(5) Chitin structure in the solid state
1. Chitin occurs as two allomorphs : the α the β forms
① α-Chitin is by far the most abundant : fungal and yeast cell walls, krill, lobster, crab tendons, shells,
shrimp shells, and insect cuticle
② It is also found in various marine living organisms harpoons of cone snails, oral grasping spine of
Sagitta and the filaments ejected by the seaweed Phaeocystis, etc.
2. α-Chitin systematically results from recrystallization from solution, in vitro biosynthesis or enzymatic
polymerization
3. β-Chitin is found in association with proteins in squid pens and in the tubes synthesized by
pogonophoran and vestimetiferan worms, aphrodite chaetae, lorica built by some seaweeds or protozoa
- Pure form of β-chitin is found in the monocrystalline spines excreted by the diatom
Thalassiosira fluviatilis
- It has not been possible to obtain β-chitin either from solution or by in vitro biosynthesis
(6) Chitosan structure and characterization
1. Chitosan is a semicrystalline polymer
2. Sponges, powders and fibers can be obtained by regeneration of chitosan or its derivatives from solutions
(7) Physical and chemical characterization
1. Cellulose is a homopolymer
2. Chitin and chitosan are heteropolymers
3. Glycol chitin, a partially O-hydroxyethylated chitin, was the first derivative of practical importance