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The molecular and crystal structure of the hydrated form of chitosan, which was obtained by deacetylation of chitin from crab tendon, was determined by the X-ray fiber diffraction method and the linked-atom least-squares method. The chitosan chains crystallize in an orthorhombic unit cell with dimensions a = 8.95(4), b = 16.97(6), c (fiber axis) = 10.34(4) Å and a space group P212121. The chain conformation is a 2-fold helix stabilized by O3---O5 hydrogen bond with the gt orientation of O6. The unit cell contains four chains and eight water molecules. There are direct hydrogen bonds (N2---O6) between adjacent chains along the b-axis, which makes a sheet structure parallel to the bc-plane. These sheets stack along the a-axis. Each sheet is related to its neighboring sheet by 21-symmetry along the b-axis. Water molecules form columns between these sheets and contribute to stabilize the structure by making water-bridges between polymer chains.

The highly enantioselective synthesis of helically chiral 1,1'-bitriphenylenes has been achieved via rhodium-catalyzed double [2 + 2 + 2] cycloaddition of biaryl-linked tetraynes with 1,4-diynes (up to 93% ee). Crystal structures and photophysical properties of these helically chiral 1,1'-bitriphenylenes have also been studied.

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Triple-helical structures of (Pro-Hyp-Gly)n (n = 10, 11) at 100 K and room temperature (RT) were analyzed at 1.26 A resolution by using synchrotron radiation data. Totals of 49 and 42 water molecules per seven triplets in an asymmetric unit were found for the structures at 100 K and RT, respectively. These water molecules were classified into two groups, those in the first and second hydration shells. Although there was no significant difference between water molecules in the first shell at 100 K and those at RT, a significant difference between those in the second shell was observed. That is, the number of water molecules at RT decreased to one half and the average distance from peptide chains at RT became longer by about 0.3 A. On the other hand, of seven triplets in an asymmetric unit, three proline residues at the X position at 100 K clearly showed an up-puckering conformation, as opposed to the recent propensity-based hypothesis for the stabilization and destabilization of triple-helical structures by proline hydroxylation. This puckering was attributed to the interaction between proline rings and the surrounding water molecules at 100 K, which is much weaker at RT, as shown by longer average distance from peptide chains.