Structure of beta-chitin or parallel chain systems of poly-beta-(1-4)-N-acetyl-D-glucosamine

The structure of β-chitin has been reexamined in an X -ray diffraction study of the highly crystalline material available from pogonophore tubes. Oriented specimens were prepared by suspending the dispersed deproteinized tube in a fibrin clot which was then stretched into an oriented fiber. The X -ray diffraction patterns of pogonophore β-chitin were explained by proposing that this material consists of a mixture of two structural phases which have been named β-chitins A and B. This view was confirmed by the preparation of specimens which gave only the diffraction pattern of the A phase by treating the tubes with diaphanol. Both A and B phases gave rise to a series of hydrate structures. The lowest hydrate of β-chitin A has been studied in detail and shown to consist of an anhydrous system of parallel chitin chains. For this form, the unit cell was monoclinic with dimensions a = 4.85 Å, b = 10.38 Å (fiber axis), c = 9.26 Å, and β = 97.5°, and space group P2₁. Reasonable agreement was obtained between the observed X -ray intensities and those calculated for such a structure. Examination of the β-chitin of Loligo pen and diatom spines showed that these materials also consist of these A and B phases.