title: Understanding the degree of condensation of phenolic and etherified C-9 units of in situ lignins.
abstract: A novel approach for the quantification of the degree of condensation at the C(5) position of etherified and phenolic phenylpropane (C-9) units of in situ lignin is described. This is achieved by degrading unmethylated and methylated wood by thioacidolysis and analyzing the resultant product mixtures by quantitative (31)P NMR spectroscopy. Applying this new method to compression wood and normal wood from  Pinus radiata  showed that, whereas 41-47% of etherified guaiacyl C-9 units are condensed at the C(5) position, almost all phenolic guaiacyl C-9 units exist as uncondensed moieties. Analysis of milled wood lignin (MWL) isolated from the same wood by (31)P NMR spectroscopy before and after thioacidolysis showed that the phenolic guaiacyl C-9 units were more condensed than those in the in situ lignin. This is likely due to partial cleavage of the more condensed etherified linkages during the lignin isolation, leading to a relative increase in condensed phenolic guaiacyl C-9 units.
authors: Department of Chemistry, The University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand. bernadette.nanayakkara@scionresearch.com
authors: Bernadette
authors: B
authors: Nanayakkara
authors: Merilyn
authors: M
authors: Manley-Harris
authors: Ian D
authors: ID
authors: Suckling
mesh_terms: D004987:Ethers / Q000737:chemistry*; D008031:Lignin / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008745:Methylation; D010636:Phenols / Q000737:chemistry*; D028223:Pinus; D014934:Wood / Q000737:chemistry
chemical_list: D004987:Ethers; D010636:Phenols; D008031:Lignin