Portland State University. Department of Environmental Sciences and Resources
Term of Graduation
Date of Publication
Doctor of Philosophy (Ph.D.) in Environmental Sciences and Resources: Chemistry
Environmental Science and Management
1 online resource (2, xvii, 216 pages)
The two major metabolites after S-Oxygenation of dimethylthiourea (N, N'-dimethylaminoiminomethanesulfinic acid (DMAIMSA) and N, N'-dimethylamino iminomethanesulfonic acid (DMAIMSOA)) were synthesized. Structural analysis by X-ray crystallography shows that DMAIMSA and DMAIMSOA exist as zwitterionic species in their solid form, with a positive charge delocalized around an sp2-hybridized carbon center flanked by two nitrogen atoms.
Kinetics and mechanistic studies on the oxidation of DMAIMSA and DMAIMSOA by acidified iodate/iodine and bromate/bromine were studied. The results reveal that DMAIMSA, unlike DMAIMSOA, is highly reactive. DMAIMSOA is very inert and unreactive in low pH environments. The difference in reactivity is attributed to the fact that the C-S bond in DMAIMSA at 1.880(2) Å is longer than the theoretical prediction of 1.79 Å. This inordinate length renders the C-S bond in DMAIMSA relatively weak and easy to cleave. The more electronegative -SO3 group in DMAIMSOA, by inductive effects, strengthen the C-S bond thus making it more difficult to cleave. The major pathway in the oxidation of DMAIMSA proceeds through an unexpected early heterolytic cleavage of the C-S bond to yield the highly reducing sulfoxylate anion,SO2 2SO-. The observation of dithionite formation in aerobic DMAIMSA solutions clearly establishes the formation of SO22- as the leaving group in the initial stages of oxidation of DMAIMSA. The apparent inertness of DMAIMSOA indicates that the oxidation of DMAIMSA through DMAIMSOA represents a minor pathway in the oxidation of DMAIMSA.
For comparative studies, the kinetics and mechanistic study of the oxidation of hydroxymethanesulfinic acid (HMSA) by acidified iodate and iodine was also performed. The first 2-electron oxidation of HMSA should yield hydroxymethanesulfonic acid (HMSOA). As with DMAIMSOA, further oxidation of HMSOA is very slow. The predominant pathway in the further oxidation of HMSOA and DMAIMSOA involves a slow initial hydrolysis of their C-S bond to yield bisulfite (HSO3-).
Genotoxicity studies on some selected organosulfur oxo-acids were examined via DNA damage studies. The results reveal that oxo-acids of thiocarbamides are the reactive metabolites leading to the toxicity of their parent compounds. Analyses of the effect of scavengers reveal the involvement of hydroxyl radicals in the damage induced by DMAIMSA and DMAIMSOA.
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Otoikhian, Adenike, "Synthesis, Characterization and Reactivity of Some Selected Organosulfur Oxo-acids" (2008). Dissertations and Theses. Paper 6144.