FIGURE 1.

Representative structures and NMR signals of chitin. (A) Substitutions at the C2 position for chitin and chitosan. (B) Polymorphic types (α, β, and γ) of chitin showing different chain orientations. Black marks denote the non-reducing ends of chains. (C) Hydrogen-bonding patterns of different chitin allomorphs. Blue and red dash lines indicate intra-chain and inter-chain hydrogen bonds, respectively. The antiparallel chains in α and γ chitins are in grey. The hydroxyl at C3 is not shown to make the structure less complex. The structural schemes are adapted from (Rudall, 1963; Kameda et al., 2005; Sawada et al., 2012a). (D) 2D ¹³C-¹³C correlation spectra simulated using literature-reported chemical shifts on model samples (Supplementary Table S2). Representative C4-2 and C3/5-2 regions were shown for single-quantum (SQ)-SQ correlation spectra. The C4 and C5 region is also shown for a double-quantum (DQ)-SQ correlation spectrum. α, β, and γ are represented in red, yellow, and blue respectively. Contour lines represent the number of data sets used (and the number of overlapped peaks).