Nouvelles méthodes de séparation et comportement des alcaloides en chromatographie en milieux tres polaires,neutres ou acides,sur gel de silice non modifié (2ème partie)

Sans résumé1^ère partie: voir Chromatographia, Vol. 10, No. 5, 1977.     

About the concept of angle in elementary school: Misconceptions and teaching sequences

This paper reports classroom research dealing with the difficulties encountered by schoolchildren in the acquisition of angle concept. Two obstacles were pointed out in previous studies: the side-length obstacle and the salience of the prototypical right angle. The first aim of the present study is to determine the extent to which a teaching sequence based on a concrete situation in the meso-space can enable pupils to progress in their conceptualization of angles. This problem situation is based on the notion of visual field. The angle appears in real space between two infinite directions that correspond to two lines of sight. The specificity of this situation is to confront pupils with an angle between two infinite directions in space. The second goal of this research is to study the links between the two obstacles. To answer these research questions, we compared two versions of the teaching sequence, one dynamic (the angle varies) and one static (the angle does not vary) in 3rd and 4th grade classes. The unfolding of the sequence was analyzed and pupils were tested individually before and after the sequence. They were requested to draw angles and angle variations. The results showed that (1) the sequence helped the pupils progress (2) the obstacle of side-length is not the only difficulty faced by pupils; the salience of the prototypical right angle constitutes a real learning obstacle and (3) the type of angle produced and the ability to change its size are linked. In conclusion, the implications for teaching are presented.     

Minimizing makespan for a bipartite graph on a single processor with an integer precedence delay

We consider the makespan minimization for a unit execution time task sequencing problem with a bipartite precedence delays graph and a positive precedence delay d. We prove that the associated decision problem is strongly NP-complete and we provide a non-trivial polynomial sub-case. We also give an approximation algorithm with ratio .     

Coherent subterahertz radiation from femtosecond infrared filaments in air

We report on what is believed to be the first observation of coherent subterahertz (sub-THz) emission from a 1-m string in the atmosphere. The sub-THz pulse emitted by the filamentary structure from an intense IR femtosecond laser pulse is detected perpendicularly to the laser propagation axis by use of two heterodyne detectors at 94+/-1 and 118+/-1GHz . We describe the characteristics of this emission and show evidence of constructive interference between two separate strings.     

Séparation de peptides sur couche mince de poudre de cellulose sans liant. 2ème Partie: Séparation par chromatographie à deux dimensions et par chromato-électrophorèse des composants des mélanges de peptides,peptides plus simples et aminoacides qui en dérivent par hydrolyse

Résumé Nous montrons que la chromatographie selon deux directions et des associations de chromatographie et d'électrophorèse en couche mince de poudre de cellulose sans liant sont des méthodes efficaces pour séparer les composants des mélanges du type «peptide, peptides plus simples et aminoacides qui en dérivent par hydrolyse». Ces résultats sont obtenus par des électrophorèses sous faible gradient de potentiel (environ 10 volts/cm), par des chromatographies de partage avec un certain nombre de nouvelles phases mobiles. Le choix du milieu d'électrophorèse tout comme celui du solvant de chromatographie a une influence capitale sur la qualité des séparations. A cette occasion, on montre l'efficacité de certains nouveaux solvants [1] pour la séparation des composants des mélanges de peptides et d'aminoacides.

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Separation of peptides on binder-free cellulose thin layers. Part II. Two-dimensional chromatography and chromato-electrophoresis of mixtures of peptides and their hydrolysis products (lower peptides and amino-acids)

Summary It is shown that two-dimensional chromatography and association of chromatography and electrophoresis on thin layers of binder-free cellulose powder are efficient methods for the separation of the components of mixtures of peptides and their hydrolysis products (lower peptides and amino-acids). These results are obtained using low-voltage electrophoresis (ca. 10 volts/cm), partition chromatography and new solvents (mobile phases). Choice of solution for electrophoresis and of solvent for chromatography has a most important bearing on the quality of separations. By way of example, the efficiency of some new solvents [1] for the separation of the components of mixtures of peptides and aminoacids is shown.

     

Séparation sur couche mince de poudre de cellulose des 1-dimethylaminonaphthaléne, 5-sulfonylaminoacides

Sommaire Tous les dansylaminoacides peuvent être séparès par deux chromatographies bi-directionnelles et une chromatoélèctrophorése sur couche mince de poudre de cellulose sans liant. Dans les trois cas, la chromatographie de partage, selon la premiére direction, est faite sur les sels d'ammonium des dansylamioacides dans le solvant toluéne/monochlorhydrine du glycol/ammoniaque 0,8 N. (150 ml. : 90 ml. : 45 ml. : 90 ml.) + alcool octylique primaire 200 mg. La séparotion des composés éthérosolubles est obtenue aprés la chromatographie de relargage selon la seconde direction: eau/eau saturée de sulfate d' ammonium/dodécylsulfate de sodium (700 ml. : 100 ml./576 mg.). Pour les dansylaminoacides dicarboxyliques, leur séparation est obtenue, aprés une seconde chromatographie de partage, sur couche mince imprégnée d'acétate de sodium (0,2 M.) à l'aide du solvant isobutanol/acide acétique glacial/eau (1503 à 520). Une électrophorése, en seconde direction, (diéthylamine 0,033 M., chlorure de sodium 0,02 M.) permet de séparer les dérivés hydro-acidosolubles. Les analyses des mélanges de dinitrophénylaminoacides et de dansylaminoacides peuvent être faites simultanément.

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Separation of 1-dimethylaminonaphthalene, 5-sulfonylaminoacids by thin layer chromatography on cellulose powder

Summary All dansylaminoacids can be separated by 2 twodimensional chromatographies, combined with chromato-electrophoresis on cellulose powder. In all three cases, partition chromatography takes place, in the first dimension, on ammoniumsalts of dansylaminoacids in the solvent toluene/glycol chlorhydrine/pyridine/ammonia 0.8 N (150 ml : 90 ml : 45 ml : 90 ml), +200 mg of primary octyl alcohol. Separation of the ether-soluble compounds is obtained by salting-out chromatography in the second dimension: Water/water saturated with ammonium sulphate/sodium dodecylsulphate (700 ml/100 ml/576 mg). As for the dicarboxyl-dansylaminoacids, their separation is obtained, after a second partition chromatography, on a thin layer impregnated with sodium acetate (0.2 M), by means of the solvent isobutanol/acetic acid/water (150/3 to 5/20). Electrophoresis, in the second dimension (diethylamine 0.033 M; sodium chloride 0.02 M), permits the separation of the acid-soluble derivatives. Mixtures of dinitrophenyl-aminoacids and dansylaminoacids can be analyzed simultaneously.

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Trennung von 1-dimethylaminonaphthalen, 5-sulfonylaminosauren an cellulose-dünnschichten

Zusammenfassung Alle Dansylaminosäuren können durch 2 zweidimensionale Trennungen in Verbindung mit der DC-Elektrophorese auf Celluloseschichten getrennt werden.In allen drei Fällen wird eine Verteilungs-Chromatographie der Ammoniumsalze der Dansylaminosäuren vorgenommen, und zwar in der 1. Richtung mit dem Lösungsmittel: Toluol+Glycolmonochlorhydrin+Pyridin+0,8 N Ammoniak (150+90+45+90)+200 mg prim. Oktanol.Die Trennung der ätherlöslichen Bestandteile wird durch die erweiterte Chromatographie in der 2. Richtung mit: Wasser+gesättigte Ammoniumsulfat-Lösung+Natriumdodecylsulfat (700 ml+100 ml+576 mg) erreicht. Die Dicarboxyl-dansylaminosäuren werden nach einer 2. Verteilungs-Chromatographie auf DC-Schichten, die mit 0,2 M Natriumacetat imprägniert sind, getrennt, mittels Isobutanol+Eisessig+Wasser (150+3–5+20). Eine Elektrophorese in 2. Richtung (Puffer: Diäthylamin 0,033 M/Natriumchlorid 0,02 M) erlaubt die Trennung der säurelöslichen Derivate. Die Analysen der Gemische von Dinitrophenylaminosäuren und der Dansylaminosäuren können auf diesem Wege gleichzeitig ausgeführt werden.

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Elaboration of poly(ethyleneimine) coated poly( , -lactic acid) particles. Effect of ionic strength on the surface properties and DNA binding capabilities

Poly( , -lactic acid) (PLA)-based particles, obtained by the emulsification–diffusion process, were surface-modified by electrostatic adsorption of poly(ethylenimine) (PEI). The amount of immobilized PEI and the conformation of the polycation at the interface were dependent on the ionic strength of the media. In the absence of salt, or at low ionic strength, the adsorbed amounts of PEI, the surface charge and the critical concentration for coagulation (CCC) of the modified particles were lower than when the adsorption was achieved at elevated ionic strength. Moreover, at low salt concentration, isotherms were of Langmuir type, suggesting the formation of monolayers. The differences in PEI surface conformation had consequences on the DNA binding capacity of the particles, on the plasmid DNA conformation at the interface and on the DNA release in various media. When PEI was adsorbed in a 50 mM phosphate buffer, the amount of bound plasmid and the strength of binding were higher than when PEI was adsorbed in water. From these differences in physico-chemical properties, one can expect differences in transfection or immunization performances of the vectors.     

Diffuse interface model for high speed cavitating underwater systems

High speed underwater systems involve many modelling and simulation difficulties related to shocks, expansion waves and evaporation fronts. Modern propulsion systems like underwater missiles also involve extra difficulties related to non-condensable high speed gas flows. Such flows involve many continuous and discontinuous waves or fronts and the difficulty is to model and compute correctly jump conditions across them, particularly in unsteady regime and in multi-dimensions. To this end a new theory has been built that considers the various transformation fronts as ‘diffuse interfaces’. Inside these diffuse interfaces relaxation effects are solved in order to reproduce the correct jump conditions. For example, an interface separating a compressible non-condensable gas and compressible water is solved as a multiphase mixture where stiff mechanical relaxation effects are solved in order to match the jump conditions of equal pressure and equal normal velocities. When an interface separates a metastable liquid and its vapor, the situation becomes more complex as jump conditions involve pressure, velocity, temperature and entropy jumps. However, the same type of multiphase mixture can be considered in the diffuse interface and stiff velocity, pressure, temperature and Gibbs free energy relaxation are used to reproduce the dynamics of such fronts and corresponding jump conditions. A general model, based on multiphase flow theory is thus built. It involves mixture energy and mixture momentum equations together with mass and volume fraction equations for each phase or constituent. For example, in high velocity flows around underwater missiles, three phases (or constituents) have to be considered: liquid, vapor and propulsion gas products. It results in a flow model with 8 partial differential equations. The model is strictly hyperbolic and involves waves speeds that vary under the degree of metastability. When none of the phase is metastable, the non-monotonic sound speed is recovered. When phase transition occurs, the sound speed decreases and phase transition fronts become expansion waves of the equilibrium system. The model is built on the basis of asymptotic analysis of a hyperbolic total non-equilibrium multiphase flow model, in the limit of stiff mechanical relaxation. Closure relations regarding heat and mass transfer are built under the examination of entropy production. The mixture equation of state (EOS) is based on energy conservation and mechanical equilibrium of the mixture. Pure phases EOS are used in the mixture EOS instead of cubic one in order to prevent loss of hyperbolicity in the spinodal zone of the phase diagram. The corresponding model is able to deal with metastable states without using Van der Waals representation.     

Synthese Des 5-Desoxy-5,5,5-Trifluoro-d- et -l-Pentofuranoses

ABSTRACT

Synthetic pathways leading to 5-deoxy-5,5,5-trifluoropentofuranoses are reported. The main difficulty was to obtain a good diastereoselectivity at the C-4 carbon bearing the CF₃ group. For the ribose and the lyxose derivatives the problem was partially solved by reacting trifluoromethyltrimethylsilane with 1,4-lactones of suitable glyconic acids leading to hemiketalic 1-deoxy-1,1,1-trifluoro-2-ketoses. Reduction of these ketoses with NaBH₄ or LiA1H₄ allowed the desired configuration at the C-4 carbon. For the arabinose and the xylose derivatives it was found more convenient to synthesize uncyclised 1-deoxy-1,1,1-trifluoro-2-ketopentoses by Dess-Martin oxidation of the corresponding protected alcohols. Highly selective reductions of these trifluoromethylketones led to arabino or xylo derivatives depending on the reducing agent.