Chitin

The English word "chitin" comes from the French word chitine, which was derived in 1821 from the Greek word χιτών (khitōn) meaning covering.{{cite journal| first= Auguste |last= Odier |publisher= presented: 1821| year= 1823| title= Mémoire sur la composition chimique des parties cornées des insectes| trans-title= Memoir on the chemical composition of the horny parts of insects| journal= Mémoires de la Société d'Histoire Naturelle de Paris| volume= 1| language= fr| pages= 29–42| url= https://books.google.com/books?id=JhhLAAAAYAAJ&pg=PA35 |quote= 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)]"}}

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

File:Chitin glucose and cellulose.svg]]

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.{{cite thesis| first= A. |last= Hofmann | year=1929| title= Über den enzymatischen Abbau des Chitins und Chitosans| trans-title= On the enzymatic degradation of chitin and chitosan| publisher= University of Zurich |place= Zurich, Switzerland}}{{cite journal| first1= P.| last1= Karrer |first2= A. |last2= Hofmann | year= 1929| title= Polysaccharide XXXIX. Über den enzymatischen Abbau von Chitin and Chitosan I| journal= Helvetica Chimica Acta| language= de| volume= 12| number= 1| pages= 616–637 | doi= 10.1002/hlca.19290120167}}{{cite journal| first1= Nathaniel S.| last1= Finney| first2= Jay S.| last2= Siegel| year= 2008| title= In Memoriam: Albert Hofmann (1906-2008)| journal= CHIMIA| volume= 62| number= 5| pages= 444–447| url= http://www.zora.uzh.ch/9154/2/Siege_Finney_Hoffmann_2008V.pdf| publisher= University of Zurich| doi= 10.2533/chimia.2008.444| access-date= 2013-04-14| archive-date= 2013-06-16| archive-url= https://web.archive.org/web/20130616034406/http://www.zora.uzh.ch/9154/2/Siege_Finney_Hoffmann_2008V.pdf| url-status= dead}}

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. 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.Campbell, N. A. (1996) Biology (4th edition) Benjamin Cummings, New Work. p.69 {{ISBN|0-8053-1957-3}} 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).{{cite book | author = Gilbert, Lawrence I. | title = Insect development : morphogenesis, molting and metamorphosis | publisher = Elsevier/Academic Press | location = Amsterdam Boston | year = 2009 | isbn = 978-0-12-375136-2 }}

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.{{cite journal|journal=Proc Natl Acad Sci U S A|year=2010|volume=107|issue=26|pages=11676–81|doi=10.1073/pnas.0909616107|title=Structure, function, and self-assembly of single network gyroid (I4132) photonic crystals in butterfly wing scales|vauthors=Saranathan V, Osuji CO, Mochrie SG, Noh H, Narayanan S, Sandy A, Dufresne ER, Prum RO|pmid=20547870|pmc=2900708|bibcode=2010PNAS..10711676S|doi-access=free}} The elaborate chitin gyroid construction in butterfly wings creates a model of optical devices having potential for innovations in biomimicry. 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.{{cite web|url=https://www.bbc.co.uk/news/science-environment-28811232|date=16 August 2014|title=Beetles' whiteness understood|author=Dasi Espuig M|publisher=BBC News: Science and Environment|access-date=15 November 2014}}{{cite journal |first1 = Matteo |last1 = Burresi |first2 = Lorenzo |last2 = Cortese| first3 = Lorenzo |last3 = Pattelli | first4 = Mathias | last4 = Kolle | first5 = Peter | last5 = Vukusic | first6 = Diederik S. | last6 = Wiersma | first7 = Ullrich | last7 = Steiner |first8 = Silvia | last8 = Vignolini |title=Bright-white beetle scales optimise multiple scattering of light |journal=Scientific Reports |volume = 4 |pages = 6075 |year = 2014 |doi = 10.1038/srep06075 | pmid=25123449 | pmc=4133710|bibcode = 2014NatSR...4E6075B }} In addition, some social wasps, such as Protopolybia chartergoides, orally secrete material containing predominantly chitin to reinforce the outer nest envelopes, composed of paper.{{Cite journal |last1=Kudô |first1=K. |last2=Yamane |first2=Sô. |last3=Mateus |first3=S. |last4=Tsuchida |first4=K. |last5=Itô |first5=Y. |last6=Miyano |first6=S. |last7=Yamamoto |first7=H. |last8=Zucchi |first8=R. |date=2001-10-01 |title=Nest materials and some chemical characteristics of nests of a New World swarm-founding polistine wasp, Polybia paulista (Hymenoptera Vespidae) |url=https://doi.org/10.1080/08927014.2001.9522766 |journal=Ethology Ecology & Evolution |volume=13 |issue=4 |pages=351–360 |doi=10.1080/08927014.2001.9522766 |bibcode=2001EtEcE..13..351K |s2cid=86452110 |issn=0394-9370}}

Chitosan is produced commercially by deacetylation of chitin by treatment with sodium hydroxide. Chitosan has a wide range of biomedical applications including wound healing, drug delivery and tissue engineering. Due to its specific intermolecular hydrogen bonding network, dissolving chitin in water is very difficult.{{cite journal|last1=Bedian|first1=L|last2=Villalba-Rodríguez|first2=AM|last3=Hernández-Vargas|first3=G|last4=Parra-Saldivar|first4=R|last5=Iqbal|first5=HM|title=Bio-based materials with novel characteristics for tissue engineering applications - A review.|journal=International Journal of Biological Macromolecules|date=May 2017|volume=98|pages=837–846|doi=10.1016/j.ijbiomac.2017.02.048|pmid=28223133}} Chitosan (with a degree of deacetylation of more than ~28%), on the other hand, can be dissolved in dilute acidic aqueous solutions below a pH of 6.0 such as acetic, formic and lactic acids. Chitosan with a degree of deacetylation greater than ~49% is soluble in water{{Cite journal |last1=Cho |first1=Yong-Woo |last2=Jang |first2=Jinho |last3=Park |first3=Chong Rae |last4=Ko |first4=Sohk-Won |date=2000-12-01 |title=Preparation and Solubility in Acid and Water of Partially Deacetylated Chitins |url=https://pubs.acs.org/doi/10.1021/bm000036j |journal=Biomacromolecules |language=en |volume=1 |issue=4 |pages=609–614 |doi=10.1021/bm000036j |pmid=11710189 |issn=1525-7797}}{{Citation |last1=Rouhani Shirvan |first1=Anahita |title=5 - Recent advances in application of chitosan and its derivatives in functional finishing of textiles |date=2019-01-01 |url=https://www.sciencedirect.com/science/article/pii/B9780081024911000058 |work=The Impact and Prospects of Green Chemistry for Textile Technology |pages=107–133 |editor-last=Shahid-ul-Islam |access-date=2023-12-18 |series=The Textile Institute Book Series |publisher=Woodhead Publishing |isbn=978-0-08-102491-1 |last2=Shakeri |first2=Mina |last3=Bashari |first3=Azadeh |editor2-last=Butola |editor2-first=B. S.}}

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, initiating an immune response.{{cite journal|last1=Elieh Ali Komi|first1=D|last2=Sharma|first2=L|last3=Dela Cruz|first3=CS|title=Chitin and Its Effects on Inflammatory and Immune Responses.|journal=Clinical Reviews in Allergy & Immunology|volume=54|issue=2|pages=213–223|date=1 March 2017|doi=10.1007/s12016-017-8600-0|pmid=28251581|pmc=5680136}}

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. Keratinocytes in skin can also react to chitin or chitin fragments.

Plants also have receptors that can cause a response to chitin, namely chitin elicitor receptor kinase 1 and chitin elicitor-binding protein. The first chitin receptor was cloned in 2006.{{cite journal|last1=Sánchez-Vallet|first1=A|last2=Mesters|first2=JR|last3=Thomma|first3=BP|title=The battle for chitin recognition in plant-microbe interactions.|journal=FEMS Microbiology Reviews|date=March 2015|volume=39|issue=2|pages=171–83|doi=10.1093/femsre/fuu003|pmid=25725011|issn=0168-6445|doi-access=free|hdl=20.500.11850/97275|hdl-access=free}} When the receptors are activated by chitin, genes related to plant defense are expressed, and jasmonate hormones are activated, which in turn activate systemic defenses. Commensal fungi have ways to interact with the host immune response that, {{as of|2016|lc=y}}, were not well understood.

Some pathogens produce chitin-binding proteins that mask the chitin they shed from these receptors.{{cite journal|last1=Sharp|first1=Russell G.|title=A Review of the Applications of Chitin and Its Derivatives in Agriculture to Modify Plant-Microbial Interactions and Improve Crop Yields|journal=Agronomy|date=21 November 2013|volume=3|issue=4|pages=757–793|doi=10.3390/agronomy3040757|language=en|doi-access=free}}{{cite journal|last1=Rovenich|first1=H|last2=Zuccaro|first2=A|last3=Thomma|first3=BP|title=Convergent evolution of filamentous microbes towards evasion of glycan-triggered immunity.|journal=The New Phytologist|date=December 2016|volume=212|issue=4|pages=896–901|doi=10.1111/nph.14064|pmid=27329426|doi-access=free}} Zymoseptoria tritici is an example of a fungal pathogen that has such blocking proteins; it is a major pest in wheat crops.

{{for|more on the preservation potential of chitin and other biopolymers|taphonomy}}

Chitin was probably present in the exoskeletons of Cambrian arthropods such as trilobites. The oldest preserved (intact) chitin samples thus far reported are dated to the Oligocene, about {{ma|25}}, from specimens encased in amber where the chitin has not completely degraded.{{Cite journal

| last = Briggs | first = DEG

| date = 29 January 1999

| title = Molecular taphonomy of animal and plant cuticles: selective preservation and diagenesis

| journal = Philosophical Transactions of the Royal Society B: Biological Sciences

| volume = 354

| issue = 1379

| pages = 7–17

| pmc = 1692454

| doi = 10.1098/rstb.1999.0356

}}

Chitin is a good inducer of plant defense mechanisms for controlling diseases.{{cite journal|pmc=2866471|year=2010|last1=El Hadrami|first1=A|title=Chitosan in plant protection|journal=Marine Drugs|volume=8|issue=4|pages=968–987|last2=Adam|first2=L. R.|last3=El Hadrami|first3=I|last4=Daayf|first4=F|doi=10.3390/md8040968|pmid=20479963|doi-access=free}} It has potential for use as a soil fertilizer or conditioner to improve fertility and plant resilience that may enhance crop yields.{{Cite journal|last1=Debode|first1=Jane|last2=De Tender|first2=Caroline|last3=Soltaninejad|first3=Saman|last4=Van Malderghem|first4=Cinzia|last5=Haegeman|first5=Annelies|last6=Van der Linden|first6=Inge|last7=Cottyn|first7=Bart|last8=Heyndrickx|first8=Marc|last9=Maes|first9=Martine|date=2016-04-21|title=Chitin mixed in potting soil alters lettuce growth, the survival of zoonotic bacteria on the leaves and associated rhizosphere microbiology|journal=Frontiers in Microbiology|volume=7|page=565|doi=10.3389/fmicb.2016.00565|issn=1664-302X|pmc=4838818|pmid=27148242|doi-access=free}}{{Cite journal|last1=Sarathchandra|first1=S. U.|last2=Watson|first2=R. N.|last3=Cox|first3=N. R.|last4=di Menna|first4=M. E.|last5=Brown|first5=J. A.|last6=Burch|first6=G.|last7=Neville|first7=F. J.|date=1996-05-01|title=Effects of chitin amendment of soil on microorganisms, nematodes, and growth of white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.)|journal=Biology and Fertility of Soils|language=en|volume=22|issue=3|pages=221–226|doi=10.1007/BF00382516|bibcode=1996BioFS..22..221S |s2cid=32594901|issn=1432-0789}}

Chitin is used in many industrial 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.{{Cite journal|last1=Tzoumaki|first1=Maria V.|last2=Moschakis|first2=Thomas|last3=Kiosseoglou|first3=Vassilios|last4=Biliaderis|first4=Costas G.|date=August 2011|title=Oil-in-water emulsions stabilized by chitin nanocrystal particles|journal=Food Hydrocolloids|volume=25|issue=6|pages=1521–1529|doi=10.1016/j.foodhyd.2011.02.008|issn=0268-005X}}{{cite journal | last1 = Shahidi | first1 = F. | last2 = Arachchi | first2 = J.K.V. | last3 = Jeon | first3 = Y.-J. | year = 1999 | title = Food applications of chitin and chitosans | journal = Trends in Food Science & Technology | volume = 10 | issue = 2| pages = 37–51 | doi=10.1016/s0924-2244(99)00017-5}} Processes to size and strengthen paper employ chitin and chitosan.{{Cite journal |last1=Hosokawa |first1=Jun |last2=Nishiyama |first2=Masashi |last3=Yoshihara |first3=Kazutoshi |last4=Kubo |first4=Takamasa |date=May 1990 |title=Biodegradable film derived from chitosan and homogenized cellulose |url=https://pubs.acs.org/doi/abs/10.1021/ie00101a015 |journal=Industrial & Engineering Chemistry Research |language=en |volume=29 |issue=5 |pages=800–805 |doi=10.1021/ie00101a015 |issn=0888-5885}}{{Cite journal |last1=Gällstedt |first1=Mikael |last2=Brottman |first2=Angela |last3=Hedenqvist |first3=Mikael S. |date=July 2005 |title=Packaging-related properties of protein- and chitosan-coated paper |url=https://onlinelibrary.wiley.com/doi/10.1002/pts.685 |journal=Packaging Technology and Science |language=en |volume=18 |issue=4 |pages=161–170 |doi=10.1002/pts.685 |s2cid=96578009 |issn=0894-3214}}

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.{{Cite journal |last1=Gómez-Casado |first1=Cristina |last2=Díaz-Perales |first2=Araceli |last3=Hedenqvist |first3=Mikael S. |date=2016-10-01 |title=Allergen-Associated Immunomodulators: Modifying Allergy Outcome |url=https://doi.org/10.1007/s00005-016-0401-2 |journal=Archivum Immunologiae et Therapiae Experimentalis |language=en |volume=64 |issue=5 |pages=339–347 |doi=10.1007/s00005-016-0401-2 |issn=1661-4917 |pmid=27178664 |s2cid=15221318}}{{cite journal|last1=Kettles|first1=GJ|last2=Kanyuka|first2=K|title=Dissecting the Molecular Interactions between Wheat and the Fungal Pathogen Zymoseptoria tritici|journal=Frontiers in Plant Science|date=15 April 2016|volume=7|pages=508|pmid=27148331|pmc=4832604|doi=10.3389/fpls.2016.00508|doi-access=free}} Chitin is deacetylated chemically or enzymatically to produce chitosan, a highly biocompatible polymer which has found a wide range of applications in the biomedical industry.{{Cite journal |last1=Kapadnis |first1=Gaurav |last2=Dey |first2=Anomitra |last3=Dandekar |first3=Prajakta |last4=Jain |first4=Ratnesh |date=June 2019 |title=Effect of degree of deacetylation on solubility of low-molecular-weight chitosan produced via enzymatic breakdown of chitosan |url=https://onlinelibrary.wiley.com/doi/10.1002/pi.5795 |journal=Polymer International |language=en |volume=68 |issue=6 |pages=1054–1063 |doi=10.1002/pi.5795 |s2cid=104427459 |issn=0959-8103}}{{Citation |last1=Desai |first1=Ranjeet |title=Review of the Structure of Chitosan in the Context of Other Sugar-Based Polymers |date=2021 |url=https://link.springer.com/10.1007/12_2021_89 |work=Chitosan for Biomaterials III |volume=287 |pages=23–74 |editor-last=Jayakumar |editor-first=R. |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/12_2021_89 |isbn=978-3-030-83806-5 |access-date=2022-12-19 |last2=Pachpore |first2=Radhika |last3=Patil |first3=Ashwini |last4=Jain |first4=Ratnesh |last5=Dandekar |first5=Prajakta |s2cid=244341955 |editor2-last=Prabaharan |editor2-first=M.}} Chitin and chitosan have been explored as a vaccine adjuvant due to its ability to stimulate an immune response.

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.{{cite journal|pmc=4557018|year=2015|last1=Cheung|first1=R. C.|title=Chitosan: An Update on Potential Biomedical and Pharmaceutical Applications|journal=Marine Drugs|volume=13|issue=8|pages=5156–5186|last2=Ng|first2=T. B.|last3=Wong|first3=J. H.|last4=Chan|first4=W. Y.|doi=10.3390/md13085156|pmid=26287217|doi-access=free}} Sutures made of chitin have been experimentally developed, but their lack of elasticity and problems making thread have prevented commercial success so far.{{cite book|editor1-last=Ducheyne|editor1-first=Paul|editor2-last=Healy|editor2-first=Kevin|editor3-last=Hutmacher|editor3-first=Dietmar E.|editor4-last=Grainger|editor4-first=David W.|editor5-last=Kirkpatrick|editor5-first=C. James|title=Comprehensive biomaterials|date=2011|publisher=Elsevier|location=Amsterdam|isbn=9780080552941|page=230|url=https://books.google.com/books?id=oa8YpRsD1kkC&pg=RA1-PA230}}

Chitosan has been demonstrated and proposed to make a reproducible form of biodegradable plastic.{{cite web | title =Team creates bioplastic made from shrimp shells|url=https://phys.org/news/2014-05-team-bioplastic-shrimp-shells.html|date=6 May 2014|access-date=14 October 2024}} Chitin nanofibers are extracted from crustacean waste and mushrooms for possible development of products in tissue engineering, drug delivery and medicine.{{cite journal|doi=10.3390/molecules191118367|pmid=25393598|pmc=6271128|title=Chitin and Chitosan Nanofibers: Preparation and Chemical Modifications|journal=Molecules|volume=19|issue=11|pages=18367–80|year=2014|last1=Ifuku|first1=Shinsuke|doi-access=free}}

Chitin has been proposed for use in building structures, tools, and other solid objects from a composite material, combining chitin with Martian regolith.{{Cite journal|last1=Shiwei|first1=Ng|last2=Dritsas|first2=Stylianos|last3=Fernandez|first3=Javier G.|date=September 16, 2020|title=Martian biolith: A bioinspired regolith composite for closed-loop extraterrestrial manufacturing|journal=PLOS ONE|volume=15|issue=9|pages=e0238606|doi=10.1371/journal.pone.0238606|pmid=32936806|pmc=7494075|bibcode=2020PLoSO..1538606S|doi-access=free}} To build this, the biopolymers in the chitin are suggested 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.

• Chitobiose
• Lorica
• Sporopollenin
• Tectin

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{{Scholia}}

• {{Commons category-inline|Chitin}}
• {{Wiktionary inline}}

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{{Insects in culture}}

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Category:Acetamides

Category:Biomolecules

Category:Biopesticides

Category:Polysaccharides