Cleavage of the β–O–4 bond in a lignin model compound using the acidic ionic liquid 1-H-3-methylimidazolium chloride as catalyst: a DFT mechanistic study

Fungal enzyme degradation of lignin-PLA composites: Insights from experiments and molecular docking simulations

Fungal enzymes are effective in degrading various polymeric materials. In this study, we assessed the initial degradation of composites consisting of lignin-poly(lactic acid) (PLA) with both unmodified lignin (LIG) and oxypropylated lignin (oLIG) incorporated at 10 % and 40 % weight within the PLA matrix in a fungal environment. Trametes versicolor fungi were used, and the samples were treated only for eight weeks. Although there was no significant difference in weight loss, the degradation process impacted the chemical and thermal properties of the composites, as shown by Fourier transform infrared spectroscopy (FTIR) and Differential scanning calorimetry (DSC) analyses. After the degradation process, the carbonyl index values decreased for all composites and the hydroxyl index values increased for LIG/PLA and a reverse trend was observed for oLIG/PLA composites. The first heating scan from DSC results showed that the melting peak and the cold crystallization peak disappeared after the degradation process. Microscopic analysis revealed that LIG/PLA exhibited higher roughness than oLIG/PLA. Molecular docking simulations were carried out using guaiacylglycerol-β-guaiacyl ether (GGE) and lactic acid (LA) as model compounds for lignin and PLA, respectively, with laccase (Lac) enzyme for Trametes versicolor. The docking results showed that GGE had the strongest binding interaction and affinity with Lac than lactic acid and oxypropylated GGE. The oxypropylated GGE formed a shorter hydrogen bonding with the Lac enzyme than GGE and LA. The trend associated with the degradation of composites from experimental and molecular docking findings was consistent. This combined approach provided insights into the degradation process using fungi and had the potential to be applied to different polymeric composites.

Promising and efficient lignin degradation versatile strategy based on DFT calculations

The extraction of higher-value products from lignin degradations under mild conditions is a challenge. Previous research reported efficient two-step oxidation and reduction strategies for lignin degradation, which has great significance to lignin degradation. In this paper, the mechanism about the C-O bond cleavage of lignin with and without Cα oxidations has been studied systematically. Our calculation results show that the degradation of anionized lignin with Cα oxidations is kinetically and thermodynamically feasible. In addition, the calculations predict that the anionized lignin compounds without Cα oxidation also could be degraded under mild conditions. Moreover, we propose special lignin catalytic degradation systems containing the characteristic structure of “double hydrogen bonds.” The double hydrogen bonds structure could further decrease the energy barriers of the C-O bond cleavage reaction. This provides a versatile strategy to design novel lignin degradation.

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Lignin anion radicals without Cα oxidation can be degraded under mild conditions

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The “double hydrogen bonds” structure is beneficial to lignin degradation

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A promising and efficient lignin degradation versatile strategy is predicted

Exopolysaccharides produced by Lactobacillus rhamnosus GG alleviate hydrogen peroxide-induced intestinal oxidative damage and apoptosis through the Keap1/Nrf2 and Bax/Bcl-2 pathways in vitro

The purpose of the study was to explore the effect of exopolysaccharides (EPSs) of Lactobacillus rhamnosus GG (LGG) on the antioxidative and antiapoptotic activities of intestinal porcine epithelial cells (IPEC-J2). EPSs exhibited promising antioxidative activities, such as 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, hydroxyl radical (˙OH) and superoxide anion radical (O₂˙^-) scavenging, as well as ferrous ion chelating ability. Moreover, EPSs of LGG could effectively alleviate the IPEC-J2 oxidative damage induced by H₂O₂ through the Bcl-2-associated (Bax)/B cell lymphoma-2 (Bcl-2) and Kelch-like ECH-associated protein 1 (Keap1)/nuclear factor-erythroid 2-related factor-2 (Nrf2) signaling pathways and up-regulated the intracellular tight junction (TJ)-related proteins. In addition, EPSs significantly improved the survival rates of H₂O₂-damaged IPEC-J2 cells and had no cytotoxic activity, suggesting that EPSs produced by LGG may be an effective drug for relieving oxidative stress. Our study provided a theoretical basis for exploration of the application of probiotic secondary metabolites in practice.

Revealing of Supercritical Water Gasification Process of Lignin by Reactive Force Field Molecular Dynamics Simulations

Gasification with supercritical water is an efficient process that can be used for the valorization of biomass. Lignin is the second most abundant biopolymer in biomass and its conversion is fundamental for future energy and value-added chemicals. In this paper, the supercritical water gasification process of lignin by employing reactive force field molecular dynamics simulations (ReaxFF MD) was investigated. Guaiacyl glycerol-β-guaiacyl ether (GGE) was considered as a lignin model to evaluate the reaction mechanism and identify the components at different temperatures from 1000 K to 5000 K. The obtained results revealed that the reactions and breaking of the lignin model started at 2000 K. At the primary stage of the reaction at 2000 K the β-O-4 bond tends to break into several compounds, forming mainly guaiacol and 1,3-benzodioxole. In particular, 1,3-benzodioxole undergoes dissociation and forms cyclopentene-based ketones. Afterward, dealkylation reaction occurred through hydroxyl radicals of water to form methanol, formaldehyde and methane. Above 2500 K, H2, CO and CO2 are predominantly formed in which water molecules contributed hydrogen and oxygen for their formation. Understanding the detailed reactive mechanism of lignin’s gasification is important for efficient energy conversion of biomass.

Evaluation of curcumin and copper acetate against Salmonella Typhimurium infection, intestinal permeability, and cecal microbiota composition in broiler chickens

BACKGROUND

Interest in the use of natural feed additives as an alternative to antimicrobials in the poultry industry has increased in recent years because of the risk of bacterial resistance. One of the most studied groups are polyphenolic compounds, given their advantages over other types of additives and their easy potentiation of effects when complexes are formed with metal ions. Therefore, the objective of the present study was to evaluate the impact of dietary supplementation of copper acetate (CA), curcumin (CR), and their combination (CA-CR) against Salmonella Typhimurium colonization, intestinal permeability, and cecal microbiota composition in broiler chickens through a laboratory Salmonella infection model. S. Typhimurium recovery was determined on day 10 post-challenge by isolating Salmonella in homogenates of the right cecal tonsil (12 chickens per group) on Xylose Lysine Tergitol-4 (XLT-4) with novobiocin and nalidixic acid. Intestinal integrity was indirectly determined by the fluorometric measurement of fluorescein isothiocyanate dextran (FITC-d) in serum samples from blood obtained on d 10 post-S. Typhimurium challenge. Finally, microbiota analysis was performed using the content of the left caecal tonsil of 5 chickens per group by sequencing V4 region of 16S rRNA gene.

RESULTS

The results showed that in two independent studies, all experimental treatments were able to significantly reduce the S. Typhimurium colonization in cecal tonsils (CT, P < 0.0001) compared to the positive control (PC) group. However, only CA-CR was the most effective treatment in reducing S. Typhimurium counts in both independent studies. Furthermore, the serum fluorescein isothiocyanate dextran (FITC-d) concentration in chickens treated with CR was significantly lower when compared to PC (P = 0.0084), which is related to a decrease in intestinal permeability and therefore intestinal integrity. The effect of dietary treatments in reducing Salmonella was further supported by the analysis of 16S rRNA gene sequences using Linear discriminant analysis effect size (LEfSe) since Salmonella was significantly enriched in PC group (LDA score > 2.0 and P < 0.05) compared to other groups. In addition, Coprobacillus, Eubacterium, and Clostridium were significantly higher in the PC group compared to other treatment groups. On the contrary, Fecalibacterium and Enterococcus in CR, unknown genus of Erysipelotrichaceae at CA-CR, and unknown genus of Lachnospiraceae at CA were significantly more abundant respectively.

CONCLUSIONS

CR treatment was the most effective treatment to reduce S. Typhimurium intestinal colonization and maintain better intestinal homeostasis which might be achieved through modulation of cecal microbiota.

Multiscale modelling investigation of wood modification with acetic anhydride

Density functional theory (DFT) and molecular dynamics (MD) simulations were employed to investigate the interaction of cellulose and lignin with acetic anhydride for explaining the wood modification process. Cellulose was modelled with a cellobiose unit and dibenzodioxocin was used to represent the lignin model. Results obtained from both methods revealed that acetic anhydride interacted substantially more with the cellobiose model than the lignin model. The interaction energy of cellobiose-acetic anhydride was higher (about 20 kJ mol-1) than that of lignin-acetic anhydride. DFT results on hydrogen bonding indicated that the hydroxyl group from cellobiose and the aromatic hydroxyl group from lignin models have similar energy values, which explain the equal strength of hydrogen bond interaction. The same trend was also obtained for the substitution of acetyl group in the hydroxyl group. MD results have also predicted that acetic anhydride forms a stronger interaction with cellobiose than with the lignin model, and these findings were in agreement with the DFT results.

Fractionation of lignin using organic solvents: A combined experimental and theoretical study

Refining of industrial lignin to produce homogeneous fractions is essential for high-value applications. However, the understanding of key interactions between a variety of solvents with lignin polymer is still uncertain. In this work, single-step fractionation of industrial hardwood kraft lignin (HKL) using organic solvents of different polarities - ethanol, acetone, diethyl ether and hexane - was investigated by combining an experimental and theoretical approach. Experimental results revealed that higher polarity solvents (ethanol and acetone) exhibited higher solubility yield compared to moderate and low polarity solvents. The chemical differences between lignin fractions were proven by pyrolysis gas chromatography mass spectrometry and near infrared spectroscopy. Density functional theory (DFT) results indicated that ethanol presented higher interaction energy followed by acetone, diethyl ether and hexane, which was consistent with experimental findings. Hydrogen bond and non-covalent interaction results from DFT demonstrated that the predominant interaction was found for high polarity of ethanol over other solvents and γ-OH in the lignin model is the key site.

Product-oriented decomposition of lignocellulose catalyzed by novel polyoxometalates-ionic liquid mixture

Lignocellulose was oxidatively decomposed in a newly developed polyoxometalates-imidazolium ionic liquid mixture. Aromatic compounds covering acids, esters, ketones, aldehydes, and phenols were selectively produced under various conditions. 4-Hydroxylbenzoic acid was dominatingly yielded under low temperature and high oxidant concentration. Phenolic compounds were mainly generated at high temperature with a selectivity of 45.1% and a yield of 4.3%, higher than those generated in similar polyoxometalates-ionic liquids system. The products distributions and residues of lignocellulose decomposition under various conditions were characterized; the influences of the ionic liquids anions on the polyoxometalates-ionic liquids complex formation, the acidic and redox properties of the catalyst, and the final products were profoundly investigated; and a tentative reacting process was proposed. The ionic liquid could be recycled for five times. This work not only provided a new lignocellulose decomposition strategy to produce aromatic products, but also offered a guidance for product-oriented lignocellulose decomposition.