HR: 16:20h
AN: B44A-01    [Abstracts]
TI: Prions, Radionuclides and Clays: Impact of clay interlayer "acidity" on toxic compound speciation
AU: * Charlet, L
EM: laurent.charlet@ujf-grenoble.fr
AF: Environmental Geochemistry Group, LGIT, University of Grenoble and CNRS, Environmental Geochemistry Group, LGIT, University of Grenoble and CNRS, BP53, 38041 Grenoble, France, Grenoble, France
AU: Hureau, C
EM: christelle.hureau@paris7.jussieu.fr
AF: Environmental Geochemistry Group, LGIT, University of Grenoble and CNRS, Environmental Geochemistry Group, LGIT, University of Grenoble and CNRS, BP53, 38041 Grenoble, France, Grenoble, France
AU: Hureau, C
EM: christelle.hureau@paris7.jussieu.fr
AF: Inorganic Chemistry Group, ICMO, Paris-Sud University, 91405 Orsay, France, Orsay, France
AU: Sobolev, O
EM: sobolev@ill.fr
AF: Environmental Geochemistry Group, LGIT, University of Grenoble and CNRS, Environmental Geochemistry Group, LGIT, University of Grenoble and CNRS, BP53, 38041 Grenoble, France, Grenoble, France
AU: Sobolev, O
EM: sobolev@ill.fr
AF: Diffraction Group, Institut Laue Langevin, BP 156, 38042 Grenoble, France, Institut Laue Langevin, BP 156, 38042 Grenoble, France, Grenoble, France
AU: Cuello, G
EM: cuello@ill.fr
AF: Diffraction Group, Institut Laue Langevin, BP 156, 38042 Grenoble, France, Institut Laue Langevin, BP 156, 38042 Grenoble, France, Grenoble, France
AU: Chapron, Y
EM: yves.chapron@wanadoo.fr
AF: 4Alpine Environmental Dynamics Institute, 38660 La Terrasse, France, Alpine Environmental Dynamics Institute, 38660 La Terrasse, France, La Terrasse, France
AB: The physical and chemical processes that are the basis of contaminant retardation in clay rich medium, such as soil or nuclear waste repository, have been studied at the molecular level by a combination of molecular dynamics (MD), electron paramagnetic spectroscopy (EPR) and neutron diffraction with isotopic substitution (NDIS). The speciation of contaminants such as Sm, a radionuclide analogue, and Cu, bound to Prion protein (PrP), has been studied upon adsorption in clay interlayers. We used as molecular probe the P5-Cu(II) complex, where the P5 pentapeptide(92-96 PrP residues) represents one of the five Cu(II) binding site present in PrP, the key protein involved in diseases known as transmissible spongiform encephalopathies. In both cases, the pH of the interlayer has been inferred from the metal ion coordination, here used as a molecular reporter. In circum neutral pH waters, samarium is present as Sm(OH)3° species and should not be adsorbed in clay interlayer by "cation exchange" unless its hydrolysis is altered. Samarium NDIS results indicate that whether the number of oxygen nearest neighbours varies only from 8.5 to 7, as Sm penetrates the interlayer, the number of hydrogen nearest neighbours drops from 12 to 6. The high affinity of clay for Sm shows that a change in Sm hydrolysis occurs in the clay interlayer, but is directly followed by the formation of a surface complex with montmorillonite siloxane plane functional groups which prevents the determination of a "local pH". Conversely, has been found to be a much more sensitive interlayer water pH probe. and this peptide domain is involved in the misfolding of the protein,a transconformation which may lead to the pathogenic PrPSc form. We have therefore studied by EPR spectroscopy the adsorption of Cu(II)-P5 complexes on montmorillonite, and found the clay to have a large and selective adsorption capacity for the various [Cu(P5)H-n](2-n)+ complexes where n is the number of deprotonated amido function. The speciation of the Cu-ligand complex was found to be different, in bulk water (Hureau et al., 2006) and in clay suspensions, where n increases. This new speciation of the copper metal ions, used as a molecular probe, allows to "measure" the pH of interlayer water which is shown to be significantly lower than in bulk water pH. Molecular models for PrP attachment to the clay basal plane and Sm location within the clay interlayer were obtained by MD computations. Implications on PrP pathogenicity, following carcase burial and particle ingestions, and on radionuclide mobility, following nuclear waste burial in clay rich repository sites, will be discussed.
DE: 0486 Soils/pedology (1865)
DE: 1030 Geochemical cycles (0330)
DE: 1040 Radiogenic isotope geochemistry
DE: 4805 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4912)
DE: 4825 Geochemistry
SC: Biogeosciences [B]
MN: 2007 Joint Assembly