Chitinn 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 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.
Etymology The English word "chitin" comes from the French
word chitine, which first appeared in 1821 and derived from the Greek word χιτών,
meaning covering.
A similar word, "chiton", refers to a marine animal with a protective shell.
Chemistry, physical properties and biological function
The structure of chitin was solved by Albert Hofmann in 1929.
Chitin is a modified polysaccharide that contains nitrogen; it is synthesized from units of
N-acetylglucosamine-2-deoxy-D-glucose).
These units form covalent β-1,4 linkages.
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.
Another difference between pure and composite forms can be seen by comparing the flexible
body wall of a caterpillar to the stiff, light elytron of a beetle.
Scarab beetles in the genus Cyphochilus demonstrate an exceptional form of chitin in the white
scales covering their bodies, as they are whiter than paper or any artificial material
produced so far.
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, and tightly packed, scattering light efficiently, deflecting all
colours with equal strength, but still able keep a degree of disorder in their shape.
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, comprising a scorpion
encased in amber.
Uses Agriculture
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.
Industrial 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.
Medicine 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.
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.
Biomedical research Chitin may be employed for affinity purification
of recombinant protein.
A chitin binding domain is genetically fused to a protein of interest and then connected
to beads coated with chitin.
The immobilized protein is purified and released from the beads by cleaving off the chitin
binding domain.
See also Biopesticide
Chitobiose Chitosan
Lorica Sporopollenin
Tectin References
External links Horseshoe Crab Chitin Research
Information about Chitin 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 211: 241–254.
doi:10.1016/0040-6031(92)87023-4.
Chitin at the US National Library of Medicine Medical Subject Headings