Photoenzymatic Hydroxylation of Ethylbenzene catalyzed by Unspecific Peroxygenase: Origin of Enzyme Inactivation and the Impact of Light Intensity and Temperature

B. O. Burek, S. R. de Boer, F. Tieves, W. Zhang, M. van Schie, S. Bormann, M. Alcalde, D. Holtmann, F. Hollmann, D. W. Bahnemann, J. Z. Bloh

ChemCatChem, 11 (2019), 3093-3100, doi:10.1002/cctc.201900610R1

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Abstract

Photoenzymatic cascades can be used for selective oxygenation of C-H-Bonds under mild conditions circumventing the hydrogen peroxide mediated peroxygenase inactivation via in situ H₂O₂ generation. Here, we report the “on demand” production of hydrogen peroxide via methanol assisted reduction of molecular oxygen using UV-illuminated titanium dioxide (Aeroxide P25) combined with the enantioselective hydroxylation of ethylbenzene to (R)-1-phenylethanole catalyzed by the Unspecific Peroxygenase from Agrocybe Aegerita. For the application of the system it is important to understand the influence of the reaction parameters to be able to optimize the system. Therefore, we systematically investigated product formation and enzyme inactivation as well as ROS formation (H₂O₂, ^•OH and ^•O₂^-) applying different light intensities and temperatures. As a result, Turnover Numbers up to 220 000, photonic efficiencies up to 13.6 % and production rates up to 0.9 mM h^-1 were achieved.