Journal
HOLZFORSCHUNG
Volume 62, Issue 5, Pages 514-526Publisher
WALTER DE GRUYTER & CO
DOI: 10.1515/HF.2008.096
Keywords
2D-NMR; desulfuration; dimers; eucalypt wood; Eucalyptus dunnii; Eucalyptus globulus; Eucalyptus grandis; Eucalyptus maidenii; Eucalyptus nitens; heteronuclear single quantum correlation (HSQC); milledwood lignin (MWL); pyrolysis-GC/MS; thioacidolysis; trimers
Categories
Funding
- CSIC
- Spanish MEC
- [AGL2005-01748]
- [BIO2007-28719E]
- [NMP2-CT-2006-026456]
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The chemical structure of milled-wood lignins from Eucalyptus globulus, E. nitens, E. maidenii, E. grandis, and E. dunnii was investigated. The lignins were characterized by analytical pyrolysis, thioacidolysis, and 2D-NMR that confirmed the predominance of syringyl over guaiacyl units and only showed traces of p-hydroxyphenyl units. E. globulus lignin had the highest syringyl content. The heteronuclear single quantum correlation (HSQC) NMR spectra yielded information about relative abundances of inter-unit linkages in the whole polymer. All the lignins showed a predominance of beta-O-4' ether linkages (66-72% of total side-chains), followed by beta-beta' resinol-type linkages (16-19%) and lower amounts of beta-5' phenylcoumarin-type (3-7%) and beta-1' spirodienone-type linkages (1-4%). The analysis of desulfurated thioacidolysis dimers provided additional information on the relative abundances of the various carbon-carbon and diaryl ether bonds, and the type of units ( syringyl or guaiacyl) involved in each of the above linkage types. Interestingly, 93-94% of the total beta-beta' dimers included two syringyl units indicating that most of the beta-beta' substructures identified in the HSQC spectra were of the syringaresinol type. Moreover, three isomers of a major trimeric compound were found which were tentatively identified as arising from a beta-beta' syringaresinol substructure attached to a guaiacyl unit through a 4-O-5' linkage.
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