21 MeV.