Student Inorganic Chemistry Seminar with Brighton Skeel (MIT - Suess Group)

4-370

The Impact of Excited States on the Chemistry of Iron-Sulfur ClustersAbstract: Electron transfer reactions are life-sustaining, and lie at the heart of all metabolic pathways. Of the many cofactors that mediate biological electron transfer reactions, iron-sulfur (Fe−S) clusters are particularly ubiquitous, and are “privileged cofactors” in this sense. In this talk, I discuss one special property of Fe−S clusters that uniquely poises them for high-fidelity electron transfer: their thermally populated excited spin states. In the first portion of my talk, I describe a new method for experimentally mapping the low-energy states of [Fe4S4] clusters, including both their low-energy excited spin states and alternate valence electron arrangements (“valence isomers”) as relevant. In the second portion of my talk, I show that the free energy associated with these excited states gives rise to reductions in the free energy barriers for electron transfer. Using our experimentally determined excited state parameters, I demonstrate this reduction in electron transfer barrier experimentally in a series of electron transfer self-exchange reactions. The implications of these findings are discussed, emphasizing that the complex excited state manifolds that characterize Fe−S clusters make them uniquely suited as “universal reductasesRefreshments will be served outside 4-370 at 4:00PM.