Figure 1.

Heteronuclear single quantum correlation nuclear magnetic resonance spectra of whole eucalypt samples swollen in dimethylsulfoxide-d₆. (A) Initial sample, (B) control without enzyme, (C) sample treated with laccase alone (50 U · g^-1) and (D) sample treated with laccase (50 U · g^-1) and methyl syringate (3%). See Table 3 for lignin signal assignment, Figure 2 for the main lignin structures identified and Table 4 for quantification of these lignin structures. Correlation signals from normal (X₁-X₅) and acetylated xylan (Xʹ₁-Xʹ₃) are also indicated. The 52/3.8 ppm signal corresponds to some methyl syringate incorporated onto the lignin (see Figure 3). The enzymatic pretreatment included four laccase-mediator treatments, each followed by an alkaline peroxide extraction step.