の総数の 3-4 倍の実測回折点が必要である．(たと えば，等方性温度因子 B を仮定した場合，N 個の原子に 対して決定すべきパラメーター総数は凡そ 4N (つまり * 1 豊田工業大学大学院工学研究科極限材料専攻 (〠 468-8511 名古屋市天白区久方 2-12-1) * 2 茨城大学工学部生体分子機能工学科 (〠 316-8511 日立市 中成沢町 4-12-1) * 3 総合科学研究機構 (CROSS) 東海事業センター (〠 319-1106 茨城県那珂郡東海村白方 162-1) * 4 日本原子力研究開発機構量子ビーム応用部門 (〠 319-1106 茨城県那珂郡東海村白方 2-4) * 5 クラレ (株) くらしき研究センター (〠 710-1801 倉敷市酒 津 2045-1) * 6 名古屋大学大学院工学研究科科学・生物工学専攻 (〠 464-8603 名古屋市千種区不老町) * 7 日本大学文理学部化学科 (〠 156-8550 東京都世田谷区桜 上水 3-25-40)

The crystal structure of polydiacetylene giant single crystal has been analyzed on the basis of the two different methods of wide-angle neutron diffraction and X-ray diffraction. The X-ray result gives us the total electron density distribution [ρ(x)] of polymer chain. The neutron result tells the positions of atomic nuclei, which can allow us to speculate the electron density distributions [ρ 0(x)] around the nonbonded isolated atoms. As a result, the so-called bonded (or deformed) electron density Δρ­(x) [≡ ρ­(x) – ρ0(x) = ρX(x) – ρN(x)], i.e., the electron density distribution due to the conjugation among the covalently bonded atoms along the polymer chain, can be estimated using the two information obtained by the X-ray and neutron data analyses (the so-called X-ray–neutron subtraction (X–N) method). The present report is the first example of the application of X–N method to the synthetic polymer species. The Δρ­(x) derived for polydiacetylene was found similar to that of the low-molecular-weight model compound having the similar electronically conjugated chemical formula. The Δρ­(x) was calculated by the density functional theory, which was in a good agreement with the experimental result qualitatively.

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In order to elucidate the intermolecular interactions involved in complex formation of chitosan with hydrogen halides, crystal structures of chitosan complexes with HBr and HI were analyzed based on synchrotron X-ray fiber diffraction data (BL40B2, SPring-8, Hyogo, Japan). Both crystals are isomorphous and belong to the monoclinic space group P21. The unit cell constants are a = 9.299(9), b = 9.504(8), c(fiber axis) = 10.41(1) Å and beta = 106.93(8) deg, and a = 9.46(2), b = 9.79(2), c(fiber axis) = 10.33(2) Å and beta = 105.1(2) deg for HBr and HI complexes, respectively. The final packing models were obtained by the linked-atom least-squares refinement, which gave R-factors of 0.192 for HBr complex (93 observed spots) and 0.193 for HI complex (44 observed spots). The halide ions are aligned along the c-axis at intervals of about 5Å and are surrounded by four polymer chains. In an asymmetric unit, there are two halide ions. One ion accepts three hydrogen bonds from NH3 + groups (N2 nitrogen). The other one participates in one hydrogen bond from N2 and two hydrogen bonds from primary hydroxyl groups (O6 oxygen). In addition, the chitosan chains are linked by N-H...O and C-H...O hydrogen bonds along the b-axis direction. The crystal structure of the hydrated form of chitosan was reanalyzed using synchrotron X-ray fiber diffraction data (BL38B1, SPring-8). The chitosan chains make sheet structures parallel to the bc-plane and these sheets stack along the a-axis. Water molecules form columns between these sheets. The sites of the halide ions in the complex crystals are similar to those of the water molecules in the hydrated form. It was suggested that the columnar structure of water in the hydrated form plays an important role for the complex formation.