UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

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 given thesis/dissertation in DRUM.

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

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2007 - 20102

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    A PHYSICAL CHEMIST'S GUIDE TO APPLIED COMPUTATIONAL CHEMISTRY: PRACTICAL CALCULATION OF POLYPROTIC ACID PKA VALUES, MERCURY HALIDES, THIOLS, AND METHYLMERCURY ANALOGUES' STABILITIES AND STRUCTURES, AND RAMAN SPECTRA OF MYO-INOSITOL HEXAKIS PHOSPHATE.
    (2010) Zimmermann, Merle; Tossell, John A; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In this thesis, we present both ab-initio investigation of the series of compounds HgClxy and the charges of each system running x=(0,1,2,3,4) and y=(+2,+1,0,-1,-2). We investigate the energies of formation using Gaussian 03 (G03), a quantum chemistry package. In our calculations, HgCl3-1 was most stable in the gas phase, and HgCl20 the most stable in the polarizable continuum model water-solvated phase. The addition of a solvent layer of H2O molecules did not significantly affect the results. DFT calculations on the series running between HgCl+, through HgCl20, and HgCl3-1 compounds done with the Amsterdam Density Functional (ADF) program from Scientific Computing and Modeling (SCM) yielded absolute Hg NMR shieldings with a Δ of approximately -1000 ppm for each additional atom of Chlorine bonding to the Mercury for the first two additions. We also investigate H3PO4, H3AsO4, and the HClOx acid series with x=(1,2,3,4). We have succeeded in determining pKas with theoretical quality results within 2 kcal/mol of experimental measurement for the majority of the systems examined by use of a discovered linear correlation between experimental and calculated pKa values. Finally, we present our contribution to a joint project involving myo-inositol hexakis phosphate with an experimental group, confirming the observed experimental trends seen in the Raman spectra.
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    Mercury methylation in dissimilatory iron reducing bacteria
    (2007-08-13) Kerin, Elizabeth; Suzuki, Marcelino; Gilmour, Cynthia; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Microbial mercury methylation is an integral factor controlling methylmercury concentrations within aquatic ecosystems. This thesis explores the phylogenetic distribution and biochemistry of methylation among the dissimilatory iron-reducing bacteria (DIRB). When distribution of methylation capacity among DIRB was examined, strains of Geobacter spp., which are closely related to mercury-methylating, sulfate-reducing Deltaproteobacteria, methylated mercury while reducing iron or other substrates. In contrast, no tested strains of the Gammaproteobacteria genus Shewanella produced methylmercury above abiotic controls. Mercury methylation by the cobalamin-dependent methionine synthase (MetH) pathway was examined. Heterologous expression of G. sulfurreducens metH in E. coli was used to evaluate involvement of MetH in methylation. Methylation by a clone expressing MetH and a non-expressing control clone was tested in vivo and in vitro. Methylation by the expressing clone was not significantly higher than either the control or abiotic assays in either experiment, suggesting that MetH is not involved in methylation in G. sulfurreducens.