PNNL

Abstract

Developing tunable and stable peroxidase mimetics with high catalytic efficiency provides a promising opportunity to improve and expand enzymatic catalysis in lignin depolymerization. A class of peptoid-based peroxidase mimetics with tunable catalytic activity and high stability is developed by constructing peptoids and hemins into programmable and self-assembled crystalline nanomaterials. By varying peptoid side chain chemistry to tailor the microenvironment of active sites, these self-assembled peptoid/hemin nanomaterials (Pep/hemin) exhibited highly modulable catalytic activities toward two lignin model substrates 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 3,3’,5,5’-tetramethylbenzidine (TMB). Among them, a Pep/hemin complex containing the pyridyl side chain showed an unprecedented catalytic efficiency (Vmax/Km = 5.81 × 10-3 s-1). In addition, these self-assembled Pep/hemin peroxidase mimetics are highly stable and remain active after exposed to elevated temperatures and a wide range of pH conditions. Kinetics studies suggest that these enzymatic mimetics follow a peroxidase-like, double-displacement (ping-pong) mechanism. Moreover, these enzyme mimetics exhibited a significantly high efficacy on depolymerization of a biorefinery lignin which is the representative of lignin polymer, a capability that has not been demonstrated by natural lignin peroxidases or other peroxidase mimetics. Because self-assembled Pep/hemin materials are highly stable and programmable, it is conceivable that these new enzyme mimetics will offer tremendous opportunities for lignin valorization to high value products.