Hydrogen Bonding Structure and Stability of α‐Chitin Studied by 13C Solid‐State NMR

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Abstract
Summary: The structure and stability of hydrogen bonds in α‐chitin were investigated by 13C solid‐state NMR measurements at different temperatures. Splitting of the carbonyl carbon signal for α‐chitin was interpreted as two types of hydrogen bonding; the peaks at 173.5 and 175.8 ppm were assigned, respectively, to a carbonyl carbon hydrogen bonded exclusively to the NH group and a carbonyl carbon hydrogen‐bonded to both NH and C(6)OH groups. Approximately 60% of carbonyl groups exclusively contributed to the intermolecular hydrogen bonding and ca. 40% of them to the combination of intermolecular and intramolecular hydrogen bonding. Internal rotation around the C(5)–C(6) bond was detected at 55 °C. 13C CP/MAS NMR spectrum of chitin (A) and decomposed spectrum in the CO region (B). magnified image 13C CP/MAS NMR spectrum of chitin (A) and decomposed spectrum in the CO region (B).