Characterization of Uniaxially Aligned Chitin Film by 2D FT-IR Spectroscopy

Two-dimensional FT-IR spectroscopy (2D FT-IR) was applied to the investigations of crystalline chitin structure. From this study, new information about spectral bands which are not observed in conventional 1D FT-IR was obtained. In 2D spectra, three specific bands were differentiated at 3482, 3421, and 3380 cm-1 in the OH region. They could be assigned as C(6)OH groups which are hydrogen-bonded to the next C(6)OH; C(3)OH groups hydrogen-bonded to O(5); and C(6)OH groups bifurcated hydrogen-bonded to C(6)OH as well as CO, respectively. Two pairs of bands appeared in the amide region, indicating the two types of hydrogen-bonded states of CO groups. This is in good agreement with the results in the OH region; half of the C(6)OH groups are hydrogen-bonded to CO as well as the next C(6)OH. The results accurately confirmed the Blackwell model which was established by an X-ray diffraction study. The temperature-dependency of hydrogen-bonds was also revealed by 2D FT-IR. Interchain hydrogen-bonds [C(6)OH···O(6)] first respond to a temperature followed by intrachain [C(6)OH···OC] and [C(3)OH···O(5)] with increasing temperature. Interchain hydrogen-bonds [NH···OC] are relatively stable in the temperature range of 40−180 °C.