A Nature’s Curiosity: The Argonaut “Shell” and Its Organic Content

33 pagesInternational audienceMolluscs are known for their ability to produce a calcified shell resulting from a genetically controlled and matrix-mediated process, performed extracellularly. The occluded organic matrix consists of a complex mixture of proteins, glycoproteins and polysaccharides that are in most cases secreted by the mantle epithelium. To our knowledge, the model studied here-the argonaut, also called paper nautilus-represents the single mollusc example where this general scheme is not valid: the shell of this cephalopod is indeed formed by its first dorsal arms pair and it functions as an eggcase, secreted by females only; furthermore, this coiled structure is fully calcitic and the organization of its layered microstructures is unique. Thus, the argonautid shell appears as an apomorphy of this restricted family, not homologous to other cephalopod shells. In the present study, we investigated the physical and biochemical properties of the shell of Argonauta hians, the winged argonaut. We show that the shell matrix contains unusual proportions of soluble and insoluble components, and that it is mostly proteinaceous, with a low proportion of sugars that appear to be mostly sulfated glycosaminoglycans. Proteomics performed on different shell fractions generated several peptide sequences and identified a number of protein hits, not shared with other molluscan shell matrices. This may suggest the recruitment of unique molecular tools for mineralizing the argonaut's shell, a finding that has some implications on the evolution of cephalopod shell matrices

Exposed and Buried Biomineral Interfaces in the Aragonitic Shell of <i>Perna canaliculus</i> Revealed by Solid-State NMR

A comprehensive molecular description of the inorganic–bioorganic interfaces and internal structure of the aragonitic shells of Perna canaliculus is derived by employing solid-state NMR spectroscopy. The primary component of the shell, the highly ordered aragonite polymorph of CaCO₃, is shown to possess a small fraction of disordered carbonates whose average chemical-structural identity is similar to that of aragonite. These disordered carbonates were found to interact with bioorganics, bicarbonates, and water molecules and are denoted as interfacial. Characterization of the bleached and of the annealed shells enables the distinguishing of two classes of interfacial carbonates: exposed, solvent accessible, which interact primarily with bioorganics, and buried, solvent inaccessible, which interact exclusively with spatially separated water and bicarbonates. Shell annealing shows that the decomposition of the buried bicarbonate defects correlates with removal of lattice distortions, as detected by XRD, a phenomenon often found in biogenic calcium carbonates. The solid-state NMR investigation exposes the molecular bioorganic–inorganic interfaces in a mollusk shell and demonstrates the unique capability of NMR to determine comprehensively the structure of biogenic composite materials

The shell matrix and microstructure of the Ram’s Horn squid: molecular and structural characterization.

20 pagesInternational audienceMolluscs are one of the most diversified phyla among metazoans. Most of them produce an external calcified shell, resulting from the secretory activity of a specialized epithelium of the calcifying mantle. This biomineralization process is controlled by a set of extracellular macromolecules, the organic matrix. In spite of several studies, these components are mainly known for bivalves and gastropods. In the present study, we investigated the physical and biochemical properties of the internal planispiral shell of the Ram's Horn squid Spirula spirula. Scanning Electron Microscope investigations of the shell reveal a complex microstructural organization. The saccharides constitute a quantitatively important moiety of the matrix, as shown by Fourier-transform infrared and solid-state nuclear magnetic resonance spectroscopies. NMR identified β-chitin and additional polysaccharides for a total amount of 80% of the insoluble fraction. Proteomics was applied to both soluble and insoluble matrices and in silico searches were performed, first on heterologous metazoans models, and secondly on an unpublished transcriptome of Spirula spirula. In the first case, several peptides were identified, some of them matching with tyrosinase, chitinase 2, protease inhibitor, or immunoglobulin. In the second case, 39 hits were obtained, including transferrin, a serine protease inhibitor, matrilin, or different histones. The very few similarities with known molluscan shell matrix proteins suggest that Spirula spirula uses a unique set of shell matrix proteins for constructing its internal shell. The absence of similarity with closely related cephalopods demonstrates that there is no obvious phylogenetic signal in the cephalopod skeletal matrix

Thermal conductivity-structure-processing relationships for amorphous nano-porous organo-silicate thin films

© 2019, Springer Science+Business Media, LLC, part of Springer Nature. While numerous thermal conductivity investigations of amorphous dielectrics have been reported, relatively few have attempted to correlate to the influence of processing conditions and the resulting atomic structure. In this regard, we have investigated the influence of growth conditions, post deposition curing, elemental composition, atomic structure, and nano-porosity on the thermal conductivity for a series of organo-silicate (SiOCH) thin films. Time-domain thermoreflectance (TDTR) was specifically utilized to measure thermal conductivity while the influence of growth conditions and post deposition curing on composition, mass density, atomic structure, and porosity were examined using nuclear reaction analysis (NRA), Rutherford backscattering spectroscopy (RBS), Fourier-transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), ellipsometric porosimetry (EP), and positronium annihilation lifetime spectroscopy (PALS). Analytical models describing the thermal conductivity dependence on mass density and vol% porosity were found to generally over-predict the measured thermal conductivity, but improved agreement was obtained when considering only the heat carrying network density determined by FTIR. Ashby’s semi-empirical relation, which assumes only 1/3 of the heat carrying bonds are aligned to the heat transport direction, was also found to reasonably describe the observed trends. However, the thermal conductivity results were best described via a model proposed by Sumirat (J Porous Mater 9:439 (2006)) which considers the effect of both vol% porosity and phonon scattering by nanometer sized pores. Post-deposition curing was additionally observed to increase thermal conductivity despite an increase in nano-porosity. This effect was attributed to an increase in the Si–O–Si network bonding produced by the cure