Chemistry of naphthazarin derivatives. 11. Trisubstituted hydroquinone derivatives in the preparative synthesis of naphthazarins

The Friedel—Crafts acylation of trimethylhydroquinone, 3,5-diethyl-2-hydroxyhydroquinone, and 3,5-diethyl-1,2,4-trimethoxybenzene with dichloromaleic or citraconic anhydride in an AlCl₃—NaCl melt is accompanied by o-C-dealkylation to afford functionally substituted naphthazarins.     

Recherches en série diazépine-1,4 et triazépine-1,2,4. XI—etude en spectrométrie de masse des fragmentations de triazépines-1,2,4

The mass spectra of eleven 1,2,4-triazepines with oxo, thioxo, methoxy and methylmercapto groups in the 3 and 5 positions are reported and analysed. Each of the five structures of the triazepine ring present is characterized by a particular group of fragmentations.     

Polymerization by transition metal derivatives. XII. Factors controlling activity and stereospecificity in the 1,4 polymerization of butadiene by monometallic nickel catalysts

In the course of investigations of polymerization of diolefins by transition metal derivatives, we have synthesized various monometallic nickel coordination catalysts. The complexes were prepared by reacting 2,6,10-dodecatriene-1,12-diyl nickel with protonic acids; they were shown to initiate the stereospecific polymerization of 1,3-butadiene. The study of these catalysts showed the strong influence of the nature of the counteranion used on the stereospecificity and the polymerization rate. Moreover, by adding various ligands, we were able to modify the behavior of the catalytic systems and to prepare either pure cis-1,4 or pure trans-1,4 or cis–trans equibinary polybutadienes, starting from the same complex and keeping a high 1,4 specificity. Some of these modifications were shown to be reversible.     

Spiral magnetic structure in non-Heisenberg magnets with an easy-axis anisotropy

The investigations performed in this work have demonstrated that an easy-axis frustrated non-Heisenberg magnet can contain homogeneous phases with the vector (ferromagnetic) and tensor (nematic) orderings, as well as a spatially inhomogeneous phase of the magnetic spiral type. Depending on the relationships between the material parameters, either a ferromagnetic spiral or a spiral of the quadrupole–ferromagnetic type with different periods of the spiral structures can be formed in the system. The phase diagram of the system has been constructed.     

Chromatographie par complexe de transfert de charge. Application à l'analyse d'hydroliquéfiats du charbon par HPLC

Résumé L'analyse de coupes lourdes (huile de distillation sous vide et huile issue du séparateur à chaud) provenant de l'hydroliquéfaction catalytique du charbon a été réalisée par mise en ouvre de différentes techniques chromatographiques. L'identification des principales structures résulte de l'application de la chromatographie par couplage de transfert de charge en mode HPLC et des spectroscopies UV et de masse.

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Donotor-acceptor complex chromatography —Application to analysis of coal liquefaction products by HPLC

Summary A Vacuum gas oil and the corresponding residue of a coal liquefaction product were investigated by means of HPLC and MS. Nearly a complete identification was performed by chromatographic, UV-spectroscopic methods and MS.

     

Loss of metallicity in metal rich lithium oxide clusters

Mixed lithium-lithium oxide aggregates are experimentally obtained from unimolecular evaporative cascades starting at metal rich Li _p ⁺ (Li₂O)_n species and ending with the stoichiometric limit Li⁺(Li₂O)_n, for several sizes of the oxide part (Li₂O)_n with 0 ≤ n ≤ 8. The results show evidence of the vanishing of the properties of the quantum metallic droplet i.e. shell closing and odd-even alternation, portrayed in the dissociation energy, with increasing size of the oxide component. The competition between monomer and dimer lithium evaporation from the heated metal rich Li _p ⁺ (Li₂O)_n species points out the influence of the perturbation induced by the oxide component on the mixed metal oxide clusters.     

Synthesis and characterization of biodegradable homopolymers and block copolymers based on adipic anhydride

Homopolymers of adipic anhydride (AA) and block copolymers of ϵ-caprolactone (ϵ-CL) and AA have been synthesized with aluminum triisopropoxide as an initiator. Homopolymerization was studied at 20°C in toluene and methylene chloride (CH₂Cl₂). The end-group analysis agrees with a coordination insertion mechanism based on the acyl-oxygen cleavage of the AA ring. Living poly(ϵ-caprolactone) (PCL) chains are very efficient macro-initiators for the polymerization of AA, with formation of diblock copolymers of a narrow molecular weight distribution. At our best knowledge, low molecular weight ω-aluminum alkoxide PCL macroinitiators (M_n < 1000) allow the first valuable synthesis of PAA with a molecular weight as high as 58,000 and a quite narrow polydispersity (M_w/M_n = 1.2). Size-exclusion chromatography (SEC) and ¹³C NMR confirm the blocky structure of the copolymers, in agreement with DSC that shows two melting endotherms and two glass transitions characteristic of the crystalline and amorphous phases of PCL and PAA, respectively. Block copolymers of ϵ-CL and AA are also sensitive to hydrolysis, which makes them possible candidates for biomedical applications. Initiation of the AA polymerization in bulk with aluminum triisopropoxide in the presence of various ligands is also discussed. © 1997 John Wiley & Sons, Inc.     

Analysis of the structure of very large bacterial aggregates by small-angle multiple light scattering and confocal image analysis

This work aims at developing a more accurate measurement of the physical parameters of fractal dimension and the size distribution of large fractal aggregates by small-angle light scattering. The theory of multiple scattering has been of particular interest in the case of fractal aggregates for which Rayleigh theory is no longer valid. The introduction of multiple scattering theory into the interpretation of scattering by large bacterial aggregates has been used to calculate the fractal dimension and size distribution. The fractal dimension is calculated from the form factor F(q) at large scattering angles. At large angles the fractal dimension can also be computed by considering only the influence of the very local environment on the optical contrast around a subunit. The fractal dimensions of E. coli strains flocculated with two different cationic polymers have been computed by two techniques: static light scattering and confocal image analysis. The fractal dimensions calculated with both techniques at different flocculation times are very similar: between 1.90 and 2.19. The comparison between two completely independent techniques confirms the theoretical approach of multiple scattering of large flocs using the Mie theory. Size distributions have been calculated from light-scattering data taking into account the linear independence of the structure factor S(q) relative to each size class and using the fractal dimension measured from F(q) in the large-angle range or from confocal image analysis. The results are very different from calculations made using hard-sphere particle models. The size distribution is displaced toward the larger sizes when multiple scattering is considered. Using this new approach to the analysis of very large fractal aggregates by static light multiple scattering, the fractal dimension and size distribution can be calculated using two independent parts of the scattering curve.     

Supramolecular organization of alpha,alpha'-disubstituted sexithiophenes

The self-assembly of alpha,alpha'-linked sexithiophenes with chiral and achiral penta(ethylene glycol) chains attached at the alpha-positions of the terminal rings, that is, 2,2':5',2':5',2':5',2':5',2'-sexithiophene-5,5'-dicarboxylic acid-2S)-2-methyl-3,6,9,12,15-pentaoxahexadecyl ester (1) and 2,2':5',2':5',2':5',2':5',2'-sexithiophene-5,5'-dicarboxylic acid-3,6,9,12,15-pentaoxahexadecyl ester (2), respectively is described. Analysis of the UV/vis, fluorescence, circular dichroism, and circular polarization of luminescence spectroscopic data shows that these compounds form chiral aggregates in polar solvents and in the solid state. In n-butanol aggregation occurs at temperatures below 30 degrees C, while above this threshold temperature the aggregates break up without an intermediate disordered state of aggregation, and the compounds are molecularly dissolved. The "melting temperature" of the aggregates depends on the concentration of sexithiophene, indicating that the optical changes observed are a result of intermolecular processes. Mass spectrometric measurements reveal that 1 and 2 can form mixed aggregates. Analysis of the optical spectra reveals that in these mixed aggregates, chiral 1 molecules act as "sergeants" to direct the packing of the "soldiers" 2, illustrating cooperativity within the columns. In water, the same type of chiral aggregates are formed as in n-butanol below 30 degrees C; however, these aggregates are still present, but the chirality is lost above 30 degrees C. In spin-coated films of 1 chiral aggregates are present. AFM studies show that 1 self-organizes into chiral fiberlike structures in the solid state. Furthermore both 1 and 2 display thermotropic liquid crystalline behavior between 180 and 200 degrees C.