Chitosan, acylated

Chitosans.—Acylated chitosan gels have been prepared by treatment of chitosan with acetic, propionic, and butyric anhydrides. The molecular aggregation of... 

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]. 

One of the simplest ways to prepare a chitin gel is to treat chitosan acetate salt solution with carbodiimide to restore acetamido groups. Thermally not reversible gels are obtained by AT-acylation of chitosans N-acetyl-, N-propionyl- and N-butyryl-chitosan gels are prepared using 10% aqueous acefic, propionic and bufyric acid as solvents for treatment with appropriate acyl anhydride. Both N- and 0-acylation are found, but the gelation also occurs by selective AT-acylation in the presence of organic solvents. 

Chitosan is the main structural component of crab and shrimp shells. Chitosan contains both reactive amino and hydroxyl groups, which can be used to chemically alter its properties under mild reaction conditions. Al-acyl chitosans were already reported as blood-compatible materials. UV irradiation grafting technique was utilized to introduce obutyrylchitosan (OBCS) onto the grafted SR film in the presence of the photosensitive heterobifunctional cross-linking agent. The platelet adhesion test revealed that films grafted on OBCS show excellent antiplatelet adhesion. 

Lee KY, Ha WS, Park WH (1995) Blood compatibility and biodegradability of partially N-acylated chitosan derivatives. Biomaterials 16(16) 1211—1216... 

Chitosan is a strong nucleophile because of the presence of a nonbonding pair of electrons on its primary amino groups. Chitosan reacts readily with most aldehydes to produce imines (Kurita et al., 1988). It also reacts with acyl chlorides to form the corresponding acylated derivatives (Hirano et al., 1976) (Figure 2). 

FIG. 2 Reactions of chitosan with an aldehyde or acyl chloride. 

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. 

A variety of acylation reactions of chitosan are possible by using different acyl-ating agents, such as aliphatic carboxylic acid chlorides (hexanoyl, dodecanoyl and tetradecanoyl chlorides), cyclic anhydrides and cyclic esters. The acylation reaction is not regioselective. When IV,0-acylated chitosans were prepared with acyl chlorides in methanesulfonic acid [62-63], the derivatives of 4-chlorobutyl and decanoyl chlorides showed higher fungidal activities than chitosan [64]. Selectively N-acylated chitosan have been obtained by Lee et al. [65-66] with butanoic, hexanoic and benzoic anhydride under homogeneous conditions... 

It has been reported that quaternary ammonium salt of chitosan exhibits good antibacterial activities, for example, diethylmethylchitosan chloride showed higher antibacterial activity than chitosan. Novel N,0-acyl chitosan... 

In an effort to improve the blood compatibility of chitosan in a fiber form, a metiianol-acetic acid solution of chitosan and tropocollagen was wet-spim into reasonably strong fibers. Using an ammonia solution with ammonium sulfate as a coagulation bath, acylation of these fibers was shown to increase their tenacity.i ... 

Tayab, R A., Hydrophobic chitosan in controlled release delivery systems, M.S. Thesis, Department of Bioengineering, Clemson University, Clemson, SC, 1995. Shalaby S. W. and Ignatious, R S., Ionic Molecular Conjugates of Biodegradable Rully n-Acylated Derivatives of Poly(2-amino-2-deoxy-d-glucose) and Bioactive Polypeptides, U.S. Patent (to Biomeasure, Inc.) 5,665,702, 1997. 

Hirano, S. and Noishiki, Y, The blood compatibility of chitosan and N-acyl-chitosans, /. Biomed. Mater. Res., 19, 413, 1984. 

KytoCel by Aspen, reported by Aspen (2014), is a highly absorbent dressing composed of natural, biodegradable acylated chitosan fibres, which bond with wound exudate to form a clear gel that locks in fluid, absorbs pathogens, and is conformable to the wound bed. 

Wu, Y, Seo, T., Maeda, S., Sasaki, T., Irie, S., and Sakurai, K. (2005). Circular dichroism induced by the helical conformations of acylated chitosan derivatives bearing cinnamate chromophores, /. Polym. Sci. Polym. Phys., 43,1354-1364. 

Zong, Z., Kimura, Y, Takahashi, M., and Yamane, H. (2000). Characterization of chemical and solid state structures of acylated chitosans. Polymer, 41, 899-906. 

The blood compatibility of chitin and chitosan remains a prime aspect almost 20 years after Hirano reported his studies on chitosan and its acyl derivatives in 1985 [183]. A resurgence of these initial studies was reported by Lee et al. [184]... 

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