Mimicking the Reactivity of LPMOs with a Mononuclear Cu Complex

Abstract

AbstractLytic polysaccharide monooxygenases (LPMOs) are Cu‐dependent metalloenzymes that catalyze the hydroxylation of strong C−H bonds in polysaccharides using O2 or H2O2 as oxidants (monooxygenase/peroxygenase). In the absence of C−H substrate, LPMOs reduce O2 to H2O2 (oxidase) and H2O2 to H2O (peroxidase) using proton/electron donors. This rich oxidative reactivity is promoted by a mononuclear Cu center in which some of the amino acid residues surrounding the metal might accept and donate protons and/or electrons during O2 and H2O2 reduction. Herein, we utilize a podal ligand containing H‐bond/proton donors (LH2) to analyze the reactivity of mononuclear Cu species towards O2 and H2O2. [(LH2)CuI]1+ (1), [(LH2)CuII]2+ (2), [(LH−)CuII]1+ (3), [(LH2)CuII(OH)]1+ (4), and [(LH2)CuII(OOH)]1+ (5) were synthesized and characterized by structural and spectroscopic means. Complex 1 reacts with O2 to produce 5, which releases H2O2 to generate 3, suggesting that O2 is used by LPMOs to generate H2O2. The reaction of 1 with H2O2 produces 4 and hydroxyl radical, which reacts with C−H substrates in a Fenton‐like fashion. Complex 3, which can generate 1 via a reversible protonation/reduction, binds H2O and H2O2 to produce 4 and 5, respectively, a mechanism that could be used by LPMOs to control oxidative reactivity.