Short description: Long-chain polymer of a N-acetylglucosamine

Structure of the chitin molecule, showing two of the N-acetylglucosamine units that repeat to form long chains in β-(1→4)-linkage.

Haworth projection of the chitin molecule.

A close-up of the wing of a leafhopper; the wing is composed of chitin.

Chitin (C8H13O5N)n (/ˈkaɪtɪn/ KY-tin) is a long-chain polymer of N-acetylglucosamine, an amide derivative of glucose. The second most abundant polysaccharide in nature[1] (behind only cellulose), it is a primary component of cell walls in fungi, the exoskeletons of arthropods such as crustaceans and insects, and the radulae, cephalopod beaks and gladii of molluscs. It is also synthesised by at least some fish and lissamphibians.[2] 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.

## Contents

* 1 Etymology
* 2 Chemistry, physical properties and biological function
* 3 Health effects
* 3.1 Humans and other mammals
* 3.2 Plants
* 4 Fossil record
* 5 Uses
* 5.1 Agriculture
* 5.2 Industrial
* 6 Research
* 7 See also
* 8 References

## Etymology

The English word "chitin" comes from the French word chitine, which was derived in 1821 from the Greek word χιτών (khitōn) meaning covering.[3]

A similar word, "chiton", refers to a marine animal with a protective shell.

## Chemistry, physical properties and biological function

Chemical configurations of the different monosaccharides (glucose and N-acetylglucosamine) and polysaccharides (chitin and cellulose) presented in Haworth projection

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.[4][5][6]

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.

A cicada emerges from its chitinous larval exoskeleton.

In its pure, unmodified form, chitin is translucent, pliable, resilient, and quite tough. In most arthropods, however, it is often modified, occurring largely as a component of composite materials, such as in sclerotin, a tanned proteinaceous matrix, which forms much of the exoskeleton of insects. 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 stiffer than pure chitin, and is tougher and less brittle than pure calcium carbonate.[7] Another difference between pure and composite forms can be seen by comparing the flexible body wall of a caterpillar (mainly chitin) to the stiff, light elytron of a beetle (containing a large proportion of sclerotin).[8]

In butterfly wing scales, chitin is organized into stacks of gyroids constructed of chitin photonic crystals that produce various iridescent colors serving phenotypic signaling and communication for mating and foraging.[9] The elaborate chitin gyroid construction in butterfly wings creates a model of optical devices having potential for innovations in biomimicry.[9] Scarab beetles in the genus Cyphochilus also utilize chitin to form extremely thin scales (five to fifteen micrometres thick) that diffusely reflect white light. These scales are networks of randomly ordered filaments of chitin with diameters on the scale of hundreds of nanometres, which serve to scatter light. The multiple scattering of light is thought to play a role in the unusual whiteness of the scales.[10][11] In addition, some social wasps, such as Protopolybia chartergoides, orally secrete material containing predominantly chitin to reinforce the outer nest envelopes, composed of paper.[12]

Chitosan is produced commercially by deacetylation of chitin; chitosan is soluble in water, while chitin is not.[13]

Nanofibrils have been made using chitin and chitosan.[14]

## Health effects

Chitin-producing organisms like protozoa, fungi, arthropods, and nematodes are often pathogens in other species.[15]

### Humans and other mammals

Humans and other mammals have chitinase and chitinase-like proteins that can degrade chitin; they also possess several immune receptors that can recognize chitin and its degradation products in a pathogen-associated molecular pattern, initiating an immune response.[15]

Chitin is sensed mostly in the lungs or gastrointestinal tract where it can activate the innate immune system through eosinophils or macrophages, as well as an adaptive immune response through T helper cells.[15] Keratinocytes in skin can also react to chitin or chitin fragments.[15] According to in vitro studies, chitin is sensed by receptors, such as FIBCD1, KLRB1, REG3G, Toll-like receptor 2, CLEC7A, and mannose receptors.[15][16]

The immune response can sometimes clear the chitin and its associated organism, but sometimes the immune response is pathological and becomes an allergy;[17] allergy to house dust mites is thought to be driven by a response to chitin.[16]

### Plants

Plants also have receptors that can cause a response to chitin, namely chitin elicitor receptor kinase 1 and chitin elicitor-binding protein.[15] The first chitin receptor was cloned in 2006.[18] When the receptors are activated by chitin, genes related to plant defense are expressed, and jasmonate hormones are activated, which in turn activate systematic defenses.[19] Commensal fungi have ways to interact with the host immune response that, (As of 2016), were not well understood.[18]

Some pathogens produce chitin-binding proteins that mask the chitin they shed from these receptors.[19][20] Zymoseptoria tritici is an example of a fungal pathogen that has such blocking proteins; it is a major pest in wheat crops.[21]

## Fossil record

Chitin was probably present in the exoskeletons of Cambrian arthropods such as trilobites. The oldest preserved chitin dates to the Oligocene, about 25 million years ago, consisting of a scorpion encased in amber.[22]

## Uses

### Agriculture

Chitin is a good inducer of plant defense mechanisms for controlling diseases.[23] It has potential for use as a soil fertilizer or conditioner to improve fertility and plant resilience that may enhance crop yields.[24][25]

### Industrial

Chitin is used in industry in many processes. Examples of the potential uses of chemically modified chitin in food processing include the formation of edible films and as an additive to thicken and stabilize foods and food emulsions.[26][27] Processes to size and strengthen paper employ chitin and chitosan.[28][29]

## Research

How chitin interacts with the immune system of plants and animals has been an active area of research, including the identity of key receptors with which chitin interacts, whether the size of chitin particles is relevant to the kind of immune response triggered, and mechanisms by which immune systems respond.[17][21] Chitin and chitosan have been explored as a vaccine adjuvant due to its ability to stimulate an immune response.[15]

Chitin and chitosan are under development as scaffolds in studies of how tissue grows and how wounds heal, and in efforts to invent better bandages, surgical thread, and materials for allotransplantation.[13][30] Sutures made of chitin have been explored for many years, but (As of 2015), none were on the market; their lack of elasticity and problems making thread have prevented commercial development.[31]

In 2014, a method for using chitosan as a reproducible form of biodegradable plastic was introduced.[32] Chitin nanofibers are extracted from crustacean waste and mushrooms for possible development of products in tissue engineering, medicine, and industry.[33]

In 2020, chitin was proposed for use in building structures, tools, and other solid objects from a composite material of chitin combined with Martian regolith.[34] In this scenario, the biopolymers in the chitin act as the binder for the regolith aggregate to form a concrete-like composite material. The authors believe that waste materials from food production (e.g. scales from fish, exoskeletons from crustaceans and insects, etc.) could be put to use as feedstock for manufacturing processes.

## See also

* Biopesticide
* Chitobiose
* Lorica
* Sporopollenin
* Tectin

## References

1. ↑ Elieh-Ali-Komi, Daniel; Hamblin, Michael R (March 1, 2016). "Chitin and Chitosan: Production and Application of Versatile Biomedical Nanomaterials". International Journal of Advanced Research 4 (3): 411–427. ISSN 2320-5407. PMID 27819009.
2. ↑ Tang, WJ; Fernandez, JG; Sohn, JJ; Amemiya, CT (2015). "Chitin is endogenously produced in vertebrates". Curr Biol 25 (7): 897–900. doi:10.1016/j.cub.2015.01.058. PMID 25772447.
3. ↑ Odier, Auguste (1823). "Mémoire sur la composition chimique des parties cornées des insectes" (in fr). Mémoires de la Société d'Histoire Naturelle de Paris (presented: 1821) 1: 29–42. https://books.google.com/books?id=JhhLAAAAYAAJ&pg=PA35. "la Chitine (c'est ainsi que je nomme cette substance de chiton, χιτον, enveloppe… [chitine (it is thus that I name this substance from chiton, χιτον, covering)]"".
4. ↑ Hofmann, A. (1929). Über den enzymatischen Abbau des Chitins und Chitosans [On the enzymatic degradation of chitin and chitosan] (Thesis). Zurich, Switzerland: University of Zurich.
5. ↑ Karrer, P.; Hofmann, A. (1929). "Polysaccharide XXXIX. Über den enzymatischen Abbau von Chitin and Chitosan I" (in de). Helvetica Chimica Acta 12 (1): 616–637. doi:10.1002/hlca.19290120167.
6. ↑ Finney, Nathaniel S.; Siegel, Jay S. (2008). "In Memoriam: Albert Hofmann (1906-2008)". Chimia (University of Zurich) 62 (5): 444–447. doi:10.2533/chimia.2008.444. http://www.zora.uzh.ch/9154/2/Siege_Finney_Hoffmann_2008V.pdf.
7. ↑ Campbell, N. A. (1996) Biology (4th edition) Benjamin Cummings, New Work. p.69 ISBN:0-8053-1957-3
8. ↑ Gilbert, Lawrence I. (2009). Insect development : morphogenesis, molting and metamorphosis. Amsterdam Boston: Elsevier/Academic Press. ISBN 978-0-12-375136-2.
9. ↑ 9.0 9.1 "Structure, function, and self-assembly of single network gyroid (I4132) photonic crystals in butterfly wing scales". Proc Natl Acad Sci U S A 107 (26): 11676–81. 2010. doi:10.1073/pnas.0909616107. PMID 20547870. Bibcode: 2010PNAS..10711676S.
10. ↑ Dasi Espuig M (16 August 2014). "Beetles' whiteness understood". BBC News: Science and Environment. https://www.bbc.co.uk/news/science-environment-28811232.
11. ↑ Burresi, Matteo; Cortese, Lorenzo; Pattelli, Lorenzo; Kolle, Mathias; Vukusic, Peter; Wiersma, Diederik S.; Steiner, Ullrich; Vignolini, Silvia (2014). "Bright-white beetle scales optimise multiple scattering of light". Scientific Reports 4: 6075. doi:10.1038/srep06075. PMID 25123449. Bibcode: 2014NatSR...4E6075B.
12. ↑ Kudô, K. Nest materials and some chemical characteristics of nests of a New World swarm-founding polistine wasp, (Hymenoptera Vespidae). Ethology, ecology & evolution 13.4 Oct 2001: 351-360. Dipartimento di biologia animale e genetica, Università di Firenze. 16 Oct 2014.
13. ↑ 13.0 13.1 Bedian, L; Villalba-Rodríguez, AM; Hernández-Vargas, G; Parra-Saldivar, R; Iqbal, HM (May 2017). "Bio-based materials with novel characteristics for tissue engineering applications - A review.". International Journal of Biological Macromolecules 98: 837–846. doi:10.1016/j.ijbiomac.2017.02.048. PMID 28223133.
14. ↑ Jeffryes, C; Agathos, SN; Rorrer, G (June 2015). "Biogenic nanomaterials from photosynthetic microorganisms.". Current Opinion in Biotechnology 33: 23–31. doi:10.1016/j.copbio.2014.10.005. PMID 25445544.
15. ↑ 15.0 15.1 15.2 15.3 15.4 15.5 15.6 Elieh Ali Komi, D; Sharma, L; Dela Cruz, CS (1 March 2017). "Chitin and Its Effects on Inflammatory and Immune Responses.". Clinical Reviews in Allergy & Immunology 54 (2): 213–223. doi:10.1007/s12016-017-8600-0. PMID 28251581.
16. ↑ 16.0 16.1 Gour, N; Lajoie, S (September 2016). "Epithelial Cell Regulation of Allergic Diseases.". Current Allergy and Asthma Reports 16 (9): 65. doi:10.1007/s11882-016-0640-7. PMID 27534656.
17. ↑ 17.0 17.1 Gómez-Casado, C; Díaz-Perales, A (October 2016). "Allergen-Associated Immunomodulators: Modifying Allergy Outcome.". Archivum Immunologiae et Therapiae Experimentalis 64 (5): 339–47. doi:10.1007/s00005-016-0401-2. PMID 27178664.
18. ↑ 18.0 18.1 Sánchez-Vallet, A; Mesters, JR; Thomma, BP (March 2015). "The battle for chitin recognition in plant-microbe interactions.". FEMS Microbiology Reviews 39 (2): 171–83. doi:10.1093/femsre/fuu003. ISSN 0168-6445. PMID 25725011.
19. ↑ 19.0 19.1 Sharp, Russell G. (21 November 2013). "A Review of the Applications of Chitin and Its Derivatives in Agriculture to Modify Plant-Microbial Interactions and Improve Crop Yields" (in en). Agronomy 3 (4): 757–793. doi:10.3390/agronomy3040757.
20. ↑ Rovenich, H; Zuccaro, A; Thomma, BP (December 2016). "Convergent evolution of filamentous microbes towards evasion of glycan-triggered immunity.". The New Phytologist 212 (4): 896–901. doi:10.1111/nph.14064. PMID 27329426.
21. ↑ 21.0 21.1 Kettles, GJ; Kanyuka, K (15 April 2016). "Dissecting the Molecular Interactions between Wheat and the Fungal Pathogen Zymoseptoria tritici". Frontiers in Plant Science 7: 508. doi:10.3389/fpls.2016.00508. PMID 27148331.
22. ↑ Briggs, DEG (29 January 1999). "Molecular taphonomy of animal and plant cuticles: selective preservation and diagenesis". Philosophical Transactions of the Royal Society B: Biological Sciences 354 (1379): 7–17. doi:10.1098/rstb.1999.0356.
23. ↑ El Hadrami, A; Adam, L. R.; El Hadrami, I; Daayf, F (2010). "Chitosan in plant protection". Marine Drugs 8 (4): 968–987. doi:10.3390/md8040968. PMID 20479963.
24. ↑ Debode, Jane; De Tender, Caroline; Soltaninejad, Saman; Van Malderghem, Cinzia; Haegeman, Annelies; Van der Linden, Inge; Cottyn, Bart; Heyndrickx, Marc et al. (2016-04-21). "Chitin mixed in potting soil alters lettuce growth, the survival of zoonotic bacteria on the leaves and associated rhizosphere microbiology". Frontiers in Microbiology 7: 565. doi:10.3389/fmicb.2016.00565. ISSN 1664-302X. PMID 27148242.
25. ↑ Sarathchandra, S. U.; Watson, R. N.; Cox, N. R.; di Menna, M. E.; Brown, J. A.; Burch, G.; Neville, F. J. (1996-05-01). "Effects of chitin amendment of soil on microorganisms, nematodes, and growth of white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.)" (in en). Biology and Fertility of Soils 22 (3): 221–226. doi:10.1007/BF00382516. ISSN 1432-0789.
26. ↑ Tzoumaki, Maria V.; Moschakis, Thomas; Kiosseoglou, Vassilios; Biliaderis, Costas G. (August 2011). "Oil-in-water emulsions stabilized by chitin nanocrystal particles". Food Hydrocolloids 25 (6): 1521–1529. doi:10.1016/j.foodhyd.2011.02.008. ISSN 0268-005X.
27. ↑ Shahidi, F.; Arachchi, J.K.V.; Jeon, Y.-J. (1999). "Food applications of chitin and chitosans". Trends in Food Science & Technology 10 (2): 37–51. doi:10.1016/s0924-2244(99)00017-5.
28. ↑ "Biodegradable film derived from chitosan & homogenized cellulose". Ind. Eng. Chem. Res. 44: 646–650. 1990.
29. ↑ "Packaging related properties of protein and chitosan coated paper". Packaging Technology and Science 18: 160–170. 2005.
30. ↑ Cheung, R. C.; Ng, T. B.; Wong, J. H.; Chan, W. Y. (2015). "Chitosan: An Update on Potential Biomedical and Pharmaceutical Applications". Marine Drugs 13 (8): 5156–5186. doi:10.3390/md13085156. PMID 26287217.
31. ↑ Ducheyne, Paul; Healy, Kevin; Hutmacher, Dietmar E. et al., eds (2011). Comprehensive biomaterials. Amsterdam: Elsevier. p. 230. ISBN 9780080552941. https://books.google.com/books?id=oa8YpRsD1kkC&pg=RA1-PA230.
32. ↑ "Harvard researchers develop bioplastic made from shrimp shells". Fox News. 16 May 2014. http://www.foxnews.com/science/2014/05/16/harvard-researchers-develop-bioplastic-made-from-shrimp-shells/.
33. ↑ Ifuku, Shinsuke (2014). "Chitin and Chitosan Nanofibers: Preparation and Chemical Modifications". Molecules 19 (11): 18367–80. doi:10.3390/molecules191118367. PMID 25393598.
34. ↑ Shiwei, Ng; Dritsas, Stylianos; Fernandez, Javier G. (September 16, 2020). "Martian biolith: A bioinspired regolith composite for closed-loop extraterrestrial manufacturing". PLOS ONE 15 (9): e0238606. doi:10.1371/journal.pone.0238606. PMID 32936806. Bibcode: 2020PLoSO..1538606S.

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Types of carbohydrates

General|

* Aldose
* Ketose
* Furanose
* Pyranose

Geometry|

* Anomer
* Cyclohexane conformation
* Mutarotation

Monosaccharides|

| Dioses|

* Aldodiose
* Glycolaldehyde

|

Trioses|

* Aldotriose
* Glyceraldehyde
* Ketotriose
* Dihydroxyacetone

Tetroses|

* Aldotetroses
* Erythrose
* Threose
* Ketotetrose
* Erythrulose

Pentoses|

* Aldopentoses
* Arabinose
* Lyxose
* Ribose
* Xylose
* Ketopentoses
* Ribulose
* Xylulose
* Deoxy sugars
* Deoxyribose

Hexoses|

* Aldohexoses
* Allose
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* Galactose
* Glucose
* Gulose
* Idose
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* Deoxy sugars
* Fucose
* Fuculose
* Rhamnose

Heptoses|

* Ketoheptoses
* Mannoheptulose
* Sedoheptulose

Above 7|

* Octoses
* Nonoses
* Neuraminic acid

Multiple|

| Disaccharides|

* Cellobiose
* Isomaltose
* Isomaltulose
* Lactose
* Lactulose
* Maltose
* Sucrose
* Trehalose
* Turanose

|

Trisaccharides|

* Maltotriose
* Melezitose
* Raffinose

Tetrasaccharides|

* Stachyose

Other
oligosaccharides|

* Acarbose
* Fructooligosaccharide (FOS)
* Galactooligosaccharide (GOS)
* Isomaltooligosaccharide (IMO)
* Maltodextrin

Polysaccharides|

* Beta-glucan
* Oat beta-glucan
* Lentinan
* Sizofiran
* Zymosan
* Cellulose
* Chitin
* Chitosan
* Dextrin / Dextran
* Fructose / Fructan
* Inulin
* Galactose / Galactan
* Glucose / Glucan
* Glycogen
* Hemicellulose
* Levan beta 2→6
* Lignin
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* Pectin
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* Amylopectin
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* Category

* v
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Human interactions with insects

Aspects
of insects
in culture|

| In the arts|

* Insects in art
* Beetlewing
* John Hampson
* Insects in film
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* Insects in music
* List of insect-inspired songs
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In fishing|

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In medicine|

* Apitherapy
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In mythology|

* Bee
* Butterfly
* Cicada
* Dragonfly
* Praying mantis
* Scarab

Entomophagy
(as food)|

| Adults|

* Ant
* Cicada
* Cricket
* Grasshopper
* Termite

|

Larvae|

* Bamboo worm
* Mealworm
* Mopane worm
* Palm weevil
* Rhinoceros beetle
* Silkworm
* Waxworm
* Witchetty grub

Other aspects|

* Biomimicry
* Cockroach racing
* Cricket fighting
* Entomological warfare
* Flea circus
* Insects in religion
* Jingzhe

Economic
entomology|

| Beneficial
insects|

| Pest control|

* Encarsia formosa
* Ladybird
* Parasitoid wasp

|

Pollination|

* Bees
* crops pollinated
* Bumblebee
* Honey bee
* western
* Beetles
* Flies
* Lepidoptera

Products|

| Beekeeping|

* Bee pollen
* Beeswax
* Honey
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* Royal jelly

|

Other insects|

* Carmine/Cochineal
* Polish
* Chitin
* Kermes
* Sericulture
* Silk
* Lac/Shellac

Model organism|

* Drosophila melanogaster

Harmful
insects|

| Crop pests|

* Aphid
* Boll weevil
* Colorado potato beetle
* Cottony cushion scale
* Japanese beetle
* Locust
* Phylloxera
* Western corn rootworm

|

Livestock pests|

* Botfly
* Deer fly
* Horn fly
* Horse-fly
* Screwworm fly
* Tsetse fly
* Warble fly

Biting/stinging|

* Insect bites and stings
* Insect sting allergy
* Bed bug
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* Fire ant
* Flea
* Horse-fly
* Louse
* Mosquito
* Wasp

Wood-eating|

* Deathwatch beetle
* Furniture beetle
* House longhorn beetle
* Termite
* Woodworm

Other pests|

* Home-stored product entomology
* Clothes moth
* Cockroach
* Housefly

Pioneers|

* Jan Swammerdam
* Alfred Russel Wallace
* Jean-Henri Fabre
* Hans Zinsser (Rats, Lice and History)
* Lafcadio Hearn (Insect Literature)

Concerns|

* Bees and toxic chemicals
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* Decline in insect populations
* Habitat destruction
* List of endangered insects
* Pesticide
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* Neonicotinoid
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Related|

* Biology in fiction
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Categories,
templates|

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