Jorge Rencoret, Gisela Marques, Ana Gutiérrez, David Ibarra, Jiebing Li, Göran Gellerstedt, J. Ignacio Santos, Jesús Jiménez-Barbero, Ángel T. Martínez, José C. del Río
Structural characterization of milled wood lignins from different eucalypt species
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 ?-O-4? ether linkages (66–72% of total side-chains), followed by ?-?? resinol-type linkages (16–19%) and lower amounts of ?-5? phenylcoumaran-type (3–7%) and ?-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 ?-?? dimers included two syringyl units indicating that most of the ?-?? 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 ?-?? syringaresinol substructure attached to a guaiacyl unit through a 4-O-5? linkage.
Holzforschung, Walter de Gruyter
Print ISSN: 0018-3830
Volume: 62, 09/2008
Pages: 514 - 526
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