Artificial Chitin Spherulites Composed of Single Crystalline Ribbons of α-Chitin via Enzymatic Polymerization

Abstract

A crystalline product of artificial chitin by chitinase-catalyzed polymerization of a chitobiose oxazoline derivative was investigated by using optical microscopy in combination with TEM and SEM techniques. Platelike single crystals of α-chitin were first formed. The crystals were gradually shaped into ribbons by the rapid growth along the a axis with the crystalline thickness being ca. 10 nm. The α-chitin ribbons then aggregated to form bundlelike or dendritic assemblies as the ribbon concentration in solution increased. They grew into spherulites by splaying and branching, which displayed birefringence with a Maltese cross by polarization microscopic observation. The present artificial chitin spherulite, in which a number of α-chitin ribbons radiated from a common center, is completely different from the helicoidal textures composed of α-chitin microfibrils which have been known so far as a typical three-dimensional organization of chitin.