Thesis (Ph. D.)--Columbia University, 1927. / Vita.

Thesis (Ph. D.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 10, 2007) Vita. Includes bibliographical references.

Thesis (M.S.)--Missouri University of Science and Technology, 2008. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 24, 2009) Includes bibliographical references (p. 68-69).

Ferrihydrite (FHYD), a nanocrystalline material has long been described as a poorly crystalline disordered mineral mainly due to its small crystal size which is typically 2−6 𝑛𝑚. The three-dimensional structure of the mineral has long been described by a multi-phase structural model that consists of Fe3+ only in octahedral (Oh) coordination. In this model ferrihydrite is described as a mixture of two major phases (akaganeite/goethite-like f-phase and feroxyhite-like d-phase) and a minor ultradispersed nanohematite phase. This model has been recently challenged and a new, single-phase model was proposed, having a basic structural motif closely related to the Baker-Figgs δ-Keggin cluster and is isostructural with the mineral akdalaite, Al10O14(OH)2. In its ideal form, the proposed new structure of FHYD consist of 80 % Oh and 20 % tetrahedral (Td) Fe3+ polyhedra which can be adequately described by a single-domain model with the hexagonal spacegroup 𝑃63𝑚𝑐 and unit cell dimensions 𝑎=5.95 Å and 𝑐=9.06 Å. In this study, nanoparticles of 2-line FHYD (FHYD2), 2-line FHYD deposited onto SiO2 (FHYD2/SiO2) and 6-line FHYD (FHYD6) synthesised using rapid hydrolysis of Fe(NO3)3.9H2O solutions were characterized using X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), Mössbauer spectroscopy (MS) as well as magnetization and magnetic susceptibility measurements. The coordination environment of iron atoms in the structure of FHYD was investigated using TEM and MS. The thermal transformation of FHYD nanoparticles was monitored through changes in the magnetization as a function of temperature and the reduction behaviour in hydrogen environment was studied using temperature programmed reduction (TPR), in-situ XRD and MS. Electron diffraction, TEM/ scanning TEM (STEM) imaging, and electron energy loss (EELS) measurements were carried out on three different microscopes viz. JEOL JEM-2100 LaB6 TEM, aberration corrected Schottky-FEG JEOL JEM-ARM200F HRTEM and cold-FEG Zeiss SESAM TEM. EELS studies were concentrated mainly on the iron 𝐿-edge of FHYD and iron oxides reference spectra with well known crystal structures. The iron oxide Fe 𝐿-edge is usually characterized by two intense sharp peaks termed “white lines”. The fine structures introduced by the crystal field effect on the 𝐿- edge contain information that is highly specific to the Fe3+ site symmetry.

Using Environmental Protection Agency occurrence and concentration data, it is estimated that about 6 million pounds of arsenic-bearing residuals (ABSR) will be generated annually in the United States when full compliance with the new standard for arsenic in drinking water (10 μg/L) is realized. Effective management of disposal of ABSR requires both a full characterization of the materials and an understanding of the environment in which the disposal will occur. Currently, there are different testing methods to evaluate the stability of ABSR, the principal of which is the EPA Toxicity Characteristics Leaching Procedure (TCLP). These tests indicate that common ABSRs may be disposed in mixed-solid waste landfills. However, this and previous work shows that these testing methods may significantly underestimate the degree and mechanism of arsenic mobilization from the residuals, because critical physical and chemical dissimilarities exist between the tests and landfill conditions. In addition, no current testing methods simulate the mineralogic aging in those ABSR, which exhibit further complexity. Landfill disposal involves liquid and solid residence times on the order of months and decades, respectively, whereas leaching tests are completed in two days or less. Consequently, time dependent re-mineralization of residuals that would be routinely expected in landfill time scales is not addressed by standard leaching tests. Treating arsenic brines by co-precipitation with iron oxyhydroxides is an established and effective remediation method for small quantities of highly concentrated liquid arsenic waste, such as brines derived from mine tailings, ion exchange resin regeneration, and reverse osmosis treatment of drinking water. However, amorphous ferric hydroxide (AFH) is expected to exhibit mineralogical aging analogous to the observed natural evolution of ferrihydrite to goethite and hematite. The aim of this research is to develop methods for characterization of AFH sludges precipitated from concentrated arsenic brines which exhibit mineralogical aging and to evaluate the impact of such aging on arsenic leachability. Overall, aging the sludge resulted in consistently higher arsenic release.

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Iron is a trace element required for a range of metabolic reactions in virtually all living organisms. Studies of prokaryotes, plants, yeast, and vertebrates have established detailed information on iron uptake and the role iron plays in metabolic processes. Iron is an essential growth requirement of schistosomes in vitro and schistosomes also express the highly conserved iron storage protein ferritin. However, studies into how this iron is taken up by the parasite have been neglected. This study aims to identify molecules involved in iron uptake and homeostasis in the human parasite Schistosoma japonicum. I have characterised two isoforms of a divalent metal transporter (DMT), a membrane bound protein of schistosomes. These DMTs have significant homology to the mammalian DMT1, the primary ferrous iron uptake protein of the intestinal brush border. Both schistosome isoforms displayed functional iron uptake by rescuing growth in a yeast strain deficient in iron uptake (fet3fet4). Interestingly schistosome DMT1 was localised to the tegument and not the gastrodermis of adult parasites, suggesting surface mediated iron uptake across the tegument. In physiological conditions, iron is abundant as largely insoluble ferric iron and hence ferric reductases are an essential component of iron uptake, reducing iron to the soluble ferrous form. Cytochromes b561 (Cyts-b561) are a family of ascorbate reducing transmembrane proteins found in most eukaryotic cells. Recent observations that Cyts-b561 may be involved in iron metabolism have opened new perspectives for their physiological function. Here, I have identified a new member of the cytochrome b561 family in Schistosoma japonicum that localises to the tegument of this trematode. Expression of the SjCytb561 in a Saccharomyces cerevisiae mutant that lacks plasma membrane ferrireductase activity (fre1fre2) was able to rescue the growth defect in iron deficient conditions, suggesting involvement in iron metabolism. Plasma membrane ferrireductase activities were also quantified using intact transformed yeast cells. These data further support the hypothesised tegumental uptake of host iron. Further, I have identified a putative schistosome transferrin. In mammals, transferrin is a glycoprotein responsible for binding and transporting iron in the bloodstream and delivering iron into cells via a specific transferrin receptor. Preliminary characterisation of the schistosome transferrin sequence has revealed it does not contain all the conserved amino acid residues associated with iron binding, with conservation seen only in the C-terminal lobe, not in both the N and C-lobes observed in mammalian transferrins. This difference makes it unclear whether the schistosome transferrin shares functional homology with its mammalian counterpart. In addition, no transferrin receptor has been identified to support an iron trafficking and uptake function, nor would this function be expected in an acoelomate organism. Further characterisation and localisation of this protein is required to elucidate its biological significance and function. The tegumental location of both the SjDMT1 and the SjCytb561 for the uptake of host iron make it possible to consider these proteins as potential vaccine candidates. A preliminary vaccination study with these proteins elicited only low to moderate protection from infection, and further studies are required to fully assess their potential. The data presented in this thesis provide evidence for surface-mediated uptake of iron by adult schistosomes, and represent the first characterisation of iron uptake proteins in any helminths. These studies show a novel method of iron uptake in schistosomes, and contribute to our understanding of how these parasites are able to survive and thrive by scavenging nutrients, in this case iron, from the host organism.