The effect of coumaryl alcohol incorporation on the structure and composition of lignin dehydrogenation polymers

Lignin nanoparticles formation by multiscale structure control to regulate morphology and their adsorption, nucleation, and growth on chitin nanofibers

The lignin nanoparticles (LNPs) synthesis relies on lignin polymers with heterogeneous molecules and properties, which impose significant limitations on the preparation and property regulation. The multiscale structure of lignin from monomers to oligomers, provides a potential pathway for precise regulation of its physical and chemical properties. The study addresses this challenge by employing coniferyl alcohol and sinapyl alcohol as monomers and separately utilizing the Zulaufverfaren (ZL) and Zutropfverfaren (ZT) methods to synthesize different types of lignin dehydrogenation polymers (DHPs) including guaiacyl (G)-ZL-DHP, G-ZT-DHP, syringyl (S)-ZL-DHP, and S-ZT-DHP. The investigation highlights the chemical bonds as essential components of lignin primary structure. Additionally, the secondary structure is influenced by branched and linear molecular structures. G unit provides some branching points, which are utilized and amplified in the ZL process of DHPs synthesis. The branched DHPs aggregate at the edge and form rod-like LNPs. While linear DHPs aggregate around the center, presenting polygonal LNPs. The study identifies that the branched LNPs, characterized by more surface charges and lower steric hindrance, can form a stable complex with chitin nanofibers. Emulsions with varying oil-to-water ratios were subsequently prepared, opening a new window for the application of LNPs in fields such as food and cosmetics.

Class III plant peroxidases: From classification to physiological functions

Peroxidases (EC 1.11.1.7) are involved in a wide range of physiological processes, hence their broad distribution across biological systems. These proteins can be classified as haem or non-haem enzymes. According to the RedOxiBase database, haem peroxidases are approximately 84 % of all known peroxidase enzymes. Class III plant peroxidases are haem-enzymes that share similar three-dimensional structures and a common catalytic mechanism for hydrogen peroxide degradation. They exist as large multigene families and are involved in metabolizing Reactive Oxygen Species (ROS), hormone synthesis and decomposition, fruit growth, defense, and cell wall synthesis and maintenance. As a result, plant peroxidases gained attention in research and became one of the most extensively studied groups of enzymes. This review provides an update on the database, classification, phylogeny, mechanism of action, structure, and physiological functions of class III plant peroxidases.

The impact of xylan on the biosynthesis and structure of extracellular lignin produced by a Norway spruce tissue culture

In order to develop more economic uses of lignin, greater knowledge regarding its native structure is required. This can inform the development of optimized extraction methods that preserve desired structural properties. Current extraction methods alter the polymeric structure of lignin, leading to a loss of valuable structural groups or the formation of new non-native ones. In this study, Norway spruce (Picea abies) tissue-cultured cells that produce lignin extracellularly in a suspension medium were employed. This system enables the investigation of unaltered native lignin, as no physicochemical extraction steps are required. For the first time, this culture was used to investigate the interactions between lignin and xylan, a secondary cell wall hemicellulose, and to study the importance of lignin-carbohydrate complexes (LCCs) on the polymerization and final structure of extracellular lignin (ECL). This has enabled us to study the impact of xylan on monolignol composition and structure of the final lignin polymer. We find that the addition of xylan to the solid culture medium accelerates cell growth and impacts the ratio of monolignols in the lignin. However, the presence of xylan in the lignin polymerization environment does not significantly alter the structural properties of lignin as analyzed by two-dimensional nuclear magnetic resonance (NMR) spectroscopy and size exclusion chromatography (SEC). Nevertheless, our data indicate that xylan can act as a nucleation point, leading to more rapid lignin polymerization, an important insight into biopolymer interactions during cell wall synthesis in wood. Lignin structure and interactions with a secondary cell wall hemicellulose were investigated in a model cell culture: we found that the polymerization and final structure of lignin are altered when the hemicellulose is present during cell growth and monolignol production. The physicochemical interactions between lignin and xylan partly define the extractability and utility of native lignin in high value applications, so this work has implications for lignin extraction as well as fundamental plant biology.

Preparation and Anti-Lung Cancer Activity Analysis of Guaiacyl-Type Dehydrogenation Polymer

In this paper, guaiacyl dehydrogenated lignin polymer (G-DHP) was synthesized using coniferin as a substrate in the presence of β-glucosidase and laccase. Carbon-13 nuclear magnetic resonance (¹³C-NMR) determination revealed that the structure of G-DHP was relatively similar to that of ginkgo milled wood lignin (MWL), with both containing β-O-4, β-5, β-1, β-β, and 5-5 substructures. G-DHP fractions with different molecular weights were obtained by classification with different polar solvents. The bioactivity assay indicated that the ether-soluble fraction (DC₂) showed the strongest inhibition of A549 lung cancer cells, with an IC₅₀ of 181.46 ± 28.01 μg/mL. The DC₂ fraction was further purified using medium-pressure liquid chromatography. Anti-cancer analysis revealed that the D₄ and D₅ compounds from DC₂ had better anti-tumor activity, with IC₅₀ values of 61.54 ± 17.10 μg/mL and 28.61 ± 8.52 μg/mL, respectively. Heating electrospray ionization tandem mass spectrometry (HESI-MS) results showed that both the D₄ and D₅ were β-5-linked dimers of coniferyl aldehyde, and the ¹³C-NMR and ¹H-NMR analyses confirmed the structure of the D₅. Together, these results indicate that the presence of an aldehyde group on the side chain of the phenylpropane unit of G-DHP enhances its anticancer activity.

Synthesis and Antibacterial Properties of Oligomeric Dehydrogenation Polymer from Lignin Precursors

The lignin precursors of coniferin and syringin were synthesised, and guaiacyl-type and guaiacyl-syringyl-type oligomeric lignin dehydrogenation polymers (DHP and DHP-GS) were prepared with the bulk method. The carbon-13 nuclear magnetic resonance spectroscopy showed that both DHP-G and DHP-GS contained β-O-4, β-5, β-β, β-1, and 5-5 substructures. Extraction with petroleum ether, ether, ethanol, and acetone resulted in four fractions for each of DHP-G (C11-C14) and DHP-GS (C21-C24). The antibacterial experiments showed that the fractions with lower molecular weight had relatively strong antibacterial activity. The ether-soluble fractions (C12 of DHP-G and C22 of DHP-GS) had strong antibacterial activities against E. coli and S. aureus. The C12 and C22 fractions were further separated by preparative chromatography, and 10 bioactive compounds (G1-G5 and GS1-GS5) were obtained. The overall antibacterial activities of these 10 compounds was stronger against E. coli than S. aureus. Compounds G1, G2, G3, and GS1, which had the most significant antibacterial activities, contained β-5 substructures. Of these, G1 had the best antibacterial activity. Its inhibition zone diameter was 19.81 ± 0.82 mm, and the minimum inhibition concentration was 56.3 ± 6.20 μg/mL. Atmospheric pressure chemical ionisation mass spectrometry (APCI-MS) showed that the antibacterial activity of G1 was attributable to a phenylcoumarin dimer, while the introduction of syringyl units reduced antibacterial activity.

Bioremediation of lignin derivatives and phenolics in wastewater with lignin modifying enzymes: Status, opportunities and challenges

Lignin modifying enzymes from fungi and bacteria are potential biocatalysts for sustainable mitigation of different potentially toxic pollutants in wastewater. Notably, the paper and pulp industry generates enormous amounts of wastewater containing high amounts of complex lignin-derived chlorinated phenolics and sulfonated pollutants. The presence of these compounds in wastewater is a critical issue from environmental and toxicological perspectives. Some chloro-phenols are harmful to the environment and human health, as they exert carcinogenic, mutagenic, cytotoxic, and endocrine-disrupting effects. In order to address these most urgent concerns, the use of oxidative lignin modifying enzymes for bioremediation has come into focus. These enzymes catalyze modification of phenolic and non-phenolic lignin-derived substances, and include laccase and a range of peroxidases, specifically lignin peroxidase (LiP), manganese peroxidase (MnP), versatile peroxidase (VP), and dye-decolorizing peroxidase (DyP). In this review, we explore the key pollutant-generating steps in paper and pulp processing, summarize the most recently reported toxicological effects of industrial lignin-derived phenolic compounds, especially chlorinated phenolic pollutants, and outline bioremediation approaches for pollutant mitigation in wastewater from this industry, emphasizing the oxidative catalytic potential of oxidative lignin modifying enzymes in this regard. We highlight other emerging biotechnical approaches, including phytobioremediation, bioaugmentation, Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-based technology, protein engineering, and degradation pathways prediction, that are currently gathering momentum for the mitigation of wastewater pollutants. Finally, we address current research needs and options for maximizing sustainable biobased and biocatalytic degradation of toxic industrial wastewater pollutants.

Caffeine Interactions with Wood Polymers

Caffeine is a verified bioactive substance suitable for wood protection against pests. Unlike studies of the biocidal effects of caffeine, caffeine-wood bonds and interactions with wood polymer structures have not been studied whatsoever thus far. For this reason, caffeine (1 g/L) interactions with the main wood components (cellulose; hemicellulose; lignin and its precursors conipheryl alcohol, sinapyl alcohol, coumaryl alcohol) were analyzed in the present study. Caffeine concentrations were analyzed using UV–VIS spectrometry at wavelength 287 nm. The results confirmed caffeine variable binding with wood components in comparison to controls (pure caffeine). Cellulose and sinapyl alcohol did not interact with caffeine. Caffeine was bonded with the rest of the wood components in an increasing rank: conipheryl alcohol = lignin < hemicellulose < coumaryl alcohol. These results have a significant role in the protection of wood depending on its chemical composition and the wood species.

Comparison of methodologies used to determine aromatic lignin unit ratios in lignocellulosic biomass

BACKGROUND

Multiple analytical methods have been developed to determine the ratios of aromatic lignin units, particularly the syringyl/guaiacyl (S/G) ratio, of lignin biopolymers in plant cell walls. Chemical degradation methods such as thioacidolysis produce aromatic lignin units that are released from certain linkages and may induce chemical changes rendering it difficult to distinguish and determine the source of specific aromatic lignin units released, as is the case with nitrobenzene oxidation methodology. NMR methods provide powerful tools used to analyze cell walls for lignin composition and linkage information. Pyrolysis-mass spectrometry methods are also widely used, particularly as high-throughput methodologies. However, the different techniques used to analyze aromatic lignin unit ratios frequently yield different results within and across particular studies, making it difficult to interpret and compare results. This also makes it difficult to obtain meaningful insights relating these measurements to other characteristics of plant cell walls that may impact biomass sustainability and conversion metrics for the production of bio-derived fuels and chemicals.

RESULTS

The authors compared the S/G lignin unit ratios obtained from thioacidolysis, pyrolysis-molecular beam mass spectrometry (py-MBMS), HSQC liquid-state NMR and solid-state (ss) NMR methodologies of pine, several genotypes of poplar, and corn stover biomass. An underutilized approach to deconvolute ssNMR spectra was implemented to derive S/G ratios. The S/G ratios obtained for the samples did not agree across the different methods, but trends were similar with the most agreement among the py-MBMS, HSQC NMR and deconvoluted ssNMR methods. The relationship between S/G, thioacidolysis yields, and linkage analysis determined by HSQC is also addressed.

CONCLUSIONS

This work demonstrates that different methods using chemical, thermal, and non-destructive NMR techniques to determine native lignin S/G ratios in plant cell walls may yield different results depending on species and linkage abundances. Spectral deconvolution can be applied to many hardwoods with lignin dominated by S and G units, but the results may not be reliable for some woody and grassy species of more diverse lignin composition. HSQC may be a better method for analyzing lignin in those species given the wealth of information provided on additional aromatic moieties and bond linkages. Additionally, trends or correlations in lignin characteristics such as S/G ratios and lignin linkages within the same species such as poplar may not necessarily exhibit the same trends or correlations made across different biomass types. Careful consideration is required when choosing a method to measure S/G ratios and the benefits and shortcomings of each method discussed here are summarized.

Recent Development of Extremophilic Bacteria and Their Application in Biorefinery

The biorefining technology for biofuels and chemicals from lignocellulosic biomass has made great progress in the world. However, mobilization of laboratory research toward industrial setup needs to meet a series of criteria, including the selection of appropriate pretreatment technology, breakthrough in enzyme screening, pathway optimization, and production technology, etc. Extremophiles play an important role in biorefinery by providing novel metabolic pathways and catalytically stable/robust enzymes that are able to act as biocatalysts under harsh industrial conditions on their own. This review summarizes the potential application of thermophilic, psychrophilic alkaliphilic, acidophilic, and halophilic bacteria and extremozymes in the pretreatment, saccharification, fermentation, and lignin valorization process. Besides, the latest studies on the engineering bacteria of extremophiles using metabolic engineering and synthetic biology technologies for high-efficiency biofuel production are also introduced. Furthermore, this review explores the comprehensive application potential of extremophiles and extremozymes in biorefinery, which is partly due to their specificity and efficiency, and points out the necessity of accelerating the commercialization of extremozymes.

Enzymatic-assisted polymerization of the lignin obtained from a macroalgae consortium, using an extracellular laccase-like enzyme (Tg-laccase) from Tetraselmis gracilis

In the past decade, Mexican coasts have received an enormous influx of macroalgae species, producing serious environmental and public health concerns. Here, we developed a green methodology to generate a new polymer from the lignin contained in the macroalgae. The methodology consists in lignin extraction-by-boiling and its subsequent polymerization with a laccase-like enzyme from the green algae Tetraselmis gracilis (Tg-laccase). Mass spectrometry revealed the presence of guaiacyl (G), p-hydroxyphenyl (H), and sinapyl alcohol as the main monolignols in the lignin from Sargassum sp. On the other hand, MALDI-TOF spectra shows an increase in the size of the lignin chain after enzymatic polymerization process with Tg-laccase. Besides, the characterization of the novel polymer -using ¹H NMR, FTIR, SEC-FPLC, and UV/Vis- allowed establishing that during the polymerization process there is a decrease in the number of phenolic groups as well as loss of aromatic protons, which allowed proposing a polimerizacion mechanism. This methodology could be promising in the development of a new lignin-based polymer and would open a new direction for the environmental management of the macroalgae on the Mexican beaches.

Lignin polymerization: how do plants manage the chemistry so well?

The final step of lignin biosynthesis is the polymerization of monolignols in apoplastic cell wall domains. In this process, monolignols secreted by lignifying cells, or occasionally neighboring non-lignifying and/or other lignifying cells, are activated by cell-wall-localized oxidation systems, such as laccase/O₂ and/or peroxidase/H₂O₂, for combinatorial radical coupling to make the final lignin polymers. Plants can precisely control when, where, and which types of lignin polymers are assembled at tissue and cellular levels, but do not control the polymers' exact chemical structures per se. Recent studies have begun to identify specific laccase and peroxidase proteins responsible for lignin polymerization in specific cell types and during different developmental stages. The coordination of polymerization machinery localization and monolignol supply is likely critical for the spatio-temporal patterning of lignin polymerization. Further advancement in this research area will continue to increase our capacity to manipulate lignin content/structure in biomass to meet our own biotechnological purposes.