Growth Kinetics and Distribution of Trace Elements in Precious Corals

The concentration and spatial distribution of major (Ca, Mg) and trace elements (Na, Sr, S, Li, Ba, Pb, and U) in different Corallium skeletons (C. rubrum, C. japonicum, C. elatius, C. konojoi) have been studied by electron microprobe (EMP) and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). EMP data show positive Na-Mg and negative Na-S and Mg-S correlations in all skeletons. LA-ICPMS data display additional Sr-Mg, Li-Mg, and U-Mg positive correlations. Medullar zones in the skeletons, corresponding to fast growing zones, are systematically richer in Mg, Na, Sr, Li, and U and poorer in S than the surrounding slow growing zones. These spatial distributions are mostly interpreted in terms of growth kinetics combined with steric effects influencing the incorporation of impurities in biogenic calcites. This interpretation is in agreement with available experimental data on kinetic effects on the incorporation of elements in calcite. At a different scale, annual growth rings in annular slow growing zones show oscillations in Mg, Na, Sr, and S. These chemical oscillations probably result from growth rate variations: fast growth would produce rings enriched in Mg, Sr, and Na, while slow growth would produce rings enriched in Ca, S and organic matter. From previous studies in C. rubrum, the Mg-rich rings would develop during the spring to fall period while the S-rich rings would form immediately after (late fall and winter). Analytical traverses performed in annular zones of different Corallium skeletons indicate that Mg, Na, Sr, Li, and U decrease from core to rim. This observation indicates that radial growth rate decreases as the colony gets older. Contrary to Mg, Na, Sr, Li, S, and U, barium and lead concentrations are identical in medullar and annular zones and appear independent of growth kinetics. Thus, concentrations in Corallium skeletons could provide indications on Ba and Pb contents in the oceans. Barium and lead concentrations are higher in Mediterranean than in Pacific precious corals, these two elements can be used to discriminate C. rubrum from C. japonicum, and contribute enforcing regulations on the trade of precious corals

Growth kinetics and distribution of trace elements in precious corals

Vielzeuf, Daniel ... et al.-- 18 pages, 9 figures, 3 tables, supplementary material https://www.frontiersin.org/articles/10.3389/feart.2018.00167/full#supplementary-materialThe concentration and spatial distribution of major (Ca, Mg) and trace elements (Na, Sr, S, Li, Ba, Pb, and U) in different Corallium skeletons (C. rubrum, C. japonicum, C. elatius, C. konojoi) have been studied by electron microprobe (EMP) and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). EMP data show positive Na-Mg and negative Na-S and Mg-S correlations in all skeletons. LA-ICPMS data display additional Sr-Mg, Li-Mg, and U-Mg positive correlations. Medullar zones in the skeletons, corresponding to fast growing zones, are systematically richer in Mg, Na, Sr, Li, and U and poorer in S than the surrounding slow growing zones. These spatial distributions are mostly interpreted in terms of growth kinetics combined with steric effects influencing the incorporation of impurities in biogenic calcites. This interpretation is in agreement with available experimental data on kinetic effects on the incorporation of elements in calcite. At a different scale, annual growth rings in annular slow growing zones show oscillations in Mg, Na, Sr, and S. These chemical oscillations probably result from growth rate variations: fast growth would produce rings enriched in Mg, Sr, and Na, while slow growth would produce rings enriched in Ca, S and organic matter. From previous studies in C. rubrum, the Mg-rich rings would develop during the spring to fall period while the S-rich rings would form immediately after (late fall and winter). Analytical traverses performed in annular zones of different Corallium skeletons indicate that Mg, Na, Sr, Li, and U decrease from core to rim. This observation indicates that radial growth rate decreases as the colony gets older. Contrary to Mg, Na, Sr, Li, S, and U, barium and lead concentrations are identical in medullar and annular zones and appear independent of growth kinetics. Thus, concentrations in Corallium skeletons could provide indications on Ba and Pb contents in the oceans. Barium and lead concentrations are higher in Mediterranean than in Pacific precious corals, these two elements can be used to discriminate C. rubrum from C. japonicum, and contribute enforcing regulations on the trade of precious coralsThis work has been supported by the Centre National de la Recherche Scientifique (CNRS), by the Institut National des Sciences de l’Univers (INSU) through grant INTERRVIE 2017 to DV, by the Agence Nationale pour la Recherche (ANR) through ANR CoRo 2011-2015, by the Centre Interdisciplinaire de Nanoscience de Marseille (CINaM) through internal grants, and by the European Union COST action TD0903Peer Reviewe

Multilevel modular mesocrystalline organization in red coral

Biominerals can achieve complex shapes as aggregates of crystalline building blocks. In the red coral skeleton, we observe that these building blocks are arranged into eight hierarchical levels of similarly (but not identically) oriented modules. The modules in each hierarchical level assemble into larger units that comprise the next higher level of the hierarchy, and consist themselves of smaller, oriented modules. EBSD and TEM studies show that the degree of crystallographic misorientation between the building blocks decreases with decreasing module size. We observe this organization down to a few nanometers. Thus, the transition from imperfect crystallographic order at millimeter scale to nearly perfect single crystalline domains at nanometer scale is progressive. The concept of >mesocrystal> involves the three-dimensional crystallographic organization of nanoparticles into a highly ordered mesostructure. We add to this concept the notion of >multilevel modularity.> This modularity has potential implications for the origin of complex biomineral shapes in nature. A multi-level modular organization with small intermodular misorientations combines a simple construction scheme, ruled by crystallographic laws, with the possibility of complex shapes. If the observations we have made on red coral extend to other biominerals, long-range crystallographic order and interfaces at all scales may be key to how some biominerals achieve complex shapes adapted to the environment in which they growThis work has been supported by Centre National de la Recherche Scientifique (CNRS), Institut National des Sciences de l’Univers (INSU) through grants ECLIPSE 2005, INTERRVIE 2009, and by Centre Interdisciplinaire de Nanoscience de Marseille (CINaM) through internal grants to D.V.Peer Reviewe

Site-Specific Anchoring of a Flavonol Dye into Zeolite β Nanoparticles

International audienceThe structural and electronic properties of the accessible CuI site of a faujasite-type zeolite have been studied, by use of large cluster models and a density functional theory-based methodology. We demonstrate that the local ideal C3 symmetry of the CuI site II is broken. The CuI cation is bonded to the zeolite framework by one bond of about 2.26 Å and two shorter ones of 2.07 Å. We demonstrate that only one cation position exists at this site. This result is also confirmed by a molecular electrostatic potential analysis. We show that local properties at site II, as well as the global properties of the solid (frontier orbitals), do not depend on the Al and cation distribution and only slightly on the cocation nature. Taking into account the present results and well-known experimental data, we propose that specific catalytic behaviors are correlated with local response properties, such as the local acid strength or, in other reactions, specific local architecture or confinement

Flavonol dye molecules in zeolite beta nanocrystals for biodiagnostic applications

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Crystallography of Complex Forms: The Case of Octocoral Sclerites

International audienceOctocorals sclerites are ideal structures to study the emergence of complex shapes from particular arrangements of crystallites in biominerals. Sinularia polydactyla sclerites have been studied by polarizing microscopy, scanning electron microscopy, and electron backscattered diffraction. Small sclerites (<100 µm) are simple mesocrystalline structures, with similarly oriented submicrometer crystallites arranged in elongated fibers, with only a low degree of ordered misorientations between them. Large sclerites (~2 mm) are composite structures: (1) at their center, small proto-sclerites (≤ 20 µm) are present and act as nuclei around which growth proceeds. (2) The large sclerite axial frame is made of crystallites with c axes arranged in three directions, at an inclination of about 22° from the long sclerite axis. The axial frame displays a center of symmetry and crystallites are arranged in opposite trihedral arrangement with respect to this center. (3) Inside the large sclerite, deeply rooted tubercles develop with crystallite c axes close to perpendicular to the long sclerite axis. The tubercles grow by a branching process and display crystallite misorientations ordered around the three a axes of the hexagonal unit cell of calcite. Crystallites in both the frame and the tubercles form trigonal inverse pyramids resulting from sudden or progressive changes of crystallite orientations. A crystallographic model emphasizes the importance of the trigonal inverse pyramid as a structural pattern. Concerning the sclerite morphology, small crystallite sizes, ordered misorientations and mesotwinning are important features to achieve concave shapes. The sclerite surface morphology results from the regulation of mesocrystalline growth and patterning by cells or vacuoles. In this respect, the sclerite morphology is the product of internal and external forces, among which crystallographic order and molding play important roles.

Synchrotron high-resolution XRD and thermal expansion of synthetic Mg calcites

International audienceThe structural parameters and the thermal behavior of a complete series of Ca–Mg carbonates synthesized at high pressure and temperature (1–1.5 GPa, 1273–1373 K) in the range 0–50 mol% MgCO3 have been investigated by in situ powder synchrotron high-resolution X-ray diffraction at ambient and up to 1073 K under self-controlled CO2 partial pressure. The crystal structures are disordered Mg calcite in the range 1–41 mol% MgCO3, and Ca dolomite at 49 mol% MgCO3. New calibration curves of the cell parameters for the Mg content and thermal expansion from ambient to 1073 K are given. Short-range structural effects of cation substitution and ordering and their thermal behavior as a function of Mg content were identified from three sets of data: the peak broadening, the cell parameter strains and the Raman band enlargements. Both intra- and inter-crystalline levels of compositional heterogeneity are identified and allow splitting the Mg calcites into two groups: low- and high-Mg calcites. The low-Mg calcites (up to 22 mol% MgCO3) are homogeneous in Mg content with short-range ordering. High-Mg calcite (up to 41 mol% MgCO3) displays domains with different local ordering configurations and similar or slightly different Mg contents, and to which is added a compositional variation between crystals, as determined by EMP, of the order of  ± 0.8 mol% MgCO3. The cation ordering in Ca-rich dolomites similarly occurs in high-Mg synthetic calcites. The role of (CO3)2− group ordering is shown to be an important factor in the formation of Ca–Mg carbonates