Chemical Modification of Chitin and Chitosan

The chemical modification of chitin and chitosan is summarized in Table 6.1. 

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Kurita, K. 1986. Chemical modification of chitin and chitosan. In Chitin in Nature and Technology (R.A.A. Muzzarelli, C. Jeuniaux, and G.W. Gooday, eds), pp. 287-293. Plenum Press, New York. 

Sashiwa, H. and Shigemasa, Y. 1999. Chemical modification of chitin and chitosan. 2 Preparation and water soluble property of N-acylated or N-alkylated partially deacetylated chitins. Carbohydr. Polym. 39 127-138. 

Hirano, S., Sato, N., Yoshida, S. et ah, 1987. Chemical modification of chitin and chitosan, and their novel applications. In M. Yalpani (ed.). Industrials Polysaccharides Genetic, Engineering, Structure/Property Relations and Applications, Amsterdam, the Netherlands Elsevier, p. 163. 

Ning M, Wang Q, Sun SL et al (2004) Progress in chemical modification of chitin and chitosan. Prog Chem 16 643-653... 

The poor solubility, low surface area, and porosity of chitin and chitosan are the major limiting factors in their utilization. Chitosan can be modified by physical or chemical processes in order to improve the mechanical and chemical properties. Chemical modification of chitosan has two main aims (a) to improve the metal adsorption properties and (b) to change the solubility properties of chitosan in water or acidic medium. The substitution chemical reactions involve the NH2 group in the C2 position or the OH groups in the C3 and Cg positions of acetylated and deacetylated units. Chitosan membrane is swollen in water the amino groups may be protonated and leave the hydroxide ions free in water, which may contribute to the ionic conduction in the membrane. 

Morimoto, M., Saimoto, H., and Shigemasa, Y. 2002. Control of functions of chitin and chitosan by chemical modifications. Trends Glycosci. Glycotech. 14 205—222. 

Chemical. A large number of chitin and chitosan derivatives have been synthesized through modification of the primary (C-6) and secondary (C-3) hydroxyl groups present on each repeat imit, including amine (C-2) functionality existing on deacetylated imits (31). Reactions typical of hydroxyl and amine groups (such as acylations with acid chlorides and anhydrides) including urethane and urea formation respectively, are feasible with isocyanates. The primary amine can be quatemized by alkyl iodides or converted to an imine with a variety of aldehydes and ketones that can subsequently be reduced to an N-alkylated derivative. Chitin and chitosan are reactive with a variety of alkyl chlorides after treatment with concentrated NaOH. Important derivatives such as carboxymethylated chitin and chitosan are commonly produced in this manner with the addition of sodium chloroacetate. 

Chitin is a (l->4)-linked 2-acetoamido-2-deoxy-g-D-glucan, and chitosan is its N-deacetylated product. These polysaccharides are naturally abundant and are present in the cuticles of insects and in the cell walls of plant pathogens, absent in the higher plant kingdom. Chitin and chitosan are (a) natural, (b) biocompatible, (c) almost nontoxic, (d) biodegradable, and (e) bioactive polymers. Our interest in these polymers is two-fold. (1) the molecular design of chitin and chitosan by chemical modification (Figure 1) in view of (a) the inversion of their molecular conformation, 3 (b) the development of their potential molecular... 

In order to improve the properties of these unique polysaccharides and to develop new advanced materials, much attention has been paid to their chemical modification. These polymers have two reactive groups suitable for this purpose, namely, primary (C6) and secondary (C3) hydroxyl groups in the case of chitin whereas chitosan has additionally the amino (C2) group on each deacetylated unit. All these functions are susceptible to a variety of classical reactions which can be applied here in a controlled fashion to obtain a vast array of novel materials based on the two polysaccharides which can also be modified by either crosslinking or graft copolymerization. This topic has been extensively studied and thoroughly documented [5-7]. 

Hirano, S. 1997. Chitin and chitosan Molecular and biological functions newly generated by chemical modifications. In A. Domard, A. F. Roberts, and K. M. Varum (eds.). Proceedings of the 7th International Conference on Chitin Chitosan and 2nd International Conference of the European Chitin Society Advances in Chitin Science), vol. II, Lyon, France Jacques Andre Publisher, p. 10. 

Chitosan (N-deacetylated derivative of chitin), a naturally abundant mucopolysaccharide and its derivatives containing COSs were prepared by enzymatic and chemical modification. In addition, chitosan and its derivatives showed potent antioxidant activity. Moreover, chemical modification of chitosan can be easily provided with more powerful antioxidative compounds. Considering the above findings, it is expected that chitosan and its derivatives contained COSs wonld be promising candidates as potent antioxidative agents leading to their valuable use in neutracenticals and expand their applications in Biomedicine. 

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