Infrared study on deuteration of highly-crystalline chitin

► Deuteration of α- and β-chitin was conducted using vapor and liquid D2O. ► Intracrystalline deuteration of the polymers was achieved using annealing. ► The deuteration among the three functional groups of α-chitin was similar. ► The deuteration of β-chitin was more specific for each functional group. ► We propose geometric states for each functional group in the hydrated β-chitin.