Etude des propriétés de sorption de la bentonite mx-80 vis-à-vis de se(iv), ni(ii) et cs(i). du système disperse au système compacte

Ce travail s inscrit dans le contexte du stockage des déchets radioactifs dans les couches géologiques profondes. Le but était d étudier les propriétés de rétention de la bentonite MX-80 vis-à-vis de Cs(I), Ni(II) et Se(IV) pour les états compactés. Ce travail était divisé en quatre parties : La première étude concernait la mise en place d une méthodologie de type batch pour étudier la rétention des éléments d intérêt dans le système compacté. Une nouvelle méthode a été développée et implique l utilisation de capillaires. Nous avons montré que la technique de RMN du proton à bas champ est une méthode de choix : elle est quantitative et permet une spéciation de l état de l eau dans les matériaux poreux saturés en eau. La troisième étude avait pour but de rendre compte des interactions de surface des éléments d intérêt dans le système bentonite MX-80/eau. Nous avons montré par une approche bottom up que la phase argileuse gouverne la rétention. Finalement, le quatrième travail a consisté à évaluer l applicabilité du modèle de rétention déduit des expériences réalisées pour les états dispersés aux états consolidés. Les résultats de l étude montrent, que la compaction n affecte pas la capacité de rétention des argiles lorsque le mécanisme d échange cationique domine la sorption. Lorsque l interaction est gouvernée par les sites de bordure, l effet apparaît variable suivant l élément étudié : pour Ni, la compaction a pour conséquence une légère diminution de la rétention alors que pour Se(IV), aucun effet n était observé. L origine de la diminution de rétention de Ni peut être expliquée quantitativement par une modification de la constante d affinité du site.In the context of the storage of the radioactive waste in the deep geological layers, the goal was to study the retention properties of bentonite MX-80 with respect to Cs(I), Ni(II) and Se(IV) for the compacted states. This work was divided into four parts: The first study related to the methodology of the type "batch" elaborated to study the retention of the elements of interest in the compacted system. A new method was developed and implying the use of capillaries. We showed that the technique of NMR of the proton with low field is a method of choice: it is quantitative and allows a speciation of the state of water in porous materials saturated with water. The purpose of the third study was to account for the interactions of surface with the elements of interest in the system bentonite MX-80/water. We showed by an approach "bottom up" that the argillaceous phase controls the retention. Finally, the fourth work consisted in evaluating the applicability of the model of retention deduces from the experiments carried out for the states dispersed with the consolidated states. The results of the study show that the compaction does not affect the holding capacity of clays when the cation exchange mechanism dominates the sorption. When the interaction is controlled by the sites of edge, the effect varies according to the studied element: for Ni, the consequence of the compaction is a light reduction of the retention whereas for Se(IV), no effect was observed. The origin of the reduction in Ni retention can be explained quantitatively by a modification of the affinity constant of the site.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Transformations rédox et phénomènes de passivation d'hydroxyde doubles lamellaires de types rouilles vertes

Conférence du 25 au 27 mars 2003. Communication par affiche

Multianalytical Approach for Deciphering the Specific MS/MS Transition and Overcoming the Challenge of the Separation of a Transient Intermediate, Quinonoid Dihydrobiopterin

Despite recent technological developments in analytical chemistry, separation and direct characterization of transient intermediates remain an analytical challenge. Among these, separation and direct characterization of quinonoid dihydrobiopterin (qH2Bip), a transient intermediate of tetrahydrobiopterin (H4Bip)-dependent hydroxylation reactions, essential in living organisms, with important and varied human pathophysiological impacts, are a clear illustration. H4Bip regeneration may be impaired by competitive nonenzymatic autoxidation reactions, such as isomerization of qH2Bip into a more stable 7,8-H2Bip (H2Bip) isomer, and subsequent nonenzymatic oxidation reactions. The quinonoid qH2Bip intermediate thus plays a key role in H4Bip-dependent hydroxylation reactions. However, only a few experimental results have indirectly confirmed this finding while revealing the difficulty of isolating qH2Bip from H4Bip-containing solutions. As a result, no current H4Bip assay method allows this isomer to be quantified even by liquid chromatography–tandem mass spectrometry (MS/MS). Here, we report isolation, structural characterization, and abundance of qH2Bip formed upon H4Bip autoxidation using three methods integrated into MS/MS. First, we characterized the structure of the two observed H2B isomers using IR photodissociation spectroscopy in conjunction with quantum chemical calculations. Then, we used differential ion mobility spectrometry to fully separate all oxidized forms of H4Bip including qH2Bip. These data are consistent and show that qH2Bip can also be unambiguously identified thanks to its specific MS/MS transition. This finding paves the way for the quantification of qH2Bip with MS/MS methods. Most importantly, the half-life value of this intermediate is nearly equivalent to that of H4Bip (tens of minutes), suggesting that an accurate method of H4Bip analysis should include the quantification of qH2Bip

Additional file 1: of Differential tissue accumulation of 2,3,7,8-Tetrachlorinated dibenzo-p-dioxin in Arabidopsis thaliana affects plant chronology, lipid metabolism and seed yield

Detection of TCDD in Arabidopsis tissues by HR/GC-MS. Diagrams indicate the presence of TCDD (Retention time ≈ 5.22) in the root (A, B and C) and in the shoot (D, E, and F) of 30-days old Arabidopsis exposed to various concentrations of TCDD 10, 50 and 100 ng L−1, respectively. G. TCDD standard. Three measurements were taken for three individual plants. Data are mean values ± SD (n = 6). (PDF 204 kb