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Fusarium Head Blight In Texas Wheat and Small Grains
Get PDFFusarium head blight (FHB), also known as head scab, is a disease of barley, oat, wheat, and other small grains caused by the fungus Fusarium graminearum and closely related Fusarium species. FHB is one of the most important diseases of wheat across most of the wheat producing regions in the world
Development of First Row Transition Metal Dithiolates, Dithiolenes, and Nitrosyls as Redox-Active Ligands in Polymetallic Complexes
No full textThe ubiquity of sulfur-metal connections in nature has inspired the design of bi- and multi-metallic systems in synthetic inorganic chemistry. Common motifs found in biocatalysts developed through evolutionary biology include the positioning of metals in close proximity using flexible sulfur bridges and the presence of ��-acidic/delocalizing ligands. This dissertation delves into how these principles have been leveraged in the development of (NO)Fe(N���S���) and Ni(N���S���) metallodithiolates as redox-active bidentate ligands. The latter, a paramagnetic metallo-ligand, serves as a powerful spin probe.
First, the exceptional stability of a [(NO)Fe(N���S���)-Fe(NO)���] species, allowing its isolation and structural characterization at three distinct redox states, is linked to charge delocalization occurring on both the Fe(NO) and the Fe(NO)��� support. This accommodates the formation of a rare non-heme {Fe(NO)}��� triplet state with a linear configuration. A subsequent FeNi complex, featuring redox-active ligands on both metals (NO on iron and dithiolene on nickel), displayed unexpected physical properties. Electrochemical studies revealed good reversibility in two redox processes, enabling the isolation of reduced and oxidized forms. Various spectroscopic and crystallographic analyses confirmed these states, with M��ssbauer data specifically supporting the redox change at the iron site upon reduction, also generating a thermally stable HS {Fe(NO)}��� state, unlike the previous diiron complex. Oxidation of the complex produced a dimeric dication, revealing intriguing magnetic behavior. In solution, the monomer appears as a spin-coupled diradical between {Fe(NO)}��� and the nickel dithiolene mono radical, while dimerization couples the latter radical units via a Ni���S��� rhomb and results in the solid-state product. Magnetic data (SQUID) on the dimer dication found a singlet ground state with a thermally accessible triplet state responsible for the magnetism. A theoretical model built on an H��� chain explains this unexpected ferromagnetic low-energy triplet state, arising from antiferromagnetic coupling of a four-radical molecular conglomerate. Notably, the Ni���S��� rhomb appears to facilitate long-range superexchange (8 ��) between the distal iron radicals.
To investigate long-range coupling interactions, two (NO)Fe(N���S���) units were connected through group 10 cations, producing di-radical trimetallic complexes with an MS��� bridge (M = NiII, PdII, PtII). Despite a 6 �� intramolecular Fe���Fe distance, antiferromagnetic coupling was observed between {Fe(NO)}��� units, with coupling constants (J) of -3, -23, and -124 cm����� for NiII, PdII, and PtII, respectively. These results demonstrate the ability of sulfur-dense metallodithiolate ligands to engender strong magnetic communication due to their enhanced covalency and polarizability.
Lastly, three new bimetallic Ni(N���S���)-Ni(S���C���R���) complexes, based on Ni(N���S���) metalloligand donors and nickel dithiolene receiver units, were designed to explore the influence of ligand environment on electronic structure and redox properties. The electronic characteristics of the nickel donor and receiver units determine which metal site, either the metallodithiolate or the dithiolene nickel site, receives the initial electron. This study showcases an exceptional demonstration of targeted electron addition control over specific metal sites within multimetallic systems.
In conclusion, this research highlights the central role of the (NO)Fe(N���S���) complex as a bidentate S-donor and its application as a metallodithiolate ligand spin probe for studying the electronic structure of bi and poly-metallic complexes. An overview and summary of this work, which is being prepared for an accounts of chemical research, can be found in Chapter VII
Distribution, Sources, and Hydrogeochemical Processes That Release Arsenic, Fluoride, and Nitrate in the Gulf Coast Aquifer, Texas
No full textIn the Gulf Coast Aquifer (GCA) in Texas, arsenic (As), fluoride (F), and nitrate (NO3) concentrations are spatially variable, and in certain areas, frequently exceed drinking water guidelines. Understanding the sources and processes that generate this contamination is important for prioritizing areas for interventions and anticipating future changes in both water quality and human health from land use changes, groundwater pumping, and climate change. The first objective of this study is to identify the sources of dissolved As and F and the relative contributions of hydrological and geochemical processes on their release to pore-waters within the GCA. The second objective is to apply this knowledge generated at the regional scale to explain the distribution of As and F concentrations within private wells across an eight-county public health study.
To achieve the first objective, spatial, climatological, and hydrologic data, as well as geological context and the chemical composition of groundwater, were analyzed. The GCA was divided into eight climate-aquifer zones across which the concentrations and processes generating the contaminants were evaluated. Kruskal-Wallis and Wilcoxon Rank Sum tests were performed on the climate-aquifer zones to determine whether wells underlying different land use types systematically deviate their As and F concentrations. To suggest sources and processes, multivariate analyses were performed on physical and chemical parameters in well water in 1183 wells. From these relationships, potential chemical reactions were proposed for each zone which influence contaminant and major ion chemistry. To test these proposed reactions, bivariate and composite plots were made. Changes in groundwater composition along the pre-developmental hydraulic gradient were visualized for each climate-aquifer zone. Lastly, geochemical stochiometric inverse modeling was performed to further constrain mineral dissolution, precipitation and ion exchange reactions operating along the groundwater flow paths within each climate-aquifer zone.
In the GCA, silicate hydrolysis forms clays. Cation exchange on these clays drives calcite dissolution. These reactions are the primary controls of the major ion chemistry. Fluorite dissolution is the primary source of F to groundwater in all but the southern climate region. In the Central Jasper Aquifer (CJA), the dissolution of iron (Fe) and manganese (Mn) oxides is the source of As contamination. In the Southern Evangeline Aquifer (SEV) and Southern Jasper Aquifer (SJA), however, silicate weathering in the Catahoula Formation ash layers is the primary source of As and F. Therefore, the interaction between climate and water-rock interactions drives much of the observed distributions of As and F. Evidence for anthropogenic sources of As and F, evaporative concentration, or seawater mixing was not found. Anthropogenic activity is the source of NO3.
The Local Public Health Study wells are approximately screened in and chemically similar to the Central Chicot Aquifer (CCH). However, As and F concentrations (median 9.4 ug/L and 2.10 mg/L, respectively) in these wells are higher than the TWDB samples from CCH (median 2.2 ug/L and 0.59 mg/L, respectively). Water isotopes indicated that the health study well water was influenced by evaporative concentration, however, As and F did not correlate with chloride (Cl) or ��18O, indicating that evaporative concentration is not responsible for high As and F in these wells.
This study advances understanding of the hydrological and geochemical processes that drive As, F, and NO3 in the GCA. This knowledge can be used to explain and prevent human exposure to these toxic elements in drinking water
The Impact of Static Physical Arousal on Attentional Networks
No full textHumans tend to perform better cognitively when physically aroused. For instance, studies have found that physical arousal can lead to improvements in executive functioning. One approach is to use the attentional network test (ANT) after physical arousal. This task is useful because it can be used to measure the executive control of attention by assessing how people allocate their limited resources to relevant visual stimuli. The task uses the flanker paradigm, where participants try and maintain focus on a centrally presented target while ignoring distracting (���flanking���) stimuli on either side. Typically, participants cannot help but attend to the flanking items, when the flanker-associated response and the target-associated response conflict, impairing their response to the target. Dynamic physical arousal can help to alleviate the influence of distracting information in the flanker paradigm. However, dynamic arousal (e.g., cycling, running, swimming) is difficult to measure in the lab and might not be generalizable (e.g., it is difficult to measure in the lab and less conducive to every settings like the classroom or office). Thus, whether static arousal improves executive functioning in the same ways as dynamic arousal remains an open question. To test this question, our participants gripped a hand dynamometer for 18 seconds at maximum strength to evoke physical arousal. Then, participants completed the ANT. Participants were tasked with reporting the direction of a centrally presented target arrow (left or right) via a keyboard press. The target was flanked by distractors that were either congruent with, incongruent with, or neutral with respect to the target response. Prior to the search array, nonpredictive cues were presented. Together, these manipulations test whether attention is captured by the salient cues and how distracting the flankers are. There were two conditions of physical arousal: grip versus no-grip. Results show that attention was captured by the salient cues and the flankers were distracting (these replicate classic patterns); however, static physical arousal did not modulate either of these effects. These results suggest that static physical arousal may not influence the executive control of attention
