Chitosan Derivatives - Chitosan Based Hydrogels: Functions and Applications - page 52

O

NH 2

NH 2

R Cl

O

RO

HO O

O

0°C MeSO 3 H

O O

O

OH

OR

O

N , N -dimethylacetamide

R ′ Cl

R ′

O

NH

HO

O

O

O

OR

Figure 2.14
Controlled synthesis of N , O- acyl-chitosans in the presence of MSA.

O -Octanoyl, N -cinnamate chitosan, and N - O -hexanoyl chitosan derivatives have been
synthesized using the aforementioned methodology [59,83]. N , O amphiphilic derivatives
containing N -phthaloyl moieties can be easily prepared by a coupling reaction in
the presence of dicyclohexylcarbodiimide [46]. For instance, N -phthaloylchitosan-g-
polyvinylpyrrolidone (PHCS-g-PVP) has been synthesized by grafting PVP onto a chitosan
derivative whose amino groups have previously reacted with phthalic anhydride. Polymeric
micelles were prepared by the dialysis method and showed a CMC of 0.83 mg/L.
Prednisone acetate was incorporated into the polymeric micelles with a loading capacity
of around 45%. In vitro tests showed that the release of prednisone acetate from the micelles
was continuous with no initial burst.

2.5 Carboxyalkyl Chitosans
O / N -Carboxymethyl chitosan is one of the most investigated derivatives of chitosan,
obtained under controlled reaction conditions with sodium monochloroacetate. The pro-
cess of carboxyalkylation introduces acidic groups on the polymer backbone. On introduc-
ing carboxyl groups into the amino groups of chitosan, amphoteric polyelectrolytes
containing both cationic and anionic fixed charges are prepared. By varying the DS of the
carboxyl-bearing group, we can obtain various charge densities on the molecular chain,
which provide a convenient way of controlling pH-dependent behavior. This amphoteric
polyelectrolyte has attracted considerable interest in a wide range of biomedical applica-
tions, such as wound dressings, artificial bone and skin, bacteriostatic agents, and blood
anticoagulants, due to its unique chemical, physical, and biological properties, especially
its excellent biocompatibility [84-88]. The presence of both carboxyl groups and amino