Content uploaded by Jorge Rencoret
Author content
All content in this area was uploaded by Jorge Rencoret
Content may be subject to copyright.
A preview of the PDF is not available
Structural characterization of milled wood lignin from different eucalypt species
Holzforschung
Abstract and Figures
The chemical structure of milled-wood lignins from Euca-lyptus 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 b-O-49 ether linkages (66–72% of total side-chains), followed by b-b9 resinol-type linkages (16–19%) and lower amounts of b-59 phe-nylcoumaran-type (3–7%) and b-19 spirodienone-type linkages (1–4%). The analysis of desulfurated thioaci-dolysis 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 b-b9 dimers included two syringyl units indicating that most of the b-b9 sub-structures 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 b-b9 syringaresinol substruc-ture attached to a guaiacyl unit through a 4-O-59 linkage. Current address: Department of Fiber and Polymer Technology, a Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden. heteronuclear single quantum correlation (HSQC); milled-wood lignin (MWL); pyrolysis-GC/MS; thioacidolysis; trimers.
Figures - uploaded by Jorge Rencoret
Author content
All figure content in this area was uploaded by Jorge Rencoret
Content may be subject to copyright.
... Gel permeation chromatography (GPC, Agilent 1200, United States) equipped with a refractive index detector was used to detect the number-average (Mn) and weight-average (Mw) molecular weights of the lignin fractions (Wang et al., 2017). The Bruker AVIII 400 MHz spectrometer (Bruker, Germany) was adopted to collect the quantitative 2D-HSQC spectra of the lignin dissolved in DMSO-d 6 (Rencoret et al., 2008;Wen et al., 2013a;Wang et al., 2017). Thermal stability and functional characteristics (i.e., UV-vis absorption) of these lignin samples were also assessed with a DTG analyzer (DTG-60, Shimadzu, Japan) and UV spectroscopy (UV-2550, Shimadzu, Japan) as previously . ...
... The advanced 2D-HSQC NMR technique was applied to characterize lignin (Rencoret et al., 2008;Wen et al., 2013b). The obtained 2D-HSQC spectra of these lignin samples from tobacco stalk are presented in Figure 2, and the quantitative results of linkages are also listed in Table 2. ...
... In the aromatic region of 2D-HSQC spectra (Figure 2), signals from the syringyl (S), guaiacyl (G), and p-hydroxyphenyl (H) units were clearly distinguished in MWL (Rencoret et al., 2008). After the delignification process, the recovered lignin showed a relatively lower signal intensity and obvious condensed signals in S units (such as L EG and HL EG ). ...
Lignin polymer as a natural aromatic macromolecule presents significant prospects in producing functional and sustainable materials, and achieving a comprehensive characterization will facilitate their target valorization. In the present study, deep eutectic solvent (DES) and alkaline delignification were adopted to deconstruct tobacco stalk before and after hydrothermal pretreatment, obtaining diverse lignin fractions with fascinating characteristics. DES lignin exhibited a higher yield and homogenous molecular structure than MWL. A severe cleavage of the inter-unit linkages in lignin was also observed. This result mostly originated from the efficient delignification of the DES deconstruction system adopted. Moreover, all the recovered lignin fractions exhibited good micro-nanoparticle size that can enhance the valorization of lignin in nanomaterial production, in which the hydrothermal-assisted DES deconstruction promoted the formation of the smaller lignin nanoparticle size. Next, all the recovered lignin presented an excellent UV absorption and structure-related absorption performance or thermal properties. Overall, this work provides an important foundation for further exploiting DES/alkaline delignification lignin that can be applied as an ideal feedstock for producing sustainable functional or micro/nanomaterials.
... The presence of tannins has been recently reported in olive stones [55]. Finally, other native lignin units corresponding to cinnamaldehyde end-groups (J) in S units (sinapaldehyde end-groups) and in G units (coniferaldehyde end-groups), previously described in lignin from olive tree pruning [56,57], could also be identified in lignin from olive stone. ...
This work describes the chemical and structural characterization of a lignin-rich residue from the bioethanol production of olive stones and its use for nanostructures development by electrospinning and castor oil structuring. The olive stones were treated by sequential acid/steam explosion pretreatment, further pre-saccharification using a hydrolytic enzyme, and simultaneous saccharification and fermentation (PSSF). The chemical composition of olive stone lignin-rich residue (OSL) was evaluated by standard analytical methods, showing a high lignin content (81.3 %). Moreover, the structural properties were determined by Fourier transform infrared spectroscopy, nuclear magnetic resonance, and size exclusion chromatography. OSL showed a predominance of β-β′ resinol, followed by β-O-4′ alkyl aryl ethers and β-5′ phenylcoumaran substructures, high molecular weight, and low S/G ratio. Subsequently, electrospun nanostructures were obtained from solutions containing 20 wt% OSL and cellulose triacetate with variable weight ratios in N, N-dimethylformamide/Acetone blends and characterized by scanning electron microscopy. Their morphologies were highly dependent on the rheological properties of polymeric solutions. Gel-like dispersions can be obtained by dispersing the electrospun OSL/CT bead nanofibers and uniform nanofiber mats in castor oil. The rheological properties were influenced by the membrane concentration and the OSL:CT weight ratio, as well as the morphology of the electrospun nanostructures.
... Stretching vibration of C-O (alcoholic hydroxyl and alkyl ether) 2.1.3. 1 H-13 C HSQC NMR Analysis 1 H-13 C NMR is a powerful tool for probing the structure of lignin and its derivatives [25]. These signals are related to structural units and the various associations between lignin units in 2D NMR spectra can be assigned according to the published literature [26][27][28][29][30][31]. The NMR spectra of the four raw materials (δ C /δ H 39.5/2.50) are shown in Figure 3. Table 3 describes the main lignin substructures shown in Figure 4. Semi-quantitative analysis based on the 2D HSQC signal was performed using Bruker's Topspin 2.1 processing software, and the integration method was adopted using the method described in previously published papers [32,33]. ...
Lignin structure is an important factor affecting the cooking part of the pulping process. In this study, the effect of lignin side chain spatial configuration on cooking performance was analyzed, and the structural characteristics of eucalyptus and acacia during cooking were compared and studied by combining ozonation, GC-MS, NBO, and 2D NMR (1H-13C HSQC). In addition, the changes in the lignin content of four different raw materials during the cooking process were studied via ball milling and UV spectrum analysis. The results showed that the content of lignin in the raw material decreased continuously during the cooking process. Only in the late cooking stage, when the lignin removal reached its limit, did the lignin content tend to be stable due to the polycondensation reaction of lignin. At the same time, the E/T ratio and S/G ratio of the reaction residual lignin also followed a similar rule. At the beginning of cooking, the values of E/T and S/G decreased rapidly and then gradually rose when they reached a low point. The different initial E/T and S/G values of different raw materials lead to the disunity of cooking efficiency and the different transformation rules of different raw materials in the cooking process. Therefore, the pulping efficiency of different raw materials can be improved using different technological means.
... [86]. In stems, S/G values have been reported for A. americana (1.27), A. angustifolia (1.29), A. fourcroydes (1.40), A. salmiana (1.33) y A. tequilana (1.57) in untreated samples [11], while for A. tequilana S/G values of 4.3 have also been reported in untreated samples [87] while in A. sisalana the proportion of S/G in stem fibers is 3.6 [88]. In the other genera analyzed here, there are no reports on the composition of lignin. ...
During the last decades, the possibility of using species resistant to droughts and extreme temperatures has been analyzed for use in the production of lignocellulosic materials and biofuels. Succulent species are considered to identify their potential use; however, little is known about Asparagaceae species. Therefore, this work aimed to characterize chemically-anatomically the stems of Asparagaceae species. Stems of 10 representative species of Asparagaceae were collected, and samples were divided into two. One part was processed to analyze the chemical composition, and the second to perform anatomical observations. The percentage of extractives and lignocellulose were quantified, and crystalline cellulose and syringyl/guaiacyl lignin were quantified by Fourier transform infrared spectroscopy. Anatomy was observed with epifluorescence microscopy. The results show that there were significant differences between the various species (p < 0.05) in the percentages of extractives and lignocellulosic compounds. In addition, there were anatomical differences in fluorescence emission that correlated with the composition of the vascular tissue. Finally, through the characterization of cellulose fibers together with the proportion of syringyl and guaiacyl, it was obtained that various species of the Asparagaceae family have the potential for use in the production of lignocellulosic materials and the production of biofuels.
... The syringyl units are of several types. In particular, using the assignments made in [28][29][30], we found S units with a substituent in the 4-position (δ C /δ H 104.5/6.70), S units with a free hydroxyl group in the 4-position (δ C /δ H 106.2/6.51), ...
For the first time, the process of birch ethanol lignin sulfation with a sulfamic acid-urea mixture in a 1,4-dioxane medium was optimized experimentally and numerically. The high yield of the sulfated ethanol lignin (more than 96%) and containing 7.1 and 7.9 wt % of sulfur was produced at process temperatures of 80 and 90 °C for 3 h. The sample with the highest sulfur content (8.1 wt %) was obtained at a temperature of 100 °C for 2 h. The structure and molecular weight distribution of the sulfated birch ethanol lignin was established by FTIR, 2D 1H and 13C NMR spectroscopy, and gel permeation chromatography. The introduction of sulfate groups into the lignin structure was confirmed by FTIR by the appearance of absorption bands characteristic of the vibrations of sulfate group bonds. According to 2D NMR spectroscopy data, both the alcohol and phenolic hydroxyl groups of the ethanol lignin were subjected to sulfation. The sulfated birch ethanol lignin with a weight average molecular weight of 7.6 kDa and a polydispersity index of 1.81 was obtained under the optimum process conditions. Differences in the structure of the phenylpropane units of birch ethanol lignin (syringyl-type predominates) and abies ethanol lignin (guaiacyl-type predominates) was manifested in the fact that the sulfation of the former proceeds more completely at moderate temperatures than the latter. In contrast to sulfated abies ethanol lignin, the sulfated birch ethanol lignin had a bimodal and wider molecular weight distribution, as well as less thermal stability. The introduction of sulfate groups into ethanol lignin reduced its thermal stability.
... This observation suggests that the DCA catabolic pathway is altered during culture. Thirdly, DCA, a guaiacyl-type -5 dimer, is generally used for catabolic studies; however, syringyl-and p-hydroxyphenyl-type -5 dimers also exist [38][39][40] . In addition, it is not known how the DCA catabolic system of SYK-6 works for the actual -5 structure-derived compounds produced by lignin biodegradation in nature. ...
The β-5 linkage is an intermolecular linkage in lignin. Sphingobium sp. strain SYK-6 can assimilate various lignin-derived dimers, including a β-5 dimer, dehydrodiconiferyl alcohol. In SYK-6, the hydroxyl group at Cγ of the Bring side chain of dehydrodiconiferyl alcohol is oxidized to generate the γ-carboxylic compound, DCA-C. Then, the hydroxyl group at Cγ of the A-ring side chain of DCA-C is oxidized to the carboxyl group to generate the dicarboxylic compound, DCA-CC. The carboxylic group at Cγ of the A-ring side chain of DCA-CC is decarboxylated, and the accompanying spontaneous ether cleavage of the coumaran ring produces a stilbene-type compound, DCA-S. The conversions of DCA-C and DCA-CC are catalyzed by enantiospecific oxidases (PhcC and PhcD) and enantiospecific decarboxylases (PhcF and PhcG), respectively. DCA-S is subjected to cleavage of the interphenyl double bond by lignostilbene α,β-dioxygenase to generate 5-formylferulate and vanillin. Among the eight lignostilbene α,β-dioxygenase genes, vanillate-induced lsdD plays a critical role in cleaving DCA-S. The formyl group of 5-formylferulate is oxidized, and the resultant carboxylic group is subsequently decarboxylated to produce ferulate. Finally, ferulate and vanillin are further catabolized via a previously characterized pathway.
Lignin dimeric units are characterized by various inter-unit linkage types such as β-O-4, β-5, β-β, and β-1. Spirodienones are the native form of the β-1 structures, but the content in lignin has not been clarified. In this study, the ring-1- ¹³ C labeled coniferin was synthesized and administered to Ginkgo biloba shoots, obtaining ring-1 selectively labeled xylem samples. Enzymatically saccharified lignin (EL) samples were prepared from the xylem sample (400–600 µm distant region from the cambial zone), and solution-state quantitative ¹³ C NMR and solid-state CP/MAS NMR measurements were conducted. Acetylated EL (ELAc) was also prepared from the xylem sample (600–800 µm distant region from the cambial zone), and solution-state quantitative ¹³ C NMR and ¹ H– ¹³ C 2D NMR measurements were conducted. Difference spectra obtained by subtracting the unlabeled spectra from the ring-1 labeled spectra showed that the ring-1 was responsible for broad signals at 134 ppm and signals of the spirodienone structure at 56.11 ppm (in solid-state), 54.70 ppm (EL in solution-state), and 54.72 ppm (ELAc in solution-state). The ratio of spirodienone structure was evaluated as 0.68 % (EL) and 0.72 % (ELAc) by the solution-state quantitative ¹³ C difference spectra, and 2.3 % (ELAc) by HSQC volume ratio of Cα′-H to G2-H.
Kraft lignins from different poplar genotypes (Populus alba L. “PO-10-10-20” and Populus x canadensis “Ballotino”) were isolated by selective acid precipitation (pH 5 and 2.5), chemically and structurally characterized and used together with cellulose acetate (CA) for the manufacture of nanostructures by electrospinning. Generally, lignins showed a predominance of β-β´ resinols substructures (4.7–5.3 linkages per 100 aromatic units) followed by β-O-4´ (1.6–3.3 linkages per 100 aromatic units) and β-5´ phenylcoumarans (0.5–2.4 linkages per 100 aromatic units) and a high abundance of S lignin units (S/G 3.0–4.3). Moreover, lignins showed low molecular weight values (between 5.14 and 5.59 KDa) and high phenolic content (529.1 –644.5 mg GAE/g lignin). Regarding the electrospun nanostructures obtained from Kraft lignins/CA solutions, all of them presented uniform cross-linked nanofibers with a few beaded fibers according to the suitable range values of surface tension (29.18–29.71 mN/cm), electrical conductivity (131.2–158.9 μS/cm) and dynamic viscosity (0.28–0.32 Pa.s) that biopolymer solutions showed. Nevertheless, electrospun Kraft lignins/CA nanostructures with larger mean diameters were generated from lignins at pH 5, which displayed higher phenolic and β-O-4´ contents compared to lignins at pH 2.5. On the other hand, the type of poplar lignin genotype did not exert a significant influence on the mean fiber diameter.
Wood fractionation is key for the integral valorization of its three main components. In this sense, recovering the hemicellulosic fraction after the ionosolv treatment of lignocellulosic materials is one of the main drawbacks of this process. Thus, the incorporation of a previous autohydrolyisis step to recover the hemicellulosic sugars before the ionosolv treatment is an interesting approach. The influence of both treatments, autohydrolysis and ionosolv, on the biomass fractions recovery yields was studied by a central composite design of experiments, varying the autohydrolysis temperature in a 175-195 °C range and ionosolv time between 1-5 h. Lignin recovery and cellulose purity were maximized at 184 °C and 3.5 h of autohydrolysis temperature and ionosolv time, respectively. In addition, lignin properties were incorporated to the statistical model, revealing lignin recondensation at severe conditions and a higher influence of the ionosolv treatment on lignin characteristics. These results remarked the importance of studying the effect of both treatments in the whole fractionation process and not each process separately and enhanced the understanding of the treatments combination in a complete fractionation biorefinery approach.
The delignification rates in kraft pulping were determined for two softwood and two hardwood species. The latter were delignified faster than the former species, the rate being fastest for the species containing more syringyl lignin. Results from experimental studies are presented in curves and a table.
The cause for the significant difference of pulping characteristics between two kinds of eucalyptus species, i.e. Eucalyptus viminalis and Eucalyptus globulus, and to discover the effect of lignin structure on pulping characteristics of eucalyptus wood was studied. The detailed structure of lignin in the eucalyptus woods was investigated by nitrobenzene oxidation and permanganate oxidation combined with gas chromatography. The results of nitrobenzene oxidation experiments of lignin showed that Eucalyptus globulus had higher syringyl- guaiacyl ratio (S/V) and higher phenolic aldehydes yield than those of Eucalyptus viminalis. The results of permanganate oxidation also proved that the lignin in Eucalyptus globulus was more syringyl-rich than that of Eucalyptus viminalis. Moreover, it was found that less derivatives of bis-vanillic acid, isohemipinic acid and metahemipic acid, which were generally derived from condensed lignin structure as biphenyl, β-5 and β-6 structure, could be obtained from Eucalyptus globulus, suggesting that Eucalyptus globulus contained less condensed type lignin. Furthermore, 13C-NMR and 2D-NMR (HMQC) spectra of MWLs from these two wood species showed that there was marked difference in their contents of biphenyl units which is also a typical condensed lignin structure. It could be concluded that the difference of S/V ratio and the content of condensed structure as phenylcoumaran, phenylisochroman and biphenyl had significant effect on the pulping characteristics of eucalyptus species.
A spiro-dienone structure (β-1/α-O-α) has been observed as one of the important structures present in spruce and aspen lignins, with abundance as high as 3% in spruce lignin.
Correlation peaks found in HMQC spectra of softwood lignins have been assigned to a dibenzodioxocin structure with the aid of model compounds. It constitutes a major hitherto unknown structure in softwood lignins.
A spiro-dienone structure (β-1/α-O-α) has been observed as one of the important structures present in spruce and aspen lignins, with abundance as high as 3% in spruce lignin.
Bauer-McNett fractions of an aspen chemi-thermomechanical pulp showed a significant variation with respect to lignin content and sugar composition, and two of the fractions were found to be particularly rich in middle lamella and secondary wall material, respectively. The secondary wall lignin of aspen was found to contain larger amounts of non-condensed beta-O-4 aryl ether structures than the middle lamella lignin and the difference was attributed to a larger amount of syringyl structures as revealed by thioacidolysis. Size exclusion chromatography of the thioacidolysis products from birch and spruce wood showed a larger part of lignin oligomers being present in the degraded spruce lignin. Moreover, birch lignin had a lower phenolic content than both aspen and spruce lignin. Thioacidolysis followed by Raney-nickel desulphuration was used for the analysis of hardwood lignin trimers.
The chemical structure of lignin in normal and compression wood of spruce has been studied. Thioacidolysis using both methanethiol and ethanethiol as nucleophiles was used for degradation. The results showed that these nucleophiles work equally well in thioacidolysis, but that methanethiol gives a somewhat higher yield than ethanethiol. In spruce compression wood, several of the monomeric, dimeric and trimeric products were structurally elucidated using gas chromatography-mass spectrometry analysis of the desulphurated thioacidolysis products. Some of the oligomeric structures contained a p-hydroxyphenyl unit, but most of the material seemed to be present in non-condensed beta-O-4 structures. A catechol structure was found and the results also indicated the presence of beta-5 stilbene structures in native spruce lignin.