Organic Sheath Research Articles

Hc-transgelin is a novel matrix protein gene involved in the shell biomineralization of triangle sail mussel (Hyriopsis cumingii)

In triangle sail mussel (Hyriopsis cumingii), shell biomineralization is a complicated process that involves multiple gene products. Shell matrix proteins are involved in the formation of the organic framework and play an important role in the regulation of calcium carbonate deposition. In this study, A new shell matrix protein gene Hc-transgelin was identified in H. cumingii. The full-length cDNA of Hc-transgelin was 1200 bp, including a 501 bp open reading frame, which encoded 166 amino acids. Hc-transgelin is rich in lysine, it accounts for 11.40% of the protein. The predicted transgelin protein contained a conserved calmodulin homologous domain. A tissue-specific expression assay indicated that Hc-transgelin exhibited significantly highest expression in the mantle. Furthermore, Hc-transgelin in situ hybridization detected positive signals at the edge of the mantle outer fold, where nacre and prismatic layer biomineralization occur. An RNA interference assay showed that the shape of aragonite flakes in nacre changed and their growth was inhibited, and cracks appeared in the prismatic layer organic sheath when the expression of Hc-transgelin was suppressed. In a shell repair assay, a higher expression of Hc-transgelin appeared from day 12 to day 25 when the nacre accumulated quickly. These findings indicate that Hc-transgelin may be involved in the formation of aragonite flakes in the nacre and play a role in the formation of the organic sheath in the prismatic layer of the shell. This study provides new insights into the role of the Hc-transgelin gene and also contributes to the molecular understanding of mollusk shell formation.

Loading Linear Arrays of CuII Inside Aromatic Amide Helices.

The very stable helices of 8‐amino‐2‐quinolinecarboxylic acid oligoamides are shown to uptake CuII ions in their cavity through deprotonation of their amide functions with minimal alteration of their shape, unlike most metallo‐organic structures which generally differ from their organic precursors. The outcome is the formation of intramolecular linear arrays of a defined number of CuII centers (up to sixteen in this study) at a 3 Å distance, forming a molecular mimic of a metal wire completely surrounded by an organic sheath. The helices pack in the solid state so that the arrays of CuII extend intermolecularly. Conductive‐AFM and cyclic voltammetry suggest that electrons are transported throughout the metal‐loaded helices in contrast with hole transport observed for analogous foldamers devoid of metal ions.

Loading Linear Arrays of CuII Inside Aromatic Amide Helices

AbstractThe very stable helices of 8‐amino‐2‐quinolinecarboxylic acid oligoamides are shown to uptake CuII ions in their cavity through deprotonation of their amide functions with minimal alteration of their shape, unlike most metallo‐organic structures which generally differ from their organic precursors. The outcome is the formation of intramolecular linear arrays of a defined number of CuII centers (up to sixteen in this study) at a 3 Å distance, forming a molecular mimic of a metal wire completely surrounded by an organic sheath. The helices pack in the solid state so that the arrays of CuII extend intermolecularly. Conductive‐AFM and cyclic voltammetry suggest that electrons are transported throughout the metal‐loaded helices in contrast with hole transport observed for analogous foldamers devoid of metal ions.

Cover Picture: Loading Linear Arrays of CuII Inside Aromatic Amide Helices (Angew. Chem. Int. Ed. 34/2021)

String-like stacks of metal ions, like tennis balls in their box, are a sought-after architecture because of the properties that may result from short distances between multiple metal centers. Ivan Huc et al. demonstrate in their Communication on page 18461 how helical aromatic foldamers enable the production of such structures and can be loaded with copper(II) centers with barely any change in their conformation, producing objects reminiscent of a wire in an organic sheath. Artwork: Victor Maurizot.

Insights into architecture, growth dynamics, and biomineralization from pulsed Sr-labelled <i>Katelysia rhytiphora</i> shells (Mollusca, Bivalvia)

Abstract. The intertidal bivalve Katelysia rhytiphora, endemic to south Australia and Tasmania, is used here for pulsed Sr-labelling experiments in aquaculture experiments to visualize shell growth at the micro- to nanoscale. The ventral margin area of the outer shell layer composed of (i) an outermost outer shell layer (oOSL) with compound composite prismatic architecture with three hierarchical orders of prisms and (ii) an innermost outer shell layer (iOSL) with crossed-acicular architecture consisting of intersecting lamellae bundles. All structural orders in both layers are enveloped by an organic sheath and the smallest mineralized units are nano-granules. Electron backscatter diffraction reveals a strong preferred orientation of the aragonite c axes perpendicular to the growth layers, while the a and b axes are scattered within a plane normal to the local growth direction and >46 % twin grain boundaries are detected. The Young's modulus shows a girdle-like maximum of elastically stiffer orientations for the shell following the inner shell surface. For 6 d, the bivalves were subjected twice to seawater with an increased Sr concentration of 18× mean ocean water by dissolving 144 µg g−1 Sr (159.88 Sr∕Ca mmol ∕ mol) in seawater. The pulse labelling intervals in the shell are 17× (oOSL) and 12× (iOSL) enriched in Sr relative to the Sr-spiked seawater. All architectural units in the shell are transected by the Sr label, demonstrating shell growth to progress homogeneously instead of forming one individual architectural unit after the other. Distribution coefficients, DSr ∕ Ca, for labelled and unlabelled shells are similar to shell proportions formed in the wild (0.12 to 0.15). All DSr ∕ Ca values are lower than values for equilibrium partitioning of Sr in synthetic aragonite.

Relict ooids off northwestern India: Inferences on their genesis and late Quaternary sea level

Relict carbonate sands dominated by ooids and faecal pellets are common on the continental shelf, between 60 and 110m, off northwestern India. The shiny tan/white aragonitic ooids closely resemble modern Bahamian ooids, with cortex thicknesses varying from <5μm to 200μm. Tangential laminae, ranging from 1μm to 20μm in diameter, occur as straight to contorted stacked tubules, similar in appearance to algal or microbial filaments. Bacteria associated with the decaying organic sheath of the laminae may have played an important role in subsequent aragonite precipitation. Bladed or radial aragonite microstructures are secondary features in the cortex, apparently formed during early diagenesis by mineralization of organic matter associated with the tangential laminae. Calibrated ages of the ooids range between 9.8 and >23kaBP, and δ18O values suggest that these relict ooids formed during cooler and drier post-LGM conditions and later during the re-intensified Holocene monsoon climate. An age vs. depth plot suggests that most of the ooids formed at water depths between ~10 and −40m, thereby calling into question whether relict shelf ooids are reliable indicators of past sea level.

Biosorption of metal elements by exopolymer nanofibrils excreted from Leptothrix cells

Leptothrix species, aquatic Fe-oxidizing bacteria, excrete nano-scaled exopolymer fibrils. Once excreted, the fibrils weave together and coalesce to form extracellular, microtubular, immature sheaths encasing catenulate cells of Leptothrix. The immature sheaths, composed of aggregated nanofibrils with a homogeneous-looking matrix, attract and bind aqueous-phase inorganics, especially Fe, P, and Si, to form seemingly solid, mature sheaths of a hybrid organic–inorganic nature. To verify our assumption that the organic skeleton of the sheaths might sorb a broad range of other metallic and nonmetallic elements, we examined the sorption potential of chemically and enzymatically prepared protein-free organic sheath remnants for 47 available elements. The sheath remnants were found by XRF to sorb each of the 47 elements, although their sorption degree varied among the elements: >35% atomic percentages for Ti, Y, Zr, Ru, Rh, Ag, and Au. Electron microscopy, energy dispersive x-ray spectroscopy, electron and x-ray diffractions, and Fourier transform infrared spectroscopy analyses of sheath remnants that had sorbed Ag, Cu, and Pt revealed that (i) the sheath remnants comprised a 5–10 nm thick aggregation of fibrils, (ii) the test elements were distributed almost homogeneously throughout the fibrillar aggregate, (iii) the nanofibril matrix sorbing the elements was nearly amorphous, and (iv) these elements plausibly were bound to the matrix by ionic binding, especially via OH. The present results show that the constitutive protein-free exopolymer nanofibrils of the sheaths can contribute to creating novel filtering materials for recovering and recycling useful and/or hazardous elements from the environment.

Multiple deformation mechanisms in the stone of a sea urchin tooth

The sea urchin tooth is a biogenic grinding tool that exhibits unique mechanical properties during food biting and rock boring, while being almost entirely composed of intrinsically brittle CaCO3 (i.e., calcite). Revealing its underlying design can broaden the potential engineering applications of low-cost, brittle structural materials (e.g., ceramics). To this end, the present study investigated the deformed stone of a Glyptocidaris crenularis tooth using transmission electron microscopy. We observed multiple deformation mechanisms associated with its structural components, i.e., the single-crystalline microfiber, meso-crystalline matrix, and organic sheath. The fiber functioned via formation of e- and r-twins, with the matrix dissipating energy mainly by crack propagation; the organic sheath located between the fiber and matrix modulated the deformation of the mineral phases, contributing to energy dissipation and damage localization of the stone component of the tooth.

Sophisticated Nanostructure in Stone Part of Sea Urchin Tooth: Enlightenment for Artificial Composites

Sea urchin teeth, which are used to scrape rocks for food, assume significant mechanical functions. Unraveling their design strategies could provide inspiration for the pursuit of high-performance artificial composites. In this work, we used scanning electron microscopy, transmission electron microscopy, and high-angle annular dark-field scanning transmission electron microscopy to probe the elaborate nanostructure in the stone part of Glyptocidaris crenularis tooth. Our results show that the mesocrystalline matrix, though diffracting as a single crystal, is composed of highly oriented nanocrystals and shares almost coincident crystal orientation with its central single-crystal fiber. Interestingly, the fiber and matrix are fitted together by numerous single-crystal nanostrips rather than being completely separated by an organic sheath. This sophisticated architecture may endow the tooth with sufficient structural stability to prevent catastrophic fractures.

Light guide lenses in trilobites?

ABSTRACTThree main types of eye have been defined in trilobites; holochroal, schizochroal and the rare abathochroal. At least in holochroal and schizochroal eyes, the lenses consist of oriented calcitic microcrystallites, the so-called trabecula, which run uninterruptedly throughout the lens from top to bottom. It is argued here that these are primary structures and not diagenetic. Holochroal eyes are commonly accepted to correspond to apposition eyes, which are the most common type of compound eyes in arthropods living today. Schizochroal eyes, present only in phacopine trilobites, are characterised by a doublet lens structure, with an aplanatic interface, correcting spherical aberration of the thick lenses to form a sharp focus for incident rays travelling parallel with the optical axis. This classic model seems to be functional for many phacopines. In these the trabecula are present, though all juxtaposed, forming a solid block. In the lenses of some phacopid species, however, the microcrystallites are separated from each other by gaps. If, during life, these gaps were filled with organic material, as the lens grew from the larval stages, or post-ecdysially, each trabeculum would be isolated from its neighbours by an organic sheath. A simple model is proposed here for the generation of the organic sheath surrounding each trabeculum. If the individual trabecula were isolated from each other, then the possibility of a new kind of visual system exists in these ‘derived’ phacopines. The differences between the refractive indexes inside and outside the trabeculum would ensure that each trabeculum acted as a light-guide, so that the whole ‘lens’ becomes a light guide bundle. This would result in a pixelled visual system, unique in the animal realm, but an archetype for modern technology of data transfer.

ChemInform Abstract: Electrochemistry of Encapsulated Redox Centers

A few examples of molecules containing a redox active core surrounded by an organic sheath have been synthesized recently. The redox nucleus may be attached covalently to the structure’s core or held there by noncovalent forces. This review article surveys the electrochemical behavior of such redox centers, emphasizing the thermodynamic and kinetic effects brought about by encapsulation.

Kevlar Functionalized Carbon Nanotubes for Next-Generation Composites

We report a sequential functionalization methodology for the covalent modification of multiwalled carbon nanotubes (MWNTs) with one and a half repeat units of the polymer poly-p-phenyleneterephthalamide (PPTA), Kevlar. Covalent attachment of PPTA monomer units, p-phenylenediamine (PDA) and terephthaloyl chloride (TPC), to the surface of MWNTs results in PPTA oligomer units forming an organic sheath around the nanotubes, PPTA-functionalized-MWNTs (PPTA-MWNTs). PPTA-MWNTs possess chemical functionality identical to that of PPTA, and thus provide nanoscale scaffolds which may be readily dispersed within a monomer solution and participate in the polymerization reaction to form a PPTA-MWNT/PPTA composite. We show that formation of PPTA in the presence of PPTA-MWNTs leads to a uniform dispersion of MWNTs within the polymer matrix, in contrast to aggregated masses of MWNTs in the case of pristine-MWNTs. The covalent attachment of oligomeric PPTA units to the surface of MWNTs represents the formation of a functio...

Needles and pins: acicular crystalline periostracal calcification in venerid bivalves (Bivalvia: Veneridae)

A scanning electron microscope study of the periostracum of 50 species of venerid bivalves revealed that periostracal calcification in the form of aragonitic needles and shorter pins is widespread within the family. Together with organic and sediment coatings that are found in some species, these needles form an integral part of the functional shell. Visible as a white ‘crust’ on the outside of shells, long slender needles (up to 400 mm long and 1 mm wide) without adherent material are seen in species of Tivela and Lioconcha and in Gomphina undulosa. Other venerids including Pitar species, Mysia undata and Compsomyax subdiaphana have short pins, capped with a fibrous organic matrix and significant coatings of sediment. Callocardia hungerfordi and Clementia papyracea have very thick sediment coatings underlain by short pins, while Gafrarium and Circe species have short pins with a thin, robust, organic coating and little particulate material. Finally, there are species, including Venus verrucosa, Chione elevata and Mercenaria mercenaria, where minute, ,1 mm long pins also underpin a thin organic coating. Details of formation were studied in Tivela lamyi and Lioconcha ornata, where the needles are elongate hexagonal crystals of aragonite enveloped by an organic sheath, which grow at their proximal ends from within the periostracum, connected to the outer mantle epithelium via narrow channels. Growth of needles ceases following the onset of shell calcification. The distribution of the periostracal structures was examined in relation to a published molecular phylogeny that recognized two major clades within the family. Larger needles and pins are confined to the clade that includes subfamilies Pitarinae, Gouldinae, Meretricinae and Petricolinae, while submicron-sized pins are found only in the Venerinae and Chioninae of the second clade. Calcified periostracal structures appear to be absent in Tapetinae and Dosiniinae.

Calcitic nanofibres in soils and caves: a putative fungal contribution to carbonatogenesis

Abstract The origin of soil mineralized nanofibres remains controversial. It is attributed to either biogenic factors or physicochemical processes. Scanning electron microscope and transmission electron microscope observations show that nanofibres could originate from the breakdown of fungal hyphae, especially its cell wall. It is hypothesized that during the decay of organic matter, cell wall microfibrils are released in the soil where they are exposed to mineralizing pore fluids, leading to their calcitic pseudomorphosis and/or are used as a template for calcite precipitation. When associated with needle fibre calcite bundles, nanofibres could indicate the relict of an organic sheath in which calcite has precipitated. This paper emphasizes the important roles of both organic matter and fungi in carbonatogenesis, and consequently in the soil carbon cycle.

A new genus of xenophyophores (Foraminifera) from Japan Trench: morphological description, molecular phylogeny and elemental analysis

The deep-sea floor is inhabited by a number of unusual and enigmatic taxa, unknown in shallow waters. These include the xenophyophores, a group of giant protists that construct fragile agglutinated tests. Here, we describe Shinkaiya lindsayigen. et sp. nov., a new xenophyophore collected by the submersible Shinkai 6500 at a depth of 5435 m near the Japan Trench. The phylogenetic analysis performed on its complete small-subunit ribosomal DNA (SSU rDNA) sequence confirms that Sh. lindsayisp. nov. is a foraminiferan that is closely related to another xenophyophore, Syringammina corbicula Richardson, 2001, and to a monothalamous (single-chambered) foraminiferan Rhizammina algaeformis Brady, 1879. In terms of morphology, the new genus resembles Syringammina, but its test wall is thicker, softer, and more weakly cemented. Moreover, the SSU rDNA sequences of the two genera are highly divergent. Mass spectra analyses reveal unusually high concentrations of some elements, such as lead, uranium, and mercury. The granellare system (the cytoplasm and the organic sheath that encloses it) is apparently devoid of barite crystals, which are usually abundant as intracellular inclusions in xenophyophores, but is rich in mercury (with 12 times the concentration of mercury found in the surrounding sediment). Fecal pellets retained within a tubular system (stercomare) concentrate heavy metals, including lead and uranium (respectively, two and six times more than that of the sediment). Based on a comparison of the compositions of the agglutinated test wall, the granellare, the stercomare, and the surrounding sediment, we discuss the impact of xenophyophores on their habitat.

One-step solid state synthesis of cappedγ-Fe2O3 nanocrystallites

The thermally induced solid state synthesis of soluble organophilic maghemite(γ-Fe2O3) nanocrystallites is described. The solvent-free one-step synthesis involves the reaction in the melt stateof Fe(NO)3·9H2O andRCOOH (R = C11H23, C15H31)at 240 °C. The method yields well-crystallized nanoparticles ofγ-Fe2O3 functionalized with the corresponding aliphatic acid. Transmission electron microscopy(TEM) and atomic force microscopy (AFM) observations reveal composite particles withfaceted magnetic cores and average size of 20 nm, which are well capped with thesurrounding organic sheath. The Fourier transform infrared (FT-IR) spectra and thermalanalysis suggest a bimodal configuration of the organic shell including chemicallycoordinated and physisorbed molecules of aliphatic acid. The chemical bonding of thecarboxylate groups to the surface iron atoms is also indicated by a paramagnetic doubletwith unchanged area in the variable temperature Mössbauer spectra. The spinelγ-Fe2O3 particles exhibit perfect structural and magnetic ordering, includingthe almost ideal ratio of octahedral to tetrahedral positions(5/3) and very low degree of spin canting, as confirmed by in-field Mössbauer spectroscopy.Magnetic measurements demonstrate the suitable properties required in various(bio)magnetic applications like superparamagnetic behavior at room temperature, highsaturation magnetization achievable at low applied fields and suppressed magneticinteractions.

Salterella and Volborthella from the Early Cambrian of Spitsbergen: the evolution of agglutinating organisms during the Neoproterozoic-Cambrian transition

The co-occurrence of the small agglutinated, conical fossils Volborthella and Salterella is documented from the Lower Cambrian Tokammane Formation of Ny Friesland, Spitsbergen. Microstructural investigations of well-preserved Volborthella tenuis Schmidt (1888), collected from the fine-grained Topiggane Shale, indicate the presence of an organic cementing matrix that may have extended around the edges of the test to form an outer organic sheath. This is clearly distinct from the carbonate cements observed in specimens of Salterella maccullochi (Murchison 1859), supporting the taxonomic validity of Volborthella and Salterella . The occurrence of both these forms in this succession may indicate a biogeographic link between the Laurentian province, where both Salterella and Volborthella are found, and the Baltic and East European Platform, where only Volborthella is reported to occur. The exclusive presence of Volborthella in the older siliciclastic Topiggane Shale Member and Salterella in the younger carbonates of the Ditlovtoppen Dolomite provides both a testable age-relation between these two forms and suggests that there may be a significant facies control on their distribution. These organisms are significant in the early history of agglutinated skeletons, especially in their use of both organic and carbonate cements significantly earlier than other Paleozoic agglutinating organisms, such as the foraminifera.

Experimental observation of magnetosome chain collapse in magnetotactic bacteria: Sedimentological, paleomagnetic, and evolutionary implications

Magnetotactic bacteria precipitate intracellular crystals of single-domain magnetite (Fe3O4) and/or greigite (Fe3S4), which have often been implicated in carrying the natural remanent magnetization (NRM) of freshwater and marine sediments. In vivo, the magnetic crystals are usually aligned in chains such that their moments add together, generating net cellular moments high enough to rotate the cells passively to align with the geomagnetic field. A magnetostatic/biophysical analysis demonstrates that this arrangement is out of dynamic equilibrium and would collapse spontaneously without a support mechanism. Past rock magnetic analyses of shallow water marine carbonates suggest that partial collapse does occur during diagenesis and dolomitization.To calibrate this effect we induced magnetosome chain collapse in Magnetospirillum magnetotacticum strain MS-1 by progressive sonification and treatment with detergents and monitored the changes with rock magnetic analysis and TEM. Although it has been speculated that the cell wall and associated membrane structures act to prevent magnetosome chain collapse, our data indicate that magnetosome linearity persists long after cells are disrupted. This is consistent with prior observations that in some magnetotcocci the magnetosome chains pass through the cell interior, precluding continuous contact with the cell wall and implying additional support structures exist in some species.Using TEM tomographic reconstructions prepared with a magnetic technique that prevents chain collapse, we examined the three dimensional ultrastructure of magnetosomes without the problem of post-mortem magnetosome motion. This method revealed the presence of an intracellular organic sheath beyond that of actin-like filaments reported recently that follows the chain of magnetosomes, which we postulate evolved to hold the crystals in place and enhances their ability to preserve NRM in sediments. As the genomes of two magnetotactic bacteria contain several apparent homologues of known eukaryotic cytoskeletal proteins, natural selection for magnetotaxis may have played a role in the evolution of precursors to the eukaryotic cytoskeleton. The presence of this sheath is also consistent with the observation of electron translucent material associated with putative magnetofossil chains in ALH84001.

A simple chemical method for the preparation of silver nanocables from self-assembling tubular Ag+precursors

A simple and efficient method for the in situ fabrication at ambient temperature of nanocables consisting of a silver core and an insulating organic shell from a self-assembling silver precursor is presented. The precursor assembles into tubular aggregates several microns in length, which template the formation of silver wires, under defined reaction conditions. Proper control of the reaction conditions, such as reagent concentrations and the method of reduction, is important in order to obtain well-defined nanocables as individual dispersed entities. These consist of 30–45 nm silver cores, 60–70 nm walls, and an aspect ratio of >200. IR spectroscopy revealed the organic sheath to be cross-linked via a bridging-type coordination to the silver ions, which helps in the formation of the tubular aggregation and provides structural rigidity.

Quantitatively Studying Nano-mechanical Properties within the Prism and Organic Sheath of Enamel

AbstractEnamel is made up of enamel prisms separated by thin layer of organic sheaths. The mechanical properties of the prisms and the organic sheaths are obviously different from each other due to different compositions and microstructures. However, quantitative measurements of such differences have been a challenge in the past. The objective of this study is to accurately study the mechanical properties in the isolated domains within single enamel prism. The technique of nanoindentation combined with Atomic Force Microscopy (AFM) was employed to test the enamel specimens from mature human maxillary third molar. It was revealed that the nanohardness and elastic modulus of the sheaths were about 73.6% and 52.7% lower than those of the prisms. AFM topographies of the residual indent impressions also visually confirmed the differences. In addition to nanoindentation tests, the microstructures of enamel were carefully investigated in terms of hierarchical levels of organization to understand the structural reasons of the mechanical differences. We found a close relation between the variations of mechanical properties of enamel and its hierarchical structure. The analysis of the mechanical properties within enamel upon hierarchy is not only helpful to understand its unique property, but may also inspire ideas for the design of novel synthetic materials.