Chemistry Reference
In-Depth Information
Info Box 1
Chitin was fi rst isolated from mushrooms in 1811 by Henry Braconnot (1781-
1855), a plant chemist and Director of the botanical garden of Nancy (France),
and therefore originally termed 'fungine'. While analyzing the alkali-resistant
fraction, Braconnot recognized that 'fungine' was different from woody materi-
als, as it contained much more nitrogen than wood. Later on, in 1823, Augustus
Odier isolated the same substance from the cuticles of beetles. He coined the
term ' chitin ' from the Greek word '
chiton
' meaning tunic or envelope. However,
Odier originally believed that his chitin preparation did not contain any nitro-
gen, which fi nally would turn out to be an error of measurement. Rather, he
thought that insect cuticles were made of the same substance that forms the
cell walls of the plants (that is cellulose). The controversy on the differences
between chitin and cellulose continued for quite a while until 1875, when
Georg Ledderhose (1855-1925), a German student, later physician, treated
lobster shells with hot concentrated hydrochloric acid (see also Chapter 1 ). After
evaporating the solution characteristic crystals remained, which contained
acetate and a novel nitrogen-containing sugar named glucosamine. As acetate
and glucosamine were formed in equimolar amounts, it became clear that
chitin consists of acetylated glucosamine and hence it was different from cel-
lulose. Already, in 1859, Charles Rouget had tested different conditions to bring
chitin into solution and found that unlike chitin the substance obtained after
the treatment with potassium hydroxide dissolved in acids. The resulting com-
pound was later named chitosan by Felix Hoppe- Seyler.
12.1
Occurrence
Chitin is widely distributed among living creatures and is detected in a striking
variety of taxonomic groups ([2] , see also Table 12.1). Next to its well-documented
presence in the cell walls of fungi and in the shells and cuticles of arthropods, it
is also found in the cyst walls of protists, in the calyces of sponges, in the egg
shells from rotifers and nematodes, in oocytes, cocoons and peritrophic matrices
of insects, in squid pens and cuttlefi sh bones, in the shells from brachiopods and
mollusks, and in the radulae of mollusks. Less known is its presence in chordates
such as tunicates, where it is a component of the test and the peritrophic matrix,
and in a few lower vertebrates, as chitin has been detected in the cuticles of pectoral
fi ns from certain bony fi shes. However, it seems as if the ability to produce chitin
has been lost at the root of the deuterostome lineage. In higher deuterostomes,
chitin appears to be replaced either by other sugar polymers, such as hyaluronan
and chondroitin, or by proteinous polymers, such as collagen or keratin. From a
