Biomimetic Modeling of the Active Site of Soluble Methane Monooxygenase Hydroxylase (sMMOH)

Soluble methane monooxygenase (sMMO) belongs to a family of metalloproteins called bacterial multicomponent monooxygenases (BMMs), which contain carboxylate-bridged non-heme diiron cores. These sMMO enzymes are of high interest because they utilize readily available molecular oxygen in their energy conversion of methane to methanol in the metabolic system of methanotrophic bacteria. Methane is abundant in natural gas, and if it can be converted to methanol, a liquid form, under mild conditions as in the enzyme, transportation of this energy source to remote areas will be safer and more convenient. Our research group has a long-term interest in developing small molecule synthetic analogs that can mimic both the structure and function of the active site of the hydroxylase component of sMMO (sMMOH). Unfortunately, no ligand system designed to date has been able to achieve this goal. In our further attempt, synthesis of a triptycene-based bis(benzimidazole) diester ligand L3 is discussed in this paper along with its coordination with iron(II) salt and an external carboxylate. Characterization of the diiron(II) complexes was achieved using UV-vis spectrophometric titrations, X-ray diffraction studies, Mössbauer spectroscopy, and IR spectroscopy. Preliminary oxygenation studies of the diiron(II) complexes with molecular oxygen is also included.