title: Revisit of alpha-chitin crystal structure using high resolution X-ray diffraction data.
abstract: High resolution synchrotron X-ray fiber diffraction data recorded from crab tendon chitin have been used to describe the crystal structure of alpha-chitin. Crystal structures at 100 and 300 K have been solved using restrained crystallographic refinement against diffraction intensities measured from the fiber diffraction patterns. The unit cell contains two polymer chains in a 2(1) helix conformation and in the antiparallel orientation. The best agreement between predicated and observed X-ray diffraction intensities is obtained for a model that includes two distinctive conformations of C6-O6 hydroxymethl group. Those conformations are different from what is proposed in the generally accepted alpha-chitin crystal structure (J. Mol. Biol. 1978, 120, 167-181). Based on refined positions of the O6 atoms, a network of hydrogen bonds involving O6 is proposed. This network of hydrogen bonds can explain the main features of the polarized FTIR spectra of alpha-chitin and sheds some light on the origin of splitting of the amide I band observed on alpha-chitin IR spectra.
authors.affiliation: Department of Physics, Norwegian University of Science and Technology, Trondheim NO-7491, Norway. pawel.sikorski@phys.ntnu.no
authors.forename: Pawel
authors.initials: P
authors.lastname: Sikorski
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Hori
authors.forename: Masahisa
authors.initials: M
authors.lastname: Wada