Recent Research Developments

An oxoiron(IV) center with a thiolate ligand has long been proposed to be involved in the catalytic cycle of cytochrome P450, a key enzyme in mammalian metabolism. Despite tremendous efforts, synthetic complexes featuring this paradoxical combination of oxidizing (Fe=O) and reducing (SR) components have thus far eluded characterization by researchers in the porphyrin field. In a paper published in Science 2005, 310, 1000-1002, the first synthetic example of a thiolate ligated oxoiron(IV) complex is reported by graduate students Michael Bukowski and Kevin Koehntop in the group of Professor Lawrence Que, in collaboration with Professor Jason Halfen of the University of Wisconsin Eau Claire, Professor Eckard Münck, Dr. Emile Bominaar, and Audria Stubna of Carnegie Mellon University, and Professor Wonwoo Nam of Ewha Woman's University. Instead of a porphyrin, they use a macrocylic nonporphyrin ligand whose rigid framework stabilizes the thiolate in the oxidizing environment. The presence of the RS-Fe(IV)=O unit has been established by a combination of electrospray mass spectrometry, Mössbauer spectroscopy, and EXAFS analysis. The synthesis of a complex with this elusive motif allows an investigation of its fundamental properties in the absence of the protein environment. Indeed the investigators find that the presence of a thiolate enhances the hydrogen atom abstraction capabilities of the Fe=O unit, which may rationalize Nature's choice of this unit in cytochrome P450 and related enzymes that cleave C-H bonds.

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