Use of natural biopolymers for diversified applications in life sciences has several advantages, such as availability from replenishable agricultural or marine food resources, biocompatibility, biodegradability, therefore leading to ecological safety and the possibility of preparing a variety of chemically or enzymatically modified derivatives for specific end uses. Polysaccharides, as a class of natural macromolecules, have the tendency to be extremely bioactive, and are generally derived from agricultural feedstock or crustacean shell wastes. Cellulose, starch, pectin, etc. are the biopolymers derived from the former while chitin and chitosan are obtained from the latter. In terms of availability, chitin is next to cellulose, available to the extent of over 10 gigatons annually. The application potential of chitosan, a deacetylated derivative of chitin, is multidimensional, such as in food and nutrition, biotechnology, material science, drugs and pharmaceuticals, agriculture and environmental protection, and recently in gene therapy too. The net cationicity as well as the presence of multiple reactive functional groups in the molecule make chitosan a sought-after biomolecule. The latter offers scope for manipulation for preparing a broad spectrum of derivatives for specific end use applications in diversified areas. The biomedical and therapeutic significance of chitin/chitosan derivatives is a subject of significant concern to many all over the world. An attempt is made in this overview to consolidate some of the recent findings on the biorelated application potential of chitosan and its derivatives.

Chitin/chitosan: modifications and their unlimited application potential—an overview

Of late, the most bountiful natural biopolymer chitin and chitosan have become cynosure of all party because of an unusual combination of biological activities plus mechanical and physical properties. However applications of chitin are limited due to its inherent insoluble and intractable nature. Chitosan, alkaline hydrolytic derivative of chitin has better solubility profile, less crystallinity and is amenable to chemical modifications due to presence of functional groups as hydroxyl, acetamido, and amine. The chemical modification of chitosan is of interest because the modification would not change the fundamental skeleton of chitosan, would keep the original physicochemical and biochemical properties and finally would bring new or improved properties. In view of rapidly growing interest in chitosan its chemical aspects and chemical modification studies is reviewed. The several chemical modifications such as oligomerization, alkylation, acylation, quternization, hydroxyalkylation, carboxyalkylation, thiolation, sulfation, phosphorylation, enzymatic modifications and graft copolymerization along with many assorted modifications have been carried out. The chemical modification affords a wide range of derivatives with modified properties for specific end use applications in diversified areas mainly of pharmaceutical, biomedical and biotechnological fields. Assorted modifications including chitosan hybrids with sugars, cyclodextrin, dendrimers, and crown ethers have also emerged as interesting multifunctional macromolecules. The versatility in possible modifications and applications of chitosan derivatives presents a great challenge to scientific community and to industry. The successful acceptance of this challenge will change the role of chitosan from being a molecule in waiting to a lead player.

Chitosan-modifications and applications: Opportunities galore

Controlled functionalization of the polysaccharide chitin

Microwave enhanced synthesis of chitosan-graft-polyacrylamide

Chitin is considered the second most plentiful organic resource on the earth next to cellulose, and is present in marine invertebrates, insects, fungi and yeasts. Chitin is essentially a homopolymer of 2-acetamido-2-deoxy-β-D-glucopyranose, although some of the glucopyranose residues are in the deacetylated form as 2-amino-2-deoxy-β-D-glucopyranose. When chitin is further deacetylated to about 50% it becomes soluble in dilute acids and is referred to as chitosan. Thus chitosan is the N-deacetylated derivative of chitin, although the N-deacetylation is almost never complete. There is not a sharp boundary in the nomenclature distinguishing chitin from chitosan. Chitin does occur in nature in the fully acetylated form and has been referred to as chitan [1]. Chitosan rarely occurs in nature, but is found in the dimorphic fungus, Mucor rouxii [2]. Its occurrence in Mucor rouxii is via the enzymatic deacetylation of chitin.

Polysaccharides: Chitin and Chitosan: Chemistry and Technology of Their Use As Structural Materials

Graft copolymerization of vinyl compounds onto chitin was studied, and an efficient and reproducible procedure has been established, cerium (IV) being used as the initiator. The reactions with acrylamide and acrylic acid onto powdery chitin were carried out under various conditions to elucidate the polymerization behavior in terms of grafting percentage. The amount of cerium (IV) affected the polymerization most strikingly, and grafting percentages showed maxima with suitable amounts of initiator for both the monomers. As a solvent water proved to be superior to aqueous nitric acid except the reaction with a small amount of initiator. Under appropriate conditions, around 240 and 200% grafting percentages were achieved for acrylamide and acrylic acid, respectively. The resulting graft copolymers showed much improved affinity for solvents and hygroscopicity compared to the original chitin.

Graft copolymerization of vinyl monomers onto chitin with cerium (IV) ion

Tri-O-acetyl-, tri-O-benzyl-, tri-O-methyl-D-glucal were copolymerized with maleic anhydride (MAnh) to afford novel vinyl copolymers containing sugar residues in the main chain. Tri-O-benzyl-D-glucal (TBG) showed higher copolymerization reactivity with MAnh than the other glucal derivatives. The copolymerization of TBG and MAnh was carried out at various monomer feed ratios to give the copolymers always rich in MAnh units. Both the complex and penultimate models could explain the compositional data, but the analysis of the copolymerization rate suggested the participation of the CT complex in the propagation.

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Polymerization of Unsaturated Sugars I. Radical Copolymerization of D -Glucal Derivatives and Maleic Anhydride

A stable furanoid glucal, 3-O-benzyl-1,2-dideoxy-5,6-O-isopropylidene-d-arabino-hex-1-enofuranose (BIF) was synthesized, and the equilibrium association constant K for the charge-transfer complex formation with maleic anhydride in CDCl3 at 25°C was 0.131 mol−1 as determined by 13C NMR. BIF copolymerized with maleic anhydride almost alternatingly, AIBN being used as the initiator. Other electron accepting monomers such as N-phenylmaleimide and acrylonitrile also copolymerized with BIF. Terpolymerization of BIF-maleic anhydride-acrylonitrile gave the copolymer containing BIF residues.

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Polymerization of Unsaturated Sugars II. Radical Copolymerization of a Furanoid Glucal, 3-O-Benzyl-1,2-dideoxy-5,6-O-isopropylidene-d-arabino-hex-1-enofuranose

Mitsuo Kawata

Papers

Graft copolymerization of vinyl monomers onto chitin with cerium (IV) ion

Polymerization of Unsaturated Sugars I. Radical Copolymerization of D -Glucal Derivatives and Maleic Anhydride

Polymerization of Unsaturated Sugars II. Radical Copolymerization of a Furanoid Glucal, 3-O-Benzyl-1,2-dideoxy-5,6-O-isopropylidene-d-arabino-hex-1-enofuranose

Pharmacological Modulation Of Krüppel-Like Factor 4 Reduces The Severity Of Experimental Osteoarthritis Via Tissue Protection And Regeneration