A growing family of O2 activating dinuclear iron enzymes with key catalytic diiron(III)-peroxo intermediates: Biological systems and chemical models

Discovery of soluble methane monooxygenase (sMMO) in 1966 aroused enthusiastic research on dinuclear iron centers, both in biological systems and chemical models. From this emulation, other O-2 activating dinuclear iron enzymes were rapidly discovered and important active intermediates such as peroxo-diiron(III) and diiron(IV)-oxo species were characterized along the different catalytic cycles. For decades solely highvalent iron-oxo species were described as the active species involved in enzyme mechanisms, demoting peroxo-diiron(III) intermediates as a unique role of precursor. Interestingly, recent discovery of new O-2 activating diiron enzymes revealed the implication of peroxo-diiron(III) species as active intermediate during catalytic cycles, placing this intermediate in the spotlight and rising new questions about its structure/function relationship. In this review, we describe the entire family of O-2 activating diiron enzymes, excluding O-2 transportation and iron storage proteins, with a special focus on recently discovered enzymes involving peroxo-diiron(III) species as active intermediate. The various reactivities of these enzymes are placed in the biological context and their mechanisms are discussed on the basis of spectroscopic characterizations of crucial intermediates. Finally, since low molecular weight models are of primary importance for both structural and functional studies, we also give an overview of handmade peroxo-diiron(III) complexes known to date, with a complete list of their UV-vis., resonance Raman and Mossbauer spectroscopic parameters. (C) 2016 Elsevier B.V. All rights reserved.