Structure of β‐chitin or parallel chain systems of poly‐β‐(1→4)‐N‐acetyl‐D‐glucosamine

Abstract

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.