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Artificial HeROs (Heme-copper Robust Oxidases) for biomass degradation

Abstract

A complex mixture of enzymes is used for the degradation of biomass. Among these enzymes are peroxidases, laccases and Lytic Polysaccharide Monooxigenases (LPMO) to aid the oxidative cleavage of the C-C bonds of lignocellulose by the use of oxygen or hydrogen peroxide as co-substrates. Oxygen is a free oxidant present in air and should be favored over the use of peroxide, as peroxide can harm the other enzymes present in the enzyme cocktail, hindering biomass degradation. To overcome protein instability, enzyme mimics that are more robust than enzymes can be synthesized. Interestingly, the oxidative enzymes used in the cocktails are metalloenzymes and can be mimicked by the use of inorganic models. However, the efficiency of enzyme models does not follow the one obtained by the biologic catalysts. Therefore, artificial metalloenzymes are proposed to overcome this barrier, since they provide an intermediate between the inorganic models and the protein. Here we propose to mimic the active site of Heme-Copper Oxidases (HCOs), owing to their ability to activate oxygen synergistically, achieving high turnovernumber. HCOs are not originally used for biomass degradation but have similarities to the active site of both peroxidase and LPMO. Therefore, we envision that a catalyst able to possess both active sites might be beneficial to biomass degradation. To achieve these catalysts, we propose the use of myoglobin and its heme center in connection to a copper complex, which will be able to activate and reduce oxygen, generating superoxide/peroxide. Here we describe the synthetic proposal of the Heme-Copper Robust Oxidases (HeROs) in conjunction to their characterization. The synthesis will start with the development of two copper complexes series, with distinct redox potentials, and their attachment to heme centers, followed by their insertion into myoglobin scaffold. Characterization of intermediates will be performed by using EPR, XAS/XANES, Mossbauer, cryo-FTIR and crystallography, envisioning a high biomass degradation. (AU)

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