Depolymerization of Laccase-Oxidized Lignin in Aqueous Alkaline Solution at 37 °C

Abstract

Lignin depolymerization is a coveted process for the generation of high-value compounds from a low-cost feedstock. This report describes a chemoenzymatic approach for the depolymerization of lignin involving a laccase-catalyzed oxidation under ambient air at room temperature followed by a base (NaOH)-induced depolymerization in aqueous solution at 37 °C. Two-dimensional nuclear magnetic resonance heteronuclear single quantum coherence spectroscopy, gel permeation chromatography, and liquid chromatography-electrospray ionization-quadrupole-time of flight-mass spectrometry (LC-ESI-Q-TOF-MS) analysis indicated the degradation of lignin and the formation of water-soluble fractions containing guaiacol, syringol, vanillic acid, m-anisic acid, and veratric acid. Furthermore, guaiacol and veratric acid are the main final products in the chemoenzymatic decomposition of a β-O-4 model compound.