M. Marcia West

Characterization of Iron-Oxides Formed by Oxidation of Ferrous Ions in the Presence of Various Bacterial Species and Inorganic Ligands

The oxidation of ferrous ions in the presence of an excess of dissolved oxygen at neutral pH generally leads to the formation of lepidocrocite. The effect of inorganic ligands (PO4, SO4, or Si(OH)4) in concentrations typical of those in sediment pore waters, and of microorganisms (Escherichia coli K12, Pseudomonas aeruginosa PA01, Bacillus subtilis or Bacillus licheniformis) on the mineralogy, chemical composition, morphology and spatial distribution of the iron-oxides were examined using various complementary techniques, including TEM, XRD, and EXAFS. The presence of inorganic ligands during the oxidation can affect the mineralogy as well as the size and structure of the Fe-oxide particles. While the presence of sulfate (SO4/Fe = 0.5) had little effect on the outcome of the Fe-oxide synthesis, low quantities of phosphate (PO4/Fe = 0.05) inhibited lepidocrocite and large quantities of aqueous silica (Si/Fe = 5) favored the formation of 2-line ferrihydrite. The presence of any of the four representative species of bacterial cells in the various systems did not modify the mineralogy of the Fe-oxides. However, the size of the Fe-oxide particles tended to be reduced, and the presence of the cells also affected the spatial organization and the morphology of the particles. In addition, in some systems, some of the iron remains adsorbed on the cells and does not contribute to the formation of mineral phases.

Formation of pore-filled ion-exchange membranes with in situ crosslinking: Poly(vinylbenzyl ammonium salt)-filled membranes

Robust, polyelectrolyte-filled, microporous membranes were prepared by the introduction and crosslinking of a preformed polymer within the pores of a poly(propylene) host membrane. Specifically, poly(vinylbenzyl chloride) (PVBCl) was reacted with piperazine or 1,4-diaminobicyclo[2.2.2]octane in an N,N-dimethylformamide (DMF) solution contained in the pores of the microporous base membrane. The remaining chloromethyl groups were reacted with an amine, such as trimethylamine, to form positively charged ammonium sites. This simple two-step procedure gave dimensionally stable, anion-exchange membranes in which the degree of crosslinking and the mass loading were determined by the concentration of PVBCl and crosslinker in the starting DMF solution. The incorporated polyelectrolyte gel was evenly distributed within the pores of the host membrane with no surface layers present. The membranes are fully characterized.

Effect of the presence of bacterial surfaces during the synthesis of Fe oxides by oxidation of ferrous ions

Natural iron-oxides are often found in close association with bacterial cells in aquatic environments, but the effect of bacteria on their formation is still under investigation. The present study was undertaken to assess the effect of two common bacteria, Bacillus subtilis and Escherichia coli , on the morphology and mineralogy of Fe oxides. All Fe oxides were synthesised by oxidation of Fe(II) (2 × 10 −4 M) at pH = 7. Three systems were studied, i.e. , abiotic Fe oxides, Fe oxides formed in the presence of bacteria (which we call “biogenic” Fe oxides) and abiotic Fe oxides mixed with bacterial cells. Samples were analysed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Fe oxide particles in all systems showed a needle-like morphology, with many needles seeming to be attached to a sheet, and were identified as lepidocrocite. However, the biogenic lepidocrocite crystals were generally shorter than the abiotic ones, and the crystals were found in association with the bacterial cell-wall, especially with B. subtilis , a Gram-positive bacterium. Biogenic lepidocrocite crystals also displayed an attenuation of the XRD 120 line, which is indicative of a low crystallinity. Growth limitation and poor crystalline order are then likely to affect the surface area of Fe oxides and indirectly, their sorptive capacity.

Poly(4-vinylpyridine)-filled microfiltration membranes: physicochemical properties and morphology

Abstract The morphology and physicochemical properties of poly(4-vinylpyridine)-filled microfiltration membranes have been examined. These membranes, which were prepared by photoinitiated grafting of up to 125 mass% of 4-vinylpyridine into the pores of polypropylene (PP) microfiltration membranes, were characterized in terms of the amount of poly(4-vinylpyridine) incorporated (graft yield), ion-exchange capacity, water content, and thickness. The morphology of samples of the grafted membranes dehydrated by freeze substitution was examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. While the ion-exchange capacities of the grafted membranes are a function of graft yield, ranging to 4.0 meq/g of dry membrane, the water contents of the grafted membranes in the free base form are essentially independent of graft yield. The porosity of the grafted membranes was shown to be almost the same as that of the starting base polypropylene membranes (60–80%). However, protonation of the grafted poly(4-vinylpyridine) was shown to lead to a further and very substantial increase of the void volume of the membranes as measured by their water content. The thickness of the grafted membranes was found to increase linearly with increasing incorporation of polyvinylpyridine. Ionization of the polyelectrolyte was shown to cause a further systematic increase in thickness which was partly reversible with reversion to the unprotonated form. These changes in thickness are attributed to the stretching of the mesh of the substrate microfiltration membranes.

Quantitative evaluation of radiation damage to polyethylene terephthalate by soft X-rays and high-energy electrons.

The chemical changes and absolute rates in radiation damage to polyethylene terephthalate (PET) caused by soft X-rays and energetic electrons have been measured using a scanning transmission X-ray microscope (STXM). Electron beam damage at two different dose rates and a range of doses was performed in an 80 keV transmission electron microscope (TEM). The STXM beam was used to create damage patterns with systematically varied doses of monochromatic soft X-rays on an adjacent piece of the same PET sample. NEXAFS spectroscopy at the C 1s and O 1s edges was used to study the chemistry of the radiation damage and to determine quantitative critical doses for PET damage by both types of radiation. The spectral changes were similar for damage by electrons and X-rays, indicating the radiation chemistry is dominated by secondary processes, not the primary event. The critical dose for chemical changes determined from C 1s spectral features is 4.2(6) x 10(8) Gy and was the same for soft X-rays and electrons within measurement uncertainties. The critical dose for specific damage processes (as defined by changes in several different, bond-specific spectral features) was found to be similar in the C 1s region and was comparable between C 1s and O 1s edges for electron beam damage. There were statistically different critical doses for soft X-ray damage as probed by changes in O 1s spectral features related to carbonyl and ester bonds.

Accumulation and Partitioning of Heavy Metals by Bacterial Cells and Associated Colloidal Minerals, with Alteration, Neoformation, and Selective Adsorption of Minerals by Bacteria, in Metal-Polluted Lake Sediment

Energy dispersive X-ray microanalysis and transmission electron microscopy were used to investigate heavy metal accumulation and partitioning by a statistically meaningful assortment of bacteria and colloidal minerals in metal-polluted lake sediment. Visually selected external and internal parts of bacterial cells were analysed individually. Variations in element distribution and relationships provided clues to small-scale biogeochemical processes and their implications for microbial ecology. Most bacteria had mineral coatings of varying composition and texture formed by adsorption of detrital clay and precipitation of authigenic oxides and clay attributable to Fe and Al complexing by cell walls and fibrils. Fe oxide precipitated abiotically and indiscriminately on bacteria and minerals, but Mn oxide was purely biogenic, precipitating only on certain bacteria. Cell walls also complexed Cu; formation of mineral coatings interfered with Cu binding, but the coatings themselves scavenged Cu. Cu and Zn were bound preferentially by oxides, but Ni was bound mainly by clay. Many bacteria accumulated metals preferentially on cell exteriors or in cytoplasmic inclusions, implying different mechanisms of bioaccumulation and detoxification, whose original purpose may have been to concentrate nutrient trace metals from dilute solution and regulate their proportions. Bacteria commonly employed both mechanisms, suggesting adaptation to different metal species. Preferential intake and exclusion of metals also occurred, and exterior-interior partition coefficients of metals in cells correlated with specific metal properties, revealing clues to the processes involved. In addition, bacteria were important agents of diagenesis. Besides precipitating oxides, they degraded adsorbed clay, synthesised intracellular and extracellular clay, and adsorbed clay minerals selectively.

Characterization of Polymer Monoliths Containing Embedded Nanoparticles by Scanning Transmission X-ray Microscopy (STXM)

The structural and chemical homogeneity of monolithic columns is a key parameter for high efficiency stationary phases in liquid chromatography. Improved characterization techniques are needed to better understand the polymer morphology and its optimization. Here the analysis of polymer monoliths by scanning transmission X-ray microscopy (STXM) is presented for the first time. Poly(butyl methacrylate-co-ethyleneglycoldimethacrylate) [poly(BuMA-co-EDMA)] monoliths containing encapsulated divinylbenzene (DVB) nanoparticles were characterized by STXM, which gives a comprehensive, quantitative chemical analysis of the monolith at a spatial resolution of 30 nm. The results are compared with other methods commonly used for the characterization of polymer monoliths [scanning electron microscopy (SEM), transmission electron microscopy (TEM), mercury porosimetry, and nitrogen adsorption]. The technique permitted chemical identification and mapping of the nanoparticles within the polymeric scaffold. Residual surfactant, which was used during the manufacture of the nanoparticles, was also detected. We show that STXM can give more in-depth chemical information for these types of materials and therefore lead to a better understanding of the link between polymer morphology and chromatographic performance.

IRON-RICH PARTICLES IN EMBRYOS OF SEEDS FROM THE FAMILY PINACEAE

SummaryIron-rich particles, previously reported in seeds of members of the genus Pinus, were found in radicle-hypocotyl tissues of dry embryos from eight other genera in the family Pinaceae. Thus, these Fe-rich particles are of common occurrence in seeds of this conifer family. These particles were most difficult to locate inPseudolarix amabilis, which has green embryos. Energy-dispersive X-ray analysis was used to determine the elements present in conifer Fe-rich particles and phytoferritin deposits in pea embryo axes. Ferich particles from all species studied contained mainly Fe and P but also contained considerable K and Mg. Abietoideae group I (genera Cedrus andAbies) had lower Fe ∶ P ratios compared to all the other combined subfamilies within the Pinaceae. Pea phytoferritin deposits contained markedly lower amounts of P relative to Fe based on peakto-background ratios and quantitative values calculated by using a ferric phosphate standard. We also found, for the first time, that pea phytoferritin contained considerable K. A strong similarity was found between the energy-dispersive X-ray analysis spectra from Ferich particles and portions of a laboratory-synthesized Fe, K, Mg phytate salt. Phytate is a common mineral-nutrient storage compound in seeds. The possibility of these Fe-rich particles being phytoferritin cannot be ruled out, but if they are phytoferritin, they have lower Fe ∶ P ratios than almost all other ferritins reported to date.

Mapping molecular orientation in dry and wet Nephila clavipes dragline spider silk

The alignment of β-sheets within spider dragline silk fibers is an important factor in their tensile strength and extensibility. We are using linear dichroism of the C 1s → π*amide transition measured using scanning transmission X-ray microscopy (STXM) to generate quantitative maps of the orientation parameters with 30 nm spatial resolution. Here we have extended these measurements from dry samples to samples with partial or full hydration. A device for monitoring and controlling the humidity of a sample in the STXM is described and used to measure the effect of saturated humidity on a section of N. clavipes dragline spider silk. The microstructure and distributions of molecular orientation change considerably with hydration in ways consistent with the supercontraction observed in free standing dragline spider silk. The STXM results are compared to infrared and Raman microscopy results.