Comparison of Experimental and Theoretical Data on the Structural and Electronic Characterization of Chitin and Chitosan

Structural characterization of powdered samples of β-chitin and chitosan is reported. β-chitin extracted from squid pens (Doryteuthis spp.) and chitosan produced by submitting beta-chitin to high intensity ultrasonication while suspended in 40% aqueous sodium hydroxide (NaOH). The samples were analyzed by field emission scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and nuclear magnetic resonance spectroscopy. Targeting a better understanding of the experimental data, the repeating units occurring predominantly in chitin (2-acetamido-2-deoxy-D-glycopiranose) and chitosan (2- amino-2-deoxy-D-glycopiranose) were adopted as model systems to study their physical and chemical properties by means of Kohn–Sham density functional theory and time-dependent density functional theory calculations using B3LYP hybrid XC functional with the 6-31+G(d, p) basis set. A fundamental understanding of the structure and electronic properties of chitin and chitosan at the atomic scale is required for the future development of new technologies based on these biopolymers.