Deacetylation, of chitin

Chitosan is a naturally amine-functionalized polysaccharide which is easily obtained by deacetylation of chitin, a zero-cost residue of the seafood industry (Fig. 

Chitosan is produced from the deacetylation of chitin. Chitosan is employed in the food industry. It is a hemostatic from which blood anticoagulants and antithrombogenic have been formed. It is often sold as a body fat-reducing agent or to be taken along with food to encapsulate fat particles. 

In the more abundant a chitin the chains in alternate sheets have opposite orientations,101102 possibly a result of hairpin folds in the strands. Native chitin exists as microfibrils of 7.25 nm diameter. These contain a 2.8-nm core consisting of 15-30 chitin chains surrounded by a sheath of 27-kDa protein subunits. The microfibrils pack in a hexagonal array, but the structure is not completely regular. Several proteins are present some of the glucosamine units of the polysaccharide are not acetylated and the chitin core is often calcified.103 The commercial product chitosan is a product of alkaline deacetylation of chitin but it also occurs naturally in some fungi.102 Chitin is also present in cell walls of yeasts and other fungi. It is covalently bonded to a P-l,3-linked glycan which may, in turn, be linked to a mannoprotein (see Section D,2)97... 

Chitosan is a cationic polysaccharide produced from the deacetylation of chitin, a component of crab and shrimp shells [7,57,58], Chitin is composed of units of 2-deoxy-2-(acetylamino) glucose joined by glycosidic bonds that form a linear polymer. Ilium et al. [7,57,58] demonstrated the ability of chitosan to increase the bioavailability of insulin and other small peptides and polar macromolecules in different animal models. In both the sheep and rat models, the addition of chitosan at concentrations of 0.2%-0.5% to nasal formulations of insulin resulted in significant increases in plasma insulin and reductions in blood glucose. Reversibility studies indicated that the effect of chitosan on the nasal absorption of insulin... 

Chitosan is produced commercially by deacetylation of chitin. It is a linear polysaccharide composed of randomly distributed /i-( l-4)-linkcd D-glucosamine (deacetylated unit) and N -acetyl-D-glucosamine (acetylated unit). The degree of deacetylation in commercial chitosans is in the range 60-100% (Figure 5.19). 

Chitosan and its derivatives are the most widely used cationic polymeric excipients. Chitosan consists of (31—>4 D-glucosamine units and is derived by the deacetylation of chitin from insects, crustaceans and fungi. It interacts ionically with the anionic substructures of sialic acid residues on the mucus layer. Chitosans are rapidly hydrated in a low pH environment like the gastric fluid and do not swell above pH levels of 6.5, exhibiting no more mucoadhesion. 

Another interesting organic material usually used to immobilize enzymes is chitosan [95, 96]. Chitosan is a poly((1 4)-2-amino-2-deoxy-P-D-glucose) (Fig. 9.5), which is a product of deacetylation of chitin, the second polysaccharide ranked by its prevalence in nature, just after cellulose. 

Chitosan An amino polysaccharide made by deacetylation of chitin. Its mucoadhesive properties make it ideal for oral and nasal administration (71-73)... 

Chitosan Natural (crab shells) Deacetylation of chitin Soluble in aqueous solutions (low pH), insoluble in organic solvents... 

Chitosan is a linear cationic polysaccharide made up of copolymers of glucosamine and A-acetylglucosaminc. It is commercially obtained by alkaline deacetylation of chitin [53, 68] and has been used for the nasal delivery of a number of drugs. The usefulness of chitosan in the enhancement of nasal absorption was reported first by Ilium [69]. Later, Ilium and his group also published experimental results indicating that solution formulations with 0.5% chitosan promoted the absorption of nasally administered insulin in rat and sheep [70]. 

The most important derivative of chitin is chitosan obtained by partial deacetylation of chitin in the solid state under alkaline conditions or by enzymatic hydrolysis in the presence of a chitin deacetylase. The ratio of 2-acetamido-2-deoxy-D-glucopyranose to 2-amino-2-deoxy-D-glucopyra-nose moieties determines the identity of the product, that is, chitin or chitosan [9]. The published methods used for the production of chitosan from chitin are summarized in Table 2.3. 

TABLE 2.3 Methods of deacetylation of chitin to form chitosan... 

The FT-IR spectrum of ot-chitin shows two absorption bands at approximately 1625 and 1655 cm , characteristic of hydrogen-bonded amide groups. The DA of chitin can be determined by the ratios of different IR absorption bands (Fig. 2.27), as these bands disappear upon deacetylation of chitin. 

Natural polysaccharides available on an industrial scale include polymers with anionic functions, like alginates (carboxylic groups) or carrageenans (sulfonic groups) derived from seaweed, or with cationic functions, like as chitosan (amino groups), obtained by deacetylation of chitin from seafood shells (Fig. 1). 

Chitosan, a polymer of j8-(I 4)-linked 2-amino-2-deoxy-D-glucose residues, is formed on deacetylation of chitin. As pointed out already, this polysaccharide takes an extended conformation similar to that of cellulose. Deacetylation of chitin is very easily evaluated in view of the NMR spectra, as illustrated in Fig. 24.5. The three polymorphs of chitosan, ten-don-chitosan (from crab shell), L-2 (from shrimp shell), An-nealed (from crab shell chitosan annealed at 22°C in the presence of water) are easily distinguished, consistent with the data for the polymorphs as obtained by a powder X-ray diffraction data [38, 39]. The observed non-equivalence of two chitosan chains, as viewed from the splittings of the C-1 and C-... 

Hirano, S., Zhang, M., Chung, B.G., and Kim, S.K. 2000. The A-acylation of chitosan fibre and the A-deacetylation of chitin fibre and chitin-cellulose blended fibre at a solid state. Carbohydr. Polymers 41, 175-179. 

Kristbergsson, K., Einarsson, J.M., Hauksson, S., Peter, M.G., and Gislason, J. 2003. Recent Developments in Deacetylation of Chitin, and Possible Applications in Food Formulations. In Proceedings of the First Joint Trans Atlantic Fisheries Technology Conference, Reykjavik, Iceland, June 10-14, 2003. 

Chitosan, an important structural component of several fungi cell walls, is a liner p-(l,4)-glucosamine polymer produced by deacetylation of chitin and was reported to be the most active ingredient contained within fungal cell walls [19]. It was convincingly demonstrated that chitosan had a potential dual role inducing... 

Chitosan, a natural-based polymer obtained by alkaline deacetylation of chitin, is nontoxic, biocompatible, and biodegradable. These properties make chitosan a promising candidate for conventional and novel drug delivery systems. Because of the high affinity of chitosan for cell membranes, it has been used as a coating agent for liposome formulations [43-45]. 

Chitosan is not widely present as such in nature and thus cannot be directly extracted from natural resources. Indeed, chitosan is a derivative of natural chitin, the second most abundant polysaccharide in nature after cellulose [2]. Typically, chitosan is obtained by deacetylation of the Ai-acetyl glucosamine units of chitin, generally by hydrolysis under alkali conditions at high temperature. The deacetylation of chitin is rarely complete. When the degree of acetylation falls below the value of 60 mol%, chitin becomes chitosan. In nature, chitin is present in life forms and more particularly in insects and crustaceans where it represents the major component of their exoskeleton. Chitin is also present in the cell wall of some mushrooms [7, 8]. Generally, chitosans produced from mushrooms present a narrow molecular weight distribution compared to chitosan produced from shrimps, and a non-animal source is considered to be safer for biomedical and healthcare uses. 

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