Table 5.
Assignment of main 13C-1H correlation signals in HSQC spectra of lignin from wheat and Chamaecytisus a shown in Figure 6.
| Label | δC | δH | Assignment |
|---|---|---|---|
| Bβ | 53.4 | 3.1 | Cβ-Hβ in resinol substructures (B) |
| OMe | 55.5 | 3.7 | C-H in methoxy groups |
| Aγ | 59.3 | 3.2 and 3.9 | Cγ-Hγ in β-O-4′ substructures (A) |
| A′γ | 62.9 | 3.9 | Cγ-Hγ in γ-acylated β-O-4′ substructures (A′) |
| X5 | 63.0 | 3.2 | C5-H5 in β-xylopyranoside |
| Aα (G) | 69.4 | 4.5 | Cα-Hα in β-O-4′ substructures (A) linked to a G-unit |
| Bγ | 70.6 | 3.3 and 3.9 | Cγ-Hγ in resinol substructures (B) |
| Cγ | 70.9 | 4.2 | Cγ-Hγ in β-5′ phenylcoumaran subunit (C) c |
| A′α (G) | 71.1 | 4.8 | Cα-Hα in γ-acylated β-O-4′ substructures linked to a G-unit (A′) c |
| X′2 | 72.4 | 4.9 | C2-H2 in 2-O-Ac-β-d-xylopyranoside c |
| X2 | 72.5 | 3.0 | C2-H2 in β-xylopyranoside |
| X3 | 73.8 | 3.3 | C3-H3 in β-xylopyranoside |
| X4 | 75.3 | 3.5 | C4-H4 in β-xylopyranoside |
| U4 | 81.6 | 3.1 | C4-H4 in 4-O-methyl-α-d-glucuronic acid |
| Bα | 85.1 | 4.6 | Cα-Hα in resinol (β-β) substructures (B) |
| Aβ (S) | 85.9 | 4.1 | Cβ−Hβ in β-O-4′ substructures (A) linked to a S-unit c |
| S2,6 | 103.9 | 6.7 | C2,6-H2,6 in etherified syringyl units (S) |
| S′2,6 | 106.8 | 7.2 | C2,6-H2,6 in oxidized (Cα=O) phenolic syringyl units (S′) |
| FA2 | 110.6 | 7.4 | C2-H2 in ferulate (FA) c |
| G2 | 111.7 | 6.6 | C2-H2 in guaiacyl units (G) |
| J2(G) | 112.1 | 7.4 | C2-H2 in cinnamyl aldehyde end-groups (J) c |
| H3,5 | 115.1 | 6.7 | C3,5-H3,5 in p-hydroxyphenyl units (H) |
| G5 | 115.6 | 6.7 | C5-H5 in guaiacyl units (G) |
| PCA3,5 | 117.1 | 6.4 | C3,5-H3,5 in p-coumarate PCA and ferulate (FA) c |
| G6 | 119.8 | 6.8 | C6-H6 in guaiacyl units (G) c |
| J6(G) | 122.7 | 7.1 | C6-H6 in cinnamyl aldehyde end-groups (J) c |
| FA6 | 122.9 | 7.1 | C6-H6 in ferulate (FA) c |
| H2,6 | 129.0 | 7.2 | C2,6-H2,6 in p-hydroxyphenyl units (H) c |
| PCA2,6 | 130.3 | 7.5 | C2,6-H2,6 in p-coumarate (PCA) c |
| PCAα and FAα | 144.5 | 7.5 | Cα-Hα in p-coumarate (PCA) and ferulate (FA) c |
| Anomeric Region | |||
| αX1 (R) | 4.9 | 92.2 | α-d-Xylopyranoside (R) [α-d-glucopyranoside (R)] |
| U1 | 5.1 | 97.2 | 4-O-Methyl-α-d-glucuronic acid b |
| βX1 (R) | 4.2 | 97.3 | β-d-Xylopyranoside (R) [β-d-glucopyranoside (R)] |
| UGA1 | 4.9 | 101.7 | Methyl(1/4)-α-d-galacturonate |
| M1 | 4.5 | 101.0 | (1/4)-β-d-Mannopyranoside b |
| X1-X′1 | 4.3 | 101.5 | β-d-Xylopyranoside + 3-O-acetyl-β-d-xylopyranoside |
a Since the 13C-1H HSQC spectra of lignins isolated from Chamaecytisus, Leucaena and barley lignins were not significantly different (Figure S2), the interpretation refers to HSQC spectrum from Chamaecytisus; b Not present in Wheat-derived lignin; c Not present in Chamaecytisus-derived lignin.