Solenn Reguer

Diffraction techniques and Vibrational spectroscopy opportunities to characterise bones

From a histological point of view, bones that allow body mobility and protection of internal organs consist not only of different organic and inorganic tissues but include vascular and nervous elements as well. Moreover, due to its ability to host different ions and cations, its mineral part represents an important reservoir, playing a key role in the metabolic activity of the organism. From a structural point of view, bones can be considered as a composite material displaying a hierarchical structure at different scales. At the nanometre scale, an organic part, i.e. collagen fibrils and an inorganic part, i.e. calcium phosphate nanocrystals are intimately mixed to assure particular mechanical properties.

Food-grade TiO 2 impairs intestinal and systemic immune homeostasis, initiates preneoplastic lesions and promotes aberrant crypt development in the rat colon

Food-grade titanium dioxide (TiO2) containing a nanoscale particle fraction (TiO2-NPs) is approved as a white pigment (E171 in Europe) in common foodstuffs, including confectionary. There are growing concerns that daily oral TiO2-NP intake is associated with an increased risk of chronic intestinal inflammation and carcinogenesis. In rats orally exposed for one week to E171 at human relevant levels, titanium was detected in the immune cells of Peyer’s patches (PP) as observed with the TiO2-NP model NM-105. Dendritic cell frequency increased in PP regardless of the TiO2 treatment, while regulatory T cells involved in dampening inflammatory responses decreased with E171 only, an effect still observed after 100 days of treatment. In all TiO2-treated rats, stimulation of immune cells isolated from PP showed a decrease in Thelper (Th)-1 IFN-γ secretion, while splenic Th1/Th17 inflammatory responses sharply increased. E171 or NM-105 for one week did not initiate intestinal inflammation, while a 100-day E171 treatment promoted colon microinflammation and initiated preneoplastic lesions while also fostering the growth of aberrant crypt foci in a chemically induced carcinogenesis model. These data should be considered for risk assessments of the susceptibility to Th17-driven autoimmune diseases and to colorectal cancer in humans exposed to TiO2 from dietary sources.

Revisiting the localisation of Zn2+ cations sorbed on pathological apatite calcifications made through X-ray absorption spectroscopy

The role of oligo-elements such as Zn in the genesis of pathological calcifications is widely debated in the literature. An essential element of discussion is given by their localisation either at the surface or within the Ca apatite crystalline network. To determine the localisation, X-ray absorption experiments have been performed at SOLEIL. The Exafs results suggest that Zn atoms, present in the Zn(2+) form, are bound to about 4 O atoms at a distance of 2.00 A, while the interatomic distance R(CaO) ranges between 2.35 A and 2.71 A. Taking into account the content of Zn (around 1000 ppm) and the difference in ionic radius between Zn(2+) (0.074 nm) and Ca(2+) (0.099 nm), a significant longer interatomic distance would be expected in the case of Zn replacing Ca within the apatite crystalline network. We thus conclude that Zn atoms are localised at the surface and not in the apatite nanocrystal structure. Such structural result has essential biological implications for at least two reasons. Some oligoelements have a marked effect on the transformation of chemical phases, and may modify the morphology of crystals. These are both major issues because, in the case of kidney stones, the medical treatment depends strongly on the precise chemical phase and on the morphology of the biological entities at both macroscopic and mesoscopic scales.

Ion specific effects on the structure of molten AF-ZrF4 systems (A+ = Li+, Na+, and K+).

The structure of AF-ZrF(4) system (A(+) = Li(+), Na(+), K(+)) compounds in the liquid state is studied using an approach combining EXAFS spectroscopy with molecular dynamics simulations. A very good agreement is observed between the two techniques, which allows us to propose a quantitative description of the liquids. From the Zr(4+) solvation shell point of view, we observe a progressive stabilization of the 7-fold and then of the 6-fold coordinated complexes when passing from Li(+) to Na(+) and K(+) as a counterion. Particular attention is given to the systems consisting of 35 mol % of ZrF(4). At that particular composition, the ZrF(6)(2-) complex predominates largely whatever the nature of the alkali. The calculated vibrational properties of this complex are in excellent agreement with a previous Raman spectroscopy experiment on molten KF-ZrF(4). The most important differences are observed for the lifetime of these octahedral units, which increases importantly with the size of the monovalent cation. On a larger scale, an intense first sharp diffraction peak is observed for the Zr(4+)-Zr(4+) partial structure factor, which can be attributed to the correlations between the octahedral units formed.

The pathogenesis of Randall's plaque: a papilla cartography of Ca compounds through an ex vivo investigation based on XANES spectroscopy.

At the surface of attached kidney stones, a particular deposit termed Randalls plaque (RP) serves as a nucleus. This structural particularity as well as other major public health problems such as diabetes type-2 may explain the dramatic increase in urolithiasis now affecting up to 20% of the population in the industrialized countries. Regarding the chemical composition, even if other phosphate phases such as whitlockite or brushite can be found as minor components (less than 5%), calcium phosphate apatite as well as amorphous carbonated calcium phosphate (ACCP) are the major components of most RPs. Through X-ray absorption spectroscopy performed at the Ca K-absorption edge, a technique specific to synchrotron radiation, the presence and crystallinity of the Ca phosphate phases present in RP were determined ex vivo. The sensitivity of the technique was used as well as the fact that the measurements can be performed directly on the papilla. The sample was stored in formol. Moreover, a first mapping of the chemical phase from the top of the papilla to the deep medulla is obtained. Direct structural evidence of the presence of ACCP as a major constituent is given for the first time. This set of data, coherent with previous studies, shows that this chemical phase can be considered as one precursor in the genesis of RP.

Very first tests on SOLEIL regarding the Zn environment in pathological calcifications made of apatite determined by X-ray absorption spectroscopy

This very first report of an X-ray absorption spectroscopy experiment at Synchrotron SOLEIL is part of a long-term study dedicated to pathological calcifications. Such biological entities composed of various inorganic and/or organic compounds also contain trace elements. In the case of urinary calculi, different papers already published have pointed out that these oligo-elements may promote or inhibit crystal nucleation as well as growth of mineral. Use of this analytical tool specific to synchrotron radiation, allowing the determination of the local environment of oligo-elements and thus their occupation site, contributes to the understanding of the role of trace elements in pathological calcifications.

Large-ion lithophile elements delivered by saline fluids to the sub-arc mantle

Geochemical signatures of arc basalts can be explained by addition of aqueous fluids, melts, and/or supercritical fluids from the subducting slab to the sub-arc mantle. Partitioning of large-ion lithophile elements between aqueous fluids and melts is crucial as these two liquid phases are present in the sub-arc pressure-temperature conditions. Using a micro-focused synchrotron X-ray beam, in situ X-ray fluorescence (XRF) spectra were obtained from aqueous fluids and haplogranite or jadeite melts at 0.3 to 1.3xa0GPa and 730°C to 830°C under varied concentrations of (Na, K)Cl (0 to 25xa0wt.%). Partition coefficients between the aqueous fluids and melts were calculated for Pb, Rb, and Sr (DPb,Rb,Srfluid/melt). There was a positive correlation between DPb,Rb,Srfluid/melt values and pressure, as well as DPb,Rb,Srfluid/melt values and salinity. As compared to the saline fluids with 25xa0wt.% (Na, K)Cl, the Cl-free aqueous fluids can only dissolve one tenth (Pb, Rb) to one fifth (Sr) of the amount of large-ion lithophile elements when they coexist with the melts. In the systems with 13 to 25xa0wt.% (Na, K)Cl, DPb,Rbfluid/melt values were greater than unity, which is indicative of the capacity of such highly saline fluids to effectively transfer Pb and Rb. Enrichment of large-ion lithophile elements such as Pb and Rb in arc basalts relative to mid-oceanic ridge basalts (MORB) has been attributed to mantle source fertilization by aqueous fluids from dehydrating oceanic plates. Such aqueous fluids are likely to contain Cl, although the amount remains to be quantified.

X-ray Photochemistry of Prussian Blue Cellulosic Materials: Evidence for a Substrate-Mediated Redox Process.

Beside its promising applications in the design of multifunctional materials, batteries and biosensors, the pigment Prussian blue is still studied in heritage science because of its capricious fading behavior due to a complex light-induced redox mechanism. We studied model heritage materials composed of Prussian blue embedded into a cellulosic fiber substrate by means of X-ray absorption near-edge spectroscopy. Significant X-ray radiation damage was observed and characterized. X-ray radiation induced first a reduction of Prussian blue, in a similar way to what visible light does, followed by a complete degradation of the pigment and the formation of iron(III) oxyhydroxide. We took advantage of this X-ray photochemistry to investigate in depth the redox behavior of Prussian blue. We could particularly demonstrate that the rate, extent, and quality of Prussian blue photoreduction can be tuned by modifying the pH and alkali cation content of the cellulosic substrate. The present study represents a step further in the understanding of Prussian blue heritage materials from an electrochemical viewpoint and provides evidence of substrate-mediated photochemistry applicable to a wider class of Prussian blue composite materials.

Light and Anoxia Fading of Prussian Blue Dyed Textiles

Although Prussian blue is a popular pigment, its stability has been questioned since its discovery in 1704. Its stability upon exposure to light and anoxia remains difficult to apprehend. The present paper focuses on the relative influences of light, anoxia and type of substrate on the discoloration of Prussian blue dyed textiles. Spectrophotometry and X-ray absorption spectroscopy measurements of samples artificially aged by light in air or anoxia show that both the extent of the reduction process at the origin of Prussian blue discoloration and the aging of the textile substrate are linked and strongly differ with the environment. The complex inter-relationship existing between Prussian blue discoloration and textile degradation and the final impact it may have on the conservation of the entire system is discussed.

Strontium speciation in archaeological otoliths

Fish otoliths (“ear stones”) are major environmental indicators used in ecology and fisheries sciences. Otoliths consist of a biomineral material containing an organically-templated mineral calcium carbonate, normally aragonite, in which strontium is incorporated at trace to minor levels depending on water chemistry and individual physiology. Sr content and fluctuations inform on the life histories of ancient specimens and provide data for palaeoenvironmental reconstructions. Identifying the impact of post-mortem alteration is a critical question to assure the reliability of such work. A central parameter for the reliability of Sr content as a palaeoenvironmental proxy is whether the mode of incorporation can be considered as stable and homogenous at the microscale in otoliths over thousands of years. In addition, it is important to know whether a different kind of speciation of Sr is observed, especially at the outer surface of the sample in contact with the soil and local environment. Here, a novel combination of synchrotron microscale point analyses and raster-scanning X-ray absorption spectroscopy is implemented and used for the first time to study otoliths at different length scales, spanning from millimetres down to micrometres. Strontium is found in substitution for calcium in aragonite in all our analyses of five Holocene otoliths and their three modern counterparts; the first set of samples from the Peruvian coast, up to 11u2006000 years old, are studied for their potential as palaeoenvironmental proxies. The chemical environment of strontium in otoliths is independent of content of this element, location in the otolith, species, and archaeological age. This is shown with a high lateral resolution (about 10 μm) over wide fields of view, as a way to consolidate macro-scale approaches. To our best knowledge, this work is the first report of the chemical environment of strontium in ancient otoliths. Our work opens the way to new approaches to validate palaeoenvironmental studies of biocarbonate paleoproxies.