MECHANISTIC STUDIES OF PROTON-COUPLED ELECTRON TRANSFER REACTIONS INVOLVING ANTIOXIDANTS

The objective of the research was to investigate proton-coupled electron transfer (PCET) reactions involving antioxidants to gain insight into the detailed mechanisms of glutathione (GSH), Trolox, and α-tocopherol (α-TOH). PCET reactions are complex redox reactions that transfer electrons and protons sequentially or in concert. These reactions are ubiquitous in natural or artificial processes that produce electrochemical energy that is extractable as electricity or as chemical fuels of high energy content. Examples of processes based on PCET are photosynthesis, respiration, nitrogen fixation, carbon dioxide reduction, redox fuel cells, and artificial photosynthesis. Antioxidants were selected as a PCET model to understand the coupling between proton transfer (PT) and electron transfer (ET) in order to elucidate structure-reactivity relationships under different experimental conditions. PCET reactions were studied with a set of electrochemical techniques to propose a preliminary mechanism that could be validated with digital simulations matching the electrochemical response. In some cases, other analytical techniques were used to aid in the system characterization. This thesis presents the results and discussion of the effects of oxidant-base pairs on the mediated oxidation of GSH, the -2e-/-H+ process of Trolox in aqueous and nonaqueous solvents with various pH values, and the particle collision electrolysis of α-tocopherol in oil-in-water emulsion droplets on an ultramicroelectrode. Ultimately our goal was to determine the kinetic and thermodynamic factors that control PCET reactions so that they can be applied in designing artificial systems for the production of energy using more abundant reagents with lower cost and better yields