Modification phenomena of solid-state lignin caused by electron-abstracting oxidative systems

Oxidative treatments of wood pulp lignin by one-electron-abstracting enzymatic or chemical systems result in modification phenomena which are not fully described in terms of those known from lignin model compound studies. The generation of, e.g., long-lived radicals necessitates nondestructive spectroscopic analysis of the lignin polymer for a proper characterization of these. The present work exposes a complexity of spectroscopic modification phenomena, which has not previously been realized. This is achieved by a laccase–mediator system, where the mediator is an aromatic low-molecular-weight compound, which mediates the electron abstraction between the lignin and the enzyme laccase. It is demonstrated that the modification generated exhibits qualitatively different temporal phases. The mechanisms are partly explained in terms of Marcus electron transfer theory, and it is suggested that these may play a role in the in vivo synthesis and degradation of lignin.