X-ray Study of Chitosan l- and d-Ascorbates

Abstract

Well-defined X-ray fiber patterns of l- and d-ascorbates of chitosan were obtained by immersing a tendon chitosan, prepared from a crab tendon chitin by a solid-state N-deacetylation, in respective ascorbic acid water−isopropyl alcohol solutions, and heating them at 70 °C. The crystalline unit cell of the l-ascorbate of chitosan was a monoclinic (pseudoorthorhombic) with the following dimensions: a = 1.122; b = 1.177; c (fiber axis) = 1.040 nm; and β = 90°. The presence of a P21 space group with b axis unique was suggested. The visible reflections on the fiber diagram of the chitosan d-ascorbate could be indexed in terms of a monoclinic unit cell with a = 0.962, b = 1.349, c (fiber axis) = 1.030 nm, and γ = 96.7°; no space group could be assigned, however. Although no 21 symmetry is present along the fiber axes in these crystals, the similarity of both fiber axes to that of the unreacted chitosan (1.043 nm) suggested that the extended 2-fold helical conformation of chitosan is retained in the backbone ch...