Ionic nanocomposites based on XNBR-OMg filled with layered nanoclays

Ionic elastomers based on carboxylated nitrile rubber (XNBR) crosslinked with magnesium oxide (OMg) and filled with layered nanoclays have been prepared. Two types of nanofillers were employed: a commercial one (Cloisite 15 A) and the other prepared in our laboratory (BCA-ODA). The properties of raw and vulcanized compounds have been studied in order to elucidate the effect of layered nanoclays. X-ray diffraction analysis shows that during compounding and crosslinking the macromolecular chains of rubber were intercalated in a commercial nanofiller, whilst our nanoclay was exfoliated. However, this fact does not affect the properties of compounds homogeneously. Vulcanization parameters, Mooney viscosity and decay and rheological properties were affected depending on the filler type. Mechanical properties were not significantly varied, but glass transition temperature and ionic transition temperature were shifted in comparison with those of the unfilled compound.     

Long-Range proton-proton coupling constants. I. Propanic coupling involving a methyl group 4JMeH

An equation is formulated on the basis of theoretical INDO/FPT calculations which describes the angular dependence of the propanic long-range coupling constant ⁴J_MeH in substituted HCCCH₃ fragments. This equation is a truncated Fourier series in the torsion angle ?, HCCMe, which takes into account the dependence of the Fourier coefficients on the bond angle θ, CCMe. The substituent effects are assumed to be additive. Some parameters in the equation may be obtained from the ⁴J_MeH couplings in propane and neopentane derivatives. The calculated effect upon ⁴J_MeH of changes in the bond angle θ is significant and it seems to be in part the cause of some effects which have been attributed to conformational dependence.     

Structures de l'odyendane et l'odyendene deux nouveaux quassinoides d'odyendea gabonensis (pierre) engl. Simaroubacees.

From the trunk bark of Odyendea gabonensis (Pierre) Engl. Simaroubaceae, two-new quassinoids have been isolated : Odyendane and Odyendene. Their structures were established from spectral data and X-Ray diffraction analysis.     

Optimization of St John's Wort flavonoid separation by reversed phase liquid chromatography on a silica-based monolithic column

Summary An optimization procedure for the separation of flavonoids from St John's Wort by reversed-phase high-performance liquid chromatography on monolithic stationary phase is described. Three-component mobile phase systems are studied using experimental design methodology. The starting experimental domain is a triangle, each vertex of which is a pure component. From preliminary isocratic experiments, truncations in the domain are performed leading to a quadrilateral shape working domain with no symmetry. To cope with both separation and analysis time, desirability functions are used. Optimal conditions are finally given by binary systems and the four flavonoids are separated in less than seven minutes.     

An overview of laboratory performance studies conducted by the IAEA for marine pollution studies of metals and organic contaminants

Aspects of the International Atomic Energy Agency (IAEA) Analytical Quality Control Services (AQCS) for marine environmental studies are discussed, focusing on recent laboratory performance studies (LPS) and the production of reference materials for trace metals and organic compounds in various marine matrices. The IAEA has organized seventeen global interlaboratory studies for a range of organic contaminants. Of note has been the inclusion of numerous polychlorinated biphenyl congeners (PCBs) and some sterols of anthropogenic origin. Concurrently, there have been eleven worldwide intercomparison exercises for trace metals in the marine environment, most of which included methylmercury. Although such interlaboratory studies can help improve performance in individual laboratories and regional laboratory networks, the results reveal that problems remain in the determination of some metals and many organic contaminants.     

Viscometric and sorption equilibrium studies on n-alkane-butanone-poly-(dimethylsiloxane) systems

Intrinsic viscosities, [η], second virial coefficients, A₂, and preferential solvation coefficients, λ, for the ternary systems n-alkane (l)-butanone (2)-poly(dimethylsiloxane) (PDMS) (3), with n-alkane = n-hexane, n-heptane, n-nonane and n-undecane, have been determined at 20°. The K and a constants of the Mark-Houwink equation have been evaluated over the whole composition range of the binary solvent mixtures. Polymer (mixed solvent) interaction parameters and unperturbed dimensions have been evaluated both from A₂ and [η] data, the feasibility of A₂ evaluation from [η] experimental data or vice versa being discussed. Experimental and calculated (through Dondos and Patterson theory) excess free energies, G^E, follow similar trends with composition; large numerical discrepancies, however, arise between both sets of G^E. Maxima in [η], in a and in A₂ are accompanied by inversion points in λ. The solvent mixture composition range in which PDMS is preferentially solvated by n-alkane, as well as the extent of solvation, decrease with increasing number of carbon atoms in the n-alkane.