Copper catechol-driven Fenton reactions and their potential role in wood degradation

Metals can potentially play a role in the non-enzymatic processes involved in wood biodegradation. Dihydroxybenzenes reduce Cu(II)-Cu(I), which then react with H2O2 driving a Fenton reaction. In this work the degradation of veratryl alcohol (VA), the simplest non-phenolic lignin model compound, via a cuprous Fenton reaction mediated by 1,2-dihydroxybenzene (catechol, CAT) was studied. A factorial experimental design was performed to assess the impact of several experimental variables including, pH, and CAT, CuCl, and H2O2 concentrations on VA degradation. Optimized conditions were determined using a response surface modeling methodology (RSM). The greatest amount of VA degradation occurred at a CAT:CuCl2:H2O2 ratio of 0.287:0.313:4.062, a pH of 3.6. A time-course measurement for VA degradation was performed under these experimental conditions and after an 8 h reaction period, 31% of the VA was degraded. Under the same experimental conditions, VA degradation by an iron CAT-driven Fenton reaction was more effective than the copper CAT-driven Fenton reaction. In a similar experiment, carboxymethyl cellulose (CMC) depolymerization was also determined. Only the iron CAT-driven Fenton reaction was found to depolymerize CMC. We suggest that the greater redox potential of the Fe(III)CAT complex compared to the Cu(II)CAT complex would dictate that under most environmental conditions, degradation of VA would occur by the iron complex only. This research has important implications for the mechanisms of brown rot fungal degradation in wood because it eliminates a pathway that had previously been proposed as a mechanism explaining free radical generation in the oxidative depolymerization of cellulose in the cell wall. (C) 2007 Elsevier Ltd. All rights reserved.