Capillary gas chromatographic properties of three new mono-ester permethylated β-cyclodextrin derivatives

2^I-O-Methoxycarbonylmethyl-2^II–VII,3^I–VII,6^I–VII-eicosa-O-methyl-cyclodextrin (20Me/P2OCH₂COOMe), 6^I-O-methoxycarbonylmethyl-2^I–VII,3^I–VII,6^II–VII-eicosa-O-methyl-cyclodextrin (20Me/P6OCH₂COOMe), 6^I-O-methoxycarbonyl-6^I-deoxy-2^I–VII,3^I–VII,6^II–VII-eicosa-O-methyl-cyclodextrin (20Me/P6COOMe) have been evaluated as chiral stationary phases (CSPs) for capillary gas chromatography. General chromatographic properties of the corresponding columns have been investigated in terms of efficiency, polarity and inertness. More than 60 solutes have been used for studying their enantioselectivity by comparison with permethylated β-cyclodextrin as a reference. Similar enantioseparation ability was established for the four studied CSPs, the 20Me/P2OCH₂COOMe exhibiting in most cases a better enantioselectivity than the other selectors.     

Lagrangian foliations and Lax equations

If X is a bihamiltonian vector field tangent to a foliation which is Lagrangian with respect to both symplectic structures, the dynamical system x=X(x) implies a local Lax equation =[L, B], but in canonical adapted coordinates, this equation reduces to the trivial equation =0.     

Torsional anharmonicity in the conformational analysis of beta-D-galactose

Schemes to include a treatment of torsional anharmonicity in the conformational analysis of biological molecules are introduced. The approaches combine ab initio electronic energies and harmonic frequencies with anharmonic torsional partition functions calculated using the torsional path integral Monte Carlo method on affordable potential energy surfaces. The schemes are applied to the conformational study of the monosaccharide beta-d-galactose in the gas phase. The global minimum structure is almost exclusively populated at 100 K, but a large number of conformers are present at ambient and higher temperatures. Both quantum mechanical and anharmonic effects in the torsional modes have little effect on the populations at all temperatures considered, and it is, therefore, expected that standard harmonic treatments are satisfactory for the conformational study of monosaccharides.     

Organic thin film pyrosensors

Recent developments in sensor technology show the suitability of thin pyroelectric films for the construction of pyroelectric sensor devices made from polymer materials. These materials are used for its advantageous thermal properties and also for its suitable frequency behaviour. Pyroelectrical measurements have been provided on thin films based upon poly(vinyl alcohol)s and poly(siloxane)s with azobenzene side chains. Relaxation behaviour and stability of poled pyroelectric polymers are discussed and related to the results of dipole relaxation measurements provided at our laboratories.     

New silicon-containing heterocyclic polyimides

New aromatic polyimides and polyamide-imides with phenylquinoxaline rings and dimethylsilane units have been synthesized by solution polycondensation reaction of aromatic diamines containing phenylquinoxaline units with bis(3,4-dicarboxyphenyl)-dimethylsilane dianhydride, or with a diacid chloride resulting from the reaction of this dianhydride with p-aminobenzoic acid. These polymers were easily soluble in organic solvents, such as N-methylpyrrolidinone and dimethylacetamide, and showed high thermal stability with decomposition temperature being above 440°C and glass transition temperature in the range of 245-285°C. Very thin coatings were deposited from polymer solutions onto silicon wafers and exhibited smooth, pinhole-free surface in atomic force microscopy investigations. Some of these polymers showed blue fluorescence in solution and films, with a maximum in the range of 415-425 nm.     

High resolution solid‐state 13C‐NMR study of as‐cured and irradiated epoxy resins

This article presents the effects of strong ionizing radiations on the physico‐chemical modifications of aliphatic or aromatic amine‐cured epoxy resins based on diglycidyl ether of bisphenol A (DGEBA). Such epoxy resins have a considerable number of applications in the nuclear industrial field and are known to be very stable under moderate irradiation conditions. Using extensively high resolution solid‐state ¹³C‐NMR spectroscopy we show that the aliphatic amine‐cured resin (DGEBA‐TETA) appears much more sensitive to gamma rays than the aromatic amine‐cured one (DGEBA‐DDM). On the one hand, qualitative analyses of the high resolution solid‐state ¹³C‐NMR spectra of both epoxy resins, irradiated under similar conditions (8.5 MGy), reveal almost no change in the aromatic amine‐cured resin whereas new resonances are observed for the aliphatic amine‐cured resin. These new peaks were interpreted as the formation of new functional groups such as amides, acids and/or esters and to alkene groups probably formed in the aliphatic amine skeleton. On the other hand, molecular dynamics of these polymers are investigated by measuring the relaxation times, T_CH, T_1ρH and T_1C , before and after irradiation. The study of relaxation data shows the formation, under irradiation, of a more rigid network, especially for the aliphatic amine‐cured system and confirms that aromatic amine‐cured resin [DGEBA‐4,4′‐diaminodiphenylmethane(DDM)] is much less affected by ionizing radiations than the aliphatic amine‐cured resin [DGEBA‐triethylenetetramine(TETA)]. Moreover, it has been shown that the molecular modifications generated by irradiation on the powder of the aliphatic‐amine‐cured resin appear to be homogeneously distributed inside the polymers as no phase separations can be deduced from the above analyses. Copyright © 2001 John Wiley & Sons, Ltd.     

Polymorphism and luminescence properties of CMONS organic crystals: bulk crystals and nanocrystals confined in gel-glasses

In order to compare the polymorphism of 1-cyano-1-(4-nitrophenyl)-2-(4-methoxyphenyl)ethene CMONS crystallized in solutions to that of CMONS nanocrystals grown in the pores of dense sol-gel matrices, we have first studied the CMONS polymorphism in various solvents which were then used in the nanocrystallization processes. The different polymorphs were characterized by differential scanning calorimetry, X-ray diffraction and absorption as well as luminescence spectroscopies. The differences observed between CMONS powders and CMONS nanocrystals illustrate the role played by the silicate matrices on the polymorphism of CMONS. This matrix effect would be used to stabilize a particular polymorph of an organic phase and thus to adjust the optical properties of the nanocomposite hybrid organic–inorganic material.     

Epoxy–amine reticulates observed by infrared spectrometry. III. Modifications of the structure and hydration abilities after irradiation in a humid atmosphere

This article is the third part of a series devoted to the study of the responsibilities of both humidity and irradiation in the aging process of amine‐cured epoxy resins. The basic technique used in this study was infrared spectrometry. In previous articles, we described the hydration of two kinds of epoxy resins widely used in the nuclear industry. In the first article, we reported results concerning the hydration of unirradiated resins; in the second article, these resins were first submitted to ionizing radiation in a dry atmosphere. In this article, we describe the effects of irradiation in a humid atmosphere and compare these effects to what was observed after irradiation in a dry atmosphere, as described in the previous articles. These effects were subtle: the humidity of the ambient atmosphere apparently protected the resins from oxidative degradation because, after irradiation in a humid atmosphere, a smaller number of carboxylic groups were formed. However, the water uptake increased after irradiation in a humid atmosphere. Thus, the humidity of the ambient atmosphere at the same time favored the rupture of chains, which released steric hindrances and allowed a greater number of H₂O molecules to reach hydrophilic sites in the resin. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1129–1136, 2001     

Dérivées de Lie des spineurs

Résumé On étudie le problème de la transformation d'un champ de spineurs sur une variété spinorielle par un groupe à un paramètre de difféomorphismes de la variété, en généralisant aux champs de spineurs la notion de dérivation de Lie. On peut alors étudier l'invariance d'un système d'équations aux dérivées partielles sur les spineurs (équations de Dirac) avec des méthodes analogues à celles qui sont valables dans le cas des tenseurs (équations de Maxwell).

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Summary The notion of a Lie derivative is generalized to spinor fields on a Spin manifold and the problem of transforming a spinor field under a one-parameter group of diffeomorphisms of the manifold is studied. The invariance of a differential system acting on spinors (Dirac's equations) is studied using methods similar to those used in the case of tensors (Maxwell's equations).

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Actuellement: Université des Sciences et Techniques de Lille.

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Entrata in Redazione il 19 aprile 1971.