Abstract
Parallel chain system for the structure of β-chitin is studied from a stereochemical point of view and the structure has been refined by least squares procedures. As a first step correct atomic positions representing standard configuration of glucopyranose ring, peptide unit and CH
OH group have been redetermined in the unit cell. The unit cell is monoclinic with dimensions a = 4.85 Å, b = 10.38 Å (fibre axis), c = 9.26 Å and β = 97.5°. The space group is P2
. The refinement has been done using five geometrical parameters, temperatur factor and the scaling factor. The R and Ø-value are found to be 0.235 and 37.61, respectively. The refined structure is found to be free from all short contacts. The refined chains form interhydrogen bond of the type N - H · · · O
= C
and intrahydrogen bond of the type O
- H · · · O
. The present calculations suggest that an intra-sheet O
-H - O
hydrogen bond cannot be formed in the present structure. This behaviour will certainly explain the different properties of β-chitin having less number of hydrogen bonds as compared to a-chitin.