Aminophenol dioxygenases (APDO) are microbial non-heme iron enzymes that play a key role in the ring-cleaving oxidation of nitrophenol and p-chloronitrobenzene. These aromatic substrates are highly toxic and abundant in the environment due to anthropogenic activity, thus their degradation pathways and mechanisms are of current interest for bioremediation. The active site of APDO contains an iron ion coordinated by a 2-His-1-Carboxylate facial triad and shares many features with well-studied extradiol dioxygenases typified by homoprotocatechuate 2, 3-dioxygenase. However, the mechanism by which dioxygen is activated at the active site of APDO and the reactive intermediates preceding the ring-opening step remain to be elucidated. The aim of this study is to use Mössbauer spectroscopy to gain insight in the electronic structures of the intermediates formed in the reaction of a complex mimicking the APDO active site with O2. The complex studied, based on the ligand hydrotris(3,5-dimethylpyrazol-1-yl)borate (R2Tp) models the facial coordination geometry of monoanionic 2-His-1-Carboxylate coordination motif and allows coordination of a bidentate substrate ligand, 4,6-di-tert-butylaminophenolate (DTBAP). In this poster, we present the initial Mössbauer characterization of the ferrous FeII(TpMe2)(DTBAP) complex, as well as the spectra of the intermediates obtained by reacting the Fe(II) complex with dioxygen in tetrahydrofuran solution at low temperatures. The starting complex has an isomer shift, δ, of 1.15 mm/s, typical for ferrous ions with N/O coordination. A first intermediate presents paramagnetic broad spectra with an isomer shift of ~ 0.7 mm/s, which quickly decays producing a quadrupole doublet with small isomer shift (0.3 mm/s), indicative of an integer spin system. The final reaction mixture contains two species with distinct spectra, one characteristic to a high-spin ferric and the other indicative of a diamagnetic ground state. The spectral analysis and interpretation will be presented.

Mössbauer studies of models for intermediates in the catalytic cycle of mononuclear non-heme iron dioxygenases

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.