X-RAY STUDY OF CHITOSAN L-ASCORBATES AND D-ASCORBATES

Well-defined X-ray fiber patterns of L- and D-ascorbates of chitosan w ere obtained by immersing a tendon chitosan, prepared from a crab tend on chitin by a solid-state N-deacetylation, in respective ascorbic aci d water-isopropyl alcohol solutions, and heating them at 70 degrees C. The crystalline unit cell of the L-ascorbate of chitosan was a monocl inic (pseudoorthorhombic) with the following dimensions: a = 1.122; b = 1.177; c (fiber axis) = 1.040 nm; and beta = 90 degrees. The presenc e of a P2(1) 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 gamma = 96.7 degrees; no space group c ould be assigned, however. Although no 2(1) 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 c hitosan chain of each ascorbate. The observed density values of both a scorbates suggested that two chitosan chains, but no water molecule ar e present in each unit cell of L- and D-ascorbates. It was suggested d uring the preparation of respective L- and D-ascorbate of chitosan tha t D-ascorbic acid has a higher reactivity with chitosan to make the sa lt than the L isomer has.