68
MeO
OMe
MeO
O
HO
OH
O
OH
OH
OMe
OMe
O
OH
OH
OH
O
OMe
O
O
OH
HO
O
O
OMe
OMe
MeO
MeO
OH
OH
HO
O
OMe
MeO
OH
HO
O
OMe
OMe
O
OH
OH
OMe
O
HO
OH
O
MeO
O
OH
HO
OMe
OMe
O
O
OMe
OH
OH
HO
HO
OH
OH
OMe
MeO
Fig. 5.3 Representation of the structure of lignin
HO
HO
O
O
β
O
O
O
OMe
O
OMe
α
α'
β
β'
γ'
γ
O
OH
OMe
MeO
A
B
S
4'
OMe
OMe
O
O
OMe
MeO
S'
O
O
α
β
γ
OMe
H
J
OH
O
FA
O
4
α
β
γ
γ
α
O
OH
H
O
HO
O
O
OMe
α
β
γ
R
O
A'
O
OH
α
β
γ
OMe
I
O
OH
OMe
G
OMe
4'
O
O
HO
OMe
O
α
β
γ
α β γ
D
O
OM e
OMe
O
α
β
C
5'
HO γ
OMe
OH
OAr
O
OMe
O
B'
O
α
α'
β
β'
γ'
γ
OMe
HO
OH
Fig. 5.4 Main substructures present in lignin: (A) β-O-4 alkyl-aryl ethers, (A′) β-O-4 alkyl-aryl
ethers with acylated γ-OH, (B) β-β resinols, (B′) tetrahydrofuran, (C) phenylcoumarans, (D) spirodienones, (I) cinnamyl alcohol end-groups, (J) cinnamyl aldehyde end-groups, (FA) ferulates, (S)
syringyl units, (S′) oxidized syringyl units bearing a carbonyl at C α , (G) guaiacyl units and (H)
p-hydroxyphenyl units
Much research has revealed that the antioxidant activity of lignin is correlated
with its structural characteristics (Mw, polydispersity, functional groups) and purity
(relative amounts of hemicellulose and other components). Dizhbite et al. (2004)
assessed the antioxidant activities of lignin fractions isolated from deciduous and
Z. Qin et al.
MeO
OMe
MeO
O
HO
OH
O
OH
OH
OMe
OMe
O
OH
OH
OH
O
OMe
O
O
OH
HO
O
O
OMe
OMe
MeO
MeO
OH
OH
HO
O
OMe
MeO
OH
HO
O
OMe
OMe
O
OH
OH
OMe
O
HO
OH
O
MeO
O
OH
HO
OMe
OMe
O
O
OMe
OH
OH
HO
HO
OH
OH
OMe
MeO
Fig. 5.3 Representation of the structure of lignin
HO
HO
O
O
β
O
O
O
OMe
O
OMe
α
α'
β
β'
γ'
γ
O
OH
OMe
MeO
A
B
S
4'
OMe
OMe
O
O
OMe
MeO
S'
O
O
α
β
γ
OMe
H
J
OH
O
FA
O
4
α
β
γ
γ
α
O
OH
H
O
HO
O
O
OMe
α
β
γ
R
O
A'
O
OH
α
β
γ
OMe
I
O
OH
OMe
G
OMe
4'
O
O
HO
OMe
O
α
β
γ
α β γ
D
O
OM e
OMe
O
α
β
C
5'
HO γ
OMe
OH
OAr
O
OMe
O
B'
O
α
α'
β
β'
γ'
γ
OMe
HO
OH
Fig. 5.4 Main substructures present in lignin: (A) β-O-4 alkyl-aryl ethers, (A′) β-O-4 alkyl-aryl
ethers with acylated γ-OH, (B) β-β resinols, (B′) tetrahydrofuran, (C) phenylcoumarans, (D) spirodienones, (I) cinnamyl alcohol end-groups, (J) cinnamyl aldehyde end-groups, (FA) ferulates, (S)
syringyl units, (S′) oxidized syringyl units bearing a carbonyl at C α , (G) guaiacyl units and (H)
p-hydroxyphenyl units
Much research has revealed that the antioxidant activity of lignin is correlated
with its structural characteristics (Mw, polydispersity, functional groups) and purity
(relative amounts of hemicellulose and other components). Dizhbite et al. (2004)
assessed the antioxidant activities of lignin fractions isolated from deciduous and
Z. Qin et al.