Chitin derivatives

Recent progress of basic and application studies in chitin chemistry was reviewed by Kurita (2001) with emphasis on the controlled modification reactions for the preparation of chitin derivatives. The reactions discussed include hydrolysis of main chain, deacetylation, acylation, M-phthaloylation, tosylation, alkylation, Schiff base formation, reductive alkylation, 0-carboxymethylation, N-carboxyalkylation, silylation, and graft copolymerization. For conducting modification reactions in a facile and controlled manner, some soluble chitin derivatives are convenient. Among soluble precursors, N-phthaloyl chitosan is particularly useful and made possible a series of regioselective and quantitative substitutions that was otherwise difficult. One of the important achievements based on this organosoluble precursor is the synthesis of nonnatural branched polysaccharides that have sugar branches at a specific site of the linear chitin or chitosan backbone [89]. 

Sodium carboxymethyl chitin and phosphoryl chitin had most evident influences on the crystallization of calcium phosphate from supersaturated solutions. They potently inhibited the growth of hydroxyapatite and retarded the rate of spontaneous calcium phosphate precipitation. These chitin derivatives were incorporated into the precipitate and influenced both the phase and morphology of the calcium phosphate formed (flaky precipitate resembling octacalcium phosphate instead of spherical clusters in the absence of polysaccharide) [175]. 

Chitin films can be manufactured from DMAc solutions or by other approaches, for example, blend films of beta-chitin (derived from squid pens) and poly(vinyl alcohol) (PVA) were prepared by a solution casting technique from corresponding solutions of beta-chitin and PVA in concentrated formic acid. Upon evaporation of the solvent, the film having 50/50 composition was found to be cloudy [224]. 

Dicarboxymethyl chitosan and 6-oxychitin sodium salt, applied to femoral surgical defects for 3 weeks produced a good histoarchitectural order in the newly formed bone tissue. The spongious trabecular architecture was restored in the defect site. The association of the chitin derivatives with the osteoblasts seemed to be the best biomaterial in terms of bone tissue recovery [128]. 

Tokura S, Azuma 1 (1992) (eds.) Chitin Derivatives in Life Sciences. Japan Soc Chitin, Sapporo... 

In conclusion, it is noteworthy that cyclodextrins, liposomes and chitin derivatives are all readily available from renewable biochemical sources and offer advantages of biodegradability and safety in use. However, it needs to be borne in mind that this fact alone does not necessarily mean that they are entirely environmentally innocuous in the long run. Demands on resources for the husbanding and processing of bioforms that may be necessary in order to sustain demand for commercially viable qualities and quantities can exert deleterious effects, not least because they may give by-products that present problems of utilisation or disposal [70]. 

Figures 3 and 4 illustrate typical rates of hydrolysis for carbamate derivatives of cellulose and chitin. The rates of release at a pH value 11.3 were considerably higher in both systems than at pH values of 3.1 and 7.0. After seven days in the basic medium the cellulose derivative had delivered 27.3 percent of the available aniline. In the acidic medium and neutral medium 15.6 and 10.6 percent were delivered. After seven days the chitin derivative delivered 27.7, 10.0, and 9.5 percent of the available p-methylaniline in the basic, acidic, and neutral media, respectively.

Chitin derivatives Anhyd roacetam ido-deoxygl ucose Seafood cooking... 

Muzzarelli RAA (1997) Human enzymatic activities related to the therapeutic administration of chitin derivatives. Cell Mol Life Sci 53 131-140 Muzzarelli RAA, Xia W, Tomasetti M and Ilari P (1995) Depolymerization of chitosan and substituted chitosans with the aid of a wheat germ lipase preparation. Enz Microbial Tech 17 541-545... 

In addition to synthetic biodegradable polymers discussed so far, naturally occurring biopolymers have also been used for fabricating implantable dmg delivery systems. Examples of natural biopolymers are proteins (e.g. albumin, casein, collagen, and gelatin) and polysaccharides (e.g. cellulose derivatives, chitin derivatives, dextran, hyaluronic acids, inulin, and starch). 

The structures of chitins derived from shrimp and various kinds of crabs are all very similar. For chitin from King crab, the unit cell is orthorhombic, with a = 0.47 nm, b (fiber axis) = 1.05 nm, andc = 1.03 nm. The molecule does not take up water, and the d spacings do not vary on drying or soaking. 

Natural polymer-based networks have also been investigated. The proteins etc comprising antibodies represent the largest group [164, 166, 169, 189] but this is of course a specialised area. Poly(saccharides), in particular starch [60], dextran [161], dextrin [161] and maltohexose [161], and also natural polypeptides, mainly enzymes [162-165], embody the more accessible biopolymers. In some instances imprinting is achieved through formation of covalent bonds, with crosslinkers like cyanuric chloride or glutaraldehyde. Likewise chitin derivatives similarly crosslinked have been exploited [136]. 

Zhao, X. Kato, K. Fukumoto, Y. Nakamae, K. Synthesis of bioadhesive hydrogels from chitin derivatives. 128. Int. J. Adhes. Adhes. 2001, 21, 227-232. 

Many polymer reagents suitable for this technique, e.g., the 2-hydroxyethyl chitin derivative, show a good binding ability for a series of elements, when used for this process under standard conditions. Inter-estingly, some elements, e g., chromium and zinc, could not be detected by conventional analysis. However, by using this hyphenated method, the determination was made possible. 

Saiki, I. Watanabe, K. Tokura, S. Azuma, I. Chitin Derivatives in Life Science, 1992,20-26. 

The M-alkyl chitosans were subsequently changed into corresponding A-alkyl chitins via acetylation using acetic anhydride followed by transesterification to eliminate partially formed O-acetyl groups. This synthetic pathway is direct and effective to provide well-defined novel chitin derivatives. The resulting /Y-methyl, M-ethyl, and A-pentyl chitins were amorphous and displayed a high affinity for solvents (Kurita et al., 2002). 

Iida, J., Une, C., Ishihara, K., Nishimura, S., Tokura, N., Mizukoshi, and Azuma, I. 1987. Stimulation of non-specific host resistance against Sendai virus and Escherichia coli by chitin derivatives... 

Chemical modifications of chitin are generally difficult owing to the lack of solubility because reactions under heterogeneous conditions are accompanied by various problems such as the poor extent of reaction, difficulty in region-selective substitution, structural ambiguity of products and partial degradation due to the severe reaction conditions. Carboxymethyl chitin is one of the most studied chitin derivatives, obtained by adding monochloro-acetic acid to chitin previously treated with sodium hydroxide at different... 

The most important chitin derivative is chitosan, obtained by its partial deacetylation under alkaline conditions or by enzymatic hydrolysis in the presence of chitin deacetylase. Because of the semicrystalline morphology of chitin, chitosan obtained by a solid-state reaction has a heterogeneous distribution of acetyl groups along the chain. On the other hand when chitin is treated with concentrated aqueous sodium hydroxide, N-deacetylation proceeds smoothly and homogeneously deacetylated samples are obtained [37]. 

Hidaka Y, Ito M, Mori K et al (1999) Flistopathological and immunohistochemical studies of membranes of deacetylated chitin derivatives implanted over rat calvaria. J Biomed Mater... 

The purpose of this chapter is to direct attention to some chemical procedures that permit modification of the porosity and surface area of chitosan. It seems that these procedures hold the key to a more expanded development of chitin-derived biomedical items. 

The commonly used biomedical polymer materials include Polytetrafluoroethene, polyurethane, polyvinyl chloride, silicone rubber, polypropylene, polysiloxane gel, poly methyl acrylate, chitin derivatives and Polymethylmethacrylate. 

It should be noted that the spectrum of chitin reflects mainly the macrostructure of the fully iV-acetylated regions, because the spectral contributions of a small number of glucosamine residues are lost in the presence of broad and intense bands caused by the bulk of the polysaccharide. Falk et al. suspect previous conclusions about the macrostructure of chitin derived from X-ray diffraction and infrared studies, and feel that in any case they are not relevant to the structure of chitan. 

Muzzarelli, R. A. Human enzymatic activities related to the therapeutic administration of chitin derivatives. Cellular and Molecular Life Sciences. 1997, 53. 131-140. 

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