Direct Determination of the Hydrogen Bonding Arrangement in Anhydrous β-Chitin by Neutron Fiber Diffraction

摘要

The hydrogen bonding arrangement in anhydrous fj-chitin, a homopolymer of N-acetylglucosamine, was directly determined by neutron fiber diffraction. Data were collected from a sample prepared from the bathophilous tubeworm Lamellibmchia satsutna in which all labile hydrogen atoms had been replaced by deuterium. Initial positions of deuterium atoms on hydroxyl and acetamide groups were directly located in Fourier maps synthesized using phases calculated from the X-ray structure and amplitudes measured from the neutron data. The hydrogen bond arrangement in tile refined structure is in general agreement with predictions based on the X-ray structure: 03 donates ahydrogen bond to the OS ring oxygen atom of a neighboring residue in the same chain; N2 and 06 donate hydrogen bonds to the same carbonyl oxygen 07 of an adjacent chain. The intramolecular O3···O5 hydrogen bond has the most energetically favorable.geometry with a hydrogen to acceptor distance of 1.77 A and a hydrogen bond angle of 171°.