Characterization of hydroxyl groups of highly crystalline β-chitin under static tension detected by FT-IR

The different behavior of the OH groups of a highly crystalline β-chitin from Lamellibrachia sp. was revealed by FT-IR spectroscopy with static tension applied in the direction of the chain. Both OH groups shifted to higher wavenumbers under the tension, possibly because the force constant of the OH vibration intensified due to the erosion of hydrogen bonds, but the shift in the OH peak occurring at 3435 cm−1 was 14% greater than that of the peak at 3470 cm−1. The band at 3435 cm−1 was assigned to O(3)H and that at 3470 cm−1 to O(6)H, because the intramolecular hydrogen bond of O(3)H⋯O(5) occurs along the chitin chainʹs backbone and is likely to be more affected under tensile stress as a load carrier, than O(6)H⋯O(7)C, which is an intermolecular hydrogen bond located in a branch of the chain. Computation of an IR spectrum under stretching was conducted and supported the assignment of the two OH groups.