Chemistry Reference
In-Depth Information
Figure 12.2
Hydrogen bonding in
- chitin. Two
types of hydrogen bonds (shown in gray) in-
volve the carbonyl groups (top left), those
which form exclusively intermolecular hydrogen
bonds (1) and a mixture of inter- and intra-
molecular hydrogen bonds (2). In
α
- chitin the
hydrogen bonds are frequently formed with in-
tercalating water molecules.
β
lecular hydrogen bonds [7]. Therefore,
- chitin. Upon
hydration water molecules can intercalate to a greater extent resulting in intracrys-
talline swelling [8]. While the diffraction patterns of
β
-chitin is less stable than
α
- chitin are well docu-
mented, and the deduced structures are widely accepted, the precise nature of
α
- and
β
γ
-chitin is still unsure because of the unusual nature of the raw material (that is,
stomach linings of squids, beetle cocoons and some insect peritrophic matrices).
Based on X-ray diffraction patterns obtained for stomach cuticles from the sepia
Loligo
, Rudall suggested that
-chitin is made of sets of two parallel strands that
alternate with single antiparallel strands [9] .
γ
12.3
Function
Chitin is used a structural component of many biological composites, which may
be divided into three categories depending on whether they contain predominately
proteins (arthropod cuticles, peritrophic matrices, cocoons), carbon hydrates
(fungal cell walls) or inorganic minerals (squid pens, cuttlebones, crustacean
shells, diatom spines). In many cases chitin function is similar to that of a steel
lattice in reinforced concrete, which makes the skeletal structures remarkably
tough and durable (see also Table 12.1). In the following we will look at several
chitinous structures found in Nature to provide closer insights into chitin
function.
