Etude conformationnelle, par rmn du 13C, d'ethers d'enol renfermant un noyau aromatique

Two series of aromatic enol ethers deriving from 1-methoxy-1-phenyl ethylene and from 1-methoxy-1-phenyl 2-methyl propene have been studied by 13C NMR. Comparisons between the chemical shifts of these enol ethers and those of styrene on the one hand, and aliphatic enol ethers on the other, led us to conclude that the non-coplanarity of the phenyl ring with the double bond and/or the non-coplanarity of the OCH3 group with the same double bond play a prominent role in determining the chemical shift values of the ethylenic carbons. Para-substitution on the phenyl ring induces chemical shift variation not only in the aromatic moiety itself but also in the ethylene part of the molecule. The significance of the observed Hammett correlation is discussed. © 1980.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Etude de la structure et de la reactivite d'ethers d'enol par utilisation d'un reactif de deplacements chimiques et mesures d'effets overhauser nucleaires en rmn 1H

SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Oxygen Effect on Photosynthetic and Glycolate Pathways in Young Maize Leaves

To study the effect of O(2) on the photosynthetic and glycolate pathways, maize leaves were exposed to (14)CO(2) during steady-state photosynthesis in 21 or 1% O(2). At the two O(2) concentrations after a (14)CO(2) pulse (4 seconds) followed by a (12)CO(2) chase, there was a slight difference in CO(2) uptake and in the total amount of (14)C fixed, but there were marked changes in (14)C distribution especially in phosphoglycerate, ribulose bisphosphate, glycine, and serine. The kinetics of (14)C incorporation into glycine and serine indicated that the glycolate pathway is inhibited at low O(2) concentrations. In 1% O(2), labeling of glycine was reduced by 90% and that of serine was reduced by 70%, relative to the control in 21% O(2). A similar effect has been observed in C(3) plants, except that, in maize leaves, only 5 to 6% of the total (14)C fixed under 21% O(2) was found in glycolate pathway intermediates after 60 seconds chase. This figure is 20% in C(3) plants. Isonicotinyl hydrazide did not completely block the conversion of glycine to serine in 21% O(2), and the first carbon atom of serine was preferentially labeled during the first seconds of the chase. These results supported the hypothesis that the labeled serine not only derives from glycine but also could be formed from phosphoglycerate, labeled in the first carbon atom during the first seconds of photosynthesis. Another noticeable O(2) effect concerned differential labeling of phosphoglycerate and ribulose bisphosphate. Phosphoglycerate is more labeled than ribulose bisphosphate in air; the reverse is observed in 1% O(2). Changes in ribulose bisphosphate and phosphoglycerate pools exhibit similar trends. To understand the effect of O(2) on the distribution of (14)C in these two intermediates, it was postulated that, in air, there remains an oxygenase function which produces additional phosphoglycerate at the expense of ribulose bisphosphate

: Préface de J. Lang

International audienceUn des leaders mondiaux de l’industrie pharmaceutique vient de consacrer plus d’un milliard de francs suisses à la construction d’un centre de recherche scientifique à Bâle. Il a notamment fait appel aux architectes les plus réputés qui ont proposé des projets très ambitieux. De même, plusieurs œuvres d’art ont été acquises pour être disposées sur le site. L’idée est simple : associer création scientifique et artistique, création de connaissances situées et de valeur. La notion centrale de création renvoie à diverses formes organisationnelles originales supposant l’expression d’interactions nouvelles entre des acteurs jadis catalogués comme ingénieurs, gestionnaires ou encore artistes. Si le processus de décloisonnement observé suscite de nombreux questionnements dans les disciplines de gestion, d’économie ou de sociologie, il importe de mieux appréhender sa mise en œuvre, ses effets ainsi que les modalités de son évaluation. Une illustration renouvelée des logiques dédiées à l’action collective est proposée dans cet ouvrage à partir d’une sélection de communications scientifiques interdisciplinaires présentées lors du quatrième colloque Métamorphose des organisations