Lignin Composition and Structure in Young versus AdultEucalyptus globulusPlants

Abstract

Lignin changes during plant growth were investigated in a selected Eucalyptus globulus clone. The lignin composition and structure were studied in situ by a new procedure enabling the acquisition of two-dimensional nuclear magnetic resonance (2D-NMR) spectra on wood gels formed in the NMR tube as well as by analytical pyrolysis-gas chromatography-mass spectrometry. In addition, milled-wood lignins were isolated and analyzed by 2D-NMR, pyrolysis-gas chromatography-mass spectrometry, and thioacidolysis. The data indicated that p-hydroxyphenyl and guaiacyl units are deposited at the earlier stages, whereas the woods are enriched in syringyl (S) lignin during late lignification. Wood 2D-NMR showed that b-O-4# and resinol linkages were predominant in the eucalypt lignin, whereas other substructures were present in much lower amounts. Interestingly, open b-1# structures could be detected in the isolated lignins. Phenylcoumarans and cinnamyl end groups were depleted with age, spirodienone abundance increased, and the main substructures (b-O-4# and resinols) were scarcely modified. Thioacidolysis revealed a higher predominance of S units in the ether-linked lignin than in the total lignin and, in agreement with NMR, also indicated that resinols are the most important nonether linkages. Dimer analysis showed that most of the resinol-type structures comprised two S units (syringaresinol), the crossed guaiacyl-S resinol appearing as a minor substructure and pinoresinol being totally absent. Changes in hemicelluloses were also shown by the 2D-NMR spectra of the wood gels without polysaccharide isolation. These include decreases of methyl galacturonosyl, arabinosyl, and galactosyl (anomeric) signals, assigned to pectin and related neutral polysaccharides, and increases of xylosyl (which are approximately 50% acetylated) and 4-O-methylglucuronosyl signals.

Comparison of Py-GC/FID and Wet Chemistry Analysis for Lignin Determination in Wood and Pulps from Eucalyptus globulus

“…The values of soluble lignin observed for wood material (3.9% and 4.0%, Table 1) are comparable with the reported 3.6% (Pereira 1988) and are in the range of 4.4% to 8.1% (Poke et al 2006). The values of Klason lignin (21.4 % and 21.8 %) were observed to be in the range of 18.9% to 25.5% reported by Poke et al (2006) and near the reported 19.8% (Rencoret et al 2011). This relation between acid-insoluble and soluble lignin is similar for other hardwoods, i.e.…”

“…However, due to the higher extractives content in heartwood, when the total lignin is reported to original wood, the values are slightly different: 24.3% and 23.5%, respectively for sapwood and heartwood (Lourenço et al 2010). These are values in the range of values reported for E. globulus wood of 24.2% to 27.9% (Miranda and Pereira 2002b); 24.7% to 31.2% (Poke et al 2006); 25.4% (Ramírez et al 2009); or 24.5% (Rencoret et al 2011), while a somewhat lower value of 21.9% was reported by Patt et al (2006). It is known that such amplitude of values is due to different factors such as wood origin (Miranda and Pereira 2002b;Poke et al 2006) or age of the tree (Miranda and Pereira 2002c).…”

Lignin‐Derived Thioacidolysis Dimers: Reevaluation, New Products, Authentication, and Quantification

“…Based on these results and the mass spectral characteristics of VI , this compound appeared to have originated from β–5 structures (somehow related to V ) during thioacidolysis or desulfurization. The peak for this compound VI (Figure 2) was originally assigned to be a β–6 dimer but, because such coupling is chemically impossible, it was later suggested to be consistent with a β–1 isochroman structure 8b, 9a, 11. From MS analysis and the herein established derivation of compound VI from a β–5 dimeric model compound, it is now clear that the structure shown in Figure 1 and Figure S1 is simply derived from an unopened phenylcoumaran, as will be described more fully elsewhere.…”

Structural Characterization of Lignin Isolated from Wheat-Straw during the Alkali Cooking Process

“…2 and 3, the HSQC NMR spectra of the lignin fractions exhibited aliphatic (C/H 10-40/0.5-2.5) and aromatic 13 C-1 H correlation regions (C/H 95-150/5.5-8.0). The main cross signals of the lignin fractions in the HSQC spectra are assigned in Table 5 according to previous reports (Rencoret et al 2011;Sun et al 2013).…”

“…Likewise, the FA2 (C2-H2), FA8 (C8-H8), and FA7 (C7-H7) correlations were observed at δC/δH 111.0/7.28, 116.4/6.40, and 143.7/7.50. Based on the quantification methodology (Rencoret et al 2011;Sun et al 2013), the main substructures among the lignin fractions and their abundances were estimated quantitatively. As shown in Table 6, the ratio of S/G/H was used to estimate the difference of lignin fractions in different conditions.…”