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2D-NMR of Lignin in the Eucalypt Pulp Mill Biorefinery: General Aspects and Enzymatic Delignification Studies

AutorMartínez, Ángel T. ; Jiménez-Barbero, Jesús ; Rencoret, Jorge ; Rico Campos, Alejandro ; Río Andrade, José Carlos del ; Gutiérrez Suárez, Ana
Palabras claveEucalypt
Fecha de publicación2013
EditorUniversidad de la República (Uruguay)
Citación6th International Colloquium on Eucalyptus Pulp (6th ICEP). Colonia del Sacramento, Uruguay, 24th to 27th, November, 2013.
ResumenThe present lecture describes the potential of two-dimensional nuclear magnetic resonance (2D-NMR) as a powerful analytical tool to characterize the modification and/or removal of lignin, a key step for the industrial utilization of plant feedstocks, during eucalypt wood deconstruction in the pulp mill biorefinery. Lignin analysis by 2D-NMR includes determination of its aromatic-unit composition and abundance of inter-unit linkages and terminal groups, after its isolation from wood. It is necessary to emphasize that some lignin substructures could only be described when this technique was available. We also describe the possibility to analyze the changes in the lignin polymer (and wood polysaccharides) without its prior isolation, by 2D-NMR of the whole wood material at the gel stage (after swelling in deuterated dimethylsulfoxide). The general structural characteristics of eucalypt lignin as shown by 2D-NMR are described first including its natural variability in several species evaluated as pulp mill feedstocks. Then, some changes observed during alkaline cooking and pulp delignification/bleaching processes are reported with the focus on Eucalyptus globulus, as a first example of the potential of 2D-NMR for the detailed analysis of lignin modification. The next examples concern the use of 2D-NMR to better understand the potential of Biotechnology for the removal of lignin in the pulp mill biorefinery. Following the natural model of wood delignification in the forest, oxidative enzymes are used to degrade lignin and their potential in both wood and pulp delignification has been evaluated. Due to their higher stability, commercial availability and independence of co-substrates, laccases are preferred for these applications, often in the presence of synthetic redox mediators. In the case of eucalypt kraft pulp, a laccase-mediator stage modifies the residual lignin and improves delignification (and bleaching) when followed by an alkaline peroxide stage, as illustrated by 2D-NMR. Moreover, NMR and other analyses showed that this oxidative biocatalysts are not only able to attack residual lignin in pulp (where its accessibility has been strongly increased by the previous cooking) but also when applied directly on ground eucalypt wood, as a biorefinery pretreatment. In this way, an enzymatic sequence (that included four successive enzymatic and alkaline extraction stages) was evaluated resulting in the removal of ¿50% of the initial eucalypt wood lignin. 2D-NMR of the treated wood (at the gel stage) revealed the differential removal of lignin units, without a substantial change in polysaccharide cross-signals. However, the most noticeable change observed in the wood and isolated lignin spectra is the strong increase of C¿-oxidized syringyl units (representing up to 60% of all the lignin units in the treated eucalypt wood) in agreement with the mechanism of lignin attack by laccase-mediator proposed after model dimer studies. Actually, 2D-NMR is being also used to characterize wood/pulp lignin modification by commercial laccases and phenolic mediators with the aim of increasing the industrial feasibility of the above biotechnological treatments.
Descripción47 diapositivas.-- El Artículo que aparece en una de las diapositivas con el título: "Enzymatic delignification of plant cell wall: from nature to mill" se encuentra en Digital CSIC http://hdl.handle.net/10261/34836
Versión del editorhttp://www.6thicep.org.uy/styles/inc4/downloads/Slides/16_Angel%20Martinez.pdf
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