Chitin (C₈H₁₃O₅N)_n (/[invalid input: 'icon']ˈkaɪt[invalid input: 'ɨ']n/) 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 radulas of mollusks, and the beaks of cephalopods, including squid and octopuses. In terms of structure, chitin may be compared to the polysaccharide cellulose and, in terms of function, to the protein keratin. Chitin has also proven useful for several medical and industrial purposes.

The structure of chitin was solved by Albert Hofmann for which he received his doctorate.

The English word "chitin" comes from the French word "chitine", which first appeared in 1836. These words were derived from the Greek word "chitōn", meaning mollusk, that is, either influenced by or related to the Greek word khitōn, meaning "tunic" or "frock", the Central Semitic word "*kittan", the Akkadian words "kitû" or "kita’um", meaning flax or linen, and the Sumerian word "gada" or "gida".^[1]

A similar word, "chiton", refers to a marine animal with a protective shell (also known as a "sea cradle").

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 substituted 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 a hardened proteinaceous matrix, which forms much of the exoskeleton. In its pure form, it is leathery, but, when encrusted in calcium carbonate, it becomes much harder.^[2] The difference between the unmodified and modified forms can be seen by comparing the body wall of a caterpillar (unmodified) to a beetle (modified).

Chitin was present in the exoskeletons of Cambrian arthropods such as trilobites. The oldest preserved chitin dates to the Oligocene, about 25 million years ago.^[3]

Most recent studies point out that chitin is a good inducer for defense mechanisms in plants.^[4] It has also been assessed as a fertilizer that can improve overall crop yields.^[5] The EPA regulates chitin for agricultural use within the USA.^[6] Chitosan is prepared from chitin by deacetylation.

Chitin is used in industry in many processes. It is used 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 resins can be made from chitin. Processes to size and strengthen paper employ chitin.^{[citation needed]}

Chitin's properties as a flexible and strong material make it favorable as surgical thread. Its biodegradibility means it wears away with time as the wound heals. Moreover, chitin has some unusual properties that accelerate healing of wounds in humans.^[7]

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.^[8]

• Biopesticide
• Chitobiose
• Chitosan (Natural Biocontrol for Agricultural & Horticultural use)
• Lorica
• Sporopollenin
• Tectin

• Martín-Gil FJ, Leal JA, Gómez-Miranda B, Martín-Gil J, Prieto A, Ramos-Sánchez MC. "Low temperature thermal behaviour of chitins and chitin-glucans". Thermochim. Acta, 1992, vol. 211, pp. 241–254.

• Horseshoe Crab Chitin Research
• Information about Chitin (Heppe Medical Chitosan)
• Chitin at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
• Chitin Product Information from China GreatVista Chemicals