Fenton &Fenton-like Reactions: The Nature of Oxidizing Intermediates Involved
Mwebi, Nixon Ogendi
Blough, Neil V
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ABSTRACT Title of Dissertation: FENTON & FENTON-LIKE REACTIONS: THE NATURE OF OXIDIZING INTERMEDIATES INVOLVED Nixon Ogendi Mwebi, Doctor of Philosophy, 2005 Dissertation Directed by: Professor Neil V. Blough Department of Chemistry and Biochemistry Accumulating evidence indicates that reactive oxygen species (ROS) such as hydroxyl radical and peroxy radicals are involved in the pathophysiology of aging and a multitude of diseases such as cancer, as well as neurodegenerative disorders. These ROS are believed to result in part from Fenton and Fenton-like reactions mainly involving reactions between metal ions or metal complexes and hydrogen peroxide. The exact nature of oxidizing intermediates involved in these Fenton reactions remains uncertain and is still a matter of considerable interest. Although many studies have been conducted examining the nature of these intermediates, a number of these have been inconclusive due to experimental artifacts in the analytical techniques involved. A highly sensitive and selective technique is hereby employed to quantify the magnitude of species involved in these reactions. The intermediate species involved in the Fenton and Fenton-like reactions have been shown to react with both dimethylsulfoxide (DMSO) and (for the first time) methane to yield methyl radicals. A comparison of the product yields in the DMSO and methane experiments performed under identical conditions yield product ratios close to those expected for free hydroxyl radical (OH). Competition studies between the primary OH scavengers, DMSO or methane with nitroxide and benzoic acid yield product distributions typical of those expected for free OH, clearly indicating free OH involvement. Free OH involvement is manifested both at acidic pH (4.2) and neutral pH (7.4) in Fenton reactions with both organic and inorganic metal complexes of iron. The yield of product II associated with free OH is found to decrease with increasing pH possibly due to competing side reactions. Fenton reactions in the presence of ferric ions indicate that the species formed in the reaction of OH with Fe (III), (possibly ferryl species, FeIV) oxidize DMSO to yield methyl radicals, but fail to oxidize methane, thereby providing a simple method to discriminate between free OH and the high valent metal species.