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Abstract Background Lignin is a complex aromatic heteropolymer comprising 15–30% dry weight of the lignocellulose. The complex structural characteristic of lignin renders it difficult for value-added utilization. Exploring efficient lignin-degrading microorganisms and investigating their lignin-degradation mechanisms would be beneficial for promoting lignin valorization. In this study, a newly isolated white-rot basidiomycete, Trametes hirsuta X-13, with capacity to utilize alkaline lignin as the sole substrate was investigated. Results The analysis of the fermentation properties of T. hirsuta X-13 using alkaline lignin as the sole substrate, including the mycelial growth, activities of ligninolytic enzymes and the rates of lignin degradation and decolorization confirmed its great ligninolysis capacity. The maximum lignin degradation rate reached 39.8% after 11 days of T. hirsuta X-13 treatment, which was higher than that of reported fungi under the same condition. Fourier transform infrared spectrometry (FTIR), gas chromatography–mass spectrometry (GC–MS) scanning electron micrographs (SEM), two-dimensional heteronuclear single quantum coherence NMR analysis (2D-HSQC NMR) collaborated with pyrolysis gas chromatography–mass spectrometry (py-GC/MS) analyses proved that lignin structure was severely deconstructed along with amounts of monomer aromatics generated. Furthermore, according to those chemical analysis, in addition to canonical Cα–Cβ breakage, the cleavage of lignin interunit linkages of β–β might also occur by T. hirsuta X-13. Conclusions This study characterized a newly isolated white-rot basidiomycete T. hirsuta X-13 with impressive alkaline lignin degradation ability and provided mechanistic insight into its ligninolysis mechanism, which will be valuable for the development of lignin valorization strategies.

The degradation of lignocellulose by fungi, especially white-rot fungi, contributes a lot to carbon cycle, bio-fuel production, and many other bio-based applications. However, the existing enzymatic and non-enzymatic degradation mechanisms cannot be unequivocally supported by in vitro simulation experiment, meaning that additional mechanisms might exist. Right now, it is still very difficult to discover new mechanisms with traditional forward genetic approaches. To disclose novel lignin degradation mechanisms in white-rot fungi, a series of fusants from wide cross by protoplast fusion between Pleurotus ostreatus, a well-known lignin-degrading fungus, and Saccharomyces cerevisiae, a well-known model organism unable to degrade lignocellulose, was investigated regarding their abilities to degrade lignin. By analyzing the activity of traditional lignin-degrading enzyme, the ability to utilize pure lignin compounds and degrade corn stalk, a fusant D1-P was screened out and proved not to contain well-recognized lignin-degrading enzyme genes by whole-genome sequencing. Further investigation with two-dimension nuclear magnetic resonance (NMR) shows that D1-P was found to be able to degrade the main lignin structure b-O-4 linkage, leading to reduced level of this structure like that of the wild-type strain P. ostreatus after a 30-day semi-solid fermentation. It was also found that D1-P shows a degradation preference to b-O-4 linkage in Ab(S)-threo. Therefore, wide cross between white-rot fungi and S. cerevisiae provides a powerful tool to uncover novel lignocellulose degradation mechanism that will contribute to green utilization of lignocellulose to produce bio-fuel and related bio-based refinery. [ABSTRACT FROM AUTHOR]

Formic acid is an attractive solvent for the fractionation of lignocellulose for the production of biomaterials and chemicals, while the operation conducted in a batch manner is not conducive to mass transfer in separation process. In this research, eucalyptus was fractionated with formic acid/hydrochloric solution in a flow-through reactor at 95 °C, and the structural characteristics and the composition of fractionated lignin in different stages were investigated. Results showed that the fractionation efficiency was notably improved with a flow-through reactor, as evidenced by the low solid residue yield of 49.5% and the lignin removal rate of 79.4% as compared to the batch manner. During the fractionation process, the dissolution rate of lignin decreased gradually, and the obtained lignin samples showed low molecular weight (<3000), good uniformity (<2), and high thermal stability. The structure analysis showed that β-O-4, β-β, and β-5 linkages in lignin were degraded to varying degrees with increased time, and the degradation of G units was more severe than S ones. • Eucalyptus was fractionated in a flow-through reactor at 95 °C. • The fractionated lignin had a low contaminated carbohydrate content. • The lignin had a low molecular weight and great uniformity. • β-O-4, β-5 and β-β linkages in lignin were degraded. [ABSTRACT FROM AUTHOR]

Background: Lignin is a complex aromatic heteropolymer comprising 15–30% dry weight of the lignocellulose. The complex structural characteristic of lignin renders it difficult for value-added utilization. Exploring efficient lignin-degrading microorganisms and investigating their lignin-degradation mechanisms would be beneficial for promoting lignin valorization. In this study, a newly isolated white-rot basidiomycete, Trametes hirsuta X-13, with capacity to utilize alkaline lignin as the sole substrate was investigated. Results: The analysis of the fermentation properties of T. hirsuta X-13 using alkaline lignin as the sole substrate, including the mycelial growth, activities of ligninolytic enzymes and the rates of lignin degradation and decolorization confirmed its great ligninolysis capacity. The maximum lignin degradation rate reached 39.8% after 11 days of T. hirsuta X-13 treatment, which was higher than that of reported fungi under the same condition. Fourier transform infrared spectrometry (FTIR), gas chromatography–mass spectrometry (GC–MS) scanning electron micrographs (SEM), two-dimensional heteronuclear single quantum coherence NMR analysis (2D-HSQC NMR) collaborated with pyrolysis gas chromatography–mass spectrometry (py-GC/MS) analyses proved that lignin structure was severely deconstructed along with amounts of monomer aromatics generated. Furthermore, according to those chemical analysis, in addition to canonical Cα–Cβ breakage, the cleavage of lignin interunit linkages of β–β might also occur by T. hirsuta X-13. Conclusions: This study characterized a newly isolated white-rot basidiomycete T. hirsuta X-13 with impressive alkaline lignin degradation ability and provided mechanistic insight into its ligninolysis mechanism, which will be valuable for the development of lignin valorization strategies. [ABSTRACT FROM AUTHOR]

Understanding and recognizing the structural characteristics of lignin-carbohydrate complexes (LCCs) and lignin in different growth stages and tissue types of bamboo will facilitate industrial processes and practical applications of bamboo biomass. Herein, the LCC and lignin samples were sequentially isolated from fibers and parenchyma cells of bamboo with different growth ages. The diverse yields of sequential fractions not only reflect the different biomass recalcitrance between bamboo fibers and parenchyma cells but also uncover the structural heterogeneity of these tissues at different growth stages. The molecular structures and structural inhomogeneities of the isolated lignin and LCC samples were comprehensively investigated. The results showed that the structural features of lignin and LCC linkages in parenchyma cells were abundant in β- O -4 linkages but less with carbon-carbon linkages, suggesting that lignin and cross-linked LCC in parenchyma cells are simple in nature and easily to be tamed and tractable in the current biorefinery. Parallelly, the different ball-milled samples were directly characterized by high-resolution (800 M) solution-state 2D-HSQC NMR to analyze the whole lignocellulosic material. Overall, the scheme presented in this study will provide a comprehensive understanding of lignin and LCC linkages in fibers and parenchyma cells of bamboo and enable the utilization of bamboo biomass.

Lignin is the most abundant aromatic biomacromolecule on the earth, which is an attractive raw material for producing bio-based chemicals, materials, and fuels. However, the complexity, heterogeneity, and variability of the lignin structure always hinders the value-added application of different sources of raw materials. In this study, double enzymatic lignin (DEL) was isolated from balsa grown for different lengths of time to understand the structural variations of lignin macromolecules during the growth of balsa for the first time. Confocal Raman microscopy and component analysis were used to monitor the lignin accumulation in balsa. Meanwhile, the structural characteristics and chemical reactivity of DELs were synthetically characterized by advanced 2D-HSQC and 31P-NMR techniques. It was found that the balsa lignin is a typical hardwood lignin and it is overwhelmingly composed of C–O bonds (i.e., β-O-4 linkages), whose content is elevated with increasing tree-age. Interestingly, carbon–carbon linkages (e.g., β-β and β-5) in these DELs isolated from 3-and 5-year-old balsa are gradually disappearing. Considering the increasing molecular weight of DELs with tree-age, it was concluded that lignin macromolecules in balsa wood were gradually polymerized within the growth period. Furthermore, abundant C–O linkages with less C–C linkages in the DELs from 3 and 5-year-old balsa wood suggested that these feedstocks are promising in current lignin-first biorefinery and will facilitate the conversion of aromatic chemicals from the lignin macromolecule. In short, a comprehensive understanding of native lignin during the growth of balsa wood will not only advance the understanding of biosynthetic pathways of lignin biopolymer, but also facilitate the deconstruction and value-added applications of this kind of feedstock.

The plant cell wall is a complex, heterogeneous structure primarily composed of cellulose, hemicelluloses, and lignin. Exploring the variations in these three macromolecules over time is crucial for understanding wood formation to enhance chemical processing and utilization. Here, we comprehensively analyzed the chemical composition of cell walls in the trunks of Pinus tabulaeformis using multiple techniques. In situ analysis showed that macromolecules accumulated gradually in the cell wall as the plant aged, and the distribution pattern of lignin was opposite that of polysaccharides, and both showed heterogenous distribution patterns. In addition, gel permeation chromatography (GPC) results revealed that the molecular weights of hemicelluloses decreased while that of lignin increased with age. Two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance (2D-HSQC NMR) analysis indicated that hemicelluloses mainly comprised galactoglucomannan and arabinoglucuronoxylan, and the lignin types were mainly comprised guaiacyl (G) and p -hydroxyphenyl (H) units with three main linkage types: β- O -4, β-β, and β-5. Furthermore, the C-O bond (β- O -4) signals of lignin decreased while the C-C bonds (β-β and β-5) signals increased over time. Taken together, these findings shed light on wood formation in P. tabulaeformis and lay the foundation for enhancing the processing and use of wood and timber products. [Display omitted] • Organelles are highly active during secondary wall thickening of tracheids. • Lignin and polysaccharides showed heterogeneous but opposing distribution patterns. • The molecular weights increased for hemicelluloses and decreased for DELs with age. • Hemicelluloses mainly comprised galactoglucomannan and arabinoglucuronoxylan. • Lignin harbored fewer C-O bonds (β- O -4) and more C-C bonds (β-β and β-5) over time. [ABSTRACT FROM AUTHOR]

Lignin represents the most abundant source of renewable aromatic resources, and depolymerization of lignin has been shown to be a prominent challenge in the production of low-molecular-mass aromatic chemicals. Herein, we report the preparation of Ni/LCNF catalyst by which Ni nanoparticles were inlaid in lignin-based carbon nanofibers (LCNF) to improve stability of the catalyst and adjust the interaction between the metal and its support. We also present its use in lignin depolymerization. The use of 10%Ni/LCNF catalyst resulted in exceptionally high yields of light lignin fragments (87%) and phenols (7%). The average molecular weight (Mw) of light lignin residue was significantly lower than that of the untreated lignin, and there was clear evidence of lignin depolymerization. Preliminary recycling studies showed that the Ni/LCNF catalyst could maintain its activity for over three recycling cycles; its selectivity towards phenols remained unchanged. The present method, in which Ni nanoparticles were inserted or partially embedded in carbon materials to avoid Ni nanoparticle aggregation, sintering and loss during lignin depolymerization, is an alternative way that can be applied to maximize the utilization of lignin. Image 1 • Ni nanoparticles inlaid in lignin-based carbon nanofibers (Ni/LCNF) was reported. • The Ni/LCF catalyst maintains activity over three catalytic cycles. • Ni/LCNF show low ring-hydrogenation and high aryl ethers hydrogenolysis activity. • The demethoxylation and alkylation plays important role in lignin depolymerization. [ABSTRACT FROM AUTHOR]

To achieve high value-added utilization of lignin extracted from the biorefinery process in the wood composite industry, binderless particle boards were manufactured by bamboo materials combined with alkaline lignin (AL) in various proportions under various hot-pressing conditions. To elucidate the reactivity and chemical transformations of lignin macromolecules during the hot-pressing process, lignin samples were isolated from the corresponding boards and characterized by high-performance anion-exchange chromatography (HPAEC), gel permeation chromatography (GPC), quantitative 31P-NMR, and 2D-HSQC NMR. The best bonding strength (1.36 MPa) of the binderless particle boards was obtained under the conditions of 180 °C, pressure 5 MPa, and lignin/bamboo mass ratio 0.4. The molecular weight of the lignin samples decreased from 3260 to 1420 g/mol during hot-pressing. The NMR results showed that the contents of β-O-4' and β-β' linkages were reduced and β-5' linkages were increased as the hot-pressing temperature rose. Simultaneously, the percentage of G-type and H-type lignins as well as the content of phenolic OH increased.

High contents of internal β-O-4 linkages in lignin are critical for high-yield production of high-value aromatic monomers by depolymerization. However, it remains great challenge due to lack of suitable protection strategy. In this work, a very effective lignin-first strategy was developed to produce ideal lignin with a super high content of β-O-4 linkages (up to 72 %) from poplar, in which the pretreatment was undertaken at low temperatures of 90–130 °C with the use of AlCl 3 -catalyzed 1, 4-butanediol solution. 2D-HSQC NMR spectra revealed that lignin β-O-4 linkages were protected from etherification of the OH group by 1, 4-butanediol at the α position of lignin aliphatic chains. Besides, the OH groups at the γ position of lignin was also etherified, leading the formation of a structure of Ph-CH=CHCH 2 O(CH 2) 4 OH. Interestingly, structure protection facilitated the formation of lignin nanoparticles via self-assembly (<100 nm). In addition, it was observed from pyrolysis results that addition of 1, 4-butanediol remarkably protected the structure of lignin by avoiding condensation, promoting the production of aromatics. The cellulose-rich fraction possessed a high cellulose digestibility of 91.64 % by enzymatic hydrolysis at a cellulase dosage of 15 FPU/g cellulose, approximately 6-fold untreated poplar (15.91 %). This low-temperature lignin-first strategy was of great importance for multi-products biorefining lignocellulose because it leads to the production of both lignin with super high content of β-O-4 linkages for depolymerization and highly digestible cellulose for sugar production. • Effective fractionation via low-temperature lignin-first strategy was developed. • Recovered ideal lignin possessed a super high content of β-O-4 linkages up to 72 %. • 1, 4-butanediol reacted with carbocation of lignin to form α-etherified structure. [ABSTRACT FROM AUTHOR]

The lignin-carbohydrate complex (LCC) was isolated from milled wood lignin of 2- and 24-month-old crude bamboo (Neosinocalamus affinis) culms using acetic acid (AcOH) and then characterized. The results have shown that the LCC preparation from 2-month-old bamboo (L2) exhibited a slightly lower molecular weight than the LCC preparation from the 24-month-old bamboo (L24). Further studies using Fourier transform infrared spectroscopy (FT-IR) and heteronuclear single quantum coherence (2D-HSQC) NMR spectra analyses indicate that the LCC preparations included glucuronoarabinoxylan and G-S-H lignin-type with G>S>>H. The content of the S lignin units of LCC in the mature bamboo was always higher than in the young bamboo. Combined with sugar composition analysis, the contents of phenyl glycoside and ether linkages in the L24 preparation were higher than in the L2 preparation; however, there was a reverse relationship of ester LCC bonds in L2 and L24. Lignin-xylan was the main type of LCC linkage in bamboo LCCs. Lignin-lignin linkages in the LCC preparations included β-β, β-5 and β-1 carbon-to-carbon, as well as β-O-4 ether linkages, but β-1 linkages were not present in L2. [ABSTRACT FROM AUTHOR]

Nanoparticles are a new frontier to valorize underutilized and abundant lignin generated by biorefineries. Typical chemical processes to synthesize lignin micro- and nano-particles (LMNPs) use large quantity of organic solvents and therefore, could adversely impact the environment. Hence, we have employed an eco-friendly mechanical approach, i.e. , ultrafine friction grinding (UFG), to produce "green" LMNPs with controlled size and micromorphology. Specifically, we investigated the effect of processing temperature, at 0, 25 and 70 °C, on lignin nanosizing. Our results showed that low temperature (0 °C) significantly favored the size reduction of lignin where we achieved a median particle size of ∼100 nm after 12 grinding passes. At 70 °C, LMNPs reached a size equilibrium of ∼160 nm within four passes but did not decrease in size upon subsequent grinding. Moreover, analysis of the LMNPs by SEM showed that samples produced at 0 °C mostly had irregular flat shapes with sharp angles, such as stars and polyhedrons, with a glabrous surface, whereas, samples produced at 25 and 70 °C featured spheres and rods with nanoscopic pores on the surface. Physico-chemical properties of LMNPs, such as molecular weight and thermal degradation, did not change significantly compared to the original lignin, however, samples generated at 0 °C exhibited significantly fewer inter-unit linkages than those generated at 70 °C. Our study thus shows that varying the grinding temperature facilitates the customization of LMNP micromorphology. Furthermore, the proposed method for LMNP manufacturing is simple and eco-friendly, and presents a viable approach for lignin valorization. [Display omitted] • Modulating grinding temperature facilitates efficient lignin nanosizing. • At 70 °C very few grinding passes were required to achieve size equilibrium. • The smallest particle size of 100 nm was achieved by processing lignin at 0 °C. • Lignin formed flat polyhedral or spherical nanoparticles at different temperatures. • Grinding causes minimal physico-chemical changes in lignin especially at 70 °C. [ABSTRACT FROM AUTHOR]

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Detailed structural features of lignin from hydroxycinnamoyl transferase (HCT) down-regulated poplar has not been thoroughly illustrated. In the present study, MWL and CEL samples were successively extracted with higher yield and purity. NMR spectra demonstrated that the MWL and CEL presented similar structural features (β-O-4', β-β', β-5', and β-1'), although the subsequent CEL had a high β-O-4' linkages content and S/G ratios, which are also related to their molecular weights. There were no significant differences in S/G ratio and the distribution of the inter-unit linkages between the control and HCT down-regulated poplar (HCT poplar). However, a minor amount of H units were detected in lignin of the HCT poplar. In addition, p-hydroxybenzoate (PB) content was observably increased in the lignin from the HCT poplar. These findings are of very importance in assessing of the digestibility of HCT down-regulated poplar in the fuel production. [ABSTRACT FROM AUTHOR]

Abstract: To possibly help in understanding the chemistry of the D process using E. urophylla E. grandis LH 107 as the pulping material, residual lignin in kraft-oxygen pulp bleached by chlorine dioxide was extracted by the dioxane/water acidolysis method. The content of functional groups in the extracted lignin was determined by C and P NMR spectroscopy. A relatively significant difference could be seen in the chemical properties of residual lignin between oxygen delignified (O) and chlorine dioxide treated (OD) pulp. The results suggest a decreased function group content in the residual lignin of chlorine dioxide treated kraft-oxygen pulps. It is quite interesting that the depletion of phenolic hydroxyl and methoxyl group present in residual lignin is due to the quinone formation during the oxidation of chlorine dioxide, based on the data obtained in HSQC and C NMR spectra of non-cyclic and cyclic MATS, and the content in condensed and unsubstituted phenolics is reduced to the same degree, which is contrary to what we generally perceive. [Copyright &y& Elsevier]

Abstract: In this study, extraction of hemicelluloses from the carbohydrate-enriched residues was successfully carried out with organic solvent and the residue was used for bio-based energy production. The chemical composition and physico-chemical properties of six hemicelluloses released were elucidated by a combination of sugar analysis, molecular determination, Fourier transform infrared, and 1H, 13C and 2D-HSQC NMR spectroscopy. The results showed that the successful treatments resulted in a fractionation of the native hemicelluloses. The sugar analysis indicated that xylose (47.14–56.91%) was found to be the major sugar components and small amounts of glucose (14.1–19.06%) and mannose (12.41–18.09%) were also observed in these hemicellulosic fractions. Further studies by NMR spectroscopy exhibited that the acetylated hemicellulosic fraction had a main structure of (1→4)-linked β-d-xylopyranosyl backbone with 4-O-methyl-α-d-glucuronic acid as a side chain and a minor structure of linear β-(1→4)-linked glucomannans. Furthermore, these hemicelluloses possessed a low substituted degree which was beneficial for enzymatic saccharification. [ABSTRACT FROM AUTHOR]

Ethanol organosolv pretreatment is a green and effective deconstruction process for main components in lignocellulose biomass. Herein, balsa wood was firstly subjected to a modified ethanol/water solution (EWS) pretreatment with different Lewis acids catalysts (AlCl 3 , CuCl 2 , FeCl 3 ) at 140-180 °C. The delignification ratios and structural characteristics of the dissociated lignin, enzymatic hydrolysis of cellulose in the pretreated substrates as well as the degradation products from hemicellulose during the pretreatment process were comprehensively investigated. Results showed that dissociation and depolymerization of lignin fragments was robust in AlCl 3 -catalyzed pretreatment than those by CuCl 2 and FeCl 3 -catalyzed pretreatment. In detail, the results showed that the optimal delignification ratio and removal of the hemicelluloses occurred in AlCl 3 -catalyzed pretreatment. Moreover, the structural characterizations of lignin fractions by 2D-HSQC, 31 P NMR and GPC also revealed that the obtained lignin has the advantages of small and homogeneous molecules as well as abundant functional groups. As a result of adequate removal of hemicellulose and lignin, the enzymatic digestibility of cellulose in the pretreated residue was significantly elevated. In short, the above findings are also in line with the concept of maximizing the utilization of bioresources, which will be beneficial for value-added applications of balsa wood in the biorefinery., (Copyright © 2021. Published by Elsevier B.V.)