Chitin (C8H13O5N)n (// KY-tin) is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world. It is the main component of the cell walls of fungi, the exoskeletons of arthropods such as crustaceans (e.g., crabs, lobsters and shrimps) and insects, the radulae of molluscs, and the beaks and internal shells of cephalopods, including squid and octopuses. The structure of chitin is comparable to the polysaccharide cellulose, forming crystalline nanofibrils or whiskers. In terms of function, it may be compared to the protein keratin. Chitin has also proven useful for several medical and industrial purposes. In butterfly wing scales, chitin is often organized into stacks of nano-layers or nano-sticks made of chitin nanocrystals that produce various iridescent colors by thin-film interference: similar, analogous structures made of keratin are found in iridescent bird plumage.
A similar word, "chiton", refers to a marine animal with a protective shell (also known as a "sea cradle").
Chemistry, physical properties and biological function
Chitin is a modified polysaccharide that contains nitrogen; it is synthesized from units of N-acetylglucosamine (to be precise, 2-(acetylamino)-2-deoxy-D-glucose). These units form covalent β-1,4 linkages (similar to 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 unmodified form, chitin is translucent, pliable, resilient, and quite tough. In arthropods, however, it is often modified, becoming embedded in sclerotin, a tanned proteinaceous matrix, which forms much of the exoskeleton. In its pure form, chitin is pliable and leathery in texture, but in most invertebrates it occurs largely as a component of composite materials. Combined with calcium carbonate, as in the shells of crustaceans and molluscs, chitin produces a much stronger composite. This composite material is much harder and more stiff than pure chitin, and is tougher and less brittle than pure calcium carbonate. Another difference between pure and composite forms can be seen by comparing the flexible body wall between the segments of a caterpillar (mainly chitin) to the stiff, light elytron of a beetle (containing a large proportion of sclerotin).
Cyphochilus beetles use the molecule chitin to produce their white scales, which are whiter than paper or any artificial material produced so far. The beetles have developed white shells to be camouflaged among white fungi. There is a complex molecular geometry to their scales, which are able to scatter light with supreme efficiency in spite of their thinness. To produce white scales, Cyphochilus beetles must deflect all colours with equal strength, something rarely found in nature. What makes these scales so white is the special arrangement of the chitin elements inside them, together with their varied shapes and sizes. The chitin filaments are just a few millionths of a metre thick - far thinner than a very fine sheet of paper. The elements are tightly packed, scattering light efficiently, but still able keep a degree of disorder in their shape.
Most recent studies point out that chitin is a good inducer of defense mechanisms in plants. It has also been assessed as a fertilizer that can improve overall crop yields. The EPA regulates chitin for agricultural use within the USA. Chitosan is prepared from chitin by deacetylation.
Chitin is used in industry in many processes. Examples of the potential uses of chemically modified chitin in food processing include the formation edible films and as an additive to thicken and stabilize foods and pharmaceuticals. It also acts as a binder in dyes, fabrics, and adhesives. Industrial separation membranes and ion-exchange media can be made from chitin. Processes to size and strengthen paper employ chitin and chitosan. Researchers have developed a method for using chitosan as a reproducible form of biodegradable plastic and as a promising substrate for engineering human tissues by use of three-dimensional bioprinting.
Chitin's flexibility and strength make it favorable as surgical thread. Its biodegradibility means it wears away with time as the wound heals. Moreover, chitin has been reported to have some unusual properties that accelerate healing of wounds in humans.[full citation needed]
Occupations associated with high environmental chitin levels, such as shellfish processors, are prone to high incidences of asthma. Recent studies have suggested that chitin may play a role in a possible pathway in human allergic disease. To be specific, mice treated with chitin develop an allergic response, characterized by a build-up of interleukin-4-expressing innate immune cells. In these treated mice, additional treatment with a chitinase enzyme abolishes the response.
Chitin may be employed for affinity purification of recombinant protein. A chitin binding domain is genetically fused to a protein of interest and then contacted to beads coated with chitin. The immobilized protein is purified and released from the beads by cleaving off the chitin binding domain.[clarification needed]
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|Wikimedia Commons has media related to Chitin.|
- Horseshoe Crab Chitin Research
- Information about Chitin (Heppe Medical Chitosan)
- Martín-Gil FJ, Leal JA, Gómez-Miranda B, Martín-Gil J, Prieto A, Ramos-Sánchez MC (1992). "Low temperature thermal behaviour of chitins and chitin-glucans". Thermochim. Acta 211: 241–254. doi:10.1016/0040-6031(92)87023-4.
- Chitin at the US National Library of Medicine Medical Subject Headings (MeSH)