Fig. 1. Solid-state NMR resolves the polymorphic structure of polysaccharides using intact wood cells.

a Representative structures of cellulose and major types of hemicellulose (xylan and galactoglucomannan). The cross-section of an elementary cellulose microfibril is shown, with a close view of an individual glucan chain and the hydroxymethyl conformation of surface (gauche-trans, gt) and internal (trans-gauche, tg) glucan chains. Xylan has two-fold or three-fold helical screw conformation in the backbone (Xn^2f and Xn^3f), with glucuronic acid (GlcA) or arabinose (Ara or A) sidechains. Acetyl motifs (Ac) are present in hemicelluloses. b Representative 2D ¹³C J-INADEQUATE spectrum of eucalyptus, which is based on ¹³C cross polarization selecting rigid molecules. Dash lines track the carbon connectivity of xylan conformers. The NMR abbreviations of the carbohydrates are given. c A model of three elementary cellulose microfibrils fitting the NMR observables. The hydrophilic (s^f) and hydrophobic (s^g) surfaces, the embedded chains (i^c), and the middle layer (i^a,b) are color-coded. d Carbon-4 regions measured using ¹³C direct polarization (orange spectra selecting mobile molecules) and cross polarization (gray spectra selecting rigid molecules). Both two- and three-fold xylan backbones are rigid while arabinose is mobile. e Arabinose carbon-1 and carbon-2 regions. The only rigid arabinose is the terminal one in xylan sidechain. f Eucalyptus has a high content of GlcA and spruce is rich in acetylated or non-acetylated mannose (M^Ac or M). g Composition of the rigid molecules in cell walls determined by peak volumes from 2D spectra. Source data are provided as a Source Data file.