Solid-state spectroscopic analysis of lignins from several Austral hardwoods

In order to gain information about lignin molecular characteristics with a direct bearing on the remarkable susceptibility of some Austral hardwoods to biological delignification, milled-wood lignins were isolated and analyzed by spectroscopic techniques in the solid state. Cross polarization and magic-angle spinning 13C nuclear magnetic resonance (13C CPMAS NMR) and Fourier-transform infrared (FTIR) spectra of the lignin preparations were obtained. The most diagnostic peaks were assigned and quantified as percentages of the total spectral area, and the differences observed discussed in terms of lignin composition. The spectral patterns obtained revealed that the woods from Gevuina avellana, Eucryphia cordifolia and Nothofagus dombeyii have lignin with high syringyl/guaiacyl ratio, as evidenced by relative areas of 13C NMR signals at 153 and 148 ppm, and FTIR bands at 1,335 and 1,275 cm-1. The presence of syringyl-rich lignins, characterized by lower redox potential and condensation degree than guaiacyl-rich lignins, could be a structural factor contributing to the ease of extensive delignification of these woods by white-rot fungi.