Fig. 3. DNP-assisted detection of long-range interactions defines lignin–carbohydrate packing.

a Overlay of long-range (1.0 s mixing; grey) and short-range (0.1 s mixing; orange) 2D ¹³C-¹³C correlation spectra. The long- and short-range spectra showed similar spectral patterns in spruce: softwood polymers are homogeneously mixed on the molecular level. b Dipolar-gated 2D ¹³C-¹³C correlation spectra showing 98 intermolecular cross peaks in eucalyptus. c Summary of 272 intermolecular interactions identified in eucalyptus, poplar, and spruce. Cellulose, lignin, mannan, and mixed sugars are color-coded in red orange, light green, light orange, and purplre, respectively. Source data are provided as a Source Data file. d The count of lignin–lignin, cellulose–lignin, and xylan–lignin interactions in eucalyptus, poplar, spruce, Arabidopsis, and grasses (maize, rice, and switchgrass). Lignin–cellulose interactions are scarce in Arabidopsis and grasses but become abundant in woods. Source data are provided as a Source Data file. e DNP enhancing NMR sensitivity of eucalyptus by 24-fold. Inset shows a picture of the plant material in a sapphire DNP-NMR rotor. f Comparison of the equilibrium spectrum (bottom) of eucalyptus that detects all components with the aromatic-edited spectrum (top) that only shows lignin-bound molecules. The lignin-bound polysaccharides include the two-fold, three-fold, and mixed conformers of xylan as well as the surface and interior cellulose. The deeply embedded glucan chains in cellulose (i^c) are absent as highlighted using the dash line circle. g DFT energy-minimized structures showing the possible packing between lignin units and polysaccharides.