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1
O'Sullivan, Matthew. "Assessment procedures for structural wrought iron." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/assessment-procedures-for-structural-wrought-iron(d8a2b7a5-db32-48c4-8ffe-983b42e5a4d8).html.
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The main objective of this research project was to develop a new methodology for the assessment of wrought iron structures using a more informed knowledge of the material.A database of tensile test data for wrought iron across the range of all types of structural elements was compiled and analysed to establish the characteristic yield strength for comparison with the value of 220N/mm2 quoted by the UK Highway Standard BD21. It was found that the characteristic yield strength of bar iron is 151N/mm2 and that of plate iron is 187N/mm2.Bending tests of wrought iron beams were conducted to investigate the potential for brittle fracture under static loads, which was observed, and further investigated by conducting Charpy impact tests, where it was found the that ductile to brittle transition temperature of the metal lies in the range 20 to 80oC, whereas that of mild steel, is typically in the range -30 to 10 oC.A new assessment method was proposed that incorporates a 'quality factor' and a 'component significance factor' into the definition of design yield strength. Comparative studies using the proposed method and the existing method were conducted on a trussed highway bridge, a long span iron roof to a railway station and the Clifton Suspension Bridge. The newly obtained lower values of characteristic yield strength tend to dominate the final design strength value of a component, but this may be improved by the expansion of the database. Furthermore, the inclusion of the quality and significance factors offset this effect and their inclusion was validated by proving that a safe yet not overly conservative design yield strength may be established by application of the proposed method.
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Kerkar, Moussa. "A structural investigation of the passive film on iron and iron/chromium alloys." Thesis, University of Warwick, 1989. http://wrap.warwick.ac.uk/106531/.
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The Electrochemical Polarisation, Photocurrent Spectroscopy and Extended X-ray Absorption Fine Structure (EXAFS) techniques have been used to study the passive film on pure iron and iron alloy samples containing up to 25% chromium. The material used in this work was prepared both as bulk and thin films. The bulk samples were passivated electro- chemically at various anodic potentials whereas the film ones were either fully converted into passive films by simple immersion in various solutions for one week or electrochemically at various anodic potentials. The Fe and Fe/Cr film samples used in the electrochemical passivation were deposited onto gold substrate and those passivated by immersion were deposited directly onto mylar. Polarisation curves for both the bulk and film materials were recorded. They suggest that the electrochemical behaviour of the two materials is similar. The wavelength and potential dependence of the photocurrent spectra were also recorded for the bulk and film samples of Fe and Fe/Cr alloys. The data were analysed to obtain the effective optical band gaps and flat band potentials of the passive films respectively. These results also show that the two materials are similar. Furthermore, the photocurrent data suggest that the passive film on Fe/Cr alloys consists of Fe(III) and Cr(III) phases. The fluorescence EXAFS above the Fe and Cr K-absorption edges of the passive film on Fe and Fe/Cr alloy films has been recorded both in-situ and en- situ. The spectra obtained in these studies were analysed to obtain average Fe-O and Fe-Fe separations as well as Cr-0 and Cr-Cr ones. These results together with a detailed examination of the XANES suggest that the passive film on iron in the absence of chromium is best described as a disordered 7—FeOOH-like structure and that on Fe/Cr alloys as well as on pure Fe passivated in chromate solution contains two simultaneous phases of disordered 7-FeOOHand Cr(OH)j. The structure of the chromium containing phase of the passive film was found to be independent of the source of chromium whether it was present in the alloy or it was incorporated from the passivating solution. The EXAFS data show also that the structure of the passive film is insensitive to drying. The results obtained in these studies have enabled the determination of the structure of the passive film on iron and iron/chromium alloys and the rôle played by chromium in improving the corrosion resistance of iron and its alloys has been identified. These conclusions are discussed in the light of other structural investigations of the passive film.
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Onda, Nicolino. "Epitaxially stabilized iron-silicides : structural and electrical properties /." [S.l.] : [s.n.], 1994. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=10513.
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Lee, Dok Won. "Structural and magnetic properties of copper/iron multilayers." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ44203.pdf.
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Brüning, Ralf. "Reversible structural relaxation in iron based metallic glasses." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65539.
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Porter, Deborah Aitken. "Structural and magnetic study of ammonium iron halides." Thesis, University of Edinburgh, 1998. http://hdl.handle.net/1842/11274.
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Some ABX3 materials, in which A is a monovalent cation, B a divalent cation and X a monovalent anion, are known to exhibit the hexagonal perovskite structure; these have a chain-like structure produced by face sharing BX6 octahedra that lie parallel to the crystal c axis. For materials in which B is a first row transition metal, this structural anisotropy leads to pseudo-one dimensional magnetic behaviour, the interchain exchange is several orders of magnitude larger than the intrachain exchange. This thesis discusses the investigation of the crystal structure and crystallographic and magnetic phase transitions in the hexagonal perovskites, ammonium iron chloride and bromide; specifically to consider the effect of the non-spherical ammonium ion on both the structure and the magnetic properties. Powder samples have been studied between 420 and 4.2 K using high resolution synchrotron X-ray diffraction, and between 470 and 1.5 K using neutron diffraction. The rotation of the ammonium ion within the structure was studied via quasi-elastic neutron diffraction. Single crystals of both materials were obtained and studied using SQUID magnetometry and X-ray diffraction (between room temperature and 10 K). Ammonium iron chloride is found to undergo a structural phase transition at 181.0(2) K where the symmetry is lowered as the FeCl3 chains twist slightly. A second structural phase transition is observed at 19.5(2) K; in this case the unit cell is found to double in the a direction with respect to the primitive cell. Quasi-elastic neutron scattering measurements show NH4FeCl3 exhibits quantum tunnelling in its low temperature phase, proving the NH4 motion is frozen at that temperature. Neutron diffraction reveals antiferromagnetic reflections corresponding to a helical magnetic array below 3.7(2) K; susceptibility data also show a transition at this temperature.
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Folgosa, Filipe dos Santos. "Structural and mechanistic studies of iron containing proteins." Doctoral thesis, FCT - UNL, 2008. http://hdl.handle.net/10362/1774.
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Dissertação apresentada para obtenção do Grau de Doutor em Bioquímica, ramo de Bioquímica-Física, pela Universidade Nova de Lisboa, Faculdade de Ciências e TecnologiaOver the last few decades a large effort has been done in the structural biochemistry field. This effort is based on the study of some proteins, namely metalloproteins, that contain cofactors and/or active sites with metal ions in their constitution. This thesis will focus on different studies performed in metalloproteins that contain non-heme iron centers. An important point is their relation to oxygen and reactive oxygen species. To perform these studies, fast kinetic techniques were used coupled to spectroscopic techniques, such as Electronic Paramagnetic Resonance (EPR), Mössbauer and UVVisible.
Fundação para a Ciência e Tecnologia (SFRH/BD/18905/2004)
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Money, Victoria A. "Structural studies of iron (II) spin crossover compounds." Thesis, Durham University, 2004. http://etheses.dur.ac.uk/2987/.
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The drive for ever smaller and faster computers has, in recent years, caused much research interest to be focussed on the development of new materials in which individual molecules or assemblies of molecules can be used for information processing. Materials which show spin crossover behaviour have great potential for use not only in molecular computing but also in applications such as optical switches and display devices and are of fundamental interest due to their importance in biological and geological systems. The results of comprehensive variable temperature and excited state crystallographic studies into the spin crossover behaviour of a family of iron (II) spin crossover complexes based on the 2,6-di(pyrazol-l-yl)pyridine ligand are presented herein. A fascinating aspect of spin crossover materials is their ability to undergo a transition from the low spin state to a metastable high spin state, with a very long lifetime, on irradiation. Crystallographic information on the structure of the metastable high spin state formed as a result of irradiation is very rare. Full structural analyses of the metastable state are reported for [FeLl(_2)](BF(_4))(_2), [Fe(L3)(_2)](BF(_4))(_2), [Fe(L3)(_2)](C1O(_4))(_2) and [Fe(L4)(_2)](BF(_4))(_2) (LI = 2,6- di(pyrazol-l-yl)pyridine, L3 = 2,6-(dipyrazol-l-yl)-4-hydroxymethylpyridine, L4 = 2,6-di(3-methylpyrazol-1 -yl)pyridine). These studies have shown that, unlike other reported materials, the metastable high spin state is structurally identical to that reached as a result of the thermal spin transition. [Fe(L4)(_2)](BF(_4)) (_2)1/3H(_2)O is shown to have a fascinating complexity of spin crossover behaviour including the existence of a number of metastable states. The effect of dehydration on the spin crossover behaviour has been determined. Spin crossover compounds are extremely sensitive to changes in pressure; nonetheless there have been very few studies of the effect of pressure on the structure of these materials. The structure of the pressure induced low spin state at ambient temperature and 4.5 kbar is reported for [FeLl2](BF4)2. The crystallographic results are supported throughout by SQUID magnetometry studies.
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Beesley, Angela M. "Structural and magnetic studies on sputtered uranium / iron multilayers." Thesis, University of Liverpool, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415747.
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Keep, Graham. "Structural and Functional Studies of Ferrous Iron Transporter B." Thesis, The University of Sydney, 2018. http://hdl.handle.net/2123/18969.
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The transmembrane bacterial iron importer FeoB has been shown to be the key component for ferrous iron acquisition for most pathogenic bacteria and has been shown to be a viable antimicrobial target. The molecular mechanisms for FeoB’s iron transport are not well understood with the most significant finding being active transport via a cytosolic GTPase. The lack of understanding is the result of inherent difficulties in obtaining pure monodispersed full length FeoB for structural and biochemical analysis. Truncated FeoB GTPase domains (termed NFeoB) from various species have been deposited in the PDB with and without bound GTP analogues. The key to furthering the knowledge of bacterial ferrous iron transport involves improving techniques in expression and purification of the full length FeoB protein. To obtain more monodispersed and pure protein, expression of FeoB was trialled with a TEV cleavable GST affinity tag, purified with the reducing agent, Sodium dithionite as well as, with and without GDP. Another construct of FeoB was tested with a small fused flexible C-terminal region (to allow for oligomerisation using an 8 histidine affinity tag). Expression was also trialled within an FtsH (a FeoB specific protease) E. coli knockout. Sodium dithionite evoked a more pure FeoB sample, compared to purification without, as did the flexible C-terminal construct, however producing no protein crystals from either experiment. FeoB expressed in FtsH knockout cells was less degraded compared to the cell’s isogenic paired counterpart. However degradation was not less than our lab’s standard membrane expression cell line ‘C41’. Important outcomes from this work include; purification with Sodium dithionite proved vitally important in stabilising FeoB during purification as well as expression (i.e. stabilised oligomerisation) and also improved expression systems with FtsH knockout cells which are all promising directions to take to obtain a more pure and monodispersed protein.
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Li, Guzhao. "Bracing design requirements for inelastic members." Access restricted to users with UT Austin EID, 2002. http://www.lib.utexas.edu/etd/r/d/2002/guzhaol022/guzhaol022.pdf#page=4.
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Busch, J. L. H. C. "Structural and spectroscopic studies of Desulfovibrio africanus ferrodoxin III." Thesis, University of East Anglia, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267262.
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Perry, Ashlee. "Structural studies of the two iron rubredoxin of Pseudomonas oleovorans." Thesis, University of Leicester, 2001. http://hdl.handle.net/2381/29656.
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Sequence alignment studies and biochemical investigations have suggested that the two iron rubredoxin of Pseudomonas oleovorans consists of two-rubredoxin type domains connected by a ~60 amino acid linker region. The rubredoxin gene (alk G) contained in the rubredoxin expression vector was targeted by site-directed mutagenesis to produce independent expression vectors for the N and C-terminal domains. The C-terminal vector directed the high-level production of the C-terminal domain and a simple procedure was used to purify the recombinant domain in the Fe-form. Attempts to directly express the N-terminal domain of the 2Fe-rubredoxin from a mini-gene were unsuccessful. However, the apo-form of the N-terminal domain was isolated through cleavage of an engineered 2Fe-rubredoxin in which a factor Xa proteolysis site had been introduced into the putative interdomain linker. The responsive proteins could readily be converted to the apoprotein, cadmium or iron forms following precipitation with trichloroacetic acid and resolubilisation in the presence or absence of cadmium chloride or ferrous ammonium sulphate, respectively. Both domains have been characterised by UV-visible, circular dichroism and 1D NMR spectroscopies. The spectra collected for the C-terminal domain are characteristic of typical rubredoxins. The spectra collected for the N-terminal domain are less characteristic of typical rubredoxins, likely reflecting poor structural stability, which is consistent with the properties of the full-length di-domain rubredoxin. In steady-state assays, both N and C-terminal domain rubredoxins were redox-active and able to transfer electrons from reduced rubredoxin reductase to cytochrome c. The solution structure of the C-terminal domain was determined using 2D NMR techniques. The structure is typical of rubredoxins and reveals that the linker region is structureless, which is consistent with limited proteolysis studies carried out on the C-terminal domain. The structures of the full-length rubredoxin and the C-terminal domain were investigated by small angle X-ray scattering methods. These analyses confirmed the finding that the linker region in the C-terminal domain is structureless, and demonstrated that the folded N and C-terminal domains of the full-length rubredoxin are associated, with their metal binding sites in close proximity.
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Kobayashi, Yuka. "Structural and Functional Analysis of Iron Ion-Coordinating Cyclic Peptides." Kyoto University, 2018. http://hdl.handle.net/2433/232327.
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Jonnalagadda, Rohan. "Structural and functional investigations of mechanisms of iron-utilizing enzymes." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/127130.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biology, May, 2020Cataloged from the official PDF of thesis. Vita.
Includes bibliographical references.
Biological systems use iron as a key cofactor to catalyze a variety of difficult chemical transformations, particularly as reservoirs from which to initiate enzymatic radical chemistry. Here, I discuss efforts to study the allosteric mechanisms of an essential human iron and free radical utilizing enzyme: ribonucleotide reductase (RNR), and efforts to elucidate the radical based mechanism of isonitrile formation by an mononuclear nonheme iron(II) α-ketoglutarate dependent dioxygenase, ScoE. The first part of this thesis focuses on mononuclear nonheme iron(II) α-ketoglutarate dependent dioxygenases: enzymes which use molecular oxygen, α-ketoglutarate and a mononuclear Fe(II) cofactor to initiate substrate radical chemistry and catalyze diverse chemistries such as hydroxylations, halogenations and desaturations. Chapter 1 of this thesis describes current understanding of the mechanisms of these enzymes. Chapter 2 describes biochemical and structural efforts to determine the catalytic mechanism of one member of these enzymes: the isonitrile formation enzyme ScoE. In the chapter 3 of this thesis, I discuss the structure, function and allosteric regulation of RNR, the sole known enzyme capable of catalyzing the de novo biosynthesis of deoxyribonucleotides in all organisms for use in DNA replication and repair. Chapter 4 concerns efforts to develop a procedure for the improved recombinant protein yield of human RNR, and chapter 5 describes the development of a new liquid chromatography-tandem mass spectrometry based assay for RNR activity that we propose holds promise for simultaneous detection of RNR activity on multiple substrates.
by Rohan Jonnalagadda.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Biology
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Liang, Shunxing. "Catalytic mechanism, multifunctionality and structural design of iron-based metallic glasses." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2019. https://ro.ecu.edu.au/theses/2274.
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Alloys with a well-defined long-range ordered crystalline structure and glasses with a highly disordered amorphous structure as two uncorrelated categories of materials have a long history with a widespread use for different purposes. With the common sense of highly ordered structure in metals/alloys, it is until the 1960s that the first metallic glass (MG, also known as amorphous alloy) has been produced by fast quenching technique to “freeze” their metallic liquid at very high critical cooling rate, realizing glass-like (amorphous/disordered atomic) structure in alloys with extraordinary properties (extreme strength at low temperature, high flexibility at high temperature, etc.) as structural and functional materials. While part of current studies focus on their fundamental and important issues including glass nature and its supercooled liquid state, many application-oriented research endeavors have achieved great successes. Motivated by the pressure of global environmental issues and potential crisis level of fresh water, recently an increasing interest of MGs in attractive catalytic applications has suggested the superior performance of MGs than their crystalline counterparts. Although the application of MGs as catalysts was firstly attempted in almost 40 years ago, their potential value in environmental and energy science has not been recognized until in recent 10 years. As such, studies of catalytic properties of MGs are still very limited and the catalytic mechanism to understand their superior performance is far from easy to achieve. A great effort is still needed for the achievement of the practical catalytic industrialization using massive produced MGs.
Chapter 1 introduces the current challenges of MGs in future development and practical applications, which present as the contradictions between massive production technique and narrow practical application range, between low development as structural materials and high promise as functional materials, and between high catalytic performance and low understanding of mechanism. Accordingly, the significance and innovation of using MGs as functional catalysts will be also described as following: 1) strategies for enhancing catalytic performance of Fe-based MGs without structural change for degradation of organic pollutants; 2) the catalytic application of Fe-based MGs for purifying diversified inorganic contaminants; 3) the potential optimized structure of Fe-based MGs for highly promoting catalytic performance.
Chapter 2 overviews the MGs with structural origin (e.g. short-to-medium-range atomic arrangement with analysis and characterization techniques), glass-forming ability as one of important characteristics for material design, manufacturing methods (i.e. for ribbons, powder and bulk MGs), mechanical and chemical properties, current catalytic properties and applications of MGs (including wastewater treatment, water splitting and fuel cell). The structural heterogeneity in catalysis and strategies to engineer catalytic structure of MGs are also shown in order to develop their future catalytic applications.
Chapter 3 shows the research methods according to different chapters, which contain materials and chemicals, characterization methods, catalytic analysis process, kinetic study methods and other measurements.
Chapter 4 shows the strategies of enhanced catalytic performance of MGs. Fe73.5Si13.5B9Cu1Nb3 MG ribbons are employed for photo-enhanced activation of persulfate (PS), indicating that 100% color removal of malachite green dye can be achieved within 30 min under optimized parameters, and the inclusion of Nb in Fe73.5Si13.5B9Cu1Nb3 MG ribbons promotes enrichment of Si to further improve the surface stability. Yet, the catalytic mechanism of MG ribbons in advanced oxidation processes (AOPs) is not sufficiently understood. As such, Fe78Si9B13 MG ribbons have been applied for the activation of three peroxides: H2O2, PS and peroxymonosulfate (PMS) to investigate catalytic mechanism. The dominant reactive radicals (•OH and/or SO4•−) in AOPs are investigated by competition kinetics using probe reaction. The order of predominant radical generation rate by Fe78Si9B13 under UV-vis irradiation is PS>H2O2>PMS, all with a radical generation rate at least ~2 times higher than other iron-containing materials. The radical evolution mechanism for H2O2, PS and PMS activation has also been investigated. On the other hand, the role of surface to enhance catalytic performance of MGs is suggested. Fe50Ni30P13C7 MG ribbons are found to have the superior corrosion resistance and an effective elimination of surface layer by chemical dealloying can highly promote the catalytic degradation rate of brilliant black BN dye from 20 min to only 10 min, which is attributed to reactivation of surface by chemical dealloying without generating nano-porous structured surface. The reactivation of ribbon surface effectively optimizes active reaction sites and the re-exposure of Fe, Ni and P with zero-valent state forms galvanic cells by atomic clusters leading to the acceleration of catalysis.
Chapter 5 indicates the novel catalytic application of MGs against diversified contaminants. As an advanced alternative of heterogeneous crystalline iron material, low-cost Fe78Si9B13 MG ribbons with mature production by melt spinning is employed in real industrial contaminated water to investigate effective separation of arsenic (As) and reduction of nitrate (NO3−). Fe-based MG ribbons demonstrate attractive high removal rate of As in 30 min with low soluble Fe (1.5 mg/L), which is ascribed to synergistic effect of reduction/adsorption by MG ribbons, precipitation of arsenic sulfide and adsorption of generated iron sulfide. On the other hand, a remarkable sustainability up to 20 reused times of Fe-based MG ribbons for NO3− reduction suggests a promising economic value of MG ribbons in industrial applications. Surface area normalized rate coefficient indicates the superior catalytic capacity of Fe-based MG ribbons compared with other iron materials.
Chapter 6 presents the strategies to engineer catalytic structure correlated to MGs. It is reported that the excellent catalytic behavior in Fe-based MGs goes through a detrimental effect with the partial crystallization but receives a compelling rejuvenation in the full crystallization. Further investigation reveals that multiple crystalline phases with electric potential differences induced by high-temperature annealing facilitate the formation of galvanic cells. The extensively reduced grain boundaries due to grain growth greatly weaken electron trapping and promote inner electron transportation. The relatively homogenous grain-boundary corrosion in the multiphase contributes to well-separated phases after reactions, leading to refreshment of surface active sites, quickly activating H2O2 and rapidly degrading organic pollutants. On the other hand, 3D printing that revolutionizes the way of material manufacturing with functional applications is employed in the manufacturing of an Fe-based MG matrix composite with three-dimensional rhombic dodecahedron microstructure. The 3D-printed porous Fe-based MG matrix composite has been employed into catalytic activation in Fenton-like process and sulfate radical-based reaction. Results demonstrate that extremely high reusability (45 times) is achieved in sulfate radical-based reaction without any apparent efficiency decay. The remarkable catalytic reusability originates from extremely low surface decay. Structural analysis indicates the α-Fe nanocrystals serve as trigger of easy electron transfer but a large amount of α-Fe lead to an inhibitive effect in the MG matrix composite. The overall catalytic ability also demonstrates the excellent catalytic performance of SLM-produced porous Fe-based MG composite in the wastewater remediation.
Chapter 7 concludes the present findings in this thesis and suggests the future challenges and development using MGs as catalysts.
With the investigation of enhanced catalytic performance, catalytic degradation of diversified pollutants and optimization of catalytic structure of Fe-based MGs, this thesis aims to further understand the catalytic mechanism of Fe-based MGs at the atomic size in wastewater treatment, to assess applicability of MGs in practical applications, to provide a novel clue of extending their multifunctional catalytic properties and to suggest the new developing catalyst design with ordered and/or disordered atomic arrangement in the future development.
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He, Didi. "Structural basis for iron (II) metabolism in encapsulated ferritin-like proteins." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/23466.
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Ferritins are ubiquitous proteins that serve the dual-function of iron reservoir and sequestering the Fe(II) toxicity. The function of ferritins totally depends on the characteristic spherical structure with a di-iron centre performing the iron oxidation and a hallow cavity enclosing the iron minerals in a bioavailable form. I have characterised the structure, assembly and function of a new member of ferritin superfamily that is natively enclosed within an encapsulin shell. Encapsulin proteins are structurally-related to a virus capsid and form 60-meric or 180-meric icosahedrons. I show that this encapsulin associated ferritin-like protein (EncFtn) possesses two main alpha helices, which assemble in a metal-dependent manner to form a ferroxidase centre at a dimer interface. EncFtn adopts an annular decamer structure in contrast to the 24-meric classical ferritins or 12-meric mini-ferritin (DPS). The resemblance of the dimeric EncFtn and monomeric classical ferritins suggests that it is likely that classical ferritin evolves from EncFtn because of the gene duplication. EncFtn is a catalytically active ferroxidase but with only a limited iron binding ability due to its open structure. The encapsulin itself is not able to oxidise Fe(II), but is able to store about 2200 iron ions. I have demonstrated that the EncFtn must be housed in the encapsulin to achieve a maximum loading of approximately 4200 iron ions. The encapsulin nanocompartments are widely-distributed in both eubacteria and archaeon with distinct life styles and represent a distinct class of iron storage system, where iron oxidation and mineralisation are distributed between two proteins.
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Yoon, Taejin. "Functionaland structural studies of human frataxin: An iron chaperone protein for mitochondrial iron-sulfur cluster and heme biosyntheses." The Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=osu1124287807.
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Yu, S.-W. A. "Synthetic, structural and dynamic studies of iron carbonyls and their derivatives." Thesis, University of Essex, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371925.
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Silva, Nuno João de Oliveira. "Structural and magnetic studies on iron oxide nanoparticles in hybrid matrices." Doctoral thesis, Universidade de Aveiro, 2006. http://hdl.handle.net/10773/8944.
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Doutoramento em FísicaEste trabalho aborda algumas propriedades magnéticas e estruturais de nanopartículas de óxidos e óxidos-hidróxidos de ferro crescidos em matrizes híbridas orgânicas-inorgânicas. As matrizes híbridas, denominadas di-ureasils e obtidas pelo processo sol-gel, são compostas por uma rede siliciosa ligada covalentemente por pontes ureia a cadeias orgânicas de diferente peso molecular. A estrutura local dos di-ureasils não dopados está modelada como grupos de domínios siliciosos com dimensões nanométricas, estruturalmente correlacionados no seio de uma matriz rica em polímero. Neste trabalho mostra-se que os di-ureasils permitem o crescimento controlado de óxidos e óxidos-hidróxidos de ferro, incluindo a magnetite, maguemite, oxihidroxinitrato de ferro e ferrihidrite. O crescimento das nanopartículas de ferrihidrite dá-se em condições ácidas à superfície dos domínios siliciosos, junto aos grupos carbonilo, que funcionam como pontos de nucleação. Desse modo dá-se uma nucleação heterogénea, onde o tamanho das nanopartículas depende da concentração de ferro (entre 1 e 6% em massa), sendo a concentração de partículas constante. As propriedades magnéticas das nanopartículas de ferrihidrite revelam a existência de interacções antiferromagnéticas e de momentos descompensados. A contribuição destas duas componentes nas curvas de magnetização em função do campo magnético pode ser separada usando um método aqui proposto, o que permite um adequado estudo da evolução do momento magnético com a temperatura. O estudo das propriedades magnéticas dinâmicas das partículas de ferrihidrite, através de susceptibilidade ac, medidas de relaxação e medidas de efeito Mossbauer, permitiu estudar a evolução das interacções dipolares em função da concentração de ferro, bem como determinar a distribuição de barreiras de energia de anisotropia no caso em que essas interacções são desprezáveis. É apresentado um novo método para comparação desta distribuição com a distribuição de tamanhos, que permitiu concluir que os momentos magnéticos descompensados estão aleatoriamente distribuídos em volume. Usando baixas concentrações de água, foi possível crescer fases de oxihidroxinitrato de ferro com diferentes graus de cristalinidade, sendo algumas precursoras da ferrihidrite (como observado noutros trabalhos) e sendo outras novas fases. O crescimento de nanopartículas de maguemite e magnetite acontece após incorporação de iões de Fe2+ e Fe3+ seguidos de tratamento básico e térmico. Estes sistemas apresentam propriedades magnéticas típicas de nanopartículas superparamagnéticas sem interacções dipolares. As propriedades magnéticas dependem criticamente da existência de grupos isocianato livres, que actuarão como pontos de nucleação.
The present work focus on the structure and the magnetic properties of iron oxide and iron oxide hydroxide nanoparticles grown in organic-inorganic hybrids. The sol-gel derived matrix, termed di-ureasils, is a siliceous network to which oligopolyoxyethilene chains with different molecular weight are grafted by means of urea cross-links. The di-ureasils local structure was modelled as groups of nanometric siloxane correlated domains embedded in a polymericrich media. In this thesis, the controlled growth of ferrihydrite, iron(III) oxyhydroxynitrate phases, maghemite and magnetite in di-ureasils is demonstrated. Ferrihydrite nanoparticles are formed at low pH on the siliceous surface, where the carbonyl groups act as nucleation points. This implies an heterogeneous nucleation, where the nanoparticles size depend on the amount of iron (in the 1 to 6% wt range) and the nanoparticles concentration is constant. The ferrihydrite nanoparticles have antiferromagnetic and uncompensated/canted moments, responsible for linear and saturation components in the dependence of the magnetization with field, respectively. These components can be separated by a new method here presented and an accurate dependence of the magnetic moment with temperature determined. The dynamic magnetic properties of ferrihydrite were studied by ac susceptibility, relaxation and Mossbauer measurements. These studies allowed the determination of the evolution of the dipolar interactions with the iron content and the determination of the anisotropy energy barrier distribution in cases where such interactions are negligible. Comparing the energy barrier distribution with the size distribution allowed to conclude that the uncompensated moments are randomly distributed in volume. This conclusion is based on a new method here presented, that uses distributions to investigate the power law relation between physical quantities. Antiferromagnetic iron(III) oxyhydroxynitrate phases with different degrees of crystallinity are formed when using low water concentrations in the sol-gel process. Some of these are precursors of ferrihydrite, as previously found in literature, but others constitute new phases. Maghemite and magnetite nanoparticles can be grown inside diureasils after the incorporation of Fe2+ and Fe3+ ions, followed by basic and thermal treatment. The magnetic properties show the existence of noninteracting superparamagnetic nanoparticles. Evidence for the possibility of tuning the magnetic properties of the system by allowing the existence of free isocyanate groups acting as nucleation sites was found.
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Mako, Teresa Louise. "Electronic, Structural, and Catalytic Analyses of Iron Pincer Complexes and Methods for the Direct Functionalization of Lactide." Thesis, Boston College, 2017. http://hdl.handle.net/2345/bc-ir:107588.
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Thesis advisor: Amir HoveydaChapter 1: A review of recent iron catalyzed cross coupling advances. Abstract: Herein, advances in iron catalyzed cross coupling from 2010-2015 are thoroughly reviewed. Newly developed protocols and the mechanistic work that has been conducted to gain understanding of these systems are discussed. Specific emphasis is placed on the techniques used for mechanistic investigations. Chapter 2: Cross coupling applications of pyridyl(diimine) iron complexes. Abstract: Versatile and redox noninnocent pyridyl(diimine) iron complexes were explored for catalytic ability in iron catalyzed cross coupling reactions. These complexes were found active for the coupling of benzyl halides and aryl Grignard reagents, producing moderate yields. Although active for the coupling of cyclohexyl chloride and aryl Grignard reagents, the catalytic ability of these complexes was not general for alkyl halides, and the majority of substrates readily underwent β- hydride elimination. Mechanistic studies indicated the role of PDIFe(I)Ph and PDIFe(0)(N2)2 as offcycle species. Additionally, these complexes were employed for the Suzuki-type coupling of alkyl halides with 1,1-bis(boronates), leading to the conclusion that the processes were instead base catalyzed. Chapter 3: Electronic structure analysis and catalytic applications of carbeno(diamidine) iron complexes. Abstract: Iron(II) pincer complexes carbeno(diamidine) iron dibromide [(CDA)FeBr2] and bis(N-heterocyclic carbene)pyridine iron dibromide [(CNC)FeBr2] were examined by magnetic circular dichroism and density functional theory studies to invesitgate the effect that NHC moieties have on electronic structure and bonding in tridentate pincer ligands. The increased Fe-C bonding and pincer-donating abilities that result from NHC incorporation have a direct impact on spin state and observed ligand fields. Additionally, the position of the NHC moiety on the tridentate ligand and the overall geometry of the molecule were found to effect the net donor ability of the pincers and the strength of the iron-pincer interactions. Three new variations of the CDA ligand were developed and evaluated for catalytic ability in olefin hydrogenation and atom transfer radical polymerization reactions. While iron CDA complexes were found to be mediocre catalysts for both transformations, a cobalt CDA dimer complex was developed that showed promising catalytic activity for olefin hydrogenation. Chapter 4: The direct functionalization of lactide. Abstract: In an effort to provide cyclic diesters that could generate useful and biodegradable polymers, the direct functionalization of lactide was pursued. Lactide undergoes ring opening under a wide range of conditions, and thus traditional methods used for the functionalization of lactones could not be employed here. Typical routes for the formation of cyclic diesters involve multi-step syntheses and low yielding cyclization reactions. Herein, C-H activation and soft enolization have been identified as promising avenues toward the direct functionalization of lactide. Palladium catalyzed C-H activation was not amenable for lactide, however, soft enolization techniques led to low yields of the desired functionalized product
Thesis (MS) — Boston College, 2017
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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Yoon, Taejin. "Functional and structural studies of human frataxin an iron chaperone protein for mitochondrial iron-sulfur cluster and heme biosyntheses /." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1124287807.
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Harry, Milton Anthony. "Structural and electrical properties of ion beam synthesised ternary iron-cobalt silicide." Thesis, University of Surrey, 1996. http://epubs.surrey.ac.uk/842748/.
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The fundamental properties of the binary disilicides CoSi2 and FeSi2 have been extensively studied. Epitaxial CoSi2 can be formed on silicon, however, it is very difficult to form epitaxial FeSi2 on silicon substrates. With the aim to improve the epitaxial quality of FeSi2 and also to study the effect of the incorporation of Fe(Co) into CoSi2(FeSi2), ternary Fe-Co silicides are explored. This thesis reports a study of the structural and electrical characterisation of surface and buried ternary Fe-Co silicide layers in Si(100) fabricated by ion beam synthesis (IBS). In all cases two sets of samples were prepared, with Fe implanted first followed by Co in the first set and the implant order was reversed in the second set. Rutherford Backscattering spectrometry, four point probe measurements, cross-sectional transmission electron microscopy (XTEM), secondary ion mass spectrometry (SIMS) and x-ray photoelectron spectroscopy (XPS) were used to assess the synthesised material. The surface layers can be grouped into three structural classes determined by the composition. The Fe(Co) rich layers were found to have the FeSi2(CoSi2) structure for both implant orders. However, the layer morphology of the samples containing approximately equal amounts of Fe and Co was determined by the implant order. When Fe was implanted first the layers were non-crystalline and annealing had no significant effect on the crystal quality. However, when Co was implanted first epitaxial layers were formed after implantation and there was a significant improvement in the crystal quality with increasing anneal temperature. Phase separation into Fe and Co rich regions running parallel to the sample surface was observed upon annealing of the sample containing approximately equal amounts of Fe and Co, when Co was implanted first. For both implant orders the sheet resistance increased with increasing Fe content. Also for the Fe rich samples the phase transition from the ? to the a phase decreased with increasing Co content. The crystal quality of the buried layers was also determined by the implant order, however phase separation was not observed upon annealing of the samples with Co implanted first. The effects of the implantation energy, implantation temperature, intermediate anneals and the annealing temperature and time on the morphology of the surface layers containing approximately equal amounts of Fe and Co were also examined.
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White, Paul. "Bacterial protein import mediated by an iron transporter." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:20298bb4-0998-4dad-9dfa-dd9e52854dec.
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Multidrug resistant bacteria (MDR) have the potential to push back society to the pre-antibiotic era. Although discovered before penicillin, the inexorable rise in antibiotic resistance has revitalised interest in bacteriocins as treatments for bacterial infections. Bacteriocins are protein antibiotics principal to competition amongst pathogens and commensals, but the mechanisms by which they translocate across the Gram-negative cell envelope are poorly understood. The work presented in this thesis demonstrates how the endonuclease bacteriocin pyocin S2 (pyoS2) exploits the iron transporter FpvAI to translocate across the outer membrane (OM) of Pseudomonas aeruginosa. FpvAI is a 22-strand β-barrel and virulence factor in P. aeruginosa that transports iron into the cell in the form of a small siderophore, ferripyoverdine (Fe-Pvd). Uptake of Fe-Pvd requires the proton motive force (PMF), which is transduced to the ligand-bound receptor by TonB1 and its partner proteins ExbB-ExbD in the inner membrane (IM). The crystal structure of the high affinity complex (Kd = 240 pM) formed between the N-terminal domain of pyoS2 (pyoS2NTD) and FpvAI is presented, which shows pyoS2NTD mimics Fe-Pvd, and induces the same conformational changes in the receptor. Fluorescently-labelled pyoS2NTD was actively imported into P. aeruginosa PAO1 cells and this import was dependent on the PMF, TonB1 and a TonB1-box motif at the N-terminus of pyoS2NTD. Finally, photo-activated crosslinking of stalled translocation intermediates demonstrated pyoS2NTD translocates through the FpvAI β-barrel lumen by a process analogous to that of Fe-Pvd. Following binding to FpvAI, translocation begins by the unfolding of a force-labile portion of the plug domain, opening a narrow channel through FpvAI. This enables pyoS2 to deliver its own TonB1-box to the periplasm where contact with TonB1 activates its import through the same channel, most likely as an unfolded polypeptide. Hence, this study demonstrates that bacteria possess a rudimentary protein import system that exploits energised nutrient transporters in the OM.
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Kuranchie, Francis Atta. "Characterisation and applications of iron ore tailings in building and construction projects." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2015. https://ro.ecu.edu.au/theses/1623.
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The mine tailings are generated as the wastes worldwide as a result of exploration, excavation, blasting, beneficiation and extraction of mineral ores. In Western Australia, due to the extensive mining activities and increasing low grade ores, there is generation of mine tailings in large quantities, which could lead to environmental and disposal problems. The common practice of handling the tailings are to store them in tailing dams or as stockpiles near mine sites. Limited quantities are sometimes used as backfills and other applications. The utilisation of tailings in building and construction projects, which may consume a large volume of wastes, have not been explored extensively so far. Additionally, the understanding of chemical composition-based utilisation of tailings has very limited investigation.
In the present research, a critical review of the literature was made focusing on the utilisation of mine tailings in large quantities. Experiments have been conducted by developing a methodology to characterise the tailings based on the relationship that exists between electrical resistivity and the relative density of the tailings in dry and wet conditions. The results show that the electrical resistivity of iron ore mine tailings produced in Western Australia in dry condition ranges from 11 kΩm in a more dense state to 19 kΩm in a very loose state, while that in fully saturated condition ranges from 20 Ωm for a very dense state to 31 Ωm in a very loose state.
The laboratory investigation has been conducted to utilise iron ore tailings to produce geopolymer bricks. The sized tailings were mixed with sodium silicate solution used as an activator to form a paste. The paste was moulded and cured for different durations. It was found that the geopolymer bricks produced from iron ore tailings could have a compressive strength as high as 50.35 MPa. This is either superior or similar to international standard specifications for conventional bricks. Additionally, the new bricks will be more economical than conventional bricks with potential cost reduction of 36.8%.
The research has also investigated the utilisation of iron ore mine tailings to replace conventional aggregates in concrete. 100% of both fine and coarse conventional aggregates were replaced with tailings in the mixed design. The concrete mix was casted into moulds and cured. It was found that the compressive strength of the concrete with tailings aggregates at 28 days was 36.95 MPa which shows an improvement of 11.56% over the concrete with conventional aggregates. Additionally, the new concrete met all other requirements for quality assessment of concrete.
Finally, the research has conducted investigation into load-settlement behaviour of iron ore tailings to be considered as a structural fill material. The experiment was conducted in a model test tank in the laboratory varying the relative density of the tailings. It was found that the load-bearing capacity is 22 times higher, and the stiffness is 13.5 times higher than their values for conventional fill materials.
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Womack, Tanya G. "Structural and synthetic studies on iron(III) complexes formed with biologically relevant ligands." Thesis, University of East Anglia, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302143.
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Lund, Loren Glen. "Mobilization of Iron Enhances the Iron-Dependent Biochemical Reactivity of Asbestos in Vitro and Contributes to the Cytotoxicity of Asbestos in Cultured Cells." DigitalCommons@USU, 1992. https://digitalcommons.usu.edu/etd/7174.
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Asbestos related research began approximately 60 years ago, yet, the mechanism(s) by which asbestos exerts its biological effects is not well understood. The hypothesis upon which this dissertation is based is that mobilization of iron from asbestos enhances the iron-dependent biochemical reactivity of asbestos in vitro and contributes to asbestos-dependent cytotoxicity. The specific aims for this hypothesis were, 1) to determine whether iron was responsible for the biochemical reactivity of asbestos in vitro and asbestos-induced cytotoxicity in cultured cells, and 2) to determine whether mobilization of iron from asbestos enhanced the reactions catalyzed by asbestos in vitro and contributes to asbestos-induced cytotoxicity.
It was shown that a chelator (e.g., citrate) had to be present to mobilize iron from asbestos in vitro at pH 7.5. Factors that affected iron mobilization from asbestos (e.g., chelator, pH, or surface area) were investigated. Iron on crocidolite reacted with reducing agents and o2, catalyzed the formation of hydroxyl radical, and induced the formation of DNA single-strand breaks in vitro. However, mobilization of iron from crocidolite by a chelator greatly enhanced crocidolite-dependent o2 consumption, hydroxyl radical formation, and DNA damage in vitro.
Crocidolite was more cytotoxic, as measured by cloning efficiency, to cultured Syrian hamster embryo cells than crocidolite that had been pretreated to reduce the amount of iron associated with the fiber, suggesting that iron was responsible for the cytotoxicity. Crocidolite-dependent transformation of these cells was not detected. Crocidolite-dependent cytotoxicity to the human lung carcinoma cell line, A549, was directly dependent upon dose. Intracellular mobilization of iron (55 Fe) from crocidolite was determined using neutron-activated crocidolite and A549 cells. A time- and dose-dependent increase in the amount of 55 Fe mobilized intracellularly from crocidolite into a soluble, 10,000 x g supernatant fraction of lysed cells was observed for cultured cells treated up to 72 h. All of the results presented here support the hypothesis that iron and/or iron mobilization from asbestos may contribute to the some of the biological effects of asbestos in vivo.
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Landgraf, Boris [Verfasser], and Wolfgang [Akademischer Betreuer] Hansen. "Structural, magnetic and electrical investigation of Iron-based III/V-semiconductor hybrid structures / Boris Landgraf. Betreuer: Wolfgang Hansen." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2014. http://d-nb.info/1048626555/34.
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Ekiert, Thomas F. Jr. "Structural and magnetic characterization of nanostructured iron composites formed in the presence of citrate." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 202 p, 2009. http://proquest.umi.com/pqdweb?did=1818417551&sid=4&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Adjimani, Jonathan P. "Mechanism of Iron Transport in Mycelia Sterilia EP-76." DigitalCommons@USU, 1987. https://digitalcommons.usu.edu/etd/7165.
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The cyclic trihydroxamic acid, N, N', N' '-triacetylfusarinine C, produced by Mycelia sterilia EP-76, is shown to be a ferric ionophore for this organism. The association constant for ferric-N, N', N' '-triacetylfusarinine C complex was determined to be log K=32.5. Other iron chelating agents, such as rhodotorulic acid, citric acid, or the monomeric subunit of triacetylfusarinine C, N-acetyl- fusarinine, delivered iron to the cells by an indirect mechanism involving iron exchange into triacetylfusarinine C. In vitro ferric ion exchange was found to be rapid with triacetylfusarinine C. Gallium uptake rates comparable to those of iron were observed with the chelating agents that transport iron into the cell. Ferrichrome, but not ferrichrome A, was also capable of delivering iron and gallium to this organism, but not by an exchange mechanism. Unlike triacetylfusarinine C, the 14C-ligand of ferrichrome was retained by the cell. A mid-point potential of -690 mV versus the saturated silver chloride electrode was obtained for the ferric-N, N', N' '-triacetylfusarinine C complex, indicating that an unfavorable reduction potential was not the reason for utilizing a hydrolytic mechanism of intracellular iron release from the ferric triacetylfusarinine C chelate. The iron transport system recognizes only the -cis coordination isomer of ferric-N, N’, N' '-triacetylfusarinine C metal ligand complex even though the -cis configuration predominates in solution. Ferrichrome and ferric-N, N', N' '-triacetylfusarinine C are both transported by the same receptor.
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Wong, Lewis. "Optical & structural properties of ion beam fabricated amorphous and polycrystalline iron disilicide." Thesis, University of Surrey, 2010. http://epubs.surrey.ac.uk/771882/.
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The dependence of the optical and structural properties of amorphous and polycrystalline FeSi2 layers fabricated by ion beam sputter deposited (IBSD) FeSi2 and ion beam mixing (IBM), have been characterised. Amorphous and polycrystalline FeSi2 were fabricated using IBSD of Fe and Si at deposition temperatures from room temperature (80 °C) up to 700 °C and post-anneals between 300 and 700 T. Optical absorption measurements revealed direct band gaps for all layers including the amorphous layers from 0.891 - 0.947 eV. Little effect on the optical properties was found for amorphous layers annealed below 500 °C. The band gap value and absorption coefficient only significantly increased upon annealing above 500 °C, coinciding with the transformation from the amorphous to crystalline , B-phase. The deposition temperature was seen to affect the crystallinity of the as-deposited thin films, and vary the optical and structural properties within the layers significantly. An increase in deposition temperature resulted in a decrease of the band gap energies and an increase in photo-absorption by an order of magnitude. Using ion beam mixing, we have demonstrated formation of semiconducting silicides possessing direct band gap energies between 0.89 - 1.43 eV via low energy process conditions on multi-layer structures of Fe - Si. RBS was successfully employed to determine the level of silicidation formed using the extracted depth profiles. Mixing was enhanced upon increasing either the irradiation temperature or the ion fluence. The increase in the silicidation was greater when irradiating similar structures at a higher fluence than at a higher temperature. Optically, the increased silicidation did not affect the band gaps, with values of 0.89 - 1.03 eV upon irradiation of structures with 4- or more layers. Comparison of the effective absorption coefficients a} of structures revealed that although there is higher silicidation within the higher fluence structures, a larger absorption coefficient a was observed for higher temperature mixing. The formation of the FeSi2 at higher temperatures allows the amorphous structure to form with more short-to mid-range order thus exhibiting stronger and sharper absorption.
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Macpherson, K. A. "Static and dynamic aspects of structural chemistry : polynuclear complexes of the iron triad." Thesis, University of Bristol, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356222.
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Longbotham, Edward. "Structural and mechanistic studies of the iron(II)- and 2-oxoglutarate-dependent dioxygenases." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/structural-and-mechanistic-studies-of-the-ironii-and-2oxoglutarate-dependent-dioxygenases(e07c1b53-a6bb-4c9f-8ef2-6c6e0c3d800d).html.
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The Fe(II)- and 2-oxoglutarate (2-OG)- dependent dioxygenases are a large superfamily of enzymes that catalyse a wide variety of oxidative reactions. They are involved in a range of essential physiological roles, such as DNA repair, antibiotic synthesis and oxygen sensing. Research into these enzymes therefore has implications for the understanding of diseases such as cancer and stroke, which could lead to the design of new drugs, as well as biotechnology applications such as the cheaper and more efficient manufacture of chemicals. In this thesis, two members of this superfamily, a viral collagen prolyl hydroxylase (vCPH) and an asparagine hydroxylase (AsnO) were used as models to investigate the conserved mechanism of these enzymes. Catalytic intermediates were characterised using stopped-flow spectroscopy. In vCPH, the metal to ligand charge transfer (MLCT) complex was characterised and attempts were made to characterise the Fe(IV) intermediate, but they proved unsuccessful. The crystal structure of vCPH was determined for the first time, which showed structural features common to this superfamily of enzymes. A structure was determined with co-substrate 2-OG bound, revealing its mode of binding. In absence of a peptide substrate bound structure, a model was produced of peptide substrate bound in the active site. Catalytic intermediates were also studied in AsnO and a significant isotope effect was found to occur on the decay of the putative Fe(IV) intermediate. An active site variant of AsnO was produced which was hoped would change the activity of AsnO from a hydroxylase to a chlorinase. However, this was determined not to be the case. Catalytic intermediates of this AsnO variant were also determined and compared to the WT AsnO. These data have allowed us to contribute to knowledge about the structural biology and the catalytic cycle involved in this important family of enzymes.
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Abenojar, Eric Chua. "Investigation of Structural Effects on the AC Magnetic Properties of Iron Oxide Nanoparticles." Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1516187103909374.
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Milford, Gabrielle Helen. "Moessbauer spectroscopic studies of the magnetic and structural properties of novel nanophase magnetic materials." Thesis, University of Liverpool, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343589.
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Masala, P. G. "IRON OXIDE NANOPARTICLES AND NANOCOMPOSITES: A DIFFRACTOMETRIC STUDY." Doctoral thesis, Università degli Studi di Milano, 2014. http://hdl.handle.net/2434/244853.
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Nanosized magnetic structures are currently key materials for advancements in electronics, optoelectronics, magnetic storage, and many bio-inspired applications. What is usually termed ‘‘nanostructured systems’’ comprises those materials whose properties are determined by particles, crystallites, or clusters with characteristic lengths between about 1 and 100 nm. If the grain or domain size becomes comparable or smaller to the characteristic length scale of the interaction processes controlling a particular property, different effects and unusual chemical and physical properties can be expected that are highly attractive in a number of technical applications. In recent times, large advancements have been achieved related to the synthesis and characterization of
well-defined, discrete magnetic nanoparticles for both fundamental and technological purposes. However, precise knowledge of the relationships between particle shape and size distribution, surface structure, and the resulting magnetic properties of magnetic nanoparticles is still lacking.
In particular, iron oxide nanoparticles have been the subject of many theoretical and experimental studies.
The goal of this thesis is to provide a crystallographic structural description of the atomic rearrangements in superparamagnetic maghemite (γ-Fe2O3) nanoparticles and in magneto-plasmonic nano heterostructures formed by metallic gold and magnetite (Fe3O4), looking for a relationship between the structure and the properties.
The thesis is organized in 3 chapters.
The first chapter is divided in two part: in the first a briefly introduction about nanomaterials is presented, in the second one all the used techniques are described. First the main concepts about powder diffraction are briefly recalled, then the Pair Distribution Function method is introduced, then there is a description of theory about Small angle X-Ray Scattering and finally ESR theory is shortly presented.
In the second chapter all the beamlines of the European Synchrotron Radiation Facility, used for the data collection, are described.
The heart of the thesis consists in the last chapter where all the data and the results about nanomaterials (γ-Fe2O3) and nanocomposites (Au-Fe3O4) are shown. In this chapter a thorough structural characterization was performed by using X-ray powder diffraction by means of conventional Rietveld analysis, Pair Distribution Function and Small Angle X-ray Scattering; in addition Electron Spin Resonance spectroscopy was performed on the systems to shed light on their magnetic properties.
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Abdel-Rahman, Nabil Mahmoud. "Cold-formed steel compression members with perforations." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ30065.pdf.
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Vernik, Isak. "Structural and kinetic studies of [mu]-oxo iron complexes of bis((dioximato)borate) macrocycles." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ27385.pdf.
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Croy, Jason Robert. "Supported mono and bimetallic platinum and iron nanoparticles electronic, structural, catalytic, and vibrational properties." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4652.
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Catalysis technologies are among the most important in the modern world. They are instrumental in the realization of a variety of products and processes including chemicals, polymers, foods, pharmaceuticals, fuels, and fuel cells. As such, interest in the catalysts that drive these processes is ongoing, and basic research has led to significant advances in the field, including the production of more environmentally friendly catalysts that can be tuned at the molecular/atomic level. However, there are many factors which influence the performance of a catalyst and many unanswered questions still remain. The first part of this work is concerned with the factors that influence the catalytic properties (activity, selectivity, and stability) of supported Pt and Pt-M nanoparticles (NPs). These factors are a synergistic combination of size, composition, support, oxidation state, and reaction environment (i.e. adsorbates, temperature, pressure, etc.). To probe the catalytic properties of complex and dynamic NP systems we have used MeOH decomposition and oxidation reactions, each of which has significant environmental and economic potential. We have given some emphasis to the state of NP oxidation, and with the aid of X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD), have followed the formation and temperature-dependent evolution of oxide species on Pt NPs. Further, we have explored how these species behave under the conditions of our probe reactions using a packed-bed mass flow reactor coupled to a quadrupole mass spectrometer (QMS). To carry out our investigations we exploit a NP synthesis method which is rather novel to nanocatalysis, micelle encapsulation. Since most available experimental techniques give information on ensemble averages, control over size distributions in NP samples is critical if unambiguous results are to be obtained. Micelle encapsulation allows us this control with several unique, inherent advantages.; It is to this end that micelle encapsulation has allowed us to probe the detailed structure of small (~1 nm), supported, Pt NPs with extended X-ray absorption fine structure spectroscopy (EXAFS). Furthermore, we were able to explore experimentally, for the first time, the vibrational density of states (VDOS) of supported, isolated, monodispersed, mono and bimetallic NP systems via nuclear resonant inelastic X-ray scattering (NRIX). These synchrotron-based techniques (EXAFS, NRIXS) rely heavily on the monodispersity of the NP ensemble for reliable information.ID: 028916773; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2010.; Includes bibliographical references (p. 204-229).
Ph.D.
Doctorate
Department of Physics
Sciences
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Smith, Stephen Findley. "Structural stability, support and excavation aspects of mine openings in stratified iron ore deposits." Thesis, University of Nottingham, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283587.
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Fern, George Robert. "Structural studies on iron sulfur clusters and ferrocenyl compounds, the importance of lattice effects." Thesis, University of Essex, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363442.
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Mizutani, Kimihiko. "Studies on the Structural Mechanism of Iron Uptake and Release in Ovotransferrin N-Lobe." Kyoto University, 2001. http://hdl.handle.net/2433/78126.
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Li, Song. "Structural design, characterization, and property investigation of iron oxide : nanoparticles with visible light photoactivity." Thesis, Metz, 2009. http://www.theses.fr/2009METZ038S/document.
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La pollution de l'environnement et l'insuffisance des ressources énergétiques dans le monde constituent deux défis majeurs auxquels l'humanité est confrontée aujourd'hui. La photocatalyse hétérogène de semiconducteur est considérée comme une stratégie prometteuse pour la collecte de l'énergie solaire et la décomposition de contaminants organique dans l'eau et l'air. TiO2 est aujourd'hui le photocatalyseur le plus largement utilisé. Cependant, TiO2 est un semi-conducteur avec une bande interdite d'environ 3.1eV. Donc, il n'absorbe pas la lumière visible. L'oxyde de fer est un bon candidat potentiel pour la photocatalyse : ce matériau est stable, moins cher, respecte l'environnement et il a une bande interdite suffisamment petite (2.1 eV) pour absorber 45% de la radiation solaire incidente. Afin de développer un photocatalyseur efficace de l'oxyde de fer, nous avons préparé des nanoparticules d'oxyde de fer de formes différentes et étudié l'influence des différents paramètres expérimentaux. L'objectif cette thèse est de développer et de caractériser un photocatalyseur à base d'oxyde de fer et hautement photoréactive capable de décomposer les molécules des polluants organiques. Des nanoparticules d'oxydes et d'oxyhydroxyde de fer avec différentes morphologies ont été conçues et synthétisées par la méthode hydrothermale. Dans le système de réaction, des agents de surface avec différents groupes fonctionnels ont été utilisés pour la contrôle de la morphologie. Les effets ont été attribués à l'interaction entre les groupes fonctionnels des agents de surface et des surfaces d'oxyde de fer. Pour élucider les mécanismes de croissance de nanoparticules d'oxyde de fer, une technique en MET basée sur une méthode de trace a été proposée afin de caractériser les plans cristallins et l'orientation de nanoparticules facettées, et donc leurs formes. Les indices de Miller de plans de surface peuvent être déterminé par la transformation de coordonnées après la détermination du vecteur des bords dans les systèmes de coordonnées de l'écran du MET. Dans ce travail, l'orange de méthyl, un représentant colorant azoïque de l'industrie textile, a été pris comme molécule modèle pour les contaminants organiques pour évaluer les capacités photocatalytiques des poudres obtenues. Une étude systématique, y compris l'influence des conditions de réaction et la cinétique, a été effectuée pour étudier le mécanisme de la dégradation photocatalytique de méthylorange à l'oxyde de fer sous irradiation de lumière visible. Il a été constaté que la photodégradation de l'orange de méthyle à l'oxyde de fer est un procédé de photocatalyse de semiconducteur. De plus, les activités photocatalytiques des IV lumières visibles d'oxyde de fer peuvent être harmonisées par le contrôle des morphologies, surtout les indices des facettes des nanoparticules d'oxyde de fer. Les techniques de traitement postérieur ont été utilisées à améliorer la capacité photocatalytique de l’oxyde de fer pour décomposer les molécules des contaminants organiques. Les nanopoudres d’oxyde de fer ont été modifiées par intégration de métaux nobles, par exemple les nanoparticules d'Ag et d'Au. Les résultats des expérimentations photocatalytiques montrent que la capacité des particules métalliques intégrées d'inhiber la recombinaison de la paire de trou électrique dépendent de la position relative entre fonctions travail et la position de la bande de conduction de l'oxyde de fer. Pour surmonter ce problème causé par la courte distance libre des charge dans l'oxyde de fer, des nanobâtonnets ont été préparés. Les résultats indiquent que l'activité photocatalytique de l'oxyde de fer peut être améliorée par l'optimisation microstructurale et la modification surfaciqueGlobal environmental pollution and energy issue are considered as two greatest challenges that human society is facing now. Semiconductor photocatalysis is expected as a highly promising strategy for both harvesting solar energy and decomposing unwanted organics in water and air by solar light irradiation. The main problem of TiO2, the most widely studied photocatalyst material by now, is that its band gap is as wide as 3.1 eV, making it absorb only the UV part of the incident solar irradiation. Iron oxide has a proper band gap of about 2.1 eV which lies in the visible region of solar spectrum and allows utilization of 45% of the solar radiation. Together with the environmental compatibility and low cost, iron oxide is considered as a good candidate for visible light photocatalyst. For the purpose of exploiting iron oxide as effective photocatalyst, we have prepared iron oxide nanoparticles of various shapes and investigated their photocatalytic activities. The objective of the present dissertation is to develop and characterize iron oxide photocatalyst which is highly responsive to visible light. Nanostructured iron oxide and oxyhydroxide nanoparticles with various morphologies were designed and synthesized via hydrothermal route. Stabilizer molecules with different capping groups were applied in the reaction system to control the morphology of the final products. The effects attributed to the interaction between capping groups of stabilizer molecules and iron oxide surfaces. To elucidate the growth mechanism of iron oxide particles, a TEM based trace method was proposed to characterize the crystalline planes and directions of a faceted nanoparticle, and therefore its shape. The Miller indices of surface planes can be determined through coordinate transformation after the determination of the edge vectors in the TEM screen coordinate system. Methyl orange, a representative azo dye pollutant in textile industry, was chosen as the model contaminant molecule to evaluate the photocatalytic performance of the obtained powders. A systematic study, including the influence of the reaction conditions, the kinetics and the route of the oxidation of the methyl orange molecules, was carried out to explore the mechanism of photocatalytic degradation of organic molecules over iron oxide under visible light irradiation. It was found that the photodegradation of methyl orange over iron oxide was more like a semiconductor photocatalysis process, rather than a surface reaction process of ligands to metal charge transfer. Moreover, the visible light photocatalytic activities of iron oxide can be tuned by controlling the morphologies, especially the crystallographic facet of the iron oxide nanoparticles. II Post-treatment techniques were adopted to enhance the ability of iron oxide photocatalyst to decompose organic pollutant molecules. The iron oxide nanopowders were modified by loading noble metals, such as Ag and Au nanoparticles. Photocatalytic experimental results showed that the abilities of loaded metal particles to inhibit the electron-hole pair recombination depend on the relative positions between their work functions and conductive band position of the iron oxide. To overcome the problem caused by the short free distance of charge carriers inside iron oxide, nanorod arrays of iron oxide were prepared. The results show that the photocatalytic activity of iron oxides can be improved by microstructure optimization and surface modification
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Aho, Mark Francis. "A database for encased and concrete-filled columns." Thesis, Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/19061.
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Al-Shihri, Marai Abdullah 1958. "BUCKLING STRENGTH OF HEAVY STEEL COLUMNS (WELDED SHAPES, INITIAL CURVED COLUMNS, HOT-ROLLED SHAPES)." Thesis, The University of Arizona, 1986. http://hdl.handle.net/10150/291869.
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Biddah, Aiman Mahmoud Samy. "Evaluation of the seismic level of protection of steel moment resisting frame building structures." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0007/NQ42833.pdf.
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Macedo, Joana Tavares. "Functional and structural studies of a mini-ferritin protein." Master's thesis, Faculdade de Ciências e Tecnologia, 2014. http://hdl.handle.net/10362/13301.
Full textAbstract:
Dissertação para obtenção do Grau de Mestre em
BioquímicaDNA-binding protein from starved cells (Dps) are mini-ferritins mainly expressed in bacteria during severe environmental stress. These proteins with a highly conserved structure provide wide protection to cells and function as iron-storage proteins. Some Dps can also bind DNA and the N-terminus has been suggested to be involved in this interaction, due to its positively charged residues. This thesis focused on the functional and structural features of recombinant Dps protein from Pseudomonas nautica 617 (P. nautica). To investigate the iron incorporation mechanism, iron uptake assays using H2O2 and O2 as co-substrate for iron oxidation were performed with Dps WT and F46G variant, using UVVisible spectroscopy. The results showed that Phe46, located close to the ferroxidase center (FOC), does not influence the amount of iron stored. Nevertheless, this residue affectes the iron core formation when O2 was used as co-substrate. Structural characterization of the incorporation of Fe(II) and Cu(II) was performed with X-ray crystallography. High resolution crystal structures of Apo-Dps, Dps incubated with 12 Fe(II)/Dps (12Fe-Dps) and Dps incubated with 12 Cu(II)/Dps (12Cu-Dps) were obtained. It was possible to observe the binding of the metals to the FOCs with different coordination geometry as well as geometrically different FOCs. Additionally Fe(II) and Cu(II) atoms were assigned in a position where hydrophilic pores can be created and serve as entry routes for the metals. For the characterization of the Dps-DNA interaction, electrophoretic mobility shift assays (EMSAs) were carried out with Dps WT and Q14E variant. The results showed that this protein can bind DNA, but the affinity for DNA significantly decreases in the presence of the negative charge in the N-terminus. In this sense, mutations in the N-terminus that may increase the affinity for DNA binding were produced by site-directed mutagenesis.
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Vey, Jessica L. (Jessica Lynn). "Structural insight into the assembly of iron-sulfur clusters and their function in radical generation." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43090.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2008.Vita.
Includes bibliographical references.
This thesis addresses two emerging areas in the study of iron-sulfur cluster biochemistry: bioassembly of iron-sulfur clusters, and their involvement in initiation of radical chemistry. The structure of a cysteine desulfurase involved in cluster bioassembly in the cyanobacterium Synechocystis PCC sp. 6803 was solved by X-ray crystallography and analyzed in terms of its mechanistic implications. We found that the active site cysteine responsible for the direct removal of sulfur from substrate cysteine is located on a short, well-ordered loop, consistent with structures solved of homologous proteins. The length of this loop is thought to restrain the active site cysteine, interfering with its ability to affect catalysis. Our results are consistent with the theory that this cysteine desulfurase requires an accessory protein for fully activity in vivo. Two structures of pyruvate formate-lyase activating enzyme from Escherichia coli, an Sadenosylmethionine radical enzyme, were also solved by X-ray crystallography, providing the first structure of an activase from this family of enzymes. These structures revealed the enzyme's active site and the residues involved in binding and orienting substrate for hydrogen atom abstraction. Comparison of the structures of the substrate-free and substrate-bound forms of the enzyme identified a conformational change associated with substrate binding. Detailed analyses of the structure of pyruvate formatelyase activating enzyme were carried out to provide insight into catalysis. These structures were also analyzed in comparison with other S-adenosylmethionine radical enzyme structures to more clearly understand the structural basis for reactivity in this superfamily.
by Jessica L. Vey.
Ph.D.
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Young, Steven E. "Crystal chemical control on intra-structural copper isotope fractionation in natural copper-iron-sulfur minerals." Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/289914.
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The nature of Cu isotope fractionation in natural Cu-Fe-S minerals was investigated through acid ferric sulfate leaching of copper ore from Morenci, Arizona. Copper isotope composition of the derived solutions varies from δ⁶⁵Cu = 0.47‰ to 5.21‰ over the course of progressive copper extraction. High δ⁶⁵Cu values characterize solutions collected in the first half of the leach, while the solutions collected between 35% and 45% copper recovery exhibit lower δ⁶⁵Cu values. This general pattern was observed for both bacterially-mediated and abiotic leaching. Sulfate solutions derived from dissolving pure djurleite show variable Cu isotope compositions as well, although the range is protracted from δ⁶⁵Cu = 0.01‰ to 1.21‰. As the Cu:S ratio of the remaining sulfide decreases, crystal structure parameters change as mineralogy passes through a series of nonstoichiometric copper sulfides. Mineralogy converges to yarrowite near 44% copper dissolution. Crystal chemical studies show that distribution of the two copper-sulfur bond coordination geometries, triangular planar and tetrahedral, in the copper sulfides, approximately corresponds to changes in δ⁶⁵Cu of the leachates. In particular, the proportion of CuS3 relative to CuS4 groups decreases from Cu/S = 2.00 (chalcocite) to 1.40 (geerite). Between Cu/S = 1.40 to 1.00 (covellite), the relative proportion of CuS3 groups increases slightly. Connection between coordination number and Cu isotope fractionation implies affinity of CuS₃ groups for the heavier, ⁶⁵Cu, isotope. This can be justified through bond length-bond strength arguments. Solutions from bornite dissolution vary from δ⁶⁵Cu = -0.79‰ to 1.14‰, with the largest values associated with solutions from early stage of reaction (up to 15% copper removal). Around 25% dissolution, δ⁶⁵Cu of the solution approaches that of the original bornite (δ⁶⁵Cu = 0.02‰). This is explained by disappearance of all remaining CuS₃ groups. Sulfur isotope compositions of solutions and sulfides derived from djurleite leaching were determined to investigate the possibility of intra-mineral fractionation. Very soon after reaction initiation, δ³⁴S of both sulfur reservoirs reach a steady-state with sulfate solutions about 2‰ enriched in ³⁴S relative to residual sulfide. Unlike the case of Cu isotopes, the main partitioning affecting S isotopes is exchange between sulfate and sulfide.
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Hewetson, C. G. "Object - oriented steel member design framework /." Thesis, Link to the online version, 2005. http://hdl.handle.net/10019/249.
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