Chitosan: Structure, Properties, and Importance in Environmental Cleanup PDF

Chapter 1 Chitosan: structure, properties, preparation, characterization, modifications, and importance in environmental cleanup Ujith S.K. Madduma-Bandarage1, Hasani G. Jayasinghe2 and Sundararajan V. Madihally1 1 School of Chemical Engineering, Oklahoma State University, Stillwater, OK, United S...

Chapter 1 Chitosan: structure, properties, preparation, characterization, modifications, and importance in environmental cleanup Ujith S.K. Madduma-Bandarage1, Hasani G. Jayasinghe2 and Sundararajan V. Madihally1 1 School of Chemical Engineering, Oklahoma State University, Stillwater, OK, United States; 2 Mathematics, Physical and Natural Sciences Division, University of New Mexico-Gallup, Gallup, NM, United States 1. Chemistry of chitosan Chitosan is a derivative of chitin, a naturally occurring mucopolysaccharide. Chitosan is the N-deacetylated form of chitin. Due to the structural similarity between chitin and chitosan and the abundance of chitin in nature, it is important to examine the structure, properties, chemistry, and synthesis of chitin first. 1.1 Chitindstructure and properties In 1811, a French scientist named Henri Braconnot extracted a mucopoly- saccharide from the cell walls of mushrooms and called it “fungine”. Later, in 1823, Auguste Odier found the same material “fungine” in insects’ cuticles. He named this mucopolysaccharide chitin. The name “chitin” comes from the French word “chitine,” which is a derivation of the Greek word “chiton”. Chiton means coveringdchitin is mostly found in the outer layers/ structures of organisms such as crustaceans, insects, fungi, and fish. Chitin is the second most abundant natural biopolymer after cellulose. In nature, chitin is found as crystalline microfibrils, in structural components of the exoskeleton in arthropods, a major constituent in the cell wall in fungi and yeast, in teeth of the radula, calcified layers of shells of mollusks, and gladii (pen) of squids [4e6]. Chitin content, by dry weight, in crustacean shells is 15%e30%, in grasshoppers is 4%e11% , in house crickets is 1%e2% , Role of Chitosan and Chitosan-Based Nanomaterials in Plant Sciences https://doi.org/10.1016/B978-0-323-85391-0.00023-X Copyright © 2022 Elsevier Inc. All rights reserved. 1 2 Role of Chitosan and Chitosan-Based Nanomaterials in Plant Sciences in cockroaches is w38% , in the filamentous fungal cell wall is 10%e30% , and in yeast cell wall is1e2%. There are three allomorphs of chitin: a, b, and g [4,11]. The degree of hydration, size of the unit cell, number of chains per unit cell, and orientation of microfibrils differentiate chitin into each allomorph. The a-chitin is the most abundant allomorph and has high thermodynamical stability. The a- chitin is found in fungal cell walls, insect cuticles, krill, shrimp shells, and crab and lobster tendons. The b-chitin is found in squid gladii, and tubes formed by polychaete annelid worms belong to the Siboglinidae family. The third isomorph g-chitin is found in Ptinus beetles, Loligo squids, and mushrooms [13,14]. Chitin (b-(1e4)-poly-N-acetyl-D-glucosamine) is a natural polysaccharide. Chitin consists of N-acetyl-D-glucosamine (GlcNAc) and Deglucosamine (GlcN) units that link via b-(1e4) linkage to produce a cationic heteropolymer (Fig. 1.1A). The sugar molecules, GlcNAc and GlcN, are rotated 180 degrees with respect to each other. The structure of chitin is analogous to that of cellulose, which contains D-glucose units connected through b-(1e4) linkages (in D- glucose, there is a hydroxyl group at the C-2 position instead of the amide and amine groups present in GlcNAc and GlcN, respectively). The degree of poly- merization in chitin is around 5000e10,000, and the molecular weight is around 1
106e2.5
106 Da. As acetyl groups present in the GlcNAc units, this polymer can be characterized via the degree of acetylation (DA). The DA is FIGURE 1.1 (A) Chemical structure of chitin and chitosan. Chitin has >90% of GlcNAc units and