Biomedical Engineering Reference
In-Depth Information
2.1 Introduction
Chitosan displays interesting properties such as biocompatibility and biodegradability,
and its degradation products are nontoxic, nonimmunogenic, and noncarcinogenic.
Therefore, chitosan has prospective applications in many fields such as biomedicine, waste
water treatment, functional membranes, and flocculation. However, the commercial or
practical use of chitin and chitosan (including monomers and oligomers) has been con-
fined to the unmodified forms. For a breakthrough in utilization, chemical modification to
introduce a variety of functional groups will be a key point. For this purpose, more funda-
mental studies on chemical modification will be required. Fortunately, chitosan is an ame-
nable molecule. Without disturbing the degree of polymerization (DP) of chitosan, one can
chemically modify this acquiescent polymer because it provides functional groups as pri-
mary amine and primary as well as secondary hydroxyl groups in its monomers.
2.2
N
-Alkyl-Chitosans
The primary amino groups of chitosan undergo Schiff reaction with aldehydes and ketones
to yield the corresponding aldimines and ketimines, which are converted to an
N
-alkyl
derivative by reduction with sodium borohydride (NaBH
4
) or sodium cyanoborohydride
(NaBH
3
CN) among other reducing agents (Figure 2.1). The choice of the reducing agent is
RCR
′
N
NH
2
ROR
′
HO
O
O
HO
O
MeOH
O
O
O
OH
OH
ROR
′
: aldehyde o ketone
Reduction
CHRR
′
NH
O
HO
O
O
OH
Figure 2.1
Synthesis of
N
-alkyl chitosans.
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