Joseph H. BANOUB
Department of Chemistry, Memorial University of Newfoundland, and Fisheries and Oceans Canada
Science Branch, Special Projects, P.O. Box 5667, St John’s, Newfoundland, A1C 5X1, Canada
Bouchra BENJELLOUN-MYLAHI
Compagnie Industrielle de la Matière Végétale (CIMV), 134 Rue Danton 92300 Levallois-Perret, France
Nicolas JOLY & Patrick MARTIN
Laboratoire de Physico-Chimie des Interfaces et Applications FRE CNRS 2485, Site de Béthune, Fédération Chevreul FR CNRS 2638, Université d’Artois, IUT de Béthune, Dépt. Chimie, BP819, 62408 Béthune cedex, France
and Michel DELMAS
École Nationale Supérieure des Ingénieurs en Arts Chimiques et Technologiques
Institut National Polythechnique de Toulouse, 118 route de Narbonne, 31077 Toulouse, Cedex 4, France
Wheat straw lignin was extracted using the novel AVIDEL, procedure which selectively separates the cellulose, hemicelluloses and lignin. Solid-state 13C-NMR experiments using the Magic Angle Spinning / Cross polarization (MAS/CP) technique were done on the extracted wheat straw lignin and some structural indices were revealed. Atmospheric Pressure PhotoIonization Mass spectrometry (APPI-MS) has proven to be powerful analytical tool capable of ionizing small to large lignin oligomers, which cannot be ionized efficiently by APCI and ESI. The APPI-MS of the extracted wheat straw lignin were recorded in the positive and negative ion modes. The positive mode APPI-MS indicated the exact presence of 39 specific oligomeric ions. The APPI-MS recorded in the negative mode, indicated the additional presence of at least 18 specific oligomeric ions. The structural characterization of this novel and complete series of 57 specific related oligomers, was achieved by calculating the exact molecular masses measured with the high resolution QqToF-MS. There were identical oligomeric species that photoionized in both the positive and negative ion modes, which formed the respective protonated and deprotonated molecules. Low energy collision tandem mass spectrometric analyses performed with a QqToF-MS/MS hybrid instrument provided unique dissociation patterns of the complete series of novel precursor ions. These MS/MS analyses provided diagnostic product ions, which assisted us to expose the exact molecular structure and arrangement of the selected different 57 related ionic species.
Notwithstanding this new finding, we want to communicate that the native lignin polymer is a micro-heterogeneous mixture, which is extremely chemically reactive when subjected to harsh chemical methods (i.e. extraction and all chemical degradations), and hence tends to either break down quite easily and/or react rapidly to produce new compounds, that were not originally present in the native lignin. This may explain the inconsistencies reported on the frivolous structures that have been proposed in the last half of a century, especially after extraction of the native lignin with extremely harsh chemical procedures.
