ReviewPreparative methods of phosphorylated chitin and chitosan—An overview
Introduction
Chitin is the second most abundant natural biopolymer derived from exoskeletons of crustaceans and also from cell walls of fungi and insect [1]. Chitin is a linear cationic heteropolymer of randomly distributed GlcNAc and GlcN residues with β-1,4-linkage. Chitobiose, 4-O-(2-amino-2-deoxy-β-d-glucopyranosyl)-(1 → 4)-2-amino-2-deoxy-d-glucose, is the structural unit of native chitin [2]. Chitosan is the deacetylated derivative of chitin a natural polysaccharide found primarily in the exoskeletons of arthropods and some fungi. It is composed of residues of glucosamine and N-acetyl glucosamine connected via a–b (1–4) linkage. The ratio of glucosamine to N-acetyl glucosamine is referred to as the degree of deacetylation (DDA). The DDA is a factor of both the source of the chitosan (crab, shrimp, fungi, etc.) and the preparation methods, and may range from as low as 30% to almost 100%. Chitosan physical properties such as crystallinity, surface energy, and degradation also vary with the DDA of the polymer. These polysaccharides are renewable resources which are currently being explored intensively for their applications in pharmaceutical, cosmetics, biomedical, biotechnological, agricultural, food, and non-food industries (water treatment, paper, and textile) [3], [4], [5], [6], [7], [8]. These unique polymers have emerged as a new class of physiological materials of highly sophisticated functions due to their versatile biological activity, excellent biocompatibility, and complete biodegradability in combination with low toxicity [9], [10], [11]. To exploit the unique properties and to realize and obtain the full potential of these versatile polysaccharides, attempts are being made to chemically modify them.
Chemical modifications of chitin and chitosan would bring new properties depending on the nature of the group introduced [12], [13], [14], [15]. Recently, several methods have been reported to obtain phosphorylated derivatives of chitin and chitosan due to their interesting biological and chemical properties [14], [15], [16], [17], [18], [19]. They could exhibit bactericidal [18], biocompatible [19], [20], [21], [22], [23], [24], bioabsorbable [19], [20], [21], [22], [23], [24], osteoinductive [19], [20], [21], [22], [23], [24] and metal chelating properties [13], [14]. Due to the wide range of biological applications of the phosphorylated chitin and chitosan, we critically overview here the recent preparative methods and the future prospects of phosphorylated chitin and chitosan.
Section snippets
Preparative methods of phosphorylated chitin and chitosan
Phosphorylated chitin and chitosan can be prepared by heating of chitin or chitosan with orthophosphoric acid and urea in N,N-dimethyl formamide (DMF) [25]. The urea is added to the reaction media, to act as a reaction promoter. The reaction scheme is shown in Fig. 1.
Phosphorylated chitin and chitosan can be prepared by the reaction of chitin or chitosan with phosphorous pentoxide in methanesulphonic acid as reported earlier [26], [27], [28]. The phosphorylation reactions of chitin and chitosan
Conclusions
In this review, we summarized the different preparative methods of phosphorylated chitin and chitosan as reported previously by us and others. Understanding the phosphorylated chitin and chitosan prepared in different methods would definitely advance their applications in biomedical field, especially in tissue engineering. We hope this review would be helpful for researchers who are interested to bring or develop the new novel preparative methods of phosphorylated chitin and chitosan in near
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