Exploring Reactivity of Bio-relevant Porphyrinoid Complexes for Propensity in Chlorite Dismutase, Catalase, Hydrogen Atom Transfer, Electron Transfer, and Oxygen Atom Transfer
The reactivity of two porphyrinoid complexes has primarily been explored in this dissertation. The manganese corrole complex, (tpfc)Mn III (tpfc = 5,10,15-tris(pentafluorophenyl) corrole, and a ruthenium porphyrin complex, Ru(TF4TMAP) (TF4TMAP=5,10,15,20-tetra(2,3,5,6-tetrafluoro- N,N,N-trimethylanilinium) porphyrin). These complexes have been shown to possess unique reactivity especially in reactions including hydrogen atom transfer, electron transfer, oxygen atom transfer, and the dismutation of chlorite. The manganese corrole complex, (tpfc)MnIII, was studied for catalase activity, hydrogen atom transfer, and oxygen atom transfer. A high-valent manganese(V)-oxo complex, (tpfc)MnV(O) can be formed with the addition of a chemical oxidant, iodosobenzene (PhIO). This complex undergoes valence tautomerization with an acid to form [(tpfc•)MnIV(O-LA)] n+, where LA = TFA, AgI, CaII, B(C 6F5)3, ScIII, YbIII, ZnII, and HOTf and n = 0, 1, 2, or 3. These complexes have been characterized using EPR and UV-vis spectroscopies. The reactivity of these complexes has also been investigated. These valence tautomers show enhanced rates of hydrogen atom transfer (HAT) and electron transfer (ET), but are no longer able to perform oxygen atom transfer (OAT), when compared to the parent (tpfc)MnV(O). The kinetic study of an ET to (tpfc)Mn V(O) and the valence tautomers reveal that the valence tautomers, 1 x10 10 M-1s-1, react 5 orders of magnitude faster than the parent (tpfc)MnV(O), 2 x105 M-1s-1. The kinetics study for the HAT reaction reveals that the Lewis acid plays a large effect on the reactivity with a range of rates varying over 2 orders of magnitude as seen for [(tpfc•)MnIV(O-Sc)] 3+, 27 M-1s-1, and [(tpfc• )MnIV(O-Ca)]2+, 1400 M-1s -1. Through this study the knowledge of how porphyrinoid complexes react has been expanded. This study also reveals that Lewis acids can play a large role in the kinetic control of reactions. The ruthenium porphyrin, RuII(TF4TMAP), was studied for its ability to replicate chlorite dismutase. This complex reacts with chlorite to form chlorine dioxide, chloride and dioxygen. During this reaction an active catalyst is formed which is capable of transforming multiple equivalents of chlorite without significant loss of activity. The kinetics of the reaction in the first addition and third additions of chlorite are essentially equivalent, 0.85 M-1s-1 and 0.93 M-1s-1 respectively. These ruthenium porphyrins are one of a small number of porphyrinoid complexes that are known to mimic chlorite dismutase.
Uyeda, Purdue University.
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