(M.A.M.) The chemical forms of zinc (Zn) in the Zn-tolerant and hyperaccumulator Arabidopsis halleri and in the non-tolerant and nonaccumulator Arabidopsis lyrata subsp. petraea were determined at the molecular level by combining chemical analyses, extended x-ray absorption spectroscopy (EXAFS), synchrotron-based x-ray microfluorescence, and EXAFS. Plants were grown in hydroponics with various Zn concentrations, and A. halleri specimens growing naturally in a contaminated site were also collected. Zn speciation in A. halleri was independent of the origin of the plants (contaminated or noncontaminated) and Zn exposure. In aerial parts, Zn was predominantly octahedrally coordinated and complexed to malate. A secondary organic species was identified in the bases of the trichomes, which contained elevated Zn concentrations, and in which Zn was tetrahedrally coordinated and complexed to carboxyl and/or hydroxyl functional groups. This species was detected thanks to the good resolution and sensitivity of synchrotron-based x-ray microfluorescence and EXAFS. In the roots of A. halleri grown in hydroponics, Zn phosphate was the only species detected, and is believed to result from chemical precipitation on the root surface. In the roots of A. halleri grown on the contaminated soil, Zn was distributed in Zn malate, Zn citrate, and Zn phosphate. Zn phosphate was present in both the roots and aerial part of A. lyrata subsp. petraea. This study illustrates the complementarity of bulk and spatially resolved techniques, allowing the identification of: (a) the predominant chemical forms of the metal, and (b) the minor forms present in particular cells, both types of information being essential for a better understanding of the bioaccumulation processes.Metal tolerant plants have the ability to survive and reproduce on soils containing high concentrations of metals in forms that are toxic or inimical to other plants (Macnair and Baker, 1994). Metalhyperaccumulating plants have the additional property of storing large amounts of metals in their aerial parts, more than typically 10,000 g g Ϫ1 dry weight for zinc (Zn;Baker and Walker, 1990). This characteristic makes hyperaccumulators highly suitable for phytoremediation, a soft method in which plants are used for the cleanup of metal-polluted soils (Brooks, 1998;Baker et al., 2000). The genetics and the biochemical processes involved in metal uptake, transport, and storage by hyperaccumulating plants are still poorly understood, although this basic information is fundamental for the improvement of the technique (Van Der Lelie et al., 2001). Zn is one of the most important metal contaminant in industrialized countries (Nriagu and Pacyna, 1988), and numerous studies have been conducted on the species Thalspi caerulescens (Vazquez et al., 1992(Vazquez et al., , 1994Pollard and Baker, 1996;Lasat et al., 1998Lasat et al., , 2000Kü pper et al., 1999;Salt et al., 1999;Frey et al., 2000;Assunçaõ et al., 2001) and, to a lesser extent, on Arabidopsis halleri (Macnair et al., 1999;Bert e...

The diameter and size-distribution of Ni nanoparticles prepared by the decomposition of [bis(1,5-cyclooctadiene)nickel(0)] organometallic precursor dissolved in 1-alkyl-3-methylimidazolium N-bis(trifluoromethanesulfonyl) amide ionic liquids depend on the length of the alkyl side-chain of the imidazolium ring. The increase of the organization range order of the ionic liquid that increases with that of the alkyl side-chain (from n-butyl to n-hexadecyl) induces the formation of nanoparticles with a smaller diameter and size-distribution. The cubic fcc Ni nanoparticles with 4.9 +/- 0.9 to 5.9 +/- 1.4 nm in mean diameter and monomodal size-distribution thus prepared are probably composed of a small cap layer of NiO around a core of Ni metal. The contribution of the oxide layer also depends on the medium i.e. the metal oxide ratio increases in salts containing four to eight carbons on their side-chains and then decreases as the number of carbons increases. The Ni nanoparticles dispersed in the ionic liquids are active catalysts for the hydrogenation of olefins under relatively mild reaction conditions.

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