Plausible molecular and crystal structures of chitosan/HI type II salt.
Chitosan/HI type II salt prepared from crab tendon was investigated by X-ray fiber diffraction. Two polymer chains and 16 iodide ions (I(-)) crystallized in a tetragonal unit cell with lattice parameters of a = b = 10.68(3), c (fiber axis) = 40.77(13) A, and a space group P4(1). Chitosan forms a fourfold helix with a 40.77 A fiber period having a disaccharide as the helical asymmetric unit. One of the O-3... O-5 intramolecular hydrogen bonds at the glycosidic linkage is weakened by interacting with iodide ions, which seems to cause the polymer to take the 4/1-helical symmetry rather than the extended 2/1-helix. The plausible orientations of two O-6 atoms in the helical asymmetric unit were found to be gt and gg. Two chains are running through at the corner and the center of the unit cell along the c-axis. They are linked by hydrogen bonds between N-21 and O-61 atoms. Two out of four independent iodide ions are packed between the corner chains while the other two are packed between the corner and center chains when viewing through the ab-plane. The crystal structure of the salt is stabilized by hydrogen bonds between these iodide ions and N-21, N-22, O-32, O-61, O-62 of the polymer chains.
Faculty of Technology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan.
Amornrat
A
Lertworasirikul
Keiichi
K
Noguchi
Kozo
K
Ogawa
Kenji
K
Okuyama
D000818:Animals; D003386:Brachyura / Q000737:chemistry; D002236:Carbohydrate Conformation; D002686:Chitin / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000145:classification* / Q000302:isolation & purification; D048271:Chitosan; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D007454:Iodides / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D016018:Least-Squares Analysis; D008958:Models, Molecular; D012492:Salts / Q000737:chemistry; D055672:Static Electricity; D013710:Tendons / Q000737:chemistry
D007454:Iodides; D007477:Ions; D012492:Salts; D002686:Chitin; D048271:Chitosan