Methane monooxygenase Bridging carboxylates

Metalloenzymes with non-heme di-iron centers in which the two irons are bridged by an oxide (or a hydroxide) and carboxylate ligands (glutamate or aspartate) constitute an important class of enzymes. Two of these enzymes, methane monooxygenase (MMO) and ribonucleotide reductase (RNR) have very similar di-iron active sites, located in the subunits MMOH and R2 respectively. Despite their structural similarity, these metal centers catalyze very different chemical reactions. We have studied the enzymatic mechanisms of these enzymes to understand what determines their catalytic activity [24, 25, 39-41]. 

Other Fe complexes are known to epoxidize olefins with peracetic acid [244]. For example, Jacobson and coworkers report a Fe(mep) complex (mep=N,N -dimethyl-N,N -bis(2-pyridylmethyl)-ethane) (Fig. 1.3c) which self-assembles under reaction conditions to form a /z-oxo, carboxylate-bridged diiron complex similar to that found in the core of the hydroxylase active site of oxidized methane monooxygenase (MMO) [236]. 

Dioxygen diiron complexes have been synthesized by mimicking the probable intermediate structures in methane monooxygenase oxygenations. Examples are summarized in the recent review. One is the Fc2(i7-0)2 diamond core type and the other is the Fe2(tJ-02) peroxo type. Recently, an unusual Fe"-X-Fe (tl -02) species has been suggested in the reaction of O2 with carboxylate-bridged diiron(II,II) paddlewheel complexes, but its role in the oxygenation has not been clarified. ... 

---