STRUCTURE ANALYSIS OF HYDRATED CHITOSAN BY UTILIZING IMAGING PLATE. By K. Okuyama, K. Suzuki, Y. Obata, T. Yui* and K. Ogawa**, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184, Japan, *Miyazaki University, Miyazaki 889-21, Japan and **University of Osaka Prefecture, Sakai, Osaka 593, Japan.

The molecular and crystal structure of the hydrated chitosan derived by deacetylation of chitin tendon was determined by the X-ray diffraction method and a linked-atom least-squares technique. The X-ray intensities were measured using the imaging plate. The data processing and structure analysis were done using an inhouse software developed recently (Okuyama, K., Obata, Y., Noguchi, K., Kusaba, T., Ito Y. and Ohno, S., Biopolymers, 1996, 38, in press.). The crystals of the polymer chains belong to the orthorhombic system, space group P2₁2₁2₁ with a=8.91(4), b=16.87(6) and c (fiber axis) =10.34(4)Å. The unit cell contains eight monomer residues and eight water molecules. Since the polymer chain has a 2₁-helical symmetry, four chains are included in a cell.

The molecular chain is stabilized by an intramolecular O3---O5 hydrogen bond similar to those found in many [[beta]](1'4) linked polysaccharides and has a gt conformation for the hydroxymethyl moiety at C5 atom. Polymer chains arranged in an antiparallel fashion are connected by an intermolecular NH---O6 hydrogen bond and a hydrogen bond bridge through water molecule, making a sheet structure along the b-axis. These sheets are stacked along the a-axis and are connected by hydrogen bond bridges through the second water molecule. The final X-ray residuals are R=0.185 and R"=0.194.

In the crystal structure of anhydrous form of chitosan (Yui, T., Imada, K., Okuyama, K., Obata, Y., Suzuki K. and Ogawa, K., Macromolecules, 1994, 27, 7601), parallel chains make a sheet structure by an intermolecular NH---O6 hydrogen bond. Therefore, the transition from the hydrous to the anhydrous form needs cleavage of the NH---O6 hydrogen bond between antiparallel molecular chains and the formation of the new NH---O6 bond between parallel polymer chains.