Fig. 2: Structural analysis of chitin and chitosan in R. delemar.

a 2D ¹⁵N-¹³C N(CA)CX spectrum of R. delemar showing correlations between the carbon sites with amide (-NH-) and amine (-NH₂) nitrogen sites in chitin and chitosan, respectively. The absence of methyl (CH₃) and carbonyl (CO) motifs in chitosan is highlighted using a dashed line circle. A 2D ¹H-¹⁵N HETCOR spectrum is presented in the rigid panel, with the spectrum rotated by 90 degrees to align the amide and amine signals with the chitin and chitosan signals observed in the N(CA)CX spectrum. b 2D hNH spectra of R. delemar acquired using short (cyan; 0.2 ms) and long (orange; 2.0 ms) CP contact times. The asterisk denotes a long-range cross peak between -NH₂ nitrogen and -NH proton. c Overlay of 2D hChH the spectrum (yellow) of R. delemar measured with 1.67 ms RFDR mixing and a 2D hCH spectrum (black). The hChH spectrum reveals long-range ¹³C-¹H cross-peaks between chitin and chitosan carbons and chitin amide proton (H^N). d Illustration of chitin-chitosan interactions observed in the spectrum. All spectra of panels (a) and (b) were acquired on an 800 MHz NMR spectrometer, and spectra in panel (c) were measured on a 600 MHz NMR spectrometer. The MAS frequency is 60 kHz for hCH, hNH, and hChH spectra and 13.5 kHz for the ¹H-¹⁵N HETCOR spectrum.