How does iron interact with sporopollenin exine capsules? An X-ray absorption study including microfocus XANES and XRF imaging

Sporopollenin exine capsules (SECs) derived from plant spores and pollen grains have been proposed as adsorption, remediation and drug delivery agents. Despite many studies there is scant structural data available. This X-ray absorption investigation represents the first direct structural data on the interaction of metals with SECs and allows elucidation of their structure–property relationships. Fe K-edge XANES and EXAFS data have shown that the iron local environment in SECs (derived from Lycopodium clavatum) reacted with aqueous ferric chloride solutions is similar to that of ferrihydrite (FeOOH) and by implication ferritin. Fe Kα XRF micro-focus experiments show that there is a poor correlation between the iron distribution and the underlying SEC structure indicating that the SEC is coated in the FeOOH material. In contrast, the Fe Kα XRF micro-focus experiments on SECs reacted with aqueous ferrous chloride solutions show that there is a very high correlation between the iron distribution and the SEC structure, indicating a much more specific form of interaction of the iron with the SEC surface functional groups. Fe K-edge XANES and EXAFS data show that the FeII can be easily oxidised to give a structure similar to, but not identical to that in the FeIII case, and that even if anaerobic conditions are used there is still partial oxidation to FeIII

Vivianite-parasymplesite solid solution: A sink for arsenic in ferruginous environments?

Vivianite, a hydrated ferrous phosphate [FeII3(PO4)2 · 8 H2O] that forms in oxygen-poor, but Fe2+-rich conditions is important in nutrient cycling in anoxic environments. In natural vivianites, isomorphic substitution of divalent cations for structural Fe(II) are typical. However, anion substitution is rare; in particular, arsenate (AsVO43−) substitution has never been documented in natural vivianites. Only partial substitution has been reported in synthetic analogues, and parasymplesite [FeII3(AsO4)2 · 8 H2O], the arsenic end member of the vivianite mineral group, is found in hydrothermal deposits. In this study, we detail structural changes in synthesised As-vivianites (FeII3[(PO4)1−x(AsO4)x]2 · 8 H2O) with systematically increased degrees of As(V) substitution (0.22 ≤ x ≤ 0.95). As(V) was successfully incorporated into the vivianite crystal structure, creating a homogenous, solid solution between AsVO43− and PO43−. Like both end members, the intermediate As-vivianites crystallised in the monoclinic system (C2/m space group), and retained the platelet crystal habit of As-free vivianite, even at the highest As(V) substitution. This uniform incorporation of As(V), and its replacement of PO43−, provides a potentially stable sink for arsenic in anoxic soils and sediments, and may have implications in ferruginous early Earth oceans

Computational study of structural and elastic properties of random AlGaInN alloys

In this work we present a detailed computational study of structural and elastic properties of cubic AlGaInN alloys in the framework of Keating valence force field model, for which we perform accurate parametrization based on state of the art DFT calculations. When analyzing structural properties, we focus on concentration dependence of lattice constant, as well as on the distribution of the nearest and the next nearest neighbour distances. Where possible, we compare our results with experiment and calculations performed within other computational schemes. We also present a detailed study of elastic constants for AlGaInN alloy over the whole concentration range. Moreover, we include there accurate quadratic parametrization for the dependence of the alloy elastic constants on the composition. Finally, we examine the sensitivity of obtained results to computational procedures commonly employed in the Keating model for studies of alloys

Do ‘passive’ medical titanium surfaces deteriorate in service in the absence of wear?

Globally, more than 1000 tonnes of titanium (Ti) is implanted into patients in the form of biomedical devices on an annual basis. Ti is perceived to be ‘biocompatible’ owing to the presence of a robust passive oxide film (approx. 4 nm thick) at the metal surface. However, surface deterioration can lead to the release of Ti ions, and particles can arise as the result of wear and/or corrosion processes. This surface deterioration can result in peri-implant inflammation, leading to the premature loss of the implanted device or the requirement for surgical revision. Soft tissues surrounding commercially pure cranial anchorage devices (bone-anchored hearing aid) were investigated using synchrotron X-ray micro-fluorescence spectroscopy and X-ray absorption near edge structure. Here, we present the first experimental evidence that minimal load-bearing Ti implants, which are not subjected to macroscopic wear processes, can release Ti debris into the surrounding soft tissue. As such debris has been shown to be pro-inflammatory, we propose that such distributions of Ti are likely to effect to the service life of the device

Processing–structure–property relations of chemically bonded phosphate ceramic composites

ABSTRACT: Mechanical properties and microstructures of a chemically bonded phosphate ceramic (CBPC) and its composite with 1⋅0 wt% graphite nanoplatelets (GNPs) reinforcement have been investigated. Microstructure was identified by using optical and scanning electron microscopes, X-ray tomography, and X-ray diffraction. In addition, weight loss of the resin at room temperature was studied. The microstructure characterization shows that CBPC is itself a composite with several crystalline (wollastonite and brushite) and amorphous phases. SEM and micro tomography show a homogeneous distribution of crystalline phases. Bending and compression strength of the CBPC was improved by reducing bubbles via preparation in vacuum

Cytotoxic activity of tumor necrosis factor is inhibited by amiloride derivatives without involvement of the Na+/H+ antiporter

AbstractCytotoxicity of tumor necrosis factor (TNF) on L929s cells was efficiently blocked by several amiloride analogs but not by amiloride itself. This protection did not require RNA or protein synthesis. Na+/H+ antiporter-negative L-M(TK−) cells (LAP) could be killed by TNF, showing that the Na+/H+ exchanger is not required for TNF-cytotoxicity. Similar protection against TNF-mediated cell lysis by amiloride derivatives was found for LAP and L929s cells, excluding a blockade of the Na+/H+ antiporter as the cause of the protection against TNF by these agents

Characterisation of carapace composition in developing and adult ostracods (Skogsbergia lerneri) and its potential for biomaterials

The protective carapace of Skogsbergia lerneri, a marine ostracod, is scratch-resistant and transparent. The compositional and structural organisation of the carapace that underlies these properties is unknown. In this study, we aimed to quantify and determine the distribution of chemical elements and chitin within the carapace of adult ostracods, as well as at different stages of ostracod development, to gain insight into its composition. Elemental analyses included X-ray absorption near-edge structure, X-ray fluorescence and X-ray diffraction. Nonlinear microscopy and spectral imaging were performed to determine chitin distribution within the carapace. High levels of calcium (20.3%) and substantial levels of magnesium (1.89%) were identified throughout development. Amorphous calcium carbonate (ACC) was detected in carapaces of all developmental stages, with the polymorph, aragonite, identified in A-1 and adult carapaces. Novel chitin-derived second harmonic generation signals (430/5 nm) were detected. Quantification of relative chitin content within the developing and adult carapaces identified negligible differences in chitin content between developmental stages and adult carapaces, except for the lower chitin contribution in A-2 (66.8 ± 7.6%) compared to A-5 (85.5 ± 10%) (p = 0.03). Skogsbergia lerneri carapace calcium carbonate composition was distinct to other myodocopid ostracods. These calcium polymorphs and ACC are described in other biological transparent materials, and with the consistent chitin distribution throughout S. lerneri development, may imply a biological adaptation to preserve carapace physical properties. Realisation of S. lerneri carapace synthesis and structural organisation will enable exploitation to manufacture biomaterials and biomimetics with huge potential in industrial and military applications

Incorporation of uranium into hematite during crystallization from ferrihydrite

Ferrihydrite was exposed to U(VI)-containing cement leachate (pH 10.5) and aged to induce crystallization of hematite. A combination of chemical extractions, TEM, and XAS techniques provided the first evidence that adsorbed U(VI) (≈3000 ppm) was incorporated into hematite during ferrihydrite aggregation and the early stages of crystallization, with continued uptake occurring during hematite ripening. Analysis of EXAFS and XANES data indicated that the U(VI) was incorporated into a distorted, octahedrally coordinated site replacing Fe(III). Fitting of the EXAFS showed the uranyl bonds lengthened from 1.81 to 1.87 Å, in contrast to previous studies that have suggested that the uranyl bond is lost altogether upon incorporation into hematite the results of this study both provide a new mechanistic understanding of uranium incorporation into hematite and define the nature of the bonding environment of uranium within the mineral structure. Immobilization of U(VI) by incorporation into hematite has clear and important implications for limiting uranium migration in natural and engineered environments. © 2014 American Chemical Society

Plutonium(IV) Sorption during Ferrihydrite Nanoparticle Formation

Understanding interactions between iron (oxyhydr)oxide nanoparticles and plutonium is essential to underpin technology to treat radioactive effluents, in cleanup of land contaminated with radionuclides, and to ensure the safe disposal of radioactive wastes. These interactions include a range of adsorption, precipitation, and incorporation processes. Here, we explore the mechanisms of plutonium sequestration during ferrihydrite precipitation from an acidic solution. The initial 1 M HNO3 solution with Fe(III)((aq)) and Pu-242(IV)((aq)) underwent controlled hydrolysis via the addition of NaOH to pH 9. The majority of Fe(III)((aq)) and Pu(IV)((aq)) was removed from solution between pH 2 and 3 during ferrihydrite formation. Analysis of Pu-ferrihydrite by extended X-ray absorption fine structure (EXAFS) spectroscopy showed that Pu(IV) formed an inner-sphere tetradentate complex on the ferrihydrite surface, with minor amounts of PuO2 present. Best fits to the EXAFS data collected from Pu-ferrihydrite samples aged for 2 and 6 months showed no statistically significant change in the Pu(IV)-Fe oxyhydroxide surface complex despite the ferrihydrite undergoing extensive recrystallization to hematite. This suggests the Pu remains strongly sorbed to the iron (oxyhydr)oxide surface and could be retained over extended time periods.Peer reviewe