Etude de la fragmentation de derives de L'uracile et de la thymine par Spectrometrie de masse

Original mass spectra of uracil and thymine derivatives are presented with the corresponding fragmentation schemes. In the first series of spectra, the fragmentations of thymine derivatives, including ¹⁴C-2-thymine, dimers, and bromo thymines, confirm the basic retro Diels-Alder mechanism. The second series includes dihydro 5,6-derivatives of uracil (hydroxy and bromo substituents). The behaviour of these molecules is quite different; they are more sensitive to the substituents and a part of the fragmentation is often explained by protonated molecular ions.     

Influence de la Structure de Diverses Fonctions sur l'Evaluation de l'Energie de Correlation

The influence of various correlation functions, multiplying the monoelectronic space function, is studied and applied to the Helium atom and its isoelectronic series. We used Slater-type basis orbitals and the ground and first excited states have been studied, taking into account the virial and cusp conditions. In the ground state, a very good value for the correlation energy is obtained, using a function of the type For the excited states, this type of function overestimates the assumed value of the correlation energy.     

Synthese regioselective de bases de mannich de cetones dissymetriques

Methods for the regioselective synthesis of Mannich bases starting from unsymmetrical ketones are described. The Mannich base on the more substituted carbon is obtained by reaction with (CH₃)₂N⁺CH₂,CF₃CO₂^- in CF₃CO₂H and its isomer on the less substituted carbon with (iPr)₂N⁺CH₂,ClO₄^- in CH₃CN. In the first case, the orientation corresponds to a non-selective attack of the immonium salt on a mixture of enols in which the more-substituted isomer is predominant. In the second ease, use of a bulky immonium salt induces a selectivity favoring the less-substituted enol.     

Processus de photopolymerisation du methacrylate de methyle en presence de chlorure de zinc

The photopolymerization of methylmethacrylate in solution or in bulk, initiated by DMPA (2,2-dimethoxy-2-phenylacetophenone) and BP (benzophenone), has been investigated in the presence of ZnCI₂ as a complexing agent. We have studied the steady state polymerization (measurement of R, and OT) and the behaviour of the excited states by laser spectroscopy. We have shown the following points: R_p and DP increase with [ZnCI₂]; the rate constant for propagation increases with [ZnC12]; the rate of initiation remains constant in presence of BP-ZnCl₂ but increases with DMPA-ZnCl₂. The results are accounted for by the results of laser spectroscopy.     

Quelques caracteristiques morphologiques de melanges de polymeres a base de propene et de butene

This paper reports a study of the morphology of blends of polypropene with polybutene as a function of composition. Techniques such as differential thermal analysis, thermomechanical analysis and dilatometry were used. The “compatibility” of these polyolefines is considered. Glass transition temperatures of the homopolymers are detectable when using the various techniques.     

Spectres de Masse de Derives de l'Atractyloside. Determination du Nombre de Substituants par Combinaison d'Acetylation et de Silylation

Different transformations of the functions fixed on a heterocyclic molecule were made. It is thus possible to quickly determine the number of functions of each type present in the molecule: e.g. (i) all the functions are silylated and (ii) the alcohols are acetylated whilst the sulfates and acids are silylated. Mass spectra of atractylate, apoatractylate and gummiferine have been studied and the substituents are counted and enumerated.     

Elaboration de capteurs de gaz a partir de ceramiques conductrices ioniques de type NaSICON

The elaboration of Na⁺ super-ionic conductor (NaSICON) ceramics is studied in this work. These solid electrolytes can be used as sensor for detection of polluted gases in air. Two sorts of ceramics with different chemical compositions are synthesised by soft chemistry route: a zirconium-based NaSICON and a hafnium-based NaSICON. DTA-TG and temperature depending X-ray diffractometry were used to follow the thermal decomposition of the precursor phases. The electrical properties of these ceramic sodium ionic conductors are investigated by complex impedance spectroscopy (CIS). The substitution of the zirconium by the hafnium increases the ceramic conductivity and decreases the activation energy E ^a (from 0.29 to 0.12 eV). This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthese de polyacrylamides porteurs de groupements iminodiacetate et etude de leur pouvoir de complexation vis-a-vis de quelques cations metalliques

Water soluble polymers were prepared by topochemical reaction of sodium iminodiacetate with polymethylolacrylamide. Their complexing properties towards some metallic cations were investigated by potentiometric and spectroscopic techniques and compared with the complexing properties of iminodiacetic acid and of a model molecule of the polymer ionic unit. The results showed that polymer and model 1-1 chelates are stronger than iminodiacetic complexes. We explain this difference by participation of the amide group in the coordination of cation by the two first ligands.     

Cinetique de polymerisation de monomeres complexes par des acides de Lewis. Etude du systeme methacrylate de methyl-chlorure de zinc-azobisisobutyronitrile

The polymerisation of methyl methacrylate (MMA) initiated by azo-bis-isobutyronitrile (AIBN) in the presence of ZnCl₂ as complexing agent has been investigated. Increase of the polymerisation rate and a minimum in the average polymerisation degree were observed by increasing the ZnCl₂ concentration. By assuming the existence of complexes {AIBN · ZnCl₂} and {MMA · ZnCl₂}, a kinetic scheme is proposed; it is in good agreement with the experimental results and allows calculation of the characteristics of the system.     

Etude par spectroscopie de photoelectrons (XPS) de la surface de profiles a base de PVC

Variations of the surface composition (over a thickness of 50 Å) of stabilized and rigid PVC for outdoor applications and of pure moulded PVC resin have been investigated by photoelectron spectroscopy (ESCA or XPS) after extrusion, outdoor and accelerated ageing and photooxidation. Extrusion is accompanied by a pronounced migration of lead thermal stabilizers and of calcium stearate, used as an external lubricant, towards the outer surface. This treatment however, induces neither significant oxidation nor formation of a great quantity of ionic chloride. Natural and accelerated weathering were compared and were characterized by a large decrease in the lead surface concentration. The surface of this material is unaffected when exposed to air in a closed vessel and protected from external radiations. Finally, surface photooxidation by u.v. exposure has been evaluated and compared for the stabilized material and for the pure resin. This treatment involves formation of carbonyl and carboxylic groups. ESCA spectroscopy, a speedy and non-destructive surface analytical method, is well suited for study migration of stabilizers and lubricants.     

Chromatographie sur couche mince de microparticules de gel de silice

Résumé On décrit la préparation de plaques efficaces pour la chromatographie en couche mince (sans liant), utilisant les pertites particules de gel de silice à présent disponibles (5–40 m). On discute le performances obtenues et les illustre par différentes séparations de mélanges faites tant en chromatographie d'adsorption qu'en chromatographie du type partage avec phases inversées. On discute les paramètres qui contrôlent la migration du solvant et l'élargissement des bandes et montre qu'il n'y a pas une nouvelle méthode révolutionnaire de chromatographie mais le progrès normal d'une technique analytique classique, progrès prévu de longue date [1].

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Thin-layer chromatography with microparticles of silica gel

Summary The preparation of efficient thin-layer plates (binder free) made with the newly available samples of small silica gel particles (5 to 40 m) is described. The performances are discussed and illustrated by various applications to the separation of mixtures by adsorption and reversed phase partition chromatography. The parameters which control solvent migration and band broadening are discussed. It is shown that there is no such revolutionary concept as high performance thin-layer chromatography, but merely the normal advance of a conventional analytical technique following predictions made long ago (1).

     

Application de quelques methodes de microanalyse a l'etude des couches de passivation de l'acier inoxydable

Résumé Dans le but de préciser les phénomènes responsables de la corrosion fissurante de l'acier inoxydable, nous avons analysé les films de passivation formés à la surface d'échantillons exposés au MgCl₂ bouillant. Suivant la durée du traitement l'épaisseur de ces films varie entre quelques centaines et quelques milliers d'angstr?ms. Les méthodes d'analyse utilisées sont l'activation aux neutrons et aux particules chargées, l'émission ionique secondaire et la io noluminescence atomique. Les résultats obtenus sont décrits et comparés entre eux. Ces expériences mettent en évidence l'intérêt qu'il y a à associer les méthodes qui apportent des renseignements complémentaires.     

Etude de la stabilite de la conformation de copolypeptides alternes

Conformation stability of alternating copolypeptides with the repeating units $\text{Nε-}\text{carbobenzoxy}\text{-}\text{l}\text{-}\text{lysyl}\text{, β-}\text{benzyl}\text{-}\text{l}\text{-}\text{aspartate}\text{(}\text{CLL}\text{-β}\text{BLA}\text{)}\text{and}\text{Nε-}\text{carbobenzoxy}\text{-}\text{l}\text{-}\text{lysyl}\text{, γ-}\text{benzyl}\text{-}\text{l}\text{-}\text{glutamate}\text{(}\text{CLL}\text{-γ}\text{BLG}\text{)}$ has been studied by NMR 220 MHz and by viscosity in deuterochloroform/trifluoroacetic acid (TFA) pair at 25°. NMR spectra show a helix-coil transition at low TFA contents for both copolypeptides as compared to other types of copolypeptides. In the case of poly (CLL-γBLG), the helix begins to collapse at 4% TFA and the transition is complete at 6% TFA. Poly(CLL-βBLA) helix is still more fragile since the transition is complete at 3% TFA. Viscosity measurements seem to indicate helix coil transition to take place at lower TFA content but the disagreement between the two sets of results is only artificial. This low helix stability of both copolypeptides is discussed according to the Lifson—Roig—Cortijo theory taking into account formation of H-bonding between side-chains having different chemical structures. This low helix stability would be due to a co-operative collapsing effect.     

Etude de l'incorporation de l'oxyde de cuivre dans le reseau de l'oxyde de nickel par traitement thermique

NiO prepared at 950° has been impregnated with a solution of copper nitrate and heated at 300°. The incorporation of CuO issued from this treatment in the lattice of NiO during sintering at 450–1100° has been studied by DTA and TG, and chemical analysis. A few experiments by radiocrystallographic analysis and electron diffraction have also been done. The process of incorporation begins at about 600° and is nearly complete at 900°. A sample elaborated at 1100° is homogeneous in the mass but presents in the surface an excess of copper ions which seems to be located at certain points.

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Zusammenfassung Bei 950° erzeugtes NiO wurde mit Kupfer(II)nitratlösung impregniert und auf 300° erhitzt. Der Einbau von CuO (5 %) in das NiO-Netz bei thermischer Behandlung von zwischen 450–1100° wurde durch DTA, TG und chemische Analyse untersucht. Einige Proben wurden auch einer Prüfung durch Radiokristallographie und Elektronendiffraktion unterworfen. Der Einbau beginnt bei 600° und ist bis 900° praktisch vollendet. Eine bei 1100° erzeugte feste Probe, obzwar homogen in der Masse, zeigt an der Oberfläche einen Überschuß von an gewissen Stellen lokalisierten Kupferionen.

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Résumé NiO préparé à 950° a été imprégné par une solution de nitrate cuivrique et chauffé à 300°. L'incorporation de CuO (5 %), ainsi engendré, dans le réseau de NiO, lors de traitements thermiques à 450–1100° a été étudiée par ATD, ATG et analyses chimiques. Quelques essais d'analyses radiocristallographiques et de diffraction électronique ont également été effectués. Le processus d'incorporation se manifeste à partir de 600°. Il est pratiquement complet vers 900°. Un solide élaboré à 1100°, bien qu'homogène dans la masse, présente, en surace, un excédent d'ions Cu^{+ +} qui semble localisé en certains points. , 950°, 300°. , , , 450° 1100°. . 600° 900°. , 1100°, , .

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Nous tenons à exprimer nos remerciements à Messieurs H. Urbain et R. Bacaud, à Mesdames G. Dalmai-Imelik, C. Leclerq et M. A. Gresteau, et à Monsieur A. Renouprez pour leur contribution à cette étude.     

Modelisation de la dynamique de fermentation alcoolique

The control of the alcoholic fermentation is necessary to obtain a wine having good organoleptic properties. Our study consists in applying the overall dynamical and phenomenological modelling to this kind of reaction suggesting however hypothesis concerning kinetic laws (order zero and order one). The first proposed models are not perfect but they allowed us to access certain chemical parameters such as the reaction enthalpy. Our aim is to determine a model of simple state (for its application) to allow the conception of the alcoholic fermentation reaction of a real-time command.     

Effets de substituants et conformation de stilbenes

Simultaneous study of para nitrostilbenes by X-ray diffraction and ¹³C nuclear magnetic resonance shows a quantitative relationship between the effect of a para nitro substituent on the chemical shift of ethylenic carbon not adjacent to the substituted phenyl ring and the dihedral angle between this phenyl ring and the central double bond. The alternative introduction of substituents in each phenyl ring discloses at the position of carbon β a certain π-polarization which extends to the double bond and to an unsaturated group carried by carbon α.     

Obtention de selenopysultones lors de l'oxydation de thio-1 chromenes par le dioxyde de selenium

Selenium dioxide oxidation of 1-thiochromene leads to 3-formyl (5,6)benzo-1,2 thiaseleninne-1,1-dioxide, which is a representative of a hitherto unknown class of heterocyclic compounds. Pyrolysis of this compound leads to 2-formyl benzo(b)selenophen, by loss of sulphur dioxide. The reaction can be applied to other 1 thiochromenes but no similar behaviour has been observed for their selenium isologues.     

Synthese de bases de mannich acetyleniques cycliques

Terminal acetylenes can be converted in excellent yields into Mannich bases by reacting them with gem-aminoethers instead of formaldehyde and a secondary amine. This provides a possibility of preparing cyclic aminoacetylenes from w-acetylenic secondary amines, via the derived gem-aminoethers, using high dilution technique.     

Spectres de masse de composes alleniques—I : Transposition de type McLafferty de groupes heteroatomiques et de phenyle sur le carbone allenique central

Mass spectra of allenic compounds substituted with a hydrocarbon chain bearing a heteroatomic group (hydroxy, alcoxy, halogen, dialkylamino) or a phenyl in the γ position exhibits a strong peak corresponding to the loss of C₂H₄ (28a.m.u.) from the molecular ion. This is commonly the base peak of the spectra and due to a McLafferty type transfer of the heteroatom or phenyl group to the central allenic carbon atom. The methyl group shows a lower migratory aptitude in such a process. This type of fragmentation involving the migration of heteroatomic groups is not observed in the spectra of γ-halogen and γ-hydroxyketones, alkenes, alkynes or arenes and seems to be characteristic of the allenic linkage. A nucleophilic attack by heteroatom group (or phenyl) on the central allenic carbon atom is proposed.