(Re~u le 15 mars 1983, revise le 27 avril, uccepte le 2 mai 1983) Résumé. 2014 On a considéré le produit smectogène : 4-acétyl-4'-n-tétradécyloxyazobenzène. On a déterminé le diagramme de phases du système binaire composé de ses deux parties constitutives, à savoir le dodécane et le 4-acétyl-4'-n-acétoyloxyazobenzène. Une lacune de miscibilité a été observée à l'état liquide et interprétée comme argument en faveur de l'importance du rôle joué par le caractère amphipathique dans l'apparition des mésophases smectiques.Abstract 2014 The smectogenic compound 4-acetyl-4'-n-tetradecanoyloxyazobenzene was considered. The phase diagram of the binary mixture of its constituent parts, that is dodecane and 4-acetyl-4'-n-acetoyloxyazobenzene, was determined. A miscibility gap in the liquid state was observed. This was considered as support for the view that the amphiphilic nature of the molecule plays an important role in the formation of the smectic mesophase.J. Physique -LETTRES 44 (1983) L-491 -L-494 15 JUIN 1983,
An investigation of the structural and thermodynamical modifications induced by gamma-irradiation in model membranes is reported. Differential scanning calorimetry and X-ray diffraction were used to study the different phases and associated transitions of distearoylphosphatidylcholine multilamellar liposomes after 60Co gamma-irradiation. Changes were observed in the shape of the calorimetric peaks and in the corresponding phase transition temperatures. In particular a shoulder was observed at about 20 kGy. The three phases characteristic of lecithins with identical acyl chains were detected also for the highest radiation dose. The formation of lysolecithin and stearic acid upon phospholipid degradation was observed. The lysolecithin concentration increases as a function of irradiation dose, until a saturation value is reached at 40 kGy. These results correlate quite well with those obtained for interlayer and interchain distances and for the width of the main phase transition calorimetric peak. At the highest dose (approximately equal to 80 kGy) cross-linked adjacent radicals and other molecular species are also formed. Appreciable differences, and some similarities, in the behaviour of DSPC and DPPC liposomes under gamma-irradiation were observed.
This paper reports an investigation by dilatometry and x-ray diffraction of the structure at the molecular level of the smectic A phases occuring in homologous series of liquid crystals, namely the 4-acetyl-4′-n alkanoyloxyazobenzene series. First, several structural parameters referring to the aromatic part and to the paraffinic chain were obtained; then, on the basis of these parameters, a model was proposed concerning the structural organization of the molecules inside the smectic A layers. According to this model, a bilayer organization of the molecules was found to occur with a strong segregation between paraffinic and polar parts of the molecules, along with a pronounced spreading of the aliphatic chains at the interface.
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