Chitosan derivatization

R = —(CH2)4CH3—Caproyl chitosan R = —(CH2)6CH3—Octanoyl chitosan R = —(CH2)i2t H3—Myristoyl chitosan R=—(CH2)i4CH3—Palmitoyl chitosan FIGURE 13.2 Chitosan derivatization with fatty acyl chlorides. 

We initially prepared the first chitosan-sialoside hybrid 19 by treating 80% de-AT-acetylated chitosan with p-formylphenyl a-sialoside 6 (Scheme 1) under reductive amination conditions (NaBH3CN) (Scheme 7) [64]. The level of sialo-side incorporation could be controlled by increasing the amount of 6 (Table 15.2). The reactivity of aldehyde 6 toward chitosan was found to be in the range 25-48% due to excessive reduction of the aldehyde under the acidic reaction conditions. Water-soluble materials were only achieved at high DS (DS > 0.53). Sialo-hybrids with lower substitutions were further derivatized with succinic... 

Besides the polymer derivatization, combining the polymers in microsphere preparations can result in improved drug delivery and absorption characteristics. Hyaluronic acid-chitosan microspheres appeared to improve the absorption of incorporated gentamicin compared to the individual polymers, assembling the mucoadhesive potential of both polymers and the penetration-enhancing effect of chitosan [51,52],... 

Several derivatized chitosans have practical applications. Py-GC and Py-MS have been used for the evaluation of free amine content in several chitosan samples [72,73]. 

Nature commonly utilizes saccharides as a source of energy, structure-forming material, water-maintaining hydrocolloids, and even sex attractants. All organism cells contain saccharide components in their membranes. Frequently, saccharides exist in naturally derivatized forms, e.g., animated, as in chitin and chitosan ... 

Although most reactions of chitosan involve the primary amino groups, it is possible to selectively derivatize the hydroxyl groups. This can be done by protecting the amino groups via reaction with formic or acetic acid to produce a polysaccharide formate or acetate salt. The chitosan formate or acetate salt may then be reacted with an electrophile (Muzzarelli, 1977). 

Peptide-chitin complexes resulting from peptide synthesis on chitin could prove useful for the induction of antipeptide antibodies. Chitin is stable to the conditions of Fmoc chemistry, including methods used to release peptides. The properties of chitin are similar to those of cellulose. Chitosan, unlike cellulose, does not have to be derivatized to create an amino group for attachment of the linker. 

The multifaceted derivatization potential of chitin and chitosan is summarized in Table 6.6. 

With the purpose of conferring thermosensitivity to chitosan-based hydrogels. Park et al. proposed the grafting of carboxylic acid-terminated poly(ethylene oxide-h-propylene oxide) block copolymer (Pluronic) onto the primary amine of chitosan, mediated by EDC coupling agent [102]. With the same purpose, Wang et al. grafted poly(N-isopropyl acrylamide) (NiPAM) chains onto chitosan by the copolymerization of acrylic acid-derivatized chitosan and N-isopropylacrylamide (NIPAAm) in aqueous solution [103]. 

Fig. 5 Production of nitrene groups in phenyl-azido derivatized RODS by UV irradiation and immobilization on chitosan surface [42]...

The reactive hydroxy and amino groups of chitosan have been used for its derivatization or chemical modification. The amino group being nucleophilic in nature allows easy formation of imine bond with aldehyde or corresponding amide derivatives. However, in acidic solution, the cationic property of chitosan is revealed and the amino groups act like alkali, receive protons, and generate salts [87]. Some of the derivatives with their method of syntheses have been summarized in Table 15.2. 

Chemical Derivatization of Chitosan for Plasmid DNA Delivery Present and Future... 

Synthesis and Derivatization of Chitosan/Poly(ethylenimine) Graft Copolymers...71... 

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