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. The HSQC-NMR spectra showed a predominance of β-O-4' ether linkages (66-72% of total side-chains), followed by β-β' resinol-type linkages (16-19% of side-chains) and lower amounts of β-5' phenylcoumaran-type (3-7% of side-chains) and β-1' spirodienone-type linkages (1-4% of side-chains). The analysis of desulphurated thioacidolysis dimers provided additional information on the carbon-carbon and diaryl ether bonds forming the most condensed moiety of the eucalypt lignins, and the type of units involved in each of the above linkage types. Interestingly, 93-94% of the total β-β' dimers included two syringyl units indicating that most of the β-β' substructures identified in the HSQC spectra were of the syringaresinol type. Moreover, three isomers of a major trimeric compound tentatively identified as arising from a β-β' syringaresinol substructure attached to a guaiacyl unit through a 4-O-5' linkage were found.

This study has been funded by the Spanish project AGL2005-01748, the CSIC project 2006-4-0I-039 and the BIORENEW EU-Project (NMP2-CT-2006-026456). J.R. thanks the CSIC for a I3P fellowship and the COST Action E-41 for funding an stay at KTH.

Rencoret, Jorge et al.-- 4 páginas, 1 figura, 2 tablas, 12 referencias.-- Congreso celebrado del 26-29 de agosto 2008, en Stockholm, Sweden.

Peer reviewed