Olivier Grauby

Nano to macroscale biomineral architecture of red coral (Corallium rubrum)

Abstract Different techniques have been used to characterize the physical and chemical structure of the red coral calcitic skeleton. A section normal to the axis of the skeleton shows a medullar zone surrounded by a circular domain composed of concentric rings. Growth rings are revealed by the cyclic variation of organic matter (OM) and Mg/Ca ratio. These growth rings are annual; thus, both OM and Mg/Ca ratio can be used to date red coral colonies. Growth rings display wavelets. The internal structure of each wavelet results from the stacking of layers with tortuous interfaces. Tortuosity is due to the presence of microprotuberances. Interfaces between layers may display sharp discontinuities indicative of interruption of the mineralizing process. SEM and TEM studies show that each layer is made of (1) fibers, organized or not in fan-shaped structures; and (2) submicrometer (apparently mono-) crystalline units. Fibers are superstructures made of submicrometer units possibly assembled by an oriented aggregation mechanism. HRTEM studies show that in spite of displaying single-crystal scattering behavior, the submicrometer crystalline units are made of 2-5 nm nanograins again possibly aggregated by a mechanism of oriented attachment. Thus, submicrometer crystalline units and polycrystalline fibers can be both defined as mesocrystals. The red coral skeleton is a hierarchically organized organic-inorganic composite that exhibits porosity and structural and compositional order on length scales from the nanoscale to the macroscale.

Hydrothermal synthesis (250 degrees C) of copper-substituted kaolinites

To obtain Cu-kaolinites with a controlled range of chemical compositions, syntheses were performed by hydrothermally ageing gels with kaolinite stoichiometric compositions. Gels were prepared with sodium metasilicate and nitrates of octahedral cations. Temperature of synthesis was 250°C with a corresponding equilibrium water pressure of 38 bars.Three samples with copper contents ranging from 0.1 to 7% and another one with the chemical composition of the Cu end-member were synthesized. While this fourth sample led to tenorite after the hydrothermal treatment, the three others crystallized well into kaolinite.Up to almost 1% CuO was measured by TEM in some isolated ‘clean’ and hexagonal kaolinite particles. EPR and XPS spectroscopies were consistent with an octahedral position of Cu2+. In IR spectra, υAl-OH-Cu absorption bands were not observed, but υAl2OH bands appeared more and more blurred when Cu content of samples increased. Weak bands situated at 868 cm−1 and 840 cm−1 are tentatively attributed to δAlCuOH. By differential thermal analysis, a downward shift of 20°C in temperature of the endothermic peak from the less Cu-rich sample to the most Cu-rich one, argued for the existence of some Al-OH-Cu bonds, whose binding energies are presumed to be less than the Al-OH-Al ones.In view of these results, Cu2+ appears incorporated in the octahedral sheet of kaolinite. Moreover, this incorporation is made without major perturbation of the kaolinite structure.

Onion morphology and microstructure of polyhedral serpentine

Abstract We describe the shape and internal structure of polyhedral spheroids found in serpentinized peridotites. Serpentine spheroids resemble geodesic domes made of ~160 to 180 triangular facets. At facet edges, the nested layers bend by ~14° along their three <010> crystallographic directions, resulting in an onion-like structure with lateral continuity of the layers. The stacking of the serpentine layers within sectors is controlled by interlayer bonding. These polyhedral onions correspond to a novel type of spherical nanostructure for layered materials.

Biomineralization in Newly Settled Recruits of the Scleractinian Coral Pocillopora damicornis

Calcium carbonate biomineralization of scleractinian coral recruits is fundamental to the construction of reefs and their survival under stress from global and local environmental change. Establishing a baseline for how normal, healthy coral recruits initiate skeletal formation is, therefore, warranted. Here, we present a thorough, multiscale, microscopic and spectroscopic investigation of skeletal elements deposited by Pocillopora damicornis recruits, from 12 h to 22 days after settlement in aquarium on a flat substrate. Six growth stages are defined, primarily based on appearance and morphology of successively deposited skeletal structures, with the following average formation time‐scales: A (<24 h), B (24–36 h), C (36–48 h), D (48–72 h), E (72–96 h), and F (>10 days). Raman and energy dispersive X‐ray spectroscopy indicate the presence of calcite among the earliest components of the basal plate, which consist of micrometer‐sized, rod‐shaped crystals with rhomboidal habit. All later CaCO3 skeletal structures are composed exclusively of aragonite. High‐resolution scanning electron microscopy reveals that, externally, all CaCO3 deposits consist of <100 nm granular units. Fusiform, dumbbell‐like, and semispherulitic structures, 25–35 µm in longest dimension, occur only during the earliest stages (Stages A–C), with morphologies similar to structures formed abiotically or induced by organics in in vitro carbonate crystallization experiments. All other skeletal structures of the basal plate are composed of vertically extending lamellar bundles of granules. From Stage D, straight fibrils, 40–45 nm in width and presumably of organic composition, form bridges between these aragonitic bundles emerging from the growing front of fusing skeletal structures. Our results show a clear evolution in the coral polyp biomineralization process as the carbonate structures develop toward those characterizing the adult skeleton. J. Morphol. 275:1349–1365, 2014.

Multi-scale mineralogical characterization of the hypercalcified sponge Petrobiona massiliana (Calcarea, Calcaronea)

The massive basal skeleton of a few remnant living hypercalcified sponges rediscovered since the 1960s are valuable representatives of ancient calcium carbonate biomineralization mechanisms in basal Metazoa. A multi-scale mineralogical characterization of the easily accessible Mediterranean living hypercalcified sponge belonging to Calcarea, Petrobiona massiliana (Vacelet and Lévi, 1958), was conducted. Oriented observations in light and electron microscopy of mature and growing areas of the Mg-calcite basal skeleton were combined in order to describe all structural levels from the submicronic to the macroscopic scale. The smallest units produced are ca. 50-100nm grains that are in a mushy amorphous state before their crystallization. Selected area electron diffraction (SAED) further demonstrated that submicronic grains are assembled into crystallographically coherent clusters or fibers, the latter are even laterally associated into single-crystal bundles. A model of crystallization propagation through amorphous submicronic granular units is proposed to explain the formation of coherent micron-scale structural units. Finally, XRD and EELS analyses highlighted, respectively, inter-individual variation of skeletal Mg contents and heterogeneous spatial distribution of Ca ions in skeletal fibers. All mineralogical features presented here cannot be explained by classical inorganic crystallization principles in super-saturated solutions, but rather underlined a highly biologically regulated formation of the basal skeleton. This study extending recent observations on corals, mollusk and echinoderms confirms that occurrence of submicronic granular units and a possible transient amorphous precursor phase in calcium carbonate skeletons is a common biomineralization strategy already selected by basal metazoans.

Biomineralization in living hypercalcified demosponges: Toward a shared mechanism?

Massive skeletons of living hypercalcified sponges, representative organisms of basal Metazoa, are uncommon models to improve our knowledge on biomineralization mechanisms and their possible evolution through time. Eight living species belonging to various orders of Demospongiae were selected for a comparative mineralogical characterization of their aragonitic or calcitic massive basal skeleton. The latter was prepared for scanning and transmission electron microscopy (SEM and TEM), selected-area electron diffraction (SAED) and X-ray diffraction (XRD) analyses. SEM results indicated distinctive macro- and micro-structural organizations of the skeleton for each species, likely resulting from a genetically dictated variation in the control exerted on their formation. However, most skeletons investigated shared submicron to nano-scale morphological and crystallographical patterns: (1) single-crystal fibers and bundles were composed of 20 to 100nm large submicronic grains, the smallest structural units, (2) nano-scale likely organic material occurred both within and between these structural units, (3) {110} micro-twin planes were observed along aragonitic fibers, and (4) individual fibers or small bundles protruded from the external growing surface of skeletons. This comparative mineralogical study of phylogenetically distant species brings further evidence to recent biomineralization models already proposed for sponges, corals, mollusks, brachiopods and echinoderms and to the hypothesis of the universal and ancestral character of such mechanisms in Metazoa.

N‐Substituted Azacalixphyrins: Synthesis, Properties, and Self‐Assembly

Pre- and postintroduction of substituents with respect to the macrocyclization step leads to previously unknown N-substituted azacalixphyrins. The stepwise synthetic approach has been studied in detail to highlight the key role of the N-substituents of the precursors and/or intermediates in terms of reactivity. Based on a combined experimental and theoretical investigation, the relationship between the properties of the macrocycles and their degree of substitution is rationalized. Depending on the nature of the N-substituents, the formation of supramolecular ribbon-like structures could also be observed, as demonstrated by combined TEM, SEM, AFM, and FTIR experiments.

Impact of swelling clays on the spalling decay of building limestones: insights from X-ray diffraction profile modeling

Abstract:IntheProvenceregion(south-easternFrance),alargepartofthebuildingheritagewaserectedusingabioclasticlimestonecalled ‘‘Pierre du Midi’’. Under this common name, the heterogeneity of the material and, specifically, its stability upon climaticexposure depend on the actual extraction location. In some cases, building stones are affected by spalling decay which is commonlyrelated to the presence of clay minerals although without quantitative support. The present study aims at characterizing andquantifying the clay mineralogy of eight ‘‘Pierre du Midi’’ samples showing various spalling degrees.The combination of transmission electron microscopy (TEM) coupled to energy-dispersive X-ray spectrometer (EDX) and of X-ray diffraction (XRD) full-profile modeling of 00‘ reflections patterns is used for quantitative phase analysis. Identification of clayminerals present in the , 4 mm fractions is performed on the basis of qualitative analysis of experimental XRD patterns recorded inbothair-dried(AD)andglycolated(EG)states.Thecrystal-chemistryofclaymineralsisthenrefinedfromTEM-EDXanalyseswhichare used as an essential constraint for the modeling of both AD and EG XRD patterns.Theresultshighlightthatthecomplexclaymineralogyoflimestonescanbeunraveledandquantifiedwhenusingthepresentcoupledapproach.Finally,thecontrastingsensitivityofsamplestospallingdecaycanbeexplainedbytheoverallproportionofexpandablelayers,essentiallypresent inFe-rich mixed-layers,inthe clayfraction.A content ofexpandable layers higherthan0.80 wt. % resultsina highsensitivitytospallingdecay,whereas rocks withlessthan0.20wt. % ofexpandablelayersremainessentially unaffected.Key-words: clay minerals; building stone; spalling decay; XRD profile modeling; TEM-EDX; mixed layer minerals; intra-crystalswelling; Fe-montmorillonite.

Photoactivated cyclization of aryl-containing enediynes coated gold nanoparticles: enhancement of the DNA cleavage ability of enediynes.

Two novel enediynes containing an aromatic ring and substituted by two thiol functions as end-groups were designed and studied as functionalizing agent of gold nanoparticles. Phototriggered cyclization of the capping agent under UV-visible irradiation was investigated. Interestingly, the length of the thiol-substituted chain was shown to influence significantly the cyclization rate. Depending on the length of the spacer, either polymerization or simple cyclization of the coating agent was evidenced. The present study underscores the possibility of finely controlling the fate of the coating agent (polymerization/cyclization). Nanocomposites were characterized by UV-visible absorption spectroscopy, dynamic light scattering (DLS) technique and transmission electron microscopy (TEM) measurements. Finally, the ability of the colloidal solutions to induce photoinitiated damages to PcDNA3 supercoiled DNA was evaluated. Interestingly, an increase as high as 50% of the DNA cleavage could be registered when adding enediynes-capped gold nanoparticles to solutions of enediynes. In particular, the enhancement of DNA scission was observed in both thermal and photochemical activation modes.

TEM-assisted dynamic scanning force microscope imaging of (001) antigorite: Surfaces and steps on a modulated silicate

Abstract Ultra-high vacuum dynamic scanning force microscopy (dynamic SFM) has been performed on in situ cleaved and as-grown (001) surfaces of low-T, m = 18 and m = 20, antigorite from the Kovdor Mine, Russia. The internal microstructure of the same crystal before cleavage has been checked by conventional TEM on FIB-cut cross-sections. The structural wave is imaged by dynamic SFM with a ~0.25 nm topographic amplitude (outcropping tetrahedral sheet) on cleaved and as-grown surfaces, and with a ~0.5 nm topographic amplitude (outcropping tetrahedral + octahedral sheets) mostly found on cleaved surfaces. Atomic resolution imaging was successfully applied on the cleavage surface through imaging individual atomic features on the outer hexagonal net of the emerging (Mg, O, OH) octahedra of the half-wave. The antigorite cleavage crack undulates through a single octahedral sheet, thereby avoiding rupture of strong Si-O bonds. The two tetrahedral reversals, which form the edges of the modulation repeat, are found to be strongly non-equivalent in structure: across <010>, one reversal is sharp as expected from the standard models of the antigorite structure, whereas the other reversal is unexpectedly “extended.” The latter suggests some scheme of anti-polar positioning of silicate tetrahedra along <010> at the 6-membered ring reversal. High-resolution transmission electron microscopy (HRTEM) structure imaging of antigorite viewed down to <010> confirms spread out electron densities at this reversal. Numerous step height measurements on (001) surfaces show incremental results as integral multiples of 0.25 nm, the spacing between O,OH surfaces along c*. Many of them differ in height from integral multiples of the unit cell repeat along c* and could be explained from carving the bulk wave structure. For all surfaces and steps, local stoichiometry and global electro-neutrality of the surface are satisfied.