Fourier transform infrared characterization of the azido complex of methane monooxygenase hydroxylase from Methylococcus capsulatus (Bath)

The azido complex formed in oxidized methane monooxygenase from Methylococcus capsulatus (Bath) was investigated with resonance Raman and FTIR techniques. These experiments show the presence of a ν_as(NNN) at ∼2077 cm^-1 which splits to two components at 2059 and 2073 cm^-1 with ¹⁵N¹⁴N₂. The vibrational data are assigned to an azido complex bound terminally to one iron(III) at the diiron center. When the azido complex is illuminated at 15 K, a new ν_as(NNN) is observed at 2136 cm^-1 which is assigned to a photodissociated HN₃ within the substrate pocket. We propose a model where an aqua ligand engages a hydrogen bond interaction with the 1N atom of the azido group and acts as at a proton donor during the photolysis process.