CHARACTERIZATION OF MILLED WOOD LIGNIN FROM REED CANARY GRASS (PHALARIS-ARUNDINACEA)

Lignin samples from reed canary grass (Phalaris arundinacea) were prep ared by milling in the dry state (MWL) or in toluene (TMWL). Further, enzymatically liberated lignin (EL) was prepared From the dioxane-wate r insoluble residue from the preparation of MWL. The NMR spectra of th e lignin preparations revealed the presence of both guaincyl and syrin gyl units, as well as p-hydroxyphenyl structures. The most prominent s ide chain linkages were identified using HMQC. In the C-13 NMR and FTI R spectra signals typical for p-coumaric esters could be observed. Per manganate oxidation revealed that some of the p-hydroxyphenyl structur es were incorporated in the lignin, together with guaiacyl and syringy l units. The lignin preparations had very similar molecular weight dis tributions and structural composition. These lignin preparations are d istinguished by high amounts of beta-O-4 structures and by low amounts of phenolic hydroxyls, resinol units (beta-beta) and of condensed uni ts (beta-5 and 5-5). This trait was even more pronounced in an ether s oluble fraction of the MWL that contained almost exclusively ide chain linkages of the beta-O-4 type. This difference in distribution of str uctural units indicates some structural heterogeneity in reed canary g rass lignin.