Deacetylation, chitosan

Other natural ingredients identified as allergens in moisturizers are placenta,70 chitin (a celluloselike biopolymer and important structural element of the integuments of arthropods, particularly crustaceans, mollusks, unicellular micro-organisms, seaweed, and fungi), and chitosan (deacetylated chitin).78-79... 

The use of chitosan as a means of controlling the release of amino-acids has been also investigated by Rhone-Poulenc (ref. 5). Chitosan (deacetylated chitin) is extracted from shrimp and crab shells. It is known as a non-toxic, biodegradable polymer (Fig. 5). It is insoluble in water at neutral pH and has the capacity to dissolve at low pH values. Chitosan solutions are prepared by dissolving the polymer in dilute acetic acid. Stearic acid and oleic acid are the hydrophobic constituents in the chitosan-based coatings. 

Zhou HY, Chen XG, Kong M, Liu CS, Cha DS, Kennedy JF. Effect of molecular weight and degree of chitosan deacetylation on the preparation and characteristics of chitosan thermosensitive hydrogel as a delivery system. Carbohydr Polym. 2008 73(2) 265-73. 

A similar methodology was applied by Xiang et al. (2009) for the synthesis of chitosan grafted with poly(L-tryptophan) chains (Scheme 15.22). Deacetylated chitosan (deacetylation degree of amino groups 75%) was employed as a multifunctional macroinitiator for the polymerization of the L-tryptophan-NCA in ethyl acetate solutions leading to the synthesis of chitosan-g-poly(L-tryptophan) graft copolymers. The products were analyzed by NMR and IR spectroscopy. 

Chitosan solutions that are physically mixed with P-glycerophosphate can be injected into the body in liquid form, forming a gel in situ at the body temperature. The rate of gelation depends on the degree of chitosan deacetylation, the concentration of p-glycerophosphate, and the temperature and pH of the final solution [134]. The in situ gelation mechanism involves neutralization of the ammonium... 

In spite of the alteration due to deacetylation, chitosan from crab tendon possesses a crystal structure showing an orthorhombic unit cell with dimensions a = 0.828, b = 0.862 and c = 1.043 nm (fiber axis). The unit cell comprises four glucosamine units two chains pass through the unit cell with an antiparallel packing arrangement. The main hydrogen bonds are 03 05 (intramolecular) and N2 06 (intermolecular) [82]. This material has also found medical uses (below). 

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]. 

Chitosan samples with degrees of deacetylation of 65,73,85, and 92% were almost completely adsorbed onto the surfaces of cellulosic fibers, especially onto the surfaces of fines in a variety of cellulosic systems used in industrial operations. Adsorption increased as the degree of deacetylation of chitosan increased. The aggregation of the fine cellulosic particles was maximum at a dosage of about 10 mg/kg. The interactions between chitosan and the cellulosic substrates were dominated by a bridging mechanism at about pH 7 [32]. 

The rate of in vivo biodegradation of subcutaneous implanted films was very high for chitin compared with that for deacetylated chitin. No tissue reaction was foimd with highly deacetylated chitosans, although they contained abundant primary amino groups [240]. 

The NMR spectra have shown the formation of Schiff base as an intermediate product in the synthesis of the fully N-deacetylated oligomers from chitosan.32 The mechanism of the Schiff base reaction leading to chain cleavage and formation of 5-hydroxymethyl-2-furfural has been proposed. 

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

Chitin and the deacetylated form, chitosan, are attractive linear amino polysaccharides found in the shell of crustaceans. These abundant biopolymers, composed mainly of poly(/T(l,4)-2-acetamido/2-amino-2-deoxy-D-glucopyranose)... 

As was made clear earlier, chitosan and its derivatives are of more value than chitin. Currently the chitin is deacetylated by a harsh alkali treatment. If they... 

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. 

Waste water treatment chitosan/ drugstore deacetylated diitin chitin of crustaceans, also fixmd in insects and fimgi... 

Commercially chitosans can have molecular weights varying from 4 to 2000 kDa and vary in the degree of deacetylation from 66% to 95%. Because of the free amino groups chitosan behaves as a weak base, with a pKa of 6.2-7.0 and is insoluble in water or organic solvents. It is a polyamine and therefore dissolves in hydrochloric... 

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