Theses and Dissertations from UMD

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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    The impact of dietary ions on rumen ion concentrations
    (2015) Catterton, Tracy Lynn; Erdman, Richard A; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Dietary cation-anion difference (DCAD) evaluates the strong ion balance in dairy cattle diets. We performed two experiments to study the impacts of strong dietary ions (Na, K, and Cl) on the rumen environment. Our overall hypothesis was that dietary strong ions would influence their corresponding rumen concentrations. Our objective was to determine the impact of the dietary strong ions on the rumen environment. In the first experiment, five fistulated dairy cows consumed the following treatments: (1) a basal diet composed of corn silage and alfalfa hay and then the basal diet supplemented with (2) NaCl, (3) KCl, (4) NaHCO3, and (5) K2CO3. Rumen samples were collected 0, 1.5, 3, 4.5, 6, 9, and 12 h post-feeding to measure ion concentrations, pH, and volatile fatty acid concentrations. In the second experiment, we conducted a meta-analysis of published literature that measured rumen strong ion concentrations.
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    USING "SMALL" MOLECULES AS TRANSMEMBRANE ANION TRANSPORTERS
    (2009) Okunola, Oluyomi Adeola; Davis, Jeffery T; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Functional, "small" molecule anion transporters have been identified and developed from natural products and synthetic organic compounds. The major discoveries include the design of a transmembrane Cl- transporter whose activity is pH-tunable, a NO3- transporter that displays unique selectivity for NO3- over Cl- anions, and a series of small molecules that efficiently transport HCO3- across liposomal membranes via a HCO3-/Cl- exchange mechanism. An assay for detecting transmembrane HCO3- transport using paramagnetic Mn2+ and 13C NMR is also described. Modulated Cl- transport was achieved by lipophilic calix[4]arene amides 2.2-2.4, all in the cone conformation. Modulation was achieved through functional group modification to one of the four side-chains. The cone conformation was confirmed by both 1H NMR and X-ray crystallography. Significantly, Cl- transport was gated by pH in the presence of triamido calixarene TAC-OH 2.3, which possesses a phenolic hydroxyl group. Using fluorescence assays, the rate of Cl- transport by TAC-OH 2.3 across liposomal membranes decreased with increasing pH, while transport rate by cone-H 2.2a, lacking an OH group, was not affected by pH. Nitrate was selectively transported over Cl- in the presence of nitro tripod 3.1, a small molecule receptor for both anions. The selective transport of NO3- by 3.1 is a significant discovery as most known synthetic Cl- transporters also transport NO3- ions and vice versa. Nitrate transport across liposomal membranes was confirmed by enzyme-coupled and fluorescence assays. Tripod 3.1 induced an increase in the intravesicular pH of liposomes that were not experiencing a pH gradient, while no pH changes occurred in the presence of calixarene 2.1 a known Cl- and NO3- transporter. This result suggests that 3.1 is an H+/NO3- symporter. Transmembrane HCO3- transport was achieved using the natural product, prodigiosin, 4.1, and synthetic isophthalamides 4.2-4.4. The Cl-/HCO3- exchange mechanism by which compounds 4.1-4.4 transport HCO3- was elucidated by ISE and NMR assays. The 13C NMR assay provided direct evidence for HCO3- transport in the presence of paramagnetic Mn2+ ions, and was adaptable to various assay conditions.