Odile Hénin

Release of trace elements in wetlands: role of seasonal variability.

Dissolved concentrations were determined for Fe, Mn, Al, Cu, Zn, La, U, Th, Cd and As in a wetland and its recipient stream to reveal the effect of seasonal changes in environmental conditions on the cycling and transfer of trace elements at the transition between terrestrial and aquatic ecosystems. These preliminary results from the wetland show marked seasonal changes in dissolved concentration for all elements except Zn and Cu. Concentrations are found to be low until about mid-February and then increase abruptly. The onset of trace element release appears to coincide with a marked decline in redox potential and increase of organic carbon content. Because this decline is itself correlated with a pronounced increase in temperature and dissolved Fe. Mn and organic carbon content, we suggest that the microorganisms which use soil iron and manganese oxy-hydroxides as electron acceptors catalyzed the change in redox conditions and induced an increase of DOC. Temporal changes were also observed in the recipient stream which showed marked positive concentration peaks during stormflow events (except Zn). The seasonal processes occurring in the wetland appear to play a major role in determining the amount of trace elements which are transferred from the wetland to the river.

Exposure of amino acids and derivatives in the Earth orbit

Abstract Amino acids and amino acid derivatives were exposed to space conditions in Earth orbit as part of the ESA BIOPAN-2 mission to test the possible delivery of extraterrestrial biological building blocks to the primitive Earth. During the Biopan-2 mission, four proteinaceous amino acids (glycine, aspartic acid, glutamic acid and tyrosine), some amino acid esters and two peptides were exposed in Earth orbit for 10 days. Samples were exposed to vacuum and to solar radiation down to 120 nm both alone or associated with montmorillonite as dry films deposited on MgF2 windows. The compounds recovered after the flight were analysed in order to assess chemical degradation, racemization and polymerization. The results confirmed the absence of racemization of the exposed molecules and the high sensitivity of acidic amino acids towards UV radiation already observed in the Biopan-1 exposure mission. Reducing the thickness of the films revealed unexpected sensitivities of exposed amino acids and peptides. A slight protecting effect was observed when the samples were embedded in 5 μm thick montmorillonite films. Several amino acid esters were also exposed to study their possible polymerization in space. Their stability and reactivity in space conditions were compared. Significant degradation was observed for exposed unprotected samples implying that some kind of protection is needed to ensure any amino acid survival in space. Montmorillonite provided some protection but is not an ideal shielding material.

Zinc-Induced Conformational Transitions of Acidic Peptides: Characterization by Circular Dichroism and Electrospray Mass Spectrometry

The addition of Zn2+to (Asp-Leu)n and (Leu-Asp-Asp-Leu)n-Asp, which adopt a random coil conformation in pure water, induces a β-sheet and an α-helix structure, respectively. These conformational transitions are dependent on the chain length. The self-association of α-helices as a function of the temperature was studied by CD spectroscopy. The number of Zn2+ ions bound by the peptides was observed to be less than the theoretically expected value.

Covalent binding of mannosyl ligand via 6-O position and glycolic arm to target a PLCA-type degradable drug carrier toward macrophages

Mononuclear phagocytes play a central role in the defense against important pathologies. Attempts were made to target drugs toward this cell type by using specific interactions between a mannose ligand and the lectin-type specific receptor present on the macrophage membrane. Basically, the use of a mannosyl radical as a homing device raised several problems: necessity to keep unmodified the part of the molecule which gives rise to lectin recognition, complex protection-deprotection chemistry, and blockage of the aldehyde function to preclude any side reaction. A new method was used to bind α-D-methylmannopy-ranoside, a commercially available precursor, through its primary hydroxyl group to the hydrosoluble bioresorbable drug carrier poly(L-lysine citramide imide). The method consisted of a few steps that did not require special protection of secondary hydroxyl groups. In the resulting conjugate, the pyranose structure of the sugar was retained. In vivo recognition of the conjugate by the lectin of mononuclear phagocytes was preserved.