Hydrogen-bonding network in anhydrous chitosan from neutron crystallography and periodic density functional theory calculations

Abstract

The hydrogen-bonding network in anhydrous chitosan crystal was studied using a combination of neutron crystallography and quantum chemical calculation. The locations of the hydroxyl hydrogen were directly resolved using Fourier omit maps applied to neutron diffraction data, whereas the amino hydrogen atoms were determined based on geometrical optimization using periodic density functional theory (DFT) calculation. Energy optimization of the hydrogen positions based on DFT calculation allowed the measurement of the hydrogen-bond energies. In the chitosan crystal, the hydroxyl groups mostly play a role as hydrogen-bond donors while the amino moiety behaves as a strong acceptor but a poor donor.