Chitin is a large water-insoluble, linear aminocarbohydrate homopolymer composed of P^-linked N-acetyl-D-glu-cosamine units with a three-dimentional a-helix configuration (Fig. J). Intramolecular hydrogen bondings stabilize the a-helical configuration of the macromolecule. In nature, chitin polymers coalesce extracellularly by intermolecular hydrogen bonds to form crystalline microfibrils that may appear in various polymorphs (a, P, and y). The most abundant one in insects is the antiparallel arrangement of the a-chitin polymorph.

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