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

Abstract

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, noninvasive 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.

Peculiarities of brown-rot fungi and biochemical Fenton reaction with regard to their potential as a model for bioprocessing biomass

“…Several similarities have been observed between brown-rotted lignin and lignin remaining after attack by biomimetic ⋅OH-producing Fenton reactions (Arantes et al 2009aArantes and Milagres 2006b;Gierer 1997;Gierer et al 1992). The demethylation or formation of phenolic groups in lignin through the cleavage of arylether bonds is considered the major initial reaction by brown-rot fungi (Eriksson et al 1990;Kirk and Adler 1970;Koenig et al 2010;Martinez et al 2011;Yelle et al 2008Yelle et al , 2011. Hydroxyl radicals generated through biomimetic brown-rot Fenton chemistry could similarly lead to substantial lignin demethylation in softwood (Arantes et al 2009a.…”

“…Brown-rotted lignins have been found to undergo extensive oxidative demethylation (Filley et al 2002;Kirk 1975;Kirk and Adler 1970;Yelle et al 2011), as well as significant side chain oxidation (Kirk and Adler 1970;Koenig et al 2010;Martinez et al 2011), depolymerization (Agosin et al 1989), and potentially repolymerization (Arantes et al 2009aKleman-Leyer et al 1992;Highley and Dashek 1998;Yelle et al 2008Yelle et al , 2011 (Fig. 5).…”

“…More recent research suggests that brown-rot fungi have a greater ligninolytic capability (Arantes et al 2009aYelle et al 2008Yelle et al , 2011Martinez et al 2011) than previously thought (Agosin et al 1989;Eriksson et al 1990). Although brown-rot fungi do not remove lignin to an appreciable extent (Cowling 1961;Koenig et al 2010;Martinez et al 2011), and the residual modified lignin retains most of its original aromatic residues (Yelle et al 2008) and several of the major types of lignin linkages (Koenig et al 2010;Martinez et al 2011), brown-rotted softwood lignin (Filley et al 2002;Yelle et al 2008) and hardwood lignin (Koenig et al 2010) residues have been shown to be highly modified (Fig. 3).…”

“…5). Other significant alterations are limited aromatic ring cleavage (Kirk and Adler 1970), hydroxylation of aromatic rings (Kirk and Adler 1970), C β -ether cleavage (Yelle et al 2011), partial side chains hydroxylation (Koenig et al 2010), formation of new aryl-O-aryl ether (Martinez et al 2011), and aryl-aryl or side-chain (Yelle et al 2008) linkages. In spite of all these alterations, brown-rotted lignin is still polymeric (Agosin et al 1989;Jin et al 1990;Kirk 1975), which may explain why earlier studies concluded that brown-rot fungi only slightly modified lignin without degrading it significantly (Agosin et al 1989;Eriksson et al 1990;Jin et al 1990;Irbe et al 2011;Kirk 1975).…”

Mode of action of brown rot decay resistance in modified wood: a review

“…Brown rot fungi circumvent lignin mineralization and degrade the polysaccharides in a straightforward manner (Koenig et al 2010;Martinez et al 2011). Lignins maintain their macromolecular nature throughout brown rot decay (Kirk 1975;Niemenmaa et al 2008;Yelle et al 2008), but their structure is modified substantially by hydroxyl radicals (Yelle et al 2008(Yelle et al , 2011Arantes et al 2009Arantes et al , 2011Martinez et al 2011).…”