Biomedical Engineering Reference
In-Depth Information
analysis of the 15 major peaks that appeared in the GC-MS spectrum is as follows:
The first peak belongs to the saturated straight-chain hydrocarbons, which were
produced because of the complete enzymolysis process in which the aromatic
ring is disconnected and methoxy is eliminated. The second peak is resveratrol
(dimethoxy benzyl alcohol, C
9
H
12
O
3,
Mw 168), produced because of the cleavage
of the C
'
-C
“
bond. Initially, LiP is considered to be hydrogen peroxide peroxidase.
When catalyzing the C
'
-C
“
cleavage in the
“
-l lignin model compounds, the
labeled oxygen is added to the
-C atom. It was found that this process occurs
in a pure chemical process between the molecular oxygen and the phenyl radical
intermediates; later, Kirk et al. found that the reaction between oxygen and hydroxyl
group-substituted benzene radical can cause the activation of oxygen. That is,
oxygen is reduced to superoxide ions and then reacts with a hydrogen proton to
generate H
2
O
2
and O
2
. This reaction also occurs in the catalytic cycle of LiP, and
O
2
becomes the ultimate electron acceptor. The enzymatic hydrolysis contains high
content of butylated
“
-cresol (peak 3), which is generated by rupture of the bond
between the C
'
-C
“
. Peak 4 may be attributed to 1,2-benzoate, methyl-n-propyl
ester, which is formed in the following way: Aromatic radical cations are formed
through one-electron oxidation after the fracture of the C
'
-C
“
bond. Then, aromatic
radical cations react with water or other nucleophilic reagents in a variety of types
of reactions according to the substrates. The other peaks are as follows: Peak 5 is a
straight olefin product; peak 6 is an ester product. The strongest peak in the spectrum
(peak 7) is a straight-chain alcohol; peak 8 represents a straight-chain acid; peak 9 is
oleic acid amide; peak 10 is dimethoxy benzaldehyde; and peak 11 is syringic acid
with lilac group structure and was generated because of the action of the enzyme
to its oxidative cleavage of C
'
-C
“
. Peak 12 is methyl vanillate, the result of wood
prime side-chain C
'
-C
“
fracture through enzymatic hydrolysis. Peak 13 is acetyl
ferulic acid produced because of the aromatic epoxidized cracking that occurred in
the enzymatic process. Peak 14 is a type of straight-chain esters with branches, and
peak 15 represents substances with a quinone structure.
The enzymatic hydrolysate of lignin consists of veratryl alcohols, low molecular
weight phenolic compounds, ferulic acid, lilac acid, vanillic acid, and other small
molecular acids, as well as some neutral substances, such as ketones, alkanes, and so
on. LiP could be used as a catalyst for one-electron oxidation and lead to a series of
free radical reactions in lignin model substance degradation, which would explain
the chemical reaction mechanism of the lignin degradation process. It was found
that the emergence of LiP activity in the white-rot fungus culture was similar to that
in the lignin degradation process. But, the enzymatic hydrolysis effect of LiP cannot
fully reflect the microbial degradation of lignin, and the microbial degradation of the
lignin mechanism has to be studied continually.
As mentioned, lignin resources not only can be used as the basic raw materials for
polymer making, which opens a new field of industrial polymer material synthesis,
but also can be used as raw materials for some small aromatic molecule products.
Because lignin degradation mechanisms, metabolic intermediates, and pathways are
not clear at present, the large-scale industrial applications of lignin still needs time
and effort.
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