Research Abstracts Online
January 2010 - March 2011
University of Minnesota Twin Cities
College of Science and Engineering
PI: Lawrence Que, Jr.
Spectroscopic and Computational Investigations of Biomimetic Iron Complexes Relevant to Oxygen Activating Nonheme Iron Enzymes
Nonheme mono- and di-iron enzymes activate dioxygen in order to carry out specific C–H bond activation in organisms ranging from archaea to humans. These chemical transformations occur by first activating dioxygen at a nonheme iron center to an iron-superoxo or -peroxo species. This activated-dioxygen-iron complex then undergoes O–O bond cleavage under ambient conditions to form a reactive intermediate, typically a high-valent iron-oxo (e.g. FeIV=O or [FeIV2O2]), which is able to activate strong C–H bonds resulting in hydroxylation (C–OH) or desaturation (C–C to C=C). The reactivity and selectivity of these enzymes is unmatched in the laboratory where harsh oxidizing conditions are typically needed. The use of synthetic model complexes to mimic the electronic structure of these actives sites and their oxygen-activated intermediates is of the utmost importance in understanding their reactivity. The Que group employs a variety of spectroscopic and kinetic techniques to deduce the electronic, magnetic, and kinetic properties of these models and to understand how nonheme iron enzymes sites carry out O–O and C–H activation. Density functional theory (DFT) methods are applied to these model complexes to predict the reactive intermediates’ geometrical and electronic structures, along with an analysis of the excited states that lead to the experimentally observed spectra. The application of DFT to these systems greatly facilitates the interpretation and elucidation of the experimental data, ultimately contributing to the understanding of how nonheme iron enzymes catalyze difficult oxidation reactions and paving the way for the development of environmentally-friendly catalysts that can be used in a number of industrial processes.
Matthew Cranswick, Research Associate
Katherine Van Heuvelen, Research Associate