Optimisation d’une sélection in vitro d’enzymes

Optimisation of an in vitro enzyme selection. Isolation of a catalyst for a given chemical reaction may be achieved by in vitro selection of enzymes from a protein library. Here, we investigate the polymerisation reaction on filamentous phage and the cross-linking of substrate on phage to optimise an in vitro selection for DNA polymerase activity. The efficiency of the optimised selection is measured by enrichment factors up to 3.8 × 10³, the highest described so far for an in vitro selection of proteins for catalysis. It should be useful for directed polymerase evolution towards novel catalytic activities. To cite this article: E. Orsi, J.-L. Jestin, C. R. Chimie 6 (2003).     

Réaction d’isomérisation de l’acide urocanique et de ses dérivés: stabilité comparée des isomères Z et E

Thermal and photochemical isomérisation of urocanic acid and its derivatives (O- and/or N-alkylated) have been studied. The data show the wavelength and the molar extinction coefficient-dependent photochemistry of E urocanic acid and its derivatives. Thermal isomérisation of these compounds is difficult and undergoes a “one-way” Z → E reaction. Thus, E isomers are thermodynamically more stable than the Z ones. Under basic conditions, derivatives having an unsubstitued imidazole ring (NH function free) exist in their anionic forms, which lowers the energy barrier without changing the isomérisation pathway.     

Caractérisation des propriétés électriques des parois de pores d’une membrane

The characterisation of the surface electrical properties of membrane materials is critical for understanding and predicting the filtration performances of membranes. In this paper, four simple experimental methods – streaming potential, electro-osmosis, pore conductivity and membrane potential –, allowing the characterisation of the charge state of membrane pore walls are presented. The four experimental parameters provide information about the sign of the electrical net charge. Examples illustrating the influence of the pH, electrolyte concentration and nature on the four experimental parameters are given. The zeta potential can be then deduced from these measurements by means of a model.     

Critère d'initiation de délaminage dans les stratifiés

A criterion is proposed to predict delamination initiation in angle-ply laminates. An analytical model permits to calculate interface stresses between two layers in any laminate. The criterion is based on the maximum value of these stresses and takes into account the scale effects (number of layers). The numerical results are validated by a comparison with experimental data.     

Étude physicochimique de nouveaux composés formés par incorporation directe d’hétéropolyacide dans une silice mésoporeuse organisée

Heteropolyacids (HPW) are known as active catalysts for various redox reactions. The direct incorporation of HPW species in a mesoporous organised silica molecular sieve during the synthesis was studied. The association of two type of surfactants is essential for the preparation of such solids. The silica-organised materials comprising heteropoly compounds thus obtained were thermally stable porous materials with mesopores and large surface areas.     

Polyacides amiques et polyimides dérivés de l'anhydride amino-4 phtalique

Various routes have been examined for the synthesis of high molecular weight polyamic acid derivatives of the poly(4-aminophthalic anhydride)-type transformable into polyimides with improved mechanical properties. Polymerization of 4-aminophthalic anhydride and of some derivatives (hydrobromide, monomethyl ester, methyl-trimethylsilyl diester) led to soluble polymers with rather low molecular weights. Limitations of molecular weights are discussed in terms of chain-end deactivation because of oxidation (NH₂), of hydrolysis (anhydride) or of the presence of monofunctional impurities. Attempts to reactivate chain-ends are described. It is shown that hydrogenation of a polyamic acid prepolymer and further polymerization double the molecular weight of the prepolymer. Among the precursors which are considered, only the methyl-trimethylsilyl diester of 4-aminophthalic acid led to glass-adherent films after polyimidification.     

Etude des réactions de l'acétylformazyle et de ses dérivés avec les ions minéraux

Résumé L'étude systématique de l'acétylformazyle et de ses dérivés pour l'analyse à la touche à fourni des réactions sensibles permettant la recherche du mercure avec la thiosemicarbazone, du cuivre et du palladium avec l'oxime.

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Summary The systematic study of acetylformazyl and its derivatives for spot test analysis has yielded sensitive reactions which permit the detection of mercury by means of the thiosemicarbazone, and of copper and palladium with the oxime.

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Zusammenfassung Die systematische Untersuchung von Acetylformazyl und seinen Derivaten für die Zwecke der Tüpfelanalyse führte zu empfindlichen Reaktionen zur Prüfung auf Quecksilber mit dem Thiosemicarbazon, auf Kupfer und Palladium mit dem Oxim.

     

Influence d’alcools aliphatiques sur l’adsorption d’acides aminés sur charbon actif

Adsorption of aqueous solution of two amino acids – phenylalanine (Phe) and tyrosine (Tyr) – on powdered activated carbon (PAC) has been studied in the presence of linear or branched alcohols. Methanol has no influence on the adsorption. For the other alcohols, the adsorption decreases when the alcohol chain gets longer, from ethanol to 1-propanol, up to 85 %. Alcohol branching reduces this phenomenon. Adsorption kinetics have been tested according two models, allowing good representation of results and determination of kinetic constants.     

Dosage des traces de gallium dans les bauxites et produits dérivés

A method for the estimation of gallium in bauxites and derived products, has been described. The gallium is estimated fluorimetrically in chloroform solution as the oxmate. The interfering ions and the means of their removal have been studied.The method allows the estimation of 1.4–4.2 γ of gallium with an accuracy of about 10%.     

Propriétés rhéologiques à l'état fondu de polyesters thermoplastiques chargés de fibres de verre

A study of rheological properties in the molten state of two short glass fibre reinforced polyesters (polyethylene terephthalate and polybutylene terephthalate) was carried out, both in steady and dynamic flow. The results lead to information on the flow behaviour of these composite materials. Moreover, this study confirms the presence of fibre tied entanglements and shows the influence of the matrix.     

Détermination de la composition énantiomérique dˈesters dˈacides aminés par spectroscopie de RMN à lˈaide dˈune chiroporphyrine de cobalt(III) comme agent chiral de déplacement chimique

We wish to propose a novel chiral shift reagent for the determination of enantiomer composition of amino acid derivatives. This reagent, chlorocobalt(III) tetramethylchiroporphyrin CoCl(TMCP), effects quantitative in situ derivatization of amino compounds in the NMR tube, without any detectable kinetic resolution. The influences of the chiral cavity and of the porphyrin ring current on the signals of the coordinated amino acid methyl ester L* can be seen in the high-field region of the ¹H NMR spectrum of the bis-adduct [Co(L*)₂(TMCP)]⁺Cl^–. The signatures of the (R) and (S) ligands are well resolved at 200 MHz, and their relative intensities can be readily determined by peak integration. To cite this article: M. Claeys-Bruno et al., C. R. Chimie 5 (2002) 21–25     

Préparation d’orthoesters originaux par addition d’acides carboxyliques sur des acétals cycliques de cétènes

Original orthoesters have been prepared by addition of carboxylic acids on the exocyclic double bond of 2- alkylidene -benzo[1,3]dioxin-4-ones. To cite this article: P. Babin et al., C. R. Chimie 6 (2003).     

Développement par déplacement sur échangeurs d'Ions séparation de plus de deux ions

In the separation of several substances by displacement development, the minimum distance is calculated that the band must travel to obtain a separation of the solutes into zones.The method has been applied to the separation of lithium, sodium, ammonium and potassium ions on Dowex-50 resin, using calcium ions as the developer.     

Synthèse de nouveaux dérivés du 1-hydroxyindole et du pyrazole

New 1-hydroxyindole derivatives have been synthesised by alkylation, acylation reactions and by condensation with acetylacetone and dehydroacetic acid. Action of hydrazines on 3-acetyl-1-hydroxy-indole leads to new pyrazole derivatives.     

La réaction mercure(ii)—p-diméthylaminobenzalrho-danine et la détermination de microouantités de cyanure

The paper opens with a critical study of several factors affecting the reaction of mercury (II) with p-dimethylaminobenzalrhodanine. The second part of the paper reviews the method ofcyanidedetermination formerly recommended by OHlweiur^2,3 based on the mashing action of cyanide ion on the color reaction of the mercuric ion with the organic reagent mentioned above. In order to avoid difficulties in keeping acidity strictly adjusted and the interference of foreigns salts, this article suggests the previous separation of the cyanide by microdiffusion and its absorption in a mercuric nitrate solution, following Conway's technique. Quantitative diffusion of CN^- up to 6 γ takes place in one hour at room temperature of approximately 27° C and in one hour at 38° C, when inside an electric oven. Recommended procedure allows the determination up to 6 γ. The standard deviation ranges from 0.02 to 0.05 γ of CN^- along the scale of the determinable cyanide quantities.     

Les différentes voies de modélisation macroscopique du procédé de dépôt de SiC par voie gazeuse

The different macroscopic modelling routes and chemical databases are reviewed for the growth of silicon carbide from the vapour phase in the Si-C-H-Ar system. Theses databases have been built up by experts over many years through the critical assessment of primary experimental data and ab-initio calculations. The thermodynamic modelling route addresses several important issues with respect to vapour deposition techniques. This approach is a useful tool in understanding the complex chemistry involved during the growth, but should be used with careful attention to the assumptions underlying the application. The transport modelling approach extends the previous analysis to dynamical systems. It is based on the conservation equations for momentum and heat transfer combined with mass transfer including thermodiffusion and chemical reactions based on thermodynamic and kinetic data. In addition to empirical, lumped chemical kinetic models, we propose a new modelling route linking transfers models with local thermochemical equilibrium (LTCE) computations. The modelling results have been validated with the help of the SiC sublimation technique for the transfer-LTCE concept, and of the chemical vapour deposition technique for lumped chemistry models. The simulated results allow the quantification of the different modelling proposals.