NMR Structural Characterization of Quercus alba (White Oak) Degraded by the Brown Rot Fungus, Laetiporus sulphureus

摘要

High resolution magic angle spinning (HRMAS) is utilized here to characterize the structure of solid lignin from Quercus alba (white oak) wood that has been biodegraded by the brown rot (BR) fungus Laetiporus sulphureus. The ground wood sample is swelled in deuterated solvent, allowing an enhanced molecular motion that is required for obtaining 2D HRMAS spectra. This technique provides for direct, non-invasive analysis of solid biodegraded lignin. Emphasis is placed on the characterization of the lignin side chains in an effort to elucidate the types of linkages connecting the various monomers. The HRMAS spectra obtained provide evidence for the presence of structures in this biodegraded lignin that have been commonly found in chemically extracted lignins and model compounds. This information supports the existence of several of the six major types of lignin linkages (β-O-4, β-5, β-1, 5-5,4-O-5, and β-β) as well as three other structures: dibenzodioxocin, isochroman, and spirodienone.