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

Abstract

Abstract Summary: The structure and stability of hydrogen bonds in α ‐chitin were investigated by 13 C 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. 13 C CP/MAS NMR spectrum of chitin (A) and decomposed spectrum in the CO region (B). magnified image 13 C CP/MAS NMR spectrum of chitin (A) and decomposed spectrum in the CO region (B).