Table 5.
Lignin units and side-chains forming different inter-unit linkages (and end-groups) from the heteronuclear single quantum correlation spectra of cellulolytic enzyme lignin preparations from treated wood and controls
| Lignin structure | Wood | Control | Laccase only | Laccase and methyl syringate |
|---|---|---|---|---|
|
Lignin units
| ||||
| Syringyl (S) (% total) |
77 |
81 |
83 |
93 |
| Guaiacyl (G) (% total) |
23 |
19 |
17 |
7 |
| Cα-oxidized S units (Sʹ) (% S) |
6 |
10 |
18 |
35 |
| S/G ratio |
3.4 |
4.3 |
4.9 |
14.1 |
|
Chains forming inter-unit linkages and end
-
groups
| ||||
| β-O-4ʹ Alkyl-aryl ethers (A) (% S + G) |
58 (82) |
61 (84) |
56 (85) |
49 (92) |
| Phenylcoumarans (B) (% S + G) |
2 (3) |
1 (1) |
1 (2) |
0 |
| Resinols (C) (% S + G) |
9 (13) |
8 (11) |
6 (9) |
2 (4) |
| Spirodienones (D) (% S + G) |
2 (3) |
2 (3) |
2 (3) |
1 (2) |
| Cinnamyl end-groups (I) (% S + G) |
1 (1) |
1 (1) |
1 (1) |
0 (1) |
| Total (% S + G) |
71 (100) |
73 (100) |
66 (100) |
53 (100) |
| Cα-oxidized β-O-4ʹ ethers (A ox ) (% A) | 2 | 2 | 5 | 14 |
The lignin composition (S and G units), the amount of Cα-oxidized S units (with respect to total S units), the S/G ratio, the abundance of side chains forming different inter-unit linkages (A-D) and cinnamyl end-groups (I) per 100 phenylpropane units, and the relative abundance of Cα-oxidized β-O-4ʹ ethers (with respect to total β-O-4ʹ ethers) were determined from the heteronuclear single quantum correlation spectra of cellulolytic enzyme lignins isolated from the eucalypt wood treated with laccase (50 U · g-1) and 3% methyl syringate and laccase alone, compared with a control without enzyme and the initial wood. The percentage of side chains forming each linkage type (or end-group) are also indicated (parentheses).