Structural Analysis Of Lignin Research Articles

Characterization of fused aromatic multirings in lignin via synchronous fluorescence spectroscopy and catalytic hydro-depolymerization

The structural analysis of lignin is highly significant in practical terms. We investigated the presence of fused aromatic multirings (FARs) distinct from conventional phenylpropane units in seven lignin types using synchronous fluorescence spectroscopy (SFS) and quantified their relative proportions. Our findings reveal that FARs are present in all lignin samples, primarily composed of 2–6 rings. The relative distribution of FARs in lignin is ranked as follows: 2 rings > 1 ring > 4 rings > 3 rings > 6 rings > 5 rings. The relative contents of these FARs (1–6 rings) exhibit slight variations across all lignin samples. Notably, FARs with 2 rings are the highest at 35 %−53 %, while those with 5 and 6 rings are the lowest, collectively accounting for less than 1.37 %. Moreover, the relative contents of FARs with 1 and 2–6 rings range approximately 24 %−32 % and 68 %−76 %, respectively. Furthermore, the catalytic hydro-depolymerization of lignin was performed and the experimental results demonstrate that the hydro-liquefied oil from lignin contains aromatic compounds with 1–7 rings, and the relative contents of aromatic compounds with 1 ring and 2–7 rings in the oil are 29 % and 71 %, respectively, which is consistent with that of lignin SFS. These findings are also consistent with the existing literature and experimental results. This study offers an explanation for the low yields observed in current depolymerization processes targeting small molecules within lignin and establishes a theoretical foundation for achieving high yields in the preparation of multiring aromatic hydrocarbons.

Mass spectrometry-based methods for the advanced characterization and structural analysis of lignin: A review.

Lignin is currently one of the most promising biologically derived resources, due to its abundance and application in biofuels, materials and conversion to value aromatic chemicals. The need to better characterize and understand this complex biopolymer has led to the development of many different analytical approaches, several of which involve mass spectrometry and subsequent data analysis. This review surveys the most important analytical methods for lignin involving mass spectrometry, first looking at methods involving gas chromatography, liquid chromatography and then continuing with more contemporary methods such as matrix assisted laser desorption ionization and time-of-flight-secondary ion mass spectrometry. Following that will be techniques that directly ionize lignin mixtures-without chromatographic separation-using softer atmospheric ionization techniques that leave the lignin oligomers intact. Finally, ultra-high resolution mass analyzers such as FT-ICR have enabled lignin analysis without major sample preparation and chromatography steps. Concurrent with an increase in the resolution of mass spectrometers, there have been a wealth of complementary data analyses and visualization methods that have allowed researchers to probe deeper into the "lignome" than ever before. These approaches extract trends such as compound series and even important analytical information about lignin substructures without performing lignin degradation either chemically or during MS analysis. These innovative methods are paving the way for a more comprehensive understanding of this important biopolymer, as we seek more sustainable solutions for our human species' energy and materials needs.

Enzyme adsorption properties on dilute acid pretreated biomass by low vacuum-scanning electron microscopy and structural analysis of lignin

In this study, enzyme adsorption properties were investigated as a function of the structural change of lignin in dilute acid pretreated biomass using oxalic and sulfuric acid catalysts under the same reaction conditions. Although the contents of glucan and lignin in the dilute acid pretreated biomass were similar regardless of the catalysts used, the enzymatic hydrolysis efficiency and degree of enzyme adsorption differed considerably. The highest efficiencies were 87.79% and 96.49% for the oxalic acid and sulfuric acid catalysts, respectively. The reasons for this observation were investigated by low vacuum-scanning electron microscopy and the structural analysis of lignin. In the oxalic acid pretreated biomass, the enzyme was irreversibly adsorbed onto the lignin. The oxalic acid pretreated biomass possessed a higher content of G-type lignin than did the sulfuric acid pretreated biomass. This type of lignin has a high affinity for the enzyme, inducing irreversible enzyme adsorption onto the biomass.

Enhanced lignin extraction process from steam exploded corn stalk

In this work, the alkaline extraction processes of lignin from untreated and steam-exploded corn stalk were compared and the enhanced extraction process was investigated by neutral solvent extraction and structural analysis of lignin. It was found that a first order model could readily simulate the lignin extraction from untreated stalk while it was helpless to describe the enhanced process after steam explosion due to the intense dissolution of lignin at the beginning stage of extraction. The lignin extracted by neutral solvent from ball-milled corn stalk and its structural characterization demonstrated that the poor description of extraction process by a first order model was mainly attributed to the considerable depolymerization during steam explosion. Due to the depolymerization of lignin, the alkaline extraction after steam explosion became the direct dissolution of depolymerized lignin and was successfully simulated by a second-order model. Finally, the activation energy of lignin alkali-extraction decreased 37.78% after steam explosion treatment with 1.8 MPa and 5 min, which indicated that milder extraction conditions were available to extract lignin from steam-exploded corn stalk. This study also provides a basic guidance for delignification approaches of lignocelluloses after steam explosion.

Kraft delignification of energy crops in view of pulp production and lignin valorization

The hardwoods Acacia dealbata (mimosa), Salix spp. (willow), and the perennial plants Arundo donax (giant reed) and Miscanthus giganteus (giant Chinese silver grass) are important energy crops, with low requirements and high productivity. The polysaccharide content of these species has drawn attention as source of sugars for biobased products. In this work, biomasses were deconstructed by kraft pulping, evaluating final pulp yields as well as residual lignin (kappa number, KN) as indicators of the pulp quality for conversion to sugars. The black liquors and lignin in the isolated materials were evaluated concerning composition and structural characterization parameters with relevance to further valorizations routes, such as production of vanillin and syringaldehyde. The best trade-off between pulp yield and KN were achieved for 160°C and pulping time 210min, with active alkali (AA) 22% for mimosa and willow and AA 18% for giant reed; these three biomasses presented similar pulp yields (45–47%) and KN (13–15). For silver grass a lower AA (16%) and the combination of higher temperature/lower pulping time (170°C/180min) were selected. Among the four, silver grass presented the highest pulp yield (51.5%) and the lowest KN (10), which is the first advantage identified for this species. Another advantage is the higher production of lignin by isolation from black liquor (128g/kg of biomass), compared to the other materials (88–119g/kg), with the additional benefit of low contamination with inorganic compounds. The isolation of lignins is favorable for the valorization route involving oxidative depolymerization. The structural analysis of lignins and the comparison between the frequency of the main interlinkages and functional groups allowed drawing remarks about their suitability for some applications. The data presented are a tool for decision about the best exploitation route for lignin, contributing for the valorization of the streams generated in biorefining processes of energy crops.

A critique on the structural analysis of lignins and application of novel tandem mass spectrometric strategies to determine lignin sequencing.

This review is devoted to the application of MS using soft ionization methods with a special emphasis on electrospray ionization, atmospheric pressure photoionization and matrix-assisted laser desorption/ionization MS and tandem MS (MS/MS) for the elucidation of the chemical structure of native and modified lignins. We describe and critically evaluate how these soft ionization methods have contributed to the present-day knowledge of the structure of lignins. Herein, we will introduce new nomenclature concerning the chemical state of lignins, namely, virgin released lignins (VRLs) and processed modified lignins (PML). VRLs are obtained by liberation of lignins through degradation of vegetable matter by either chemical hydrolysis and/or enzymatic hydrolysis. PMLs are produced by subjecting the VRL to a series of further chemical transformations and purifications that are likely to alter their original chemical structures. We are proposing that native lignin polymers, present in the lignocellulosic biomass, are not made of macromolecules linked to cellulose fibres as has been frequently reported. Instead, we propose that the lignins are composed of vast series of linear related oligomers, having different lengths that are covalently linked in a criss-cross pattern to cellulose and hemicellulose fibres forming the network of vegetal matter. Consequently, structural elucidation of VRLs, which presumably have not been purified and processed by any other type of additional chemical treatment and purification, may reflect the structure of the native lignin. In this review, we present an introduction to a MS/MS top-down concept of lignin sequencing and how this technique may be used to address the challenge of characterizing the structure of VRLs. Finally, we offer the case that although lignins have been reported to have very high or high molecular weights, they might not exist on the basis that such polymers have never been identified by the mild ionizing techniques used in modern MS.

A critique on the structural analysis of lignins and application of novel tandem mass spectrometric strategies to determine lignin sequencing

A critique on the structural analysis of lignins and application of novel tandem mass spectrometric strategies to determine lignin sequencing

Structural Analysis of Lignin and its Thermal Performance under Supercritical Water Conditions

This study investigated the application of supercritical water as green and environmentally friendly treatment medium for hydrolysis and decomposition lignin in order to obtain the relation the products of phenolic compounds and the lignin structural. The processes were studied using three different biomass feed-stocks: poplar alkali lignin (AL), corncob enzymatic/mild acidolysis lignin (EMAL), and cornstalk or benzene–ethanol-extracted lignin (BEL), and lignin were identified by elemental analysis, FTIR, 31P-NMR. Experiments were performed in a batch stainless steel reactor at supercritical water 375°C at residence time of 10min. Main phenolic compounds from decomposition of lignin were identified by external standard method. Results indicated that the functional groups of AL, EMAL and BEL had a marked influence on the produces. More phenol OH groups and more benzene and phenolic contents could be gained under supercritical water conditions. The total produces reached to 74mg/g of dry EMAL and which was a high quality raw material as the source of phenol and 4-ethylphenol. The AL compositions of guaiacol, 4-methylguaiacol, 3-methoxycatechol, 2,6-dimethoxyphenol, 1,2,3-trimethoxybenzene had more than EMAL and BEL.

Structural analysis of lignin in chestnut wood by pyrolysis-gas chromatography/mass spectrometry

The goal of the study was to determine the percentage of lignin in chestnut wood and to characterize structurally this polymer by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) according to a possible influence on ring shake defect. The sampling was performed in different sites of Lazio Region in Italy. Wood disks from trees with ring shake defect and without ring shake defect were selected and little amount of heartwood (1–2 g) sampled between 6th and 10th and between 11th and 15th annual growth ring were analyzed. The study allowed quantifying lignin content, which is in average 26% and syringyl/guaiacyl (S/G) ratio, which present an average value of 2.43. Belong the pyrolysis products of wood, the trees characterized by ring shake show a higher concentration of the phenol homosyringaldehyde respect to the healthy trees. There is not any evident difference in the products composition of pyrolysis in respect to trees’ age, especially the critical period of 12–14 years in which ring shake generally becomes more evident. The site of wood provenance is the higher factor of variability in the structure of lignin for many phenols.

Structural Analysis of Lignin by Resonance Raman Spectroscopy

Resonance Raman (RR) spectroscopy, combined with Kerr gated fluorescence rejection in the time domain, has recently elucidated lignin structure with unique sensitivity and selectivity. This promises structural studies of fluorescent natural macromolecules, such as lignin, which were previously not possible. Such studies rely on an improved understanding of the RR spectral behavior of lignin, which is today scarcely understood. We explain for the first time this behavior by a semi-empirical theory, and observe its pertinent features for lignin in vascular plants. We have used well-defined oxidative treatments as means of probing lignin structural elements, and show that RR sensitivity and selectivity depend crucially on excitation wavelength. Through the theory we relate these results to basic structural aspects of lignin. Spectra obtained by blue light laser excitation (400 nm) are dominated by low redox potential syringyl lignin groups, whereas lower photon energy (500 nm) decreases the selectivity markedly. RR bands depend on molecular structure but also on molecular environment. Thus charge transfer donor-acceptor interactions within lignin reduce the intensity of bands associated with electron rich moieties. New possibilities for basic and selective structural information on fluorescent natural materials, such as lignin, have thus appeared.

Structural Analysis of Lignin by Pyrolysis-Gas Chromatography (VI)

Pyrograms of pyrolysis-gas chromatography (Py-GC) from thirteen species of tropical hardwoods were obtained under pyrolytic conditions with a Curie-point pyrolyzer at 500°Cfor 4 seconds to determine twenty six pyrolysis products and to estimate ratios of syringylunits to guaiacyl units (S/G ratios) of lignin and lignin-like substances. Before thepyrolysis, wood meals were extracted with benzene and successively with 70% acetone/wa-ter to remove tannins and other phenols. The observed S/G ratios were in good agreementwith syringaldehyde/vanillin (S/V) ratios obtained by nitrobenzene oxidation. The extractedkapur wood meals were treated with hot 1% NaOH solution to extract lignin-like sub-stances. On a pyrogram of the 70% acetone/water extractives, guaiacol, 4-vinylguaiacol, syringol, and 4-vinylsyringol were identified as main pyrolysis products. On a pyrogram ofa chloroform-soluble part of the hot 1% NaOH extractives, vanillin and acetoguaiaconewere identified as main peaks, and the characteristic of the pyrogram was quite differentfrom that of lignin. In order to simplify a method for determination of acid-insoluble (Klason) lignin in tropical hardwoods, wood samples extracted with 70% acetone/waterwere hydrolyzed at 121°C, and the acid-insoluble residues were characterized by Py-GC.The conents of acid-insoluble residues, which were given by hydrolysis with 3% or 4%sulfuric acid at 121t for 1 hour, were slightly smaller than the Klason lignin contents. Onpyrograms of the acid-insoluble residues given by hydrolysis with 4% sulfuric acid, ratios of 4-methyl guaiacol (4-methylsyringol) to guaiacol (syringol) were higher than those on pyrograms of the Klason lignins.

熱分解ガスクロマトグラフィーによるリグニンの構造解析 第７報 木材パルプの酸加水分解条件と酸不溶性残さの性状

熱分解ガスクロマトグラフィーによるリグニンの構造解析 第７報 木材パルプの酸加水分解条件と酸不溶性残さの性状

熱分解ガスクロマトグラフィーによるリグニンの構造解析（第２報） 腐朽材リグニンの分析

Pyrolysis-gas chromatography (Py-GC) was applied to the characterization of lignin in decayed woods. Recently, Py-GC becomes one of the powerful tools for analyses of synthetic polymers. Very small amounts of solid materials are analyzed rapidly by using PyGC. In the structural analysis of lignin in woods, lignin can be analyzed by Py-GC without being isolated from woods.When sugi (Ctyptomeria japonica) woods is analyzed by Py-GC, the eight main ligninderived pyrolysis products (guaiacol, 4-methylguaiacol, 4-vinylguaiacol, vanillin, trans-isoeugenol dihydroconiferyl alcohol, coniferaldehyde and trans-coniferyl alcohol) can be detected. Pyrolysis of woods decayed by Coriolus versicolor and Tyromyces palustris provided the eight pyrolysis products in a smaller yield than that of the sound wood.In pyrolysis of sugi woods decayed by C. versicolor, the ratios of the peak area of guaiacol to the combined peak areas of the eight pyrolysis products (cpaG) increased with decreasing combined peak areas. On the other hand, in pyrolysis of sugi woods decayed by T. palustris, no cleas relationship was found between the ratios of the peak area of pyrolysis products to cpaG and cpaG per sample weight.Beech (Fagus crenata) woods were also decayed by C. versicolor, Daedalea dickinsii, Ganoderma lucidum and T. palustris, and analyzed by Py-GC. All decayed beech woods showed the smaller ratios of the combined peak areas of the four main syringyl type compounds (Syringol. 4-methylsyringol, 4-vinylsyringol, trans-4-propenylsyringol) (sumS) to the combined peak areas of the four main guaiacyl type compounds (guaiacol, 4-methylguaiacol, 4-vinylguaiacol, trans-isoeugenol) (sumG) than that of sound wood. This suggests that syringyl units of lignin were preferentially degraded to guaiacyl units. The ratios of the peak area of guaiacol to sumG and the ratios of the peak area of syringol to sumS increased in pyrolysis of beech woods decayed by the above four fungi.To clarify the convincing pyrolytic origins of the lignin structures giving syringol and guaiacol in high yields, some lignin dimer model compounds were subjected to Py-GC : syringlglycol-β-guaiacyl ether (SG-OH), dehydrodiisoeugenol (DDI) and α-guaiacoxyacetosyringone (SG=O). A phenylocoumaran type lignin model compound, DDI, did not give guaiacol. Similarly syringol was not formed from SG-OH, which is the β-O-4 analogue having a hydroxyl group at the Cα-position. On the other hand, the β-O-4 analogue having a carbonyl group at the Cα-position, SG=O, gave syringol by the pyrolytic cleavage of the bond between the Cα atom and aromatic ring in a 3 mol% yield. These findings suggest that the formation of α-carbonyl groups in the lignin macromolecule by fungal treatments should be one of the reasons why the ratios of guaiacol and syringol increased in Py-GC of the decayed woods. Py-GC is expected to be a promising method for characterization of the decayed wood lignin.

熱分解ガスクロマトグラフィーによるリグニンの構造解析（第３報） 広葉樹材のアルカリ性ニトロベンゼン酸化との比較

In order to study the effectiveness of pyrolysis-gas chromatography (Py-GC) on the structural analysis of lignin, wood meals of 13 Japanese hardwood species were subjected to Py-GC and the results were compared with those of nitrobenzene oxidation. Thirteen compounds with guaiacyl nucleus were identified as pyrolysis products along with their syringyl analogues by comparing their retention times and mass spectra with those of authentic compounds. Quantitative analyses were performed by using the calibration factors which determined by quantitative gas chromatographic analysis of authentic compounds. Total yields of monomeric pyrolysis products were between 12.2 and 26.1% of Klason lignin and were found to be different among wood species. Total yields of vanillin (V) and syringaldehyde (S) obtained by nitrobenzene oxidation were between 31.7 and 43.9% of Klason lignin and were almost twice as large as those of the pyrolysis products. The ratios of syringyl type products to guaiacyl type products were in good agreement with the S/V molar ratios obtained by nitrobenzene oxidation. Accordingly, Py-GC is expected to be a time saving and convenient routine method for characterizing hardwood lignin because the method requires only small amount of samples and no preliminary chemical processing. However, accumulation of analyses data on the yields of pyrolysis monomers is still insufficient. Further studies using other hardwood species are considered to be necessary.

Structural analysis of lignins by high-resolution13C nuclear magnetic resonance in a solid

Structural analysis of lignins by high-resolution13C nuclear magnetic resonance in a solid