Characterization Methods and Techniques 131
It should be noted that all of the integration of cross-peaks should be done at the same
contour level.
Table 4.5 summarizes important chemical shifts and assignments of cross-peaks of
interunit linkages and/or subunits in HSQC spectra of lignin.
The 2D HSQC has proven to be a powerful tool to evaluate changes in transgenic
plants [28, 29, 115, 116] and changes due to chemical and biological modifications of
plant biomass [46, 47, 52, 117–123].
Table 4.5Assignments of carbohydrates/lignin^13 C–^1 H correlation peaks in the 2D HSQC.
Region Label 휹C/휹H(ppm) Assignment
Aliphatic A훼 71.8/4.83 C훼–H훼inβ-O-4′substructures (A)
A훽(G) 83.4/4.27 C훽–H훽inβ-O-4′substructures (A)linkedtoaG
unit
A훽(S) 85.9/4.10 C훽–H훽inβ-O-4′substructures linked (A)toaS
unit
B훼 86.8/5.43 C훼–H훼inα-5 phenylcoumaran substructures (B)
C훼 84.8/4.65 C훼–H훼inα–α′resinol substructures (C)
C훽 53.5/3.05 C훽–H훽inβ–β′resinol substructures (C)
C훾 71.1/3.81 and 4.16 C훾–H훾inβ–β′resinol substructures (C)
D훼 83.5/4.98 C훼–H훼in 5–5′dibenzodioxocin
substructures (D)
E훾 61.3/4.08 C훾–H훾in cinnamyl alcohol end groups (E)
overlaps with carbohydrate signals
MeO (-OCH 3 ) 55.6/3.73 C–H in methoxyls
X 2 ′ 99.4/4.50 2-O-Ac-β-d-Xylp(R)
X 3 ′ 101.5/4.39 3-O-Ac-β-d-Xylp(R)
Aromatic H2,6 127.1/7.17 C 2 –H 2 and C 6 –H 6 p-hydroxyphenyl units (H)
G 2 110.9/6.99 C 2 –H 2 in guaiacyl units (G)
G 5
G 6
114.9/6.72 and
6.94
118.7/6.77
C 5 –H 5 in guaiacyl units (G)
C 5 –H 5 in guaiacyl units (G)
S2,6 103.8/6.69 C 2 –H 2 and C 6 –H 6 in etherified syringyl units (S)
pCA2,6 130.1/7.45 C 2 –H 2 and C 6 –H 6 inp-coumarate (pCA)
pCA훽+FA훽 111.0/7.32 C 2 –H 2 in ferulate (FA)
Anomeric (1–4)-β-D-Glcp 102.8/4.40 Cellulose
d-α-Glcp(R) 92.2/5.10 C훼–H훼reducing end of glucose
d-β-Glcp(R) 97.1/4.44 C훽–H훽reducing end of glucose
(1–4)-β-d-Xylp 102.4/4.50 Xylan
d-α-Xylp(R) 92.4/5.10 C훼–H훼reducing end of xylose
d-β-Xylp(R) 97.5/4.38 C훽–H훽reducing end of xylose
2-O-Ac-β-d-Manp 98.9/4.86 O-2 Acetylated mannan
3-O-Ac-β-d-Manp 99.9/4.78 O-3 Acetylated mannan
Source: Adapted from Refs [4, 114].
