Production of H2O2 from H2 and O2
Hydrogenase enzymes catalyse production and utilization of hydrogen gas, which is considered as a future energy carrier. Scientists at the Max Planck Institute for Terrestrial Microbiology in Marburg and collaborators in the other institute discovered that [Fe]-hydrogenase produces H2O2 from H2 and O2. This finding is crucial to understand the catalytic mechanism of this enzyme and is also important to design new H2O2-forming catalysts.
[Fe]-hydrogenase mediates reversible hydride transfer from H2 to an organic compound. This catalytic capability makes [Fe]-hydrogenase an attractive model system for designing mimetic hydrogenation catalysts; numerous mimetic compounds of the [Fe]-hydrogenase active site have already been synthesized. To design superior mimetic compounds, a more profound understanding of the reaction of [Fe]-hydrogenase on an atomic basis is necessary.
For industrial use of hydrogenases and their mimic catalysts, sensitivity against O2 is an important problem because most of the hydrogenases lose activity in the presence of O2. The research group of Seigo Shima at the Max Planck Institute for Terrestrial Microbiology in Marburg together with Ulrich Ermler from Max Planck Institute of Biophysics, Eckhard Bill from Max Planck Institute for Chemical Energy Conversion, and Kenichi Ataka from Freie Universität Berlin discovered that [Fe]-hydrogenase is only inactivated by O2 in the presence of reducing substrates. The O2 added was converted in H2O2, which aggressively inactivates the enzyme. This finding indicated that during the catalytic reaction, O2 is reduced by an intermediate of the [Fe]-hydrogenase to form H2O2 (Fig. 1). This is the first experimental evidence of the presence of an O2-reactive iron-hydride intermediate in the catalytic cycle of [Fe]-hydrogenase, which is of prime importance to understand the reaction mechanism in detail. In addition, this finding paves a new way for developing a biomimetic H2O2-producing catalyst, an important industrial compound. H2O2 is produced commercially by an indirect chemical process using Ni or Pd as catalyst; however, cleaner and direct processes are preferred. [Fe]-hydrogenase mechanistically catalyses only two-electron reduction with a hydride transfer; therefore, this catalytic reaction should selectively produce H2O2. This chemical properties could be applied to design a new H2O2-forming catalyst.
Huang, G., Wagner, T., Ermler, U. Bill, E., Ataka, K. & Shima, S. (2018)
Dioxygen sensitivity of [Fe]-hydrogenase in the presence of reducing substrates. Angewandte Chemie International Edition. DOI: 10.1002/anie.201712293 and 10.1002/ange.201712293.