Guaiacyl Units Research Articles

The characterization of South Moravian lignite in its natural and treated forms using thermal degradation methods

Thermal degradation experiments were performed on South Moravian lignite in its natural and treated forms primarily to investigate the changes taking place during pyrolysis, and, secondarily, to determine the structural characteristics of lignite using thermal degradation methods The lignite was treated by extraction with chloroform, demineralization, and the remineralization or sorption of calcium ions on the demineralized lignite. The analysis of pyrolysis products was performed in solid and gaseous states using FTIR analysis and the thermogravimetric technique coupled with FTIR (TG-FTIR). Experiments were complemented by thermochemolysis with tetramethylammonium hydroxide (TMAH). South Moravian lignite was characterized by the bimodal distribution of saturated fatty acids, with two maxima at n-C16 and at n-C28, and the dominance of guaiacyl units indicating a gymnosperm origin. FTIR analysis of the examined sample set showed that lignite contains different functional groups with various thermal stabilities degrading to the evolution of gases such as H2O, CO, CO2 and CH4. Precursors of the gaseous products generated and an analysis of functional groups in the samples are discussed in the paper. The results show that treatments of lignite may be reflected in their thermal behaviors during pyrolysis.

Deep Eutectic Solvents (DESs) for the Isolation of Willow Lignin (Salix matsudana cv. Zhuliu).

Deep eutectic solvents (DESs) are a potentially high-value lignin extraction methodology. DESs prepared from choline chloride (ChCl) and three hydrogen-bond donors (HBD)—lactic acid (Lac), glycerol, and urea—were evaluated for isolation of willow (Salix matsudana cv. Zhuliu) lignin. DESs types, mole ratio of ChCl to HBD, extraction temperature, and time on the fractionated DES-lignin yield demonstrated that the optimal DES-lignin yield (91.8 wt % based on the initial lignin in willow) with high purity of 94.5% can be reached at a ChCl-to-Lac molar ratio of 1:10, extraction temperature of 120 °C, and time of 12 h. Fourier transform infrared spectroscopy (FT-IR) , 13C-NMR, and 31P-NMR showed that willow lignin extracted by ChCl-Lac was mainly composed of syringyl and guaiacyl units. Serendipitously, a majority of the glucan in willow was preserved after ChCl-Lac treatment.

Thermogravimetric analysis of cork and cork components from Quercus variabilis

Cork and cork components (suberin, lignin, holocellulose, sclereids, and lenticels) were obtained by manual and chemical methods. Dynamic thermogravimetric analysis was used to investigate the thermal behavior of cork and its components. Thermal decomposition of cork was different from that of natural fibers. Characteristic temperatures of thermal decomposition for cork and impurities (sclereids and lenticels) were related to their chemical components. Cork lignin has the decomposition characteristics of G-type (guaiacyl units) lignin, typical of softwood with high residual solids. The pyrolysis characteristics of Quercus variabilis Blume (Q. variabilis) suberin was close to Quercus cerris L. (Q. cerris) suberin. The decomposition temperature range of cork, lignin, or suberin was wider than that of sclereids, lenticels, or holocellulose. Activation energy of cork was lower than that of natural fibers. The activation energy of cork and the extracted suberin was slightly increased when the conversion rate α was greater than 0.35. Activation energies of sclereids and lenticels were close to each other due to similar composition and proportion in them.

Yields analysis and structural characterizations of lignin extracted from Eucalyptus globulus with catalyzed ethanol systems

A mild and successive method was proposed and evaluated for fractionating lignin samples from Eucalyptus globulus. The extraction efficiency and structural features of the extracted lignin samples were comprehensively investigated by a yields analysis, 1H-nuclear magnetic resonance (NMR), 13C-NMR, and two-dimensional heteronuclear single quantum coherence (2D-HSQC) NMR. The catalyzed ethanol systems consisting of ethanol, 4-methyl-2-pentanone, dimethyl sulfoxide (DMSO), formic acid, and distilled water were effective for extracting lignin from Eucalyptus globulus, and the yield of lignin was 75.2% when the extraction process was held at 145 °C for 180 min. Compared with that of the milled wood lignin (MWL), the NMR spectra of the extracted lignin fractions supported the destruction of β-O-4 units for the disappearance of Hα signals. Moreover, the striking characteristics of the extracted lignin were the destruction of ether bonds of S3,5 and the condensation of syringyl (S) and guaiacyl (G) units. In short, lignin fractions with relatively complete structures were effectively extracted with the catalyzed ethanol systems.

Silencing CAFFEOYL SHIKIMATE ESTERASE Affects Lignification and Improves Saccharification in Poplar.

Caffeoyl shikimate esterase (CSE) was recently shown to play an essential role in lignin biosynthesis in Arabidopsis (Arabidopsis thaliana) and later in Medicago truncatula However, the general function of this enzyme was recently questioned by the apparent lack of CSE activity in lignifying tissues of different plant species. Here, we show that down-regulation of CSE in hybrid poplar (Populus tremula × Populus alba) resulted in up to 25% reduced lignin deposition, increased levels of p-hydroxyphenyl units in the lignin polymer, and a relatively higher cellulose content. The transgenic trees were morphologically indistinguishable from the wild type. Ultra-high-performance liquid chromatography-mass spectrometry-based phenolic profiling revealed a reduced abundance of several oligolignols containing guaiacyl and syringyl units and their corresponding hydroxycinnamaldehyde units, in agreement with the reduced flux toward coniferyl and sinapyl alcohol. These trees accumulated the CSE substrate caffeoyl shikimate along with other compounds belonging to the metabolic classes of benzenoids and hydroxycinnamates. Furthermore, the reduced lignin amount combined with the relative increase in cellulose content in the CSE down-regulated lines resulted in up to 62% more glucose released per plant upon limited saccharification when no pretreatment was applied and by up to 86% and 91% when acid and alkaline pretreatments were used. Our results show that CSE is not only important for the lignification process in poplar but is also a promising target for the development of improved lignocellulosic biomass crops for sugar platform biorefineries.

Characterization of lignins isolated with alkali from the hydrothermal or dilute-acid pretreated rapeseed straw during bioethanol production

A better understanding of the lignin in the straw of rapeseed, Brassica campestris L., is a prerequisite for promoting the biorefinery industry of rapeseed. Two different methods for fractionating lignin from rapeseed straw were proposed in this study. Lignin in the raw material was isolated with alkaline solution and recovered by acid precipitation. A comparison between two lignin preparations obtained from two different methods has been made in terms of yield and purity. The structural features were investigated by gel permeation chromatography, FT-IR spectroscopy, 2D-HSQC NMR and 31P NMR. Taking into consideration of the yield and purity, the proposed methods are effective for extracting lignin. NMR results showed that syringyl (S) was the predominant unit over guaiacyl (G) or p-hydroxyphenyl (H) units in the lignin preparations, and linkages β-O-4’, β-β’ and β-5’ were also identified and quantified by NMR techniques. This study demonstrated that the combination of hydrothermal or dilute-acid pretreatment and alkaline process could efficiently isolate the lignins from the rapeseed straw to further applications for industries. It was found that the enzymatic hydrolysis of the two-step pretreated rapeseed straw increased 5.9 times than the straw without treatment, which is benefit for bioethanol production from rapeseed straw.

Adsorption of cellobiohydrolases I onto lignin fractions from dilute acid pretreated Broussonetia papyrifera

Broussonetia papyrifera, known as paper mulberry, is a potential feed stock for bioethanol production because of its cellulose-rich composition. Lignin in dilute acid pretreated Broussonetia papyrifera was fractionated to three different fractions, and their physiochemical properties were determined by FT-IR, GPC and NMR analyses. Different structural characteristics were observed from each lignin fraction. Cellobiohydrolases I (CBH) adsorption to each lignin was understood by the lignin properties. The results showed that aliphatic hydroxyl groups in lignin showed positive correlations with the maximum binding ability of CBH onto lignin samples. Also, the contents of phenolic compounds such as p-hydroxyphenyl benzoate (PB), syringyl (S) and guaiacyl (G) units in the lignin influenced their CBH binding.

Molecular Changes in Corn Stover Lignin Resulting from Pretreatment Chemistry

Lignin is an amorphous polymer that limits the enzymatic conversion of polysaccharides to fermentable sugars. Thus, a pretreatment that can enhance the accessibility of carbohydrates is a key step of successful biofuel conversion schemes. In this study, corn stover was fractioned into stem, cob, and leaf because their lignin is different. To elucidate the lignin changes, autohydrolysis, diluted acid, and alkali pretreatments were applied on the samples, followed by the isolation of cellulolytic enzyme lignin preparations. Alkaline nitrobenzene oxidation, 13C-Nuclear Magnetic Resonance (NMR), and 1H-13C heteronuclear single quantum coherence NMR were used to profile the lignin changes. The results indicated that corn stover lignin is a p-hydroxyphenyl-guaiacyl-syringyl-type lignin that incorporates p-coumarate and ferulate esters. The β-aryl-ether was the most abundant inter-unit linkage, followed by condensed linkages, e.g. pino-/syringaresinol, phenylcoumaran, and spirodienone. As for the non-pretreated samples, leaf lignin was more condensed than stem lignin and cob lignin. More lignin was removed by the alkali pretreatment due to more cleavage of β-aryl-ether linkages. As a comparison, more condensed linkages were generated by the acidic pretreatments. The decrease of the syringyl/guaiacyl ratio indicated that the residual lignin became more condensed and confirmed that guaiacyl and p-hydroxyphenyl units were more stable than syringyl units during the pretreatment.

Multi-step biocatalytic depolymerization of lignin.

Lignin is a biomass-derived aromatic polymer that has been identified as a potential renewable source of aromatic chemicals and other valuable compounds. The valorization of lignin, however, represents a great challenge due to its high inherent functionalization, what compromises the identification of chemical routes for its selective depolymerization. In this work, an in vitro biocatalytic depolymerization process is presented, that was applied to lignin samples obtained from beech wood through OrganoCat pretreatment, resulting in a mixture of lignin-derived aromatic monomers. The reported biocracking route comprises first a laccase-mediator system to specifically oxidize the Cα hydroxyl group in the β-O-4 structure of lignin. Subsequently, selective β-O-4 ether cleavage of the oxidized β-O-4 linkages is achieved with β-etherases and a glutathione lyase. The combined enzymatic approach yielded an oily fraction of low-molecular-mass aromatic compounds, comprising coniferylaldehyde and other guaiacyl and syringyl units, as well as some larger (soluble) fractions. Upon further optimization, the reported biocatalytic route may open a valuable approach for lignin processing and valorization under mild reaction conditions.

Alkaline Pretreatment Severity Leads to Different Lignin Applications in Sugar Cane Biorefineries

Lignin, a multifunctional major biomass component, has a prominent potential as feedstock to be converted into high value-added products. Lignin is available in high amounts as side streams during cellulosic ethanol production, and within the biorefinery context, it is important to assess its structural characteristics in order to explore its potential to replace some petroleum-based reactants. In this study, some important features were evaluated for different lignins such as lignin purity and the amounts of syringyl (S), guaiacyl (G), and p-hydroxyphenyl (H) units. Four alkaline lignins, generated from a pilot-scale pretreatment of sugar cane bagasse (NaOH 1.5%, 30 min), were evaluated according to the severity of the alkaline pretreatment (130 or 170 °C, with or without the addition of anthraquinone). The different pretreatments produced lignins with different chemical characteristics that can be used for different purposes in sugar cane biorefineries. As the severity of alkaline pretreatment increased...

Products of hydrothermal treatment of lignin and the importance of ortho-directed repolymerization reactions

Alkaline hydrothermal treatment (HTT) of Protobind 1000 lignin was studied to improve the understanding of lignin conversion paths. HTT was performed at 300°C using NaOH as base catalyst. Product separation by acidification and solvent fractionation resulted in a liquid product of low molecular mass and narrow molecular mass distribution and two high molecular mass solid fractions. Twenty volatile compounds accounted for about 36wt% of the liquid product, however, the analysis by liquid injection GC–MS was estimated to detect only about 12wt% of the total products. Analytical pyrolysis was applied to investigate the pyrolyzable fraction of the liquid product and the high molecular mass fractions. The pyrolyzable mass accounted for 49wt% of the total products. The liquid product was quantitatively pyrolyzed at 500°C (91±10wt%) while less than half of the high molecular mass fractions were pyrolyzed. Several chemical features of the pyrolysates suggested that ortho-directed alkylation and condensation reactions of phenolate ions were important for the production of oligomeric and polymeric aromatic compounds during HTT. Increased abundancy of hydroxyphenyl and o-alkyl aromatic pyrolysates in the high molecular mass fractions suggested that the syringyl units of the raw lignin were less affected by repolymerization reactions than hydroxyphenyl and guaiacyl units. These results suggest that the monolignol composition of lignin is an important factor for the valorization of lignin by alkaline hydrothermal treatment.

Development and validation of a sensitive UPLC-MS/MS instrumentation and alkaline nitrobenzene oxidation method for the determination of lignin monomers in wheat straw.

A method to determine the lignin monomers (p-hydroxybenzaldehyde, vanillin and syringaldehyde) in plant cell wall of wheat internode was developed and validated using a high-throughput nitrobenzene oxidation step and ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) for quantification. UPLC analyses were carried out using an reversed phase C18 column (ACQUITY UPLC BEH, 1.7μm, 2.1×100mm) and gradient elution with water and acetonitrile. This method was completely validated in terms of analyzing speed, linearity, sensitivity, limits of detection (LODs) and limits of quantification (LOQs).The three lignin monomers were successfully separated within 6min and only 2min were required to regain its equilibrium. The method linearity with regression coefficients values (R2) greater than 0.997. Additionally, LODs ranged from 0.21 to 0.89μgL-1 and LOQs ranged from 0.69 to 2.95μgL-1. The applicability of this analytical approach for determining the three lignin monomers was confirmed by the successful analysis of real samples of wheat stem internodes. The nitrobenzene oxidation method was used for the analysis of lignin monomers. We have optimized the treatment temperature (170°C, 1h) and realized the high-throughput using the microwave digestion instrument. Recovery of this extraction method ranged from 68.4% to 77.7%. The analysis result showed that the guaiacyl unit (G) was the major component of lignin and there was a higher content of the syringyl unit (S) than that of the hydroxybenzyl unit (H).

Unravelling Some of the Key Transformations in the Hydrothermal Liquefaction of Lignin.

Using both experimental and computational methods, focusing on intermediates and model compounds, some of the main features of the reaction mechanisms that operate during the hydrothermal processing of lignin were elucidated. Key reaction pathways and their connection to different structural features of lignin were proposed. Under neutral conditions, subcritical water was demonstrated to act as a bifunctional acid/base catalyst for the dissection of lignin structures. In a complex web of mutually dependent interactions, guaiacyl units within lignin were shown to significantly affect overall lignin reactivity.

Lignification of Sheepgrass Internodes at Different Developmental Stages and Associated Alteration of Cell Wall Saccharification Efficiency.

Sheepgrass (Leymus chinensis) is a high-quality cool-season forage crop used as pasture and hay for livestock feeds. The presence of lignin in cell walls, however, impairs forage digestibility of such lignocellulosic feedstock. Here, the structural characterization and cell wall composition of sheepgrass internodes were studied, and a progressive increase in cell wall lignification was observed with internode maturation. Lignin composition analysis further revealed a gradual accumulation of guaiacyl and syringyl lignin units during internode development. Consistently, the transcript abundance of lignin-related genes was upregulated in mature internodes, suggesting their potential roles in lignin biosynthesis. Furthermore, the effects of cell wall composition and lignification extent on biomass saccharification efficiency were examined in sheepgrass. The results showed that lignin content, guaiacyl and syringyl lignin unit levels inversely correlated with cell wall digestibility, indicating that lignin is a crucial obstacle for utilizing sheepgrass feedstock. The baseline information obtained in this work will facilitate establishment, grazing management, harvesting and feedstock utilization of sheepgrass in future.

Litter quality control of decomposition of leaves, twigs, and sapwood by the white-rot fungus Trametes versicolor

Litter quality plays predominant roles in plant litter decomposition by modifying the activity of decomposer fungi, but little is known about the response of the decomposing activity of individual fungal strains to variations in litter quality. In the present study, the variability in the decomposing ability of a single fungal strain (Trametes versicolor IFO30340) was quantified under pure culture conditions to elucidate litter quality measures that control the decomposition. We used a total of 72 litters from 51 plant species, including leaves, twigs, sapwood, bark, heartwood, and petioles of broad-leaved trees, coniferous trees, and grass. Mass loss of litter caused by the fungus ranged from 0.9 to 59.8% of the original litter mass, was significantly higher in leaves, twigs, and petioles than in heartwood, and was significantly higher in broad-leaved than in coniferous litter. Tissue type (leaf, sapwood, or twig) and the relative amount of acid-unhydrolyzable residues to total nitrogen were selected as predictor variables of the mass loss of litters. Fourier transform infrared (FT-IR) spectroscopy showed that guaiacyl units of lignin negatively affected the fungal decomposition.

BLISS: A Bioorthogonal Dual-Labeling Strategy to Unravel Lignification Dynamics in Plants

A better in vivo understanding of lignin formation within plant cell walls will contribute to improving the valorization of plant-derived biomass. Although bioorthogonal chemistry provides a promising platform to study the lignification process, methodologies that simultaneously detect multiple chemical reporters in living organisms are still scarce. Here, we have developed an original bioorthogonal labeling imaging sequential strategy (BLISS) to visualize and analyze the incorporation of both p-hydroxyphenyl (H) and guaiacyl (G) units into lignin invivo with a combination of strain-promoted and copper-catalyzed azide-alkyne cycloadditions. On our path to BLISS, we designed a new azide-tagged monolignol reporter for H units in metabolic lignin engineering and used it in conjunction with an alkyne-tagged G unit surrogate to study lignification dynamics in flax. Here, we show that BLISS provides precise spatial information on the zones of active lignification and reveals polarization in single-cell lignification dynamics.

Manipulation of lignin metabolism by plant densities and its relationship with lodging resistance in wheat

Increasing plant density is one of the most efficient ways of increasing wheat (Triticum aestivum L.) grain production. However, overly dense plant populations have an increased risk of lodging. We examined lignin deposition during wheat stem development and the regulatory effects of plant density using the wheat cultivars shannong23 and weimai8. Plants were cultivated at densities of 75, 225 and 375 plants per m2 during two growing seasons. Our results showed that decreasing plant density enhanced culm quality, as revealed by increased culm diameter, wall thickness and dry weight per unit length, and improved the structure of sclerenchyma and vascular bundles by increasing lignification. In addition, more lignins were deposited in the secondary cell walls, resulting in strong lodging resistance. The guaiacyl unit was the major component of lignin and there was a higher content of the syringyl unit than that of the hydroxybenzyl unit. Furthermore, we hypothesised that the syringyl unit may correlate with stem stiffness. We describe here, to the best of our knowledge, the systematic study of the mechanism involved in the regulation of stem breaking strength by plant density, particularly the effect of plant density on lignin biosynthesis and its relationship with lodging resistance in wheat.

Fractionation and physicochemical characterization of lignin from waste jute bags: Effect of process parameters on yield and thermal degradation

In this work lignin was extracted from waste jute bags using soda cooking method and effect of varying alkali concentration and pH on yield, purity, structure and thermal degradation of lignin were studied. The Lignin yield, chemical composition and purity were assessed using TAPPI method and UV–vis spectroscopy. Yield and purity of lignin ranged from 27 to 58% and 50–94%, respectively for all the samples and was maximum for 8% alkali concentration and at pH 2 giving higher thermal stability. Chemical structure, thermal stability and elementary analysis of lignin were studied using FTIR, HNMR, thermo gravimetric analysis (TGA) and Elemental analyzer. FTIR and HNMR results showed that core structure of lignin starts breaking beyond 10% alkali concentration. S/G ratio shows the dominance of Syringyl unit over guaiacyl unit.

Investigation of oil palm based Kraft and auto-catalyzed organosolv lignin susceptibility as a green wood adhesives

The aim of this study is to highlight the application and potentiality of oil palm based lignins in the synthesis of green phenolic resins. The delignification processes were conducted using Kraft and auto-catalyzed ethanol–water pulping processes. The extracted lignins were characterized using elemental analysis, Fourier transform-infrared, 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, molecular weight distribution (Mn, Mw and polydispersity), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The obtained FTIR results revealed that the Kraft lignin contained substantial amounts of guaiacyl units with smaller amounts of syringyl units. The molecular weight of Kraft lignin was 1564gmol−1 which is higher than organosolv lignin at 1231gmol−1. The activated free ring position (2.99%) of Kraft lignin was comparatively higher than that of organosolv lignin (2.06%) which was measured using Mannich reactivity analysis. Thermal analysis of Kraft lignin showed higher thermal stability compared to organosolv lignin. The structural and thermal characteristics implied that Kraft lignin had higher potential for the production of green phenolic resins when compared with organosolv lignin.

Assessment of the thermal behavior of lignins from softwood and hardwood species

The thermal behavior of lignins from softwood and hardwood species has been investigated using thermogravimetry and differential scanning calorimetry. Klason Lignin from Pinus taeda and Klason lignin from Eucalyptus grandis were studied. The differential scanning calorimetry results showed that both Klason lignins studied presented similar glass transition temperature. Thermogravimetric results showed that the lignin degradation occurs in three stages. The Klason lignin of Pinus taeda is more thermally stable than Eucalyptus grandis, probably because of the higher thermal stability of the guaiacyl units in softwood lignin. The degradation of both lignins initiate by a diffusion process. However when the conversion values are higher than 0,1 the lignin degradation mechanism is a complex procedure and involves the degradation of a highly condensed aromatic structure formed at the previous degradation stages.