Copper (Cu) is an essential trace element in ruminants such as the cow. Its deficiency leads to a number of debilitating symptoms and can eventually cause death. Secondary Cu deficiency is caused by the presence of chemical antagonists such as the thiomolybdates (TMs) (MoOxS4-x2-; x = 0 3). TMs form in the rumen and then form tightly bound insoluble complexes with Cu. These complexes are then excreted and the Cu is unavailable to the animal. The TMs and their effects on ruminant Cu are the focus of this thesis.<p>This study includes three main bodies of work. First, a method for quantifying the composition of TM mixtures in solution was developed. Second, the rate constants of TM interconversions were determined. Third, reactions between Cu and the TMs were studied. This work is part of an ongoing study in the Reid group to model Cu-ligand speciation in the rumen. <p>Thiomolybdates form by successive replacement of molybdate (MoO42-) O ligands with S. This makes synthesis of the uncontaminated compounds difficult. Mixtures of TMs are best analyzed by UV-visible spectroscopy despite the considerable spectral overlap. The combination of these two issues makes the characterization of the spectra difficult. In this study, a method was developed to establish the spectra of the pure TMs despite cross-contamination. Multivariate curve fitting methods were used to establish the composition of synthesized samples simultaneously with the molar absorptivities of the pure TMs. This was done using a Beers Law model. The composition was determined from a fit using assumed molar absorptivities. The absorptivities were then refined using the composition results. These processes were successively reiterated until both were optimized. The optimized absorptivities could then be used to determine the composition of any TM solution mixture. <p>The kinetics of TM formation under biologically relevant conditions were followed by UV-visible spectroscopy. The spectra were then analyzed, using the method developed above, to determine all TM concentrations. Curve fitting methods were used to simultaneously determine the rate constants of all processes that occurred. Integrated rate equations used in the fitting process were developed using the Laplace Transform method. Rate constants were determined at varying pH, ionic strengths and temperatures. From this information it was shown that TM formation and hydrolysis occurs via an associative mechanism. It was also determined that H2S and not HS- was the sulfide nucleophile in TM formation reactions.<p>This study was then extended to include reactions involving Cu and the TMs. First, the UV-visible spectra of the reaction products of Cu with each TM were characterized. This allowed the kinetics of reactions between Cu and the TMs to be followed. This reaction has been found to proceed via an intermediate. Molar absorptivities for this intermediate were optimized along with the appropriate rate constants. This was done using a combination of mathematical simulations and the curve fitting methods used for the TM kinetics. The resulting rate constants can be compared with those obtained previously in the group using a Cu ion selective electrode. <p>These rate constants were used in conjunction with the TM formation rate constants to perform simulations. The results of these simulations provide a picture of what is expected to occur in the rumen. Reactions were also performed in which TM formation occurred in the presence of Cu. This was then extended to mimic bovine feeding habits. Here, portions of the reactions mixture was removed at various time intervals and replaced with fresh reagents. These experiments were used to gain a qualitative picture of Cu speciation in the presence of the TMs over time. The work presented in this thesis provides a crucial step toward understanding the problem of bovine copper deficiency.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:SSU.etd-09152008-111332 |
| Date | 29 September 2008 |
| Creators | Clark, Rhett Jason |
| Contributors | Reid, R Stephen, Urquhart, Stephen, Dalai, Ajay, Goltz, Doug, Wilson, Lee, Foley, Stephen |
| Publisher | University of Saskatchewan |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-09152008-111332/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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