No description available.

Chromium has been used extensively in the industry process of metal refinishing and electroplating. It is also a byproduct of the processing of fissionable materials at United States Department of Energy facilities. Chromate (Cr (VI)) is soluble and readily absorbed by cells, while the reduced form of chromium, Cr (III), is insoluble. Thus means of reducing Cr (VI) to Cr (III) in the environment is a potential means of remediation. Desulfovibrio desulfuricans strain 27774 is a sulfate reducing bacterium that can reduce Cr (VI). It also can respire nitrate to ammonia. As some sites of chromium contamination also contain high concentrations of nitrate, an investigation of Cr (VI) reduction under nitrate reducing growth conditions by D. desulfuricans strain 27774 was conducted. A growth medium that was compatible with the colorimetric assay for Cr (VI) and did not itself reduce Cr (VI) was formulated. Cell assays determined that Cr (VI) reduction was primarily in the supernatant, catalyzed by a secreted secondary metabolite. A genomics investigation identified two pathways as possible mechanisms. / Bayer School of Natural and Environmental Sciences / Environmental Science and Management (ESM);= / MS / Thesis

No description available.

Allosteric regulation of important enzymes is a mechanism frequently employed by organisms to exert control over their metabolism. The shikimate pathway is ultimately responsible for the biosynthesis of the aromatic amino acids in plants, microorganisms and apicomplexans. Two enzymes of the pathway, 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase (DAH7PS) and chorismate mutase (CM) are located at critical positions along the aromatic amino acid biosynthetic pathway and are often tightly feedback regulated in order to control the flux of metabolites through the pathway. This research presents studies on the allosteric function of these two enzymes. These studies emphasise the complexity of the intersecting network of allosteric response, which alters the catalytic activity of each enzyme in response to metabolic demand for the aromatic amino acids.

No description available.

Universiẗat-Gesamthochsch., Diss.--Paderborn, 1997.

abstract: Contamination of drinking water supplies from oxo-anion pollutants necessitates treatment prior to potable use. This dissertation aims to inform and improve light delivery (emission spectra, radiant intensity, reactor configuration) in order to enhance the photocatalytic reduction of hexavalent chromium (Cr(VI)) and nitrate, two common oxo-anions in drinking water, and photocatalytic oxidation of two model organic pollutants (methylene blue, (MB) and para-chlorobenzoic acid (pCBA)). By varying the photon fluence dose, two metrics (contaminant quantum yield (Φ), and electrical energy per order (EEO)) were used to assess photocatalytic reactor performance. A detailed literature review and experimental results demonstrated how different irradiance sources with variable intensity and emission spectra synergistically enhanced contaminant removal by a coupled photolytic/photocatalytic reaction mechanism. Cr(VI) was photocatalytically reduced on TiO2 and formed Cr(OH)3(s) in a large-scale slurry reactor, but Cr(III) was then photolyzed and reformed Cr(VI). UV light also led to photo-aggregation of TiO2 which improved its recovery by the ceramic membrane within the reactor. For nitrate reduction, light source emission spectra and fluence dose delineate the preferred pathways as intermediates were reduced via wavelength-dependent mechanisms. HONO was identified as a key nitrate reduction intermediate, which was reduced photocatalytically (UV wavelengths) and/or readily photolyzed at 365nm, to yield nitrogen gases. Photocatalytic nitrate reduction efficiency was higher for discrete wavelength irradiation than polychromatic irradiation. Light delivery through aqueous media to the catalyst surface limits efficiency of slurry-based photocatalysts because absorption and scattering of light in nanomaterial slurries decreases effective photon transmittance and minimizes photolytic reactions. The use of optical fibers coupled to light emitting diodes (OF-LED) with immobilized catalyst demonstrated higher performance compared to slurry systems. OF-LED increased Φ for MB degradation by increasing direct photon delivery to the photocatalyst. Design of OF-LED reactors using bundled optical fibers demonstrated photocatalytic pCBA removal with high Φ and reduced EEO due to increased surface area and catalytic sites compared to single OF/LED couples. This work advances light delivery as well as the suspension and attachment of nanoparticles in photocatalytic water treatment for selective transformation of oxo-anions and organic compounds to innocuous species. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2017

No description available.

No description available.

No description available.