Page 334 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Naturally Occurring Polymers—Plants 297

are examples of fructans. Levans are short linear polysaccharides composed of β 2→1 linked fruc-
tose units as pictured below:

O O O O
O O O O R
R H HO H HO H HO H HO
H H H H (9.21)
OH H OH OH H OH OH H OH OH H OH

Levan

9.7.2 CHITIN AND CHITOSAN

Chitin is generally a homopolymer of 2-acetamido-2-deoxy-d-glucose (n-acetylglucosamine)

1→4 linked in a β configuration; it is thus an amino sugar analog of cellulose. While it is widely
distributed in bacteria and fungi, the major source is crustaceans. In fact, chitin is the most abun-
dant organic skeletal component of invertebrates. It is believed to be the most widely distributed
polysaccharide with the Copepoda alone synthesizing on the order of 10 tons each year. It is an
9
important structural material often replacing cellulose in cell walls of lower plants. It is generally
found covalently bonded to protein. Invertebrate exoskeletons often contain chitin that provides
strength with some flexibility along with inorganic salts such as calcium carbonate that provide

strength. In a real sense this is a composite where the chitin holds together the calcium carbonate
domains.

O
O
CH
H HN 3 H HN CH 3
OH H H
OH H OH OH
H H
H O O H O H
H H O O H O R (9.22)
OH H H H
R H OH OH OH
O H
H HN
H HN
CH 3 CH
O 3
O
Chitin
Chitosan is produced from the deacetylation of chitin. Chitosan is employed in the food indus-
try. It is a hemostatic from which blood anticoagulants and antithrombogenic have been formed.
It is often sold as a body fat reducing agent or to be taken along with eating to encapsulate fat
particles.

H NH 2 H NH 2
OH H H
OH H OH OH
H H
H O O H O H
H H O O H O R
OH H H H
R H OH OH OH
O H
H NH
2 H NH 2
Chitosan (9.23)
Both chitosan and chitin are greatly underused readily available abundant materials that deserve
additional study as commercial materials and feedstocks. Chitin itself is not antigenic to human

9/14/2010 3:40:45 PM
K10478.indb 297 9/14/2010 3:40:45 PM
K10478.indb 297