Laccase mediator systems (LMS) use small-molecule radical mediators with the enzyme laccase to oxidize non-phenolic substrates with redox potentials outside the range of the enzyme itself. LMS have been shown in the literature to catalyze the oxidation of benzylic hydroxyl groups in model lignin monomers (for example, veratryl alcohol and similar compounds), dimers (nonphenolic β-O-4 linked dimer models), and in kraft pulp. Furthermore, oxidation of benzylic hydroxyl groups in lignin is well known to increase the base-catalyze decomposition of both β-O-4 and α-O-4 model linkages in model lignin and has been shown to decrease the molecular weight of kraft lignin.
The kinetics of LMS have been investigated on monomeric model substrates, however, detailed investigations on the effect of mediator, lignin model, enzyme, and oxygen concentration have not been done on nonphenolic dimer molecules, which should more closely represent the behavior of native lignin in this system. In this work, we compare the kinetics of monomer and dimer oxidation, using techniques including HPLC, cyclic voltammetry, and UV absorbance, in order to better evaluate the utility of the LMS in lignin modification and breakdown.