Identification and spectroscopic characterization of nonheme iron(III) hypochlorite intermediates

Fe^III-hypohalite complexes have been implicated in a wide range of important enzyme-catalyzed halogenation reactions including the biosynthesis of natural products and antibiotics and post-translational modification of proteins. The absence of spectroscopic data on such species precludes their identification. Herein, we report the generation and spectroscopic characterization of nonheme Fe^III-hypohalite intermediates of possible relevance to iron halogenases. We show that Fe^III-OCl polypyridylamine complexes can be sufficiently stable at room temperature to be characterized by UV/Vis absorption, resonance Raman and EPR spectroscopies, and cryo-ESIMS. DFT methods rationalize the pathways to the formation of the Fe^III-OCl, and ultimately Fe^IV=O, species and provide indirect evidence for a short-lived Fe^II-OCl intermediate. The species observed and the pathways involved offer insight into and, importantly, a spectroscopic database for the investigation of iron halogenases.