Biomedical subjects

Jean Susini

Publications and source records attributed to Jean Susini.

10 recordsLinked to original sources

PubMed2006

Mineralogy and petrology of comet 81P/Wild 2 nucleus samples.

The bulk of the comet 81P/Wild 2 (hereafter Wild 2) samples returned to Earth by the Stardust spacecraft appear to be weakly constructed mixtures of nanometer-scale grains, with occasional much larger (over 1 micrometer) ferromagnesian silicates, Fe-Ni sulfides, Fe-Ni metal, and accessory phases. The very wide range of olivine and low-Ca pyroxene compositions in comet Wild 2 requires a wide range of formation conditions, probably reflecting very different formation locations in the protoplanetary disk. The restricted compositional ranges of Fe-Ni sulfides, the wide range for silicates, and the absence of hydrous phases indicate that comet Wild 2 experienced little or no aqueous alteration. Less abundant Wild 2 materials include a refractory particle, whose presence appears to require radial transport in the early protoplanetary disk.

Journal Article↗

PubMed2006

Elemental compositions of comet 81P/Wild 2 samples collected by Stardust.

We measured the elemental compositions of material from 23 particles in aerogel and from residue in seven craters in aluminum foil that was collected during passage of the Stardust spacecraft through the coma of comet 81P/Wild 2. These particles are chemically heterogeneous at the largest size scale analyzed ( approximately 180 ng). The mean elemental composition of this Wild 2 material is consistent with the CI meteorite composition, which is thought to represent the bulk composition of the solar system, for the elements Mg, Si, Mn, Fe, and Ni to 35%, and for Ca and Ti to 60%. The elements Cu, Zn, and Ga appear enriched in this Wild 2 material, which suggests that the CI meteorites may not represent the solar system composition for these moderately volatile minor elements.

Journal Article↗

PubMed2006

Blackening of Pompeian cinnabar paintings: X-ray microspectroscopy analysis.

Red Pompeian paintings, very famous for their deep intensity, are currently suffering from darkening. The origins of this darkening degradation are not clearly identified yet and remain a major issue for curators. In the specific case of cinnabar (HgS)-based red pigment, a photoinduced conversion into black metacinnabar is usually suspected. This work is focused on the blackening of red cinnabar paintings coated on a sparry calcite mortar. Different samples exhibiting different levels of degradation were selected upon visual observations and analyzed by synchrotron-based microanalytical techniques. Atomic and molecular compositions of the different debased regions revealed two possible degradation mechanisms. On one hand, micro X-ray fluorescence elemental maps show peculiar distributions of chlorine and sulfur. On the other hand, X-ray absorption spectroscopy performed at both Cl and S K-edges confirms the presence of characteristic degradation products: (i) Hg-Cl compounds (e.g., corderoite, calomel, and terlinguaite), which may result from the reaction with exogenous NaCl, in gray areas; (ii) gypsum, produced by the calcite sulfation, in black coatings. Metacinnabar is never detected. Finally, a cross section was analyzed to map the in-depth alteration gradient. Reduced and oxidized sulfur distributions reveal that the sulfated black coating consists of a approximately 5-mum-thick layer covering intact cinnabar.

Journal Article↗

PubMed2006

Microstructure and chemical composition of giant avian eggshells.

The microstructure and composition of the layers of two giant avian eggshells were investigated using a combination of scanning electron microscopy, electron probe microanalyses, and X-ray absorption near-edge structure spectroscopy (XANES). The two species have some similarities and differences in their microstructure and composition; the composition is not homogeneous throughout the eggshell thickness. XANES studies show that sulfur is associated with amino acids in the inner organic membranes, whereas in the mineralised layers the sulfur is mainly associated with sulfated polysaccharides. These results are similar to those obtained on chicken eggshells, and confirm the active role of sulfated acidic polysaccharides in biomineralisation processes of carbonate skeletons.

Animals↗

PubMed2005

Chromium oxidation state imaging in mammalian cells exposed in vitro to soluble or particulate chromate compounds.

Hexavalent chromium compounds are known carcinogens for the respiratory tract in humans. The mechanism of cell transformation by hexavalent chromium compounds is not fully understood although a role for intracellular reduction is sought. The aim of this study was to determine the distribution of Cr valence states in human cells after in vitro exposure to soluble or particulate chromium compounds. A synchrotron X-ray-based microprobe was used to investigate the cellular reduction of Cr(VI) and to image chromium oxidation states in cells. It was shown that soluble Cr(VI) compounds are fully reduced to Cr(III) in cells. Cr(III) is homogeneously distributed within the cell volume and therefore present within the nucleus. In the case of low solubility particulate chromate compounds, Cr(VI) can coexist in the cell environment, as particles in the perinuclear region, together with intracellular and intranuclear Cr(III). Chemical distribution maps also suggest that intracellular Cr(III) originates from extracellular dissolution and reduction of lead chromate rather than from intracellular engulfed particles. The possible stronger carcinogenicity of low solubility chromate vs soluble chromate compounds may derive from the combinative genotoxic effects of intranuclear Cr(III) and the persistent exposure to a strong oxidant, Cr(VI).

Animals↗

PubMed2003

First insights of Cr speciation in leached Portland cement using X-ray spectromicroscopy.

X-ray spectromicroscopy has been successfully applied to determine the evolution of the Cr oxidation state in Portland cement during leaching experiments. To our knowledge, this is the first study that demonstrates the possibility to study the chromium oxidoreduction phenomena in cement materials at natural Cr concentration (approximately 60 ppm) and at the micron scale. Line scans of Cr for Cr(VI) doped (2000 ppm) and undoped samples indicate that the altered layer (0-1000 microm from the surface) is characterized by a lower amount of Cr as compared to the core part, whereas an accumulation appears in the intermediate region (1000-1300 microm). This Cr-rich interface could correspond to an accumulation of ettringite (3CaO x Al2O3 x 3CaSO4 x 32H2O) as reported by previous works. This mineral exhibits the property to incorporate Cr(III) and Cr(VI) by replacement of aluminum and sulfate, respectively, in the structure. The most surprising result concerns the evolution of the Cr(VI)/Cr(tot) ratio along the line spectra, which is constant from the altered layer to the core (both for doped and undoped samples). This means thatthe same amounts of Cr(VI) and Cr(tot) are released during leaching. Even for the undoped sample, Cr(VI) was detected in the altered layer at 40 microm from the surface. This result is not in perfect agreement with literature, which usually states that Cr(VI) is mainly leached out. Although this result must be confirmed, it clearly indicates that Cr(VI) may be less mobile than predicted by models. An attempt is made to identify potential Cr(VI) fixation phases.

Chromium↗

PubMed2003

In situ chemical speciation of sulfur in calcitic biominerals and the simple prism concept.

The microstructure and composition of two mollusc shells were investigated using a combination of light microscopy, SEM, EPMA, and XANES. The shells of Pinna and Pinctada are composed of calcite prisms separated by organic walls. The prismatic units of Pinna are monocrystalline, and those of Pinctada are polycrystalline with internal organic radial membranes. High-spatial-resolution XANES maps for the different S species across adjacent prisms show that sulfate is the principal component in both the intraprismatic organic matrices and the outer membranes. Additionally, these maps confirm that the inner structures of the prismatic units are different for both genera. In many ways, the prisms of Pinna and Pinctada are different and invalidate the "simple prism" concept.

Animals↗

PubMed2003

Bacterial diversity in hydrothermal sediment and epsilonproteobacterial dominance in experimental microcolonizers at the Mid-Atlantic Ridge.

We report here a molecular survey based on 16S rRNA genes of the bacterial diversity found in two deep-sea vent niches at the Mid-Atlantic Ridge: hydrothermal sediment (Rainbow site), and microcolonizers made of three different substrates (organic-rich, iron-rich and pumice) that were exposed for 15 days to a vent emission. Bacterial diversity in sediment samples was scattered through many bacterial divisions. The most abundant and diverse environmental sequences (phylotypes) in our libraries corresponded to the Gammaproteobacteria, followed by the Acidobacteria. We detected members of all the subdivisions within the Proteobacteria. Myxobacterial lineages were the most represented within the delta subdivision. Phylotypes ascribing to the Cytophaga-Flavobacterium-Bacteroides, Planctomycetales, high and low G + C Gram-positives, Nitrospirae, and the candidate division TM7 were also identified. Compared to this broad taxonomic coverage, microcolonizers were almost exclusively colonized by epsilonproteobacteria, although these exhibited considerable morphological and phylogenetic in-group diversity. No specificity for any of the substrates tested was seen. This observation further supports the idea of the ecological dominance of epsilonproteobacteria in the fluid-seawater interface environment. Because oxidation of reduced S species and/or sulphur-reduction is thought to be essential for their energetic metabolism in these areas, we mapped different oxidation states of S in individual bacterial filaments from the iron-rich microcolonizer. For this, we used high-resolution, non-destructive synchrotron micro-X-ray Absorption Near-Edge Spectroscopy (micro-XANES), which revealed the co-existence of different S oxidation states, from sulphide to sulphate, at the level of individual cells. This suggests that these cells were metabolizing sulphur in situ.

Atlantic Ocean↗

PubMed2002

Differential interference contrast x-ray microscopy with twin zone plates.

X-ray imaging in differential interference contrast (DIC) with submicrometer optical resolution was performed by using a twin zone plate (TZP) setup generating focal spots closely spaced within the TZP spatial resolution of 160 nm. Optical path differences introduced by the sample are recorded by a CCD camera in a standard full-field imaging and by an aperture photodiode in a standard scanning transmission x-ray microscope. Applying this x-ray DIC technique, we demonstrate for both the full-field imaging and scanning x-ray microscope methods a drastic increase in image contrast (approximately 20x) for a low-absorbing specimen, similar to the Nomarski DIC method for visible-light microscopy.

Journal Article↗

PubMed2002

Scanning x-ray microscopy of living and freeze-dried blood cells in two vanadium-rich ascidian species, Phallusia mammillata and Ascidia sydneiensis samea.

Some ascidians (sea squirts) accumulate the transitional metal vanadium in their blood cells at concentrations of up to 350 mM, about 10(7) times its concentration found in seawater. There are approximately 10 different types of blood cell in ascidians. The identity of the true vanadium-containing blood cell (vanadocyte) is controversial and little is known about the subcellular distribution of vanadium. A scanning x-ray microscope installed at the ID21 beamline of the European Synchroton Radiation Facility to visualize vanadium in ascidian blood cells. Without fixation, freezing or staining realized the visualization of vanadium localized in living signet ring cells and vacuolated amoebocytes of two vanadium-rich ascidian species, Phallusia mammillata and Ascidia sydneiensis samea. A combination of transmission and fluorescence images of signet ring cells suggested that in both species the vacuoles contain vanadium.

Animals↗