Chitin

Chitin (C8H13O5N)n (ˈkaɪtᵻn ) is a long-chain polymer of N-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chitin are produced each year in the biosphere. It is a primary component of cell walls in fungi (especially filamentous and mushroom forming fungi), the exoskeletons of arthropods such as crustaceans and insects, the radulae, cephalopod beaks and gladii of molluscs and in some nematodes and diatoms. It is also synthesised by at least some fish and lissamphibians. Commercially, chitin is extracted from the shells of crabs, shrimps, shellfish and lobsters, which are major by-products of the seafood industry. The structure of chitin is comparable to cellulose, forming crystalline nanofibrils or whiskers. It is functionally comparable to the protein keratin. Chitin has proved useful for several medicinal, industrial and biotechnological purposes. The English word "chitin" comes from the French word chitine, which was derived in 1821 from the Greek word χιτών (khitōn) meaning covering. A similar word, "chiton", refers to a marine animal with a protective shell. The structure of chitin was determined by Albert Hofmann in 1929. Hofmann hydrolyzed chitin using a crude preparation of the enzyme chitinase, which he obtained from the snail Helix pomatia. Chitin is a modified polysaccharide that contains nitrogen; it is synthesized from units of N-acetyl-D-glucosamine (to be precise, 2-(acetylamino)-2-deoxy-D-glucose). These units form covalent β-(1→4)-linkages (like the linkages between glucose units forming cellulose). Therefore, chitin may be described as cellulose with one hydroxyl group on each monomer replaced with an acetyl amine group. This allows for increased hydrogen bonding between adjacent polymers, giving the chitin-polymer matrix increased strength. In its pure, unmodified form, chitin is translucent, pliable, resilient, and quite tough.