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Wilfrid Laurier University Faculty of Science
June 30, 2015

Canadian Excellence

Katie Lalonde, Honours BSc Chemistry/Coop 2004


Katie Lalonde Thesis Abstract:

Fluorescence Analysis of Silver Binding to Amino Acids and Sewage Derived Organic Matter
A fluorescence quenching method is used to analyze silver binding to two specific amino acids, tyrosine and tryptophan, which possibly exist in natural water samples and sewage derived organic matter. Fluorescence surfaces obtained, which graphically show the fluorescence through a range of excitation and emission wavelength combinations. It was determined that each component has a specific fluorescence maxima, and that each maximum exists independently in solution, as long as the mixture is dulute, that is less than 10mM. Excitation/emission wavelengths corresponding to fluorescence maxima were determined to be 270nm/300nm and 225/300nm for tyrosine and 270nm/359nm for tryptophan. Upon addition of silver at constant pH, the fluorescence decreased, suggesting silver binding to the amino acids. The fluorescence quenching data is fit to a two site binding model describing silver speciation in these solutions, which estabilishes Ag+ binding constants (logK) for tyrosine and tryptophan of 5.30 and 5.44 respectively. The technqiue developed for the simple amino acid mixture is applied to three natural water samples, including one allochthonous sample, and autochthonous sample, as well as sewage effluent. Stability constants and binding capacities for silver and amino acid-like components are determined. The autochthonous sample showed reasonable agreement with the model data, yielding a stability constant for tyrosine-like component of 5.44, as well as a binding capacity of 3.16 umol/mg of dissolved organic carbon.