Nuclear Resonance Vibrational Spectroscopy and DFT study of Peroxo-Bridged Biferric Complexes: Structural Insight into Peroxo Intermediates of Binuclear Non-heme Iron Enzymes

摘要

Binuclear non-heme iron enzymes utilize O2 to catalyze a variety of reactions, including hydrogen atom abstraction, desaturation, electrophilic aromatic substitution, and so on. In most cases, their catalytic cycles begin with the reductive binding of O2 by biferrous centers to form high-spin antiferromagnetically coupled (AFC) peroxo-bridged biferric intermediates. These peroxo intermediates can either react with substrate or convert to more reactive high-valent species. Because of their transient nature, structural information must be deduced from spectroscopic data, which are rich for some peroxo intermediates, while for others too limited for geometric and electronic structural insight. The peroxo intermediate of W48F/D84E ribonucleotide reductase (RR), referred to as P, does exhibit distinct spectral features. These include electronic absorption (Abs) and resonance Raman (rR) spectra that are equivalent to those of cis μ-1,2 end-on peroxo-bridged Fe~(III)2 model complexes, thus providing a basis for the computational model of P as a cis μ-1,2 peroxo-bridged Fe~(III)2 species (with the (Glu)4(His)2 ligand set of this protein active site). However, P is not reactive and must convert to a second-peroxo-level intermediate P' that does not have Abs spectral features for rR-based structural elucidation.