Biomedical Engineering Reference
In-Depth Information
-
O
3
SO-CH
2
NH
+ -
O
3
SO
CH
2
H
O
O
NH
+
H
O
O
O
O
O
HO
O
O
H
O
NH
+ -
O
3
SO
CH
2
O
NH
+ -
O
3
SO
CH
2
Figure 1.10
Conformation of chitosan 6-
O
-sulfate in solution.
sulfuric groups will be formed on aminos when a DMF solution of chitosan reacts with
chlorosulfonic acid at 80°C.
O
-sulfate and
N
-sulfuric groups will be formed when chitosan reacts with excess SO
3
-
DMF in homogeneous phase. The product is amorphous and has better anticoagulant
activity than heparin.
Like cellulose, chitin can be transformed into xanthate by carbon disulfide after being
treated with alkali. See
Figure 1.11.
Sodium chitosan
N
-xanthate, which is a brilliant yellow powder, can be formed by add-
ing chitosan in a water solution of carbon disulfide and sodium hydroxide, reacting at
60°C for 6 h, and pouring the mixture into acetone. The powder is water soluble and has
strong heavy-metal-chelating capacity. The chelate composites are insoluble in water and
can be removed by filtering. So xanthate is an effective heavy-metal remover. Chitosan
fibers can be made by spraying a water solution of the xanthate. The equation is shown in
Phosphates of chitin and chitosan can be formed by treating them with phosphorus
pentoxide in methanesulfonic acid. Chitin phosphate has water solubility increasing with
degree of substitution. In case the aminos are unprotected, the chitin is water soluble at a
low degree of substitution and water insoluble at a high degree of substitution due to the
formation of phosphate. Prolonging the reaction time will increase the degree of substitu-
tion, but in the meantime the main chain will degrade.
1.5.3 etherification
Ethers, such as methyl ether, ethyl ether, benzyl ether, hydroxylethyl ether, hydroxylpropyl
ether, cyanoethyl ether, and carboxylmethyl ether, can be formed by hydroxyls of chitin
and chitosan and hydrocarbylation agents. Such reactions have attracted more attention in
recent years, and subsequently a few new materials have been developed.
S
CH
2
O
C
O
SNa
CH
2
OH
O
NaOH, CS
2
O
O
OH
OH
*
*
*
*
NHCOCH
3
NHCOCH
3
n
n
Figure 1.11
Transformation of chitin to xanthate.
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