Infrared study on deuteration of highly-crystalline chitin

We report an infrared study of the deuteration of highly crystalline α- and β-chitin. With exposure to D2O vapor, the deuteration of α-chitin progressed on surface molecules, in contrast with β-chitin, which is partially deuterated on the inner part of the crystal. The intracrystalline deuteration occurred with high-temperature annealing in liquid D2O for α- and β-chitin. In α-chitin, the deuteration was similar between all the three functional groups. The ratio of deuterium/hydrogen increased with treatment temperature, and all the hydrogen in the functional groups was accessible above 200 °C. In β-chitin, the deuteration was more specific for each functional group. The deuteration of O3-H groups progressed rapidly, even below 100 °C, and, by contrast, that of O6-H and N-H progressed relatively slowly. These differences of deuteration between α- and β-chitin presumably arises from the particular ability of β-chitin to form a complex with water molecules.