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Chitin and chitosan polymers: Chemistry, solubility and fiber formation

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

Chitosan as biomaterial in drug delivery and tissue engineering.

Chitosan, a natural-based polymer obtained by alkaline deacetylation of chitin, is nontoxic, biocompatible, and biodegradable. These properties make chitosan a good candidate for conventional and novel drug delivery systems. This article reviews the approaches aimed to associate bioactive molecules to chitosan in the form of colloidal structures and analyzes the evidence of their efficacy in improving the transport of the associated molecule through mucosae and epithelia. Chitosan forms colloidal particles and entraps bioactive molecules through a number of mechanisms, including chemical crosslinking, ionic crosslinking, and ionic complexation. A possible alternative of chitosan by the chemical modification also has been useful for the association of bioactive molecules to polymer and controlling the drug release profile. Because of the high affinity of chitosan for cell membranes, it has been used as a coating agent for liposome formulations. This review also examines the advances in the application of chitosan and its derivatives to nonviral gene delivery and gives an overview of transfection studies that use chitosan as a transfection agent. From the studies reviewed, we concluded that chitosan and its derivatives are promising materials for controlled drug and nonviral gene delivery.

Chitosan-Based Particles as Controlled Drug Delivery Systems

Novel carboxymethyl derivatives of chitin and chitosan materials and their biomedical applications

Preparation of partially N-succinylated chitosans and their cross-linked gels

Some structural features of amylomaize starch

Branching enzyme from amylomaize endosperms

Polymer ampholites, partially N-succinylated chitosans (PSC), and partially N-succinylated glycolchitosans (PSGC) were prepared from chitosan (an N-deacetylated chitin) and glycolchitosan (a partially O-2-hydroxyethylated chitosan), and they were utilized as novel supports for the immobilization of enzymes. The immobilization was conducted simultaneously with gelation of PSC and PSGC by reaction with water-soluble carbodiimide in the presence of enzymes. Enzymes were covalently bonded on PSC and PSGC chains. Maximum activity yields of glucoamylase, beta-fructosidase, and D-glucose isomerase were 58.8, 64.3, and 65.2%, respectively. Favorable activity yields of glucoamylase and beta-fructosidase were attained with PSC and PSGC having high degree of N-succinylation, but those of D-glucose isomerase were not affected by the degree of N-succinylation (DS). The activity of immobilized glucoamylase was retained up to 85.5% over 30 batch reactions.

Utilization of partially N-succinylated derivatives of chitosan and glycolchitosan as supports for the immobilization of enzymes.

A lectin was purified from a shellfish, Saxidomus purpuratus, using ion-exchange chromatography on DEAE-cellulose and affinity chromatography on N-acetylglucosamine-Sepharose. The lectin purified by affinity chromatography showed seven protein bands in polyacrylamide gel electrophoresis. The two major lectins (SPA-I and SPA-III) were purified by a second DEAE-cellulose column chromatography. The molecular weights of the lectins were almost the same and were estimated to be around 40,000 by gel filtration on a Sepharose 6B column. On SDS-polyacrylamide gel electrophoresis in the presence of 2-mercaptoethanol, the lectins showed molecular weights of 14,000. The isoelectric points of SPA-I and -III were estimated to be 4.4 and 4.1, respectively. The two lectins (SPA-I and -III) differed slightly in amino acid composition and were glycoproteins containing 2.1 and 3.8 mol of GlcNAc per 40,000 g of the lectin, respectively. The binding constant of SPA-I or SPA-III for methyl N-acetyl-a-D-glucosamide, the strongest inhibitor of hemagglutination in this experiment, was estimated to be 1.3 X 10(3) or 4.2 X 10(4) M-1, respectively, by the UV difference spectroscopy method.

Tatsuro Itoh

Papers

Preparation of partially N-succinylated chitosans and their cross-linked gels

Some structural features of amylomaize starch

Branching enzyme from amylomaize endosperms

Utilization of partially N-succinylated derivatives of chitosan and glycolchitosan as supports for the immobilization of enzymes.

Purification and characterization of a lectin from the shellfish, Saxidomus purpuratus.