Les Systèmes B2O3?MO?MS Boracites M?S (M = Mg,Mn, Fe,Cd) et Sodalites M?S (M = Co,Zn)

In the B₂O₃? MO? MS (M = Mg, Mn, Fe, Co, Zn, Cd) systems six ternary phases have been isolated, four of them having the structure of the cubic variety of the boracite, Mg₃B₇O₁₃Cl, and two the structure of the sodalite, Na₄(SiAlO₄)₃Cl. Some properties of the new phases have been investigated.     

A microcomputer-controlled modulation technique for the detection of transient species in UV photoelectron spectroscopy

A microcomputer-controlled modulation method is described to measure UV photoelectron spectra of transient species generated in a microwave discharge. Spectra at low and high microwave power levels are simultaneously recorded and afterwards linearly combined in order to remove parent compound signals. The method is applied to discharged oxygen where the transition O₂⁺ (²Φ_u) ← O₂ (¹Δ_g) becomes visible without interference from the parent molecule O₂ (³Σ_g^?), and to discharged sulphur dioxide where SO (³Σ^?) and S (³P) photoelectron spectra are obtained free from SO₂ bands. Finally the build-up of transient bands as a function of time is recorded.     

Immobilization of dermatan sulphate on a silica matrix and its possible use as an affinity chromatography support for heparin cofactor II purification.

Dermatan sulphate (DS) is a glycosaminoglycan which catalyses specifically thrombin inhibition by a plasmatic inhibitor, Heparin cofactor II (HCII). DS was insolubilized on a silica matrix to study its interaction with HCII. The immobilization of DS was performed with a good yield on a silica previously coated with polysaccharides in order to neutralize the negatively charged silanol groups. The value of the affinity constant of insolubilized DS for HCII, measured by the adsorption isotherm, is consistent with the value obtained for soluble DS. The DS bound to the silica matrix was also tested as a chromatographic support for the purification of HCII from human plasma; the optimum conditions for HCII adsorption and desorption were determined. The eluted HCII was obtained with a good yield (21%) and with no contamination by antithrombin III, the other main plasmatic inhibitor of thrombin.     

Elektronenmikroskopische Beobachtungen der L?slichkeiten von mit Flammschutzmitteln behandelten Baumwoll/Polyester-Mischungen

Ohne Zusammenfassung     

Influences of ClH and BrH on the pyrolyses of neopentane and ethane at small extents of reaction

A symbolic mechanism “μH, YH” has been proposed to account for the homogeneous chain pyrolysis of an organic compound μH in the presence of a hydrogenated additive YH at small extents of reaction. An analysis of this mechanism leads to two limiting cases: the thermal decomposition of neopentane corresponds to the first one (A), that of ethane to the second one (B). Previous experimental work has shown that this mechanism seems to account for a number of experimental observations, especially the inhibition of alkane pyrolyses by alkenes. Experimental investigations were extended by examining the influences oftwo hydrogen halides (ClH and BrH) upon the pyrolyses of neopentane (at 480°C) and ethane (around 540°C). The experiments have been performed in a conventional static Pyrex apparatus and reaction products have been analyzed by gas-liquid chromatography. The study shows that ClH and BrH accelerate the pyrolysis of neopentane (into i-C₄H₈ + CH₄). The experimental results are interpreted by reaction schemes which appear as examples of the mechanism “μH, YH” in the first limiting case (A). The proposed schemes enable one to understand why the accelerating influence of ClH is lower or higher than that of BrH, depending on the concentration of the additive. An evaluation of the rate constant of the elementary steps neo-C₅H₁₁ · → i-C₄H₈ + CH₃ · is discussed. In the case of ethane pyrolysis, BrH inhibits the formation of the majorproducts (C₂H₄ + H₂) and, even more, that of n-butane traces. The experimental results are interpreted by a reaction scheme which appears as an example of the mechanism “μH, YH” in the second limiting case (B). On the contrary, ClH has no noticeable influence on the reaction kinetics. This result inessentially due to the fact that the bond dissociation energy of Cl? H(?103 kcal/mol) is higher than that of C₂H₅—H (?98 kcal/mol), whereas that of Br—H (?88 kcal/mol) is lower.     

Use of the NH indices in the natural abundance15N NMR spectra in studying the tautomerism of acylmethylazines

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, p. 202, January, 1988.     

First-order phase transition to strongly anisotropic ferromagnetism in Tl2Fe6Te6

The magnetic susceptibility, magnetization, specific heat and electrical resistivity were measured on the new material Tl₂Fe₆Te₆. All the data show a very sharp anomaly revealing a phase transition to ferromagnetism at T_c≈220 K. The presence in the structure of one-dimensional metallic clusters $\text{¦Fe}{}_3\text{¦}{}^1{}_{\mathrm{\infty }}$ is evidenced by a very strong magnetic anisotropy in the ferromagnetic state, showing an interesting intermediate situation between a pure linear chain and 3-dimensional iron. Furthermore, the unusual sharpness of the transition leads us to anticipate a first-order phase transformation, but the lack of detectable thermal hysteresis was surprising. The molecular field model proposed by Bean and Rodbell in order to account for the similar behavior of MnAs gives a close representation of our magnetic data. Thus, a pronounced dependence of the exchange interaction upon interatomic spacing may well be the dominant mechanism leading to the observed phenomena.     

Accès à quelques gem-méthoxy hydroperoxydes stéroïdes

L'ozonolyse en méthanol permet d'accéder, en série stéroïde, à des méthoxy-hydroperoxydes géminés. Des 20-cétopregnanes ont ainsi fourni des méthoxy-hydroperoxydes en 20, par l'intermédiaire d'un dérivé 20-méthylénique, ou en 17, par l'intermédiaire d'un acétate énolique.