Date of Graduation

1999

Document Type

Dissertation/Thesis

Abstract

Complex mechanisms of oxidation of selected sulfur compounds by various oxidants are studied. Chapter 1 is an overall introduction to the field of sulfur chemistry with emphasis on chemical reaction dynamics and the biological significance of aminothiols and substituted thioureas. The rest of the dissertation can be divided into 3 parts based on the type of information obtained from the reaction systems studied. Chapters 2 gives an overview of most of the experimental methods used to come up with a reasonable answer to a given kinetics problem. Chapters 3 and 4 form the basis of the first part in which the oxidation of the sulfur center in different electronic environment is investigated. Whilst the oxidation of 2-aminoethanethiolsulfuric acid, AETSA, (Chapter 3) with bromate was fairly simple and well behaved, the oxidation of 4-methyl-3-thiosemicarbazide with iodate (Chapter 4) was complex with transient formation of what appeared to be a charge transfer complex. Product control was elusive and thus determination of kinetic parameters was difficult. This complex behavior set the stage for the investigation into the reactivity of the postulated intermediates in the oxidation of thiourea: the sulfinic and sulfonic acids. This formed the basis of the second part of this thesis. The second part of this work investigates the structure, stability and reactivity of sulfinic and sulfonic acids. It was established that there is a fundamental difference in bonding between the sulfonic and sulfinic acids of thiourea. It was also established that the oxidation of thiourea to sulfate does not necessarily pass through the sulfonic acid but instead, under certain conditions, through the bisulfite, HSO3−, formed when the C-S bond of sulfinic acids cleave. The sulfite radical was found to be the predominant reactive oxygen species and it has deleterious effects on DNA. Chapters 6 and 7 form the last segment of this thesis in which the role of dl-cysteine and hypotaurine as antioxidants is studied. Chapter 6 is a study of the reactivity of dl-cysteine with a variety of oxidants. It was observed that the extent of oxidation was dependent on the nature of the oxidant. Chapter 7 is a study of the antioxidant properties of hypotaurine, a precursor to taurine. Hypotaurine is stable and reacts slowly with chlorite to give taurine, hypotaurine sulfonic acid, monochloro- and dichlorotaurine. It however, reacts rapidly with chlorine dioxide with a second order rate constant of 801 M−1s−1 to give taurine.

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