Polarization Selectivity in Vibrational Electron-Energy-Loss Spectroscopy.

Orientation-dependent aloof-beam vibrational electron-energy-loss spectroscopy is carried out on uniaxial icosahedral B_{12}P_{2} submicron crystals. We demonstrate that the high sensitivity of the signal to the crystal orientation allows for an unambiguous determination of the symmetry of normal modes occurring at the Brillouin zone center of this anisotropic compound. The experimental results are assessed using first-principles quantum mechanical calculations (density functional theory) of the dielectric response of the specimen. The high spatial resolution inherent to this technique when implemented in the transmission electron microscope thus opens the door to nanoscale orientation-dependent vibrational spectroscopy.

Behavior and fate of industrial zinc oxide nanoparticles in a carbonate-rich river water.

The present study precisely describes the solubility patterns of commercial uncoated and organic coated ZnO NPs (nc-NPs and c-NPs, respectively) in a natural carbonate-rich water and the physicochemical processes involved. NPs transformation rates were determined with the Donnan Membrane approach (DMT, to obtain Zn(2+) concentration) and ultrafiltration (i.e. Zn(2+) and Zn bound to small organic ligands) and modeled with VMinteQ. XPS measurements evidenced the presence on native nc-NPs of a Zn(OH)2 layer which accounts for almost 22% of total Zn. This Zn(OH)2 phase is more soluble than ZnO, and could control the early dissolution steps of the nc-NPs in our system. Indeed, nc-NPs display a fast (<1 h) dissolution step reaching 19 µM Zn in solution (<1% of the total initial zinc concentration). Comparatively, c-NPs progressively release zinc during the first 48 h, to finally reach a maximum of 197 µM (10% of total Zn), which is 10 times the maximum value measured for nc-NPs. Over the long term, dissolved Zn concentrations decrease in both systems, corresponding to the neoformation of carbonate phases observed by TEM imaging. The kinetic modeling allows highlighting two different ranges of time, corresponding to (i) first 10h with a fast precipitation (kp(')=-182.10(-4)) related to a highly oversaturated solution with respect to carbonate zinc mineral and (ii) a second slower precipitation step (kp(')=-8.10(-4)), related to the embedding of NPs in the precipitated carbonate matrix. The steady state is reached after 3 months of interaction.

Structural properties of the tubular appendage spinae from marine bacterium Roseobacter sp. strain YSCB.

Spinae are tubular surface appendages broadly found in Gram-negative bacteria. Little is known about their architecture, function or origin. Here, we report structural characterization of the spinae from marine bacteria Roseobacter sp. YSCB. Electron cryo-tomography revealed that a single filament winds into a hollow flared base with progressive change to a cylinder. Proteinase K unwound the spinae into proteolysis-resistant filaments. Thermal treatment ripped the spinae into ribbons that were melted with prolonged heating. Circular dichroism spectroscopy revealed a dominant beta-structure of the spinae. Differential scanning calorimetry analyses showed three endothermic transformations at 50-85°C, 98°C and 123°C, respectively. The heating almost completely disintegrated the spinae, abolished the 98°C transition and destroyed the beta-structure. Infrared spectroscopy identified the amide I spectrum maximum at a position similar to that of amyloid fibrils. Therefore, the spinae distinguish from other bacterial appendages, e.g. flagella and stalks, in both the structure and mechanism of assembly.

Morphological preservation of carbonaceous plant fossils in blueschist metamorphic rocks from New Zealand.

Morphological and chemical evidence of ancient life is widespread in sedimentary rocks retrieved from shallow depths in the Earth's crust. Metamorphism is highly detrimental to the preservation of biological information in rocks, thus limiting the geological record in which traces of life might be found. Deformation and increasing pressure/temperature during deep burial may alter the morphology as well as the composition and structure of both the organic and mineral constituents of fossils. However, microspore fossils have been previously observed in intensely metamorphosed rocks. It has been suggested that their small size, and/or the nature of the polymer composing their wall, and/or the mineralogy of their surrounding matrix were key parameters explaining their exceptional preservation. Here, we describe the remarkable morphological preservation of plant macrofossils in blueschist metamorphic rocks from New Zealand containing lawsonite. Leaves and stems can be easily identified at the macroscale. At the microscale, polygonal structures with walls mineralized by micas within the leaf midribs and blades may derive from the original cellular ultrastructure or, alternatively, from the shrinkage during burial of the gelified remnants of the leaves in an abiotic process. Processes and important parameters involved in the remarkable preservation of these fossils during metamorphism are discussed. Despite the excellent morphological preservation, the initial biological polymers have been completely transformed to graphitic carbonaceous matter down to the nanometer scale. This occurrence demonstrates that plant macrofossils may experience major geodynamic processes such as metamorphism and exhumation involving deep changes and homogenization of their carbon chemistry and structure but still retain their morphology with remarkable integrity even if they are not shielded by any hard-mineralized concretion.

Effect of radiation-induced amorphization on smectite dissolution.

Effects of radiation-induced amorphization of smectite were investigated using artificial irradiation. Beams of 925 MeV Xenon ions with radiation dose reaching 73 MGy were used to simulate the effects generated by alpha recoil nuclei or fission products in the context of high level nuclear waste repository. Amorphization was controlled by X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy. An important coalescence of the smectite sheets was observed which lead to a loss of interparticle porosity. The amorphization is revealed by a loss of long-range structure and accompanied by dehydroxylation. The dissolution rate far-from-equilibrium shows that the amount of silica in solution is two times larger in the amorphous sample than in the reference clay, a value which may be enhanced by orders of magnitude when considering the relative surface area of the samples. Irradiation-induced amorphization thus facilitates dissolution of the clay-derived material. This has to be taken into account for the safety assessment of high level nuclear waste repository, particularly in a scenario of leakage of the waste package which would deliver alpha emitters able to amorphize smectite after a limited period of time.