Alkane Hydroxylation by Anchored Unspecific Peroxygenase

The selective oxidation of methane to methanol with molecular oxygen remains a long-standing challenge in heterogeneous catalysis due to the high stability of its C-H bonds. Interestingly, both of these molecules are essential for a more sustainable chemicals market, as biomethane is a sustainable carbon source while methanol is a key precursor to value-added chemicals. Here, we show that this challenge can be addressed through reaction engineering by using an anchored unspecific peroxygenase from Agrocybe aegerita (AaeUPO) for alkanes partial hydroxylation in liquid phase, and ultimately to perform the reaction in gas phase.

The AaeUPO is a heme-dependent enzyme which can insert oxygen atoms into various organic molecules using only hydrogen peroxide as a co-substrate without the need for cofactors or auxiliary electron transport proteins with regenerative systems. Herein, we optimized the reaction chemistry of recombinantly produced free rAaeUPO under a range of conditions (i.e. pH, temperature, reaction times, oxidants concentrations, and enzyme loadings) using n-octane as a benchmark substrate to access catalytic efficiency of the rAaeUPO for C-H hydroxylation in liquid phase. Furthermore, we anchored the rAaeUPO on novel polymer brush solid supports to enhance its reactivity in the best optimized reaction conditions developed previously in liquid phase.

To the best of our knowledge, this is the first time that the testing and characterizing of the anchored rAaeUPO systems has been carried out for alkanes partial hydroxylation in either liquid or gas phase. The results obtained so far will be used to ultimately focus on the challenging partial oxidation of methane. These findings showcase the bio-catalytic performance as well as the synthetic potential of anchored rAaeUPO for C-H hydroxylation under mild conditions and most importantly, guide the reaction engineering for sustainable alkanes valorization.