ANALYSE DES FACTEURS D'ORDRE DES MÉTAUX DE TRANSITION DANS LES PHOSPHURES ET ARSÉNIURES MM'P ET MM'As

Les études magnétiques, par spectrométrie Mössbauer, par diffraction des neutrons et des rayons X sur les composés MM'P et MM'As ont mis en évidence un ordre très marqué des métaux de transition 3d et 4d, qui ne peut s'expliquer simplement que dans une description cristallochimique analogue à celle des oxydes. Les 4 facteurs d'ordre : facteur géométrique, nombre d'électrons d, effets de champ cristallin et transfert électronique s-d sont discutés successivement.The 3d and 4d transition metal ordering in MM'P and MM'As pnictides has been studied by Mössbauer spectroscopy, neutron and X ray diffraction, magnetic measurement. Like in the crystallochemistry of oxides, the order can be correlated with the non metal surrounding of the transition metal site. Four ordering factors : size factor, d electron number, crystalline field and s-d electron transfert are discussed

Long-term high fructose and saturated fat diet affects plasma fatty acid profile in rats

As the consumption of fructose and saturated fatty acids (FAs) has greatly increased in western diets and is linked with an increased risk of metabolic syndrome, the aim of this study was to investigate the effects of a moderate (10 weeks) and a prolonged (30 weeks) high fructose and saturated fatty acid (HFS) diet on plasma FA composition in rats. The effects of a few weeks of HFS diet had already been described, but in this paper we tried to establish whether these effects persist or if they are modified after 10 or 30 weeks. We hypothesized that the plasma FA profile would be altered between 10 and 30 weeks of the HFS diet. Rats fed with either the HFS or a standard diet were tested after 10 weeks and again after 30 weeks. After 10 weeks of feeding, HFS-fed rats developed the metabolic syndrome, as manifested by an increase in fasting insulinemia, total cholesterol and triglyceride levels, as well as by impaired glucose tolerance. Furthermore, the plasma FA profile of the HFS group showed higher proportions of monounsaturated FAs like palmitoleic acid [16:1(n-7)] and oleic acid [18:1(n-9)], whereas the proportions of some polyunsaturated n-6 FAs, such as linoleic acid [18:2(n-6)] and arachidonic acid [20:4(n-6)], were lower than those in the control group. After 30 weeks of the HFS diet, we observed changes mainly in the levels of 16:1(n-7) (decreased) and 20:4(n-6) (increased). Together, our results suggest that an HFS diet could lead to an adaptive response of the plasma FA profile over time, in association with the development of the metabolic syndrome