Biomedical Engineering Reference
In-Depth Information
1 . 1 C h i t i n
1.1.1 Discovery and Origin
Chitosan usually exists in nature as chitin, which is a natural macromolecular compound,
namely, a polysaccharide formed by connecting N -acetyl-2-amino-2-deoxy-d-glucoses
through β-(1,4) glycoside bonds. The structural formula of chitosan is shown in Figure 1.1.
Chitosan is formed when some acetyls are removed from chitin. Usually, products with
over 60% deacetylation degree (DD) or that can be dissolved in dilute acid are called
chitosan.
In 1811, H. Braconnot, a French professor of natural science history, repeatedly treated
mushroom with a warm dilute alkali solution and finally harvested white fibroid residues
[1]. He believed that they were celluloses from mushroom and named the residues fungine.
In 1823, another French scientist, A. Order, separated the same substance from the elytra of
beetles. He named the compound chitin because he thought that the compound was a new
cellulose. In 1843, J. L. Lassaigne found that chitin contains nitrogen, which proved that
chitin is not a cellulose, but a new compound with fiber quality. In 1878 glucosamine and
acetic acid in chitin were identified by G. Ledderhose through hydrolysis, and in 1894
E. Gilson further proved that chitin contains glucosamine. Later research showed that
chitin is formed by polymerizing N -acetylglucosamine.
In 1859, a Frenchman, C. Rouget, boiled chitin in a concentrated alkali solution for a
while and found that the product can dissolve in organic acid after washing it [2]. In 1894,
F. Hoppe-Seiler confirmed that the product is deacetylated chitin and therefore named it
chitosan.
(a)
(b)
OH
NH 2
H 2 C
O
HO
*
*
O
O
*
H
*
O
H 2 C
NH
OH
O
C
n
n
CH 3
(c)
OH
NH 2
H 2 C
HO
*
O
*
O
O
H
O
H 2 C
NH
OH
O
C
1-DA
DA
CH 3
Figure 1.1
Chemical structure of (a) chitin and (b) chitosan repeat units. (c) Structure of partially acetylated chitosan, a
copolymer characterized by its average degree of acetylation DA.
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