Browsing by Subject "iron"

Now showing 1 - 7 of 7
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    Biogeochemical Interactions And Ecological Consequences Of Sulfur In Stands Of Wild Rice
    (2020-05) LaFond-Hudson, Sophia
    Wild rice is an ecologically and culturally important plant that typically grows in lakes and rivers in Minnesota that have low sulfate concentrations. Previous work demonstrated that elevated sulfate concentrations contribute to the decline in wild rice populations when conditions allow for the reaction of sulfate to sulfide. This dissertation investigates the fate of sulfate in the rooting zone of wild rice, mechanisms and consequences of sulfide exposure to plants, and the long-term effects of sulfide exposure on population dynamics. Key findings include 1) iron plaques on root surfaces transition from iron oxide to iron sulfide during reproduction if sulfate is elevated; 2) in elevated sulfate, seed production is delayed and shortened and plants produce fewer, smaller seeds with less nitrogen; and 3) populations of wild rice grown in low sulfate have stable biomass oscillations with a period of approximately 4 years, but elevated sulfate destabilizes these cycles and drives the population toward extinction.
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    Characterization and Reactivity of Synthetic Nonheme Oxoiron(IV) Complexes
    (2015-05) Bigelow, Jennifer
    Nonheme iron enzymes are prevalent throughout nature and utilize oxygen as the oxidant. While some intermediates are proposed, such as iron(IV)-oxo and iron(III)-peroxo species, the nature of the reactivity of these species has not yet been fully explored. Nonheme synthetic iron model complexes allow for easy modification to probe the reactivity of such species, and allow for characterization for later comparison with enzymes. This dissertation explores the reactivity of iron(IV)-oxo species supported by a tetramethycyclam framework. Interesting, in contrast to what had been reported previously, the electron-donating properties of the axial ligand do not correspond to the hydrogen atom transfer (HAT) reactivity, while a consistent trend for oxygen atom transfer (OAT) is observed. Ligand tethering is found to have a large impact on the enthalpy of activation. It is proposed that the iron(IV)-oxo moiety rises out of the plane to react, which forces tethered ligands to weaken the axial bond. The activation of oxygen by synthetic iron complexes, in the presence of either a hydrogen atom donor or an acid and a proton source, has been proposed to mimic enzymatic activity. However, the reexamination of mechanisms previously reported to follow an enzyme-mimicking pathway are instead due to peroxyl radicals. This highlights the importance of testing such mechanisms, as autooxidation is a common problem with many compounds in the presence of dioxygen. Finally, species such as iron(IV)-oxo and iron(III)-peroxo complexes, as well as related complexes, are characterized by resonance Raman spectroscopy. Many of these complexes have a ligand with a carboxylate moiety, as seen in nonheme enzymes. Characterization of these complexes show similarities between iron(IV)-oxo and iron(III)-peroxo and chromium(IV)-peroxo species reported previously, having similar vibration values, while major differences exist in vibrations between previously reported iodosylarene-iron(III) complexes and new iodosylarene-iron(III) complexes.
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    Geologic Map Mesabi Iron Range, Minnesota, second edition
    (Mesabi Range Geological Society (MRGS) and Minnesota Geological Survey, 1999) Meineke, David G; Buchheit, Richard L; Dahlberg, Henk E; Morey, G B; Warren, LeRoy E
    Historic strip-map of a 100 mile-long, 10 mile-wide area covering portions of St. Louis and Itasca counties, and enclosing the Mesabi Iron Range and parts of the Duluth Complex. Scale 1: 62500. First compiled and released in 1993, this map has never been formally published with a cite-able reference. Data and assistance for the compilation was provided by numerous companies, individuals and organizations which are listed on the map plate. The map has been in the charge of the Mesabi Range Geological Society and they have provided the MGS permission to host a scanned version of this map under the MGS holdings on the University of Minnesota Digital Conservancy (2019). The original map of 1993 has been superseded by the 1999 edition to correct certain errors in the cartographic base. The geology portion of the map was not altered.
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    The Impact of Iron Deficiency During Development on Mammalian Target of Rapamycin Signaling, Neuronal Structure, and Learning and Memory Behavior
    (2010-11) Fretham, Stephanie
    Iron deficiency (ID) is the most common micronutrient deficiency, affecting an estimated 2 billion people world wide including 20-30% of pregnant women and their offspring. Many human studies have demonstrated negative effects of early life ID on learning and memory which persist beyond the period of ID despite of prompt iron treatment, observations which are supported by rodent models of early iron deficiency anemia (IDA). In spite of a large, observational literature the mechanisms through which early ID causes acute and persistent brain dysfunction are largely unknown. Mammalian target of rapamycin (mTOR) signaling is an attractive candidate for mediating the effects of early ID because it integrates cellular metabolic status to regulate fundamental aspects of cellular growth and differentiation. The overall goal of the current studies is to understand the role of iron in regulating mTOR signaling during a critical period of development in the hippocampus by using unique genetic mouse models of hippocampal ID to: 1) Determine when iron is required for hippocampal development 2) Determine the role of iron in mTOR signaling 3) Manipulate iron and mTOR to determine effects on hippocampal structure and behavior. The findings from these experiments demonstrate that mTOR signaling is upregulated by neuronal ID during the same period that rapid hippocampal development requires large amounts of iron. Additionally, rescue of behavioral outcomes in adult animals following restoration of mTOR signaling (through either timely iron repletion or pharmacological suppression) provides functional evidence for a connection between mTOR and the persistent effects of early ID.
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    Iron Sulfide Formation on the Root Surfaces of Wild Rice
    (2017-08-16) LaFond-Hudson, Sophia; Johnson, Nathan; Pastor, John; Dewey, Brad; lafo0062@d.umn.edu; LaFond-Hudson, Sophia
    The data are from an experiment showing life-cycle induced iron sulfide formation on root surfaces of wild rice. Plants with and without added sulfate were harvested during the reproductive stage of the life cycle to quantify concentrations of iron and sulfide on root surfaces. Seed and plant N was measured to examine the effect of iron sulfide root plaques on seed production. On amended roots, iron transitioned from mostly Fe(III) to mostly Fe(II) as sulfide concentrations increased rapidly. Amended plants produced fewer, lighter seeds with less nitrogen.
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    Mechanistic Investigation of Oxygen Activation and cis-Dihydroxylation by Rieske Dearomatizing Dioxygenases
    (2016-03) Rivard, Brent
    Rieske dearomatizing dioxygenases are multicomponent enzymes that catalyze a biochemically unique regio and stereospecific cis-dihydroxylation of aromatic compounds. The active site of the terminal oxygenase component contains a nonheme mononuclear iron and a [2Fe-2S] Rieske cluster. The isolated oxygenase component (hereafter RDD) can rapidly form product in a single turnover (STO) reaction after stoichiometric reduction of the metal centers and exposure to substrate and O2. After product formation, both metal centers are oxidized, indicating that two non-substrate-derived electrons are required for the reaction. The normal O2-driven STO reaction is complete in ≪1 second and no reaction cycle intermediates have been detected. Past studies have also shown that the fully oxidized RDDs can form product by utilizing H2O2 as the source of both oxygen and electrons. In the specific case of the RDD benzoate 1,2-dioxygenase, product formation during H2O2-driven reactions is much slower (completion requires ≥ 60 min), and a kinetically competent Fe3+-hydroperoxo species has been detected. These results, combined with several other logical and experimentally supported arguments, engendered the hypothesis that an Fe3+-hydroperoxo or an electronically equivalent Fe5+-oxo/hydroxo was the initial substrate oxidant of the RDD reaction. This thesis presents the most complete presteady-state kinetic analysis of O2-driven RDD cis-dihydroxylation to date. In contrast to the previous mechanistic hypotheses, the results support a model in which an Fe3+-superoxo-like species is the initial substrate oxidant. The use of this oxidant significantly changes the predicted reaction coordinate utilized by RDD for cis-dihydroxylation under O2-driven conditions. Additionally, the structure of the Fe3+-hydroperoxo species formed during H2O2-driven turnover and the conditions that allow its formation are further defined. In total, the new insights gained from the studies herein provide the first evidence that O2- and H2O2-driven turnover reactions utilize different reaction coordinates, but nevertheless lead to formation of the same unique cis-diol product.
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    Optimizing Biofiltration Media for the Capture of Phosphate and the Support of Vegetation Growth
    (2022-06) Kramarczuk, Kathryn
    AbstractBiofiltration is a stormwater management practice designed to treat runoff for harmful contaminants. A critical component of these systems is the granular media. In this study, I investigated six different types of base media (10% leaf compost, 20% leaf compost, 10% food compost, 20% food compost, sphagnum peat, reed sedge peat) and four different amendments (spent lime, biochar, iron and sphagnum peat) in various combinations with sand to test their capacity in mitigating phosphate release and supporting the growth of Switchgrass (Panicum virgatum) as an indicator of potential to support vegetation. The study consisted of an outdoor mesocosm experiment over three years, with 34 events total where 30 seeded mesocosms containing various media mixes received water from the Mississippi River (near downtown Minneapolis, MN, USA) that was spiked with phosphorus to simulate stormwater inputs. Soluble reactive phosphorus and nitrate concentration, pH, Switchgrass height over time, and Switchgrass biomass at senescence was measured each year. In general, mixes containing food compost, leaf compost, biochar with compost and spent lime with compost leached phosphorus whereas mixes containing peat, iron with compost, and sand adsorbed phosphorus. The mixes that leached phosphorus supported the most plant growth. Spent lime mixes and biochar mixes had the highest effluent nitrate concentrations indicating effects on N mineralization or nitrification. The iron and leaf compost layered media mix performed the best of all the mixes tested in terms of mitigating the release of phosphate and having the potential to support vegetation. Future research is necessary to determine if it can continue preventing phosphorus leaching and support vegetative growth with a higher percentage of compost and different plant species. Keywords: phosphate, nitrate, biofiltration, stormwater treatment, switchgrass (Panicum virgatum), compost, peat, biochar, water treatment residuals, iron