Effects of 3, 4-divanillyltetrahydrofuran from Urtica fissa on sexual dysfunction in diabetic mice.

ETHNOPHARMACOLOGICAL RELEVANCE: Urtica fissa E. Pritz. are important herbs and have been traditionally used as ethnic medicine to treat rheumatism, inflammation, diabetes, and benign prostatic hyperplasia by the Han, Uighur, and other minorities in China, and also as an aphrodisiac in Uighur medicine. AIMS OF THE STUDY: To determine the effect and potential mechanism of 3, 4-divanillyltetrahydrofuran (DVTF), one of the main active components isolated from U. fissa on hypogonadism in diabetic mice. MATERIALS AND METHODS: The active compound DVTF was extracted and separated from the roots of U. fissa and identified using mass spectrometry and nuclear magnetic resonance spectroscopy. A mouse model of diabetes was established using high fat and sugar diet combined with streptozotocin. In the treatment groups, mice were received different doses of DVTF for 4 weeks. Fasting blood glucose levels, physiological and biochemical indices, and the mating behavior of DM mice were analyzed. Changes in testicular morphology were assessed using light microscopy and transmission electron microscopy. The expression of testosterone synthesis-related signaling proteins was detected using western blotting. Molecular docking was used to determine the binding ability of DVTF to Nur77. RESULTS: In diabetic mice, body weight and fasting blood glucose levels decreased. Mating behavior, including mount latency, mount number, and intromission number, was improved following DVTF treatment. Plasma total testosterone, free testosterone, and insulin resistance were positively associated with the recovery of testicular pathological structures in diabetic mice. DVTF treatment increased the expression of Nur77, StAR, and P450scc in the testes of diabetic mice. DVTF and Nur77 formed chemical bonds at five sites. CONCLUSION: As one of the main active components of U. fissa, DVTF exert potential therapeutic effects on testicular injury and hypogonadism caused by diabetes through activating the expression of Nur77 and testosterone synthesis related proteins. Our result will provide new insight for the clinical application of Urtica fissa E. Pritz., especially DVTF, as a potential drug candidate in the treatment of hypogonadism in diabetes.

Characterization of lignin extracted from Acanthopanax senticosus residue using different methods on UV-resistant behavior.

Acanthopanax senticosus has been used to extract active products. However, abundant Acanthopanax senticosus residues (ASR), which contain plenty of lignin are discarded after extraction. An appropriate extraction method should be chosen to obtain the lignin with such desirable properties. Thus, this study investigated the effect of alkali, milled wood, deep eutectic solvent and ethanol methods on the lignin. Lignin obtained from different extraction methods were characterized, yields, chemical structure, thermal behavior, molecular weight and phenolic content were evaluated. The results show that the process of lignin acquisition has a great influence on the properties of lignin. Moreover, the multifarious functional groups exist in lignin macromolecules, such as phenolic, ether groups and other chromophores, conferred good UV resistance to lignin. Among them, the lignin from alkali method has the most phenolic-OH groups and smallest molecular weight result in a good UV-resistant, the SPF value achieves 2.39 at 1% AL content, the alkali method was the best way to make sunscreen blended with cream take various factors into consideration. This study used lignin as a bioactive ingredient to provide UV-resistant property to sunscreen formulations. Furthermore, lignin extracted from Acanthopanax senticosus residue provides a new application for the treatment of herb residue waste.

Characterization of a lignin from Crataeva tapia leaves and potential applications in medicinal and cosmetic formulations.

Lignins are phenolic macromolecules that have several applications. In this work, we examine some biological activities of a lignin-like macromolecule isolated from the Crataeva tapia leaves, not yet studied to evaluate its potential applications in medicinal and cosmetic formulations. Lignin was obtained by alkaline delignification and its physical-chemical characterization was made by means of FT-IR, UV-Vis, NMR spectroscopy, elementary analysis, molecular mass determination and thermal analysis. Lignin is of the GSH type, with levels of hydrogen (5.10%), oxygen (27.18%), carbon (67.60%), nitrogen (0.12%) and phenolic content of 189.6 ± 9.6 mg GAE/g. In addition, it is a thermally stable macromolecule with low antioxidant activity. Cytotoxicity and cytokine production were assessed by flow cytometry. The photoprotective activity was evaluated by adding different concentrations of lignin to a commercial cream. Lignin was not cytotoxic, it stimulated the production of TNF-α, IL-6 and IL-10 and did not promote a significant change in nitric oxide levels. In addition, this macromolecule was able to promote increased absorption of ultraviolet light from a commercial cream. These results reinforce the ethnopharmacological use of C. tapia leaves and suggest the need for further studies to determine the potential medicinal and cosmetic applications (sunscreen) of lignin from C. tapia leaves.

Tuning structure of spent coffee ground lignin by temperature fractionation to improve lignin-based carbon nanofibers mechanical performance.

Fabricating lignin-based carbon nanofibers (LCNFs) with the lignin in spent coffee grounds (SCG) as raw material which are disposed as waste amounting to millions tons annual is benefit to promote economy and environmental protection. However, due to the heterogeneity and complex three-dimensional structure, the mechanic property is very poor. In this study, we propose a fractionating pretreatment method to overcome the above problems by regulating the structure of SCG lignin in which high-performance LCNFs were fabricated. On one hand, the linear structure of SCG lignin was optimized to fit the raw material of LCNFs by tuning the content of ß-O-4 and C5-substituted condensed phenolic compounds. On the other hand, the carboxyl as the hydrophilic groups was removed so as to promote the mixing of lignin and polyacrylonitrile (PAN, blending agent) in organic solvents. Additionally, the heterogeneity was reduced by screening large molecular weight SCG lignin with low polydispersity index (PDI). Fortunately, with 1:1 mass ratio of the above fractionated lignin and PAN as substrate, the LCNFs could reach to comparable mechanic properties with those of pure PAN CNFs. This work can provide a new way to not only promote the utilization of SCG lignin but also accelerate the development of LCNFs.

Steam explosion pretreatment improves acetic acid organosolv delignification of oil palm mesocarp fibers and sugarcane bagasse.

Steam explosion can be used to pretreat lignocellulosic materials to decrease energy and chemical consumption during pulping to obtain environmentally friendly lignin and to improve lignin yield without changing its structure. The objective of this study was to evaluate the extraction of lignin from oil palm mesocarp fibers and sugarcane bagasse using steam explosion pretreatment followed by acetosolv. The biomasses were pretreated at 168 °C for a reaction time of 10 min. Steam explosion combined with acetosolv at lower severities was also carried out. Steam explosion followed by acetosolv increased the lignin yield by approximately 15% and 17% in oil palm mesocarp fibers and sugarcane bagasse, respectively. In addition, steam explosion decreased the reaction time of acetosolv four-fold while maintaining the lignin yield from sugarcane bagasse. Similar results were not obtained for oil palm mesocarp. High-purity and high-quality lignins were obtained using steam explosion pretreatment with structural characteristics similar to raw ones. Sugarcane bagasse lignin seems to be a better option for application in material science due its higher lignin yield and higher thermal stability. Our findings demonstrate that steam explosion is efficient for improving lignin yield and/or decreasing pulping severity.

Fast pyrolysis as an alternative to the valorization of olive mill wastes.

BACKGROUND: The valorization of organic wastes through fast pyrolysis appears to be a highly promising option for decreasing pollutants and reducing consumption of natural resources. For this purpose, three different olive pomace samples were studied to determine how olive crop location and the extraction process could influence bio-oil product distribution. Olive pomace was selected as the feedstock due to the importance of the olive oil industry in Spain. RESULTS: In this study, the conditions of fast pyrolysis were optimized using lignin as a reference, with the optimum conditions being 500 °C, 20 °C ms-1 as the heating rate and 15 s as the vapour residence time. The olive pomace results determined that not only their chemical composition, but also their fat content had a remarkable effect on product distribution obtained after fast pyrolysis. However, whereas high lignin content enhanced phenol production, cellulose decomposed to carboxylic acids. In addition, due to current global warming, the carbon dioxide (CO2 ) burden of the three samples was calculated using mass spectroscopy. The OPGC sample gave off the lowest amount of greenhouse gases, followed by OPMNE and OPMN. CONCLUSIONS: The higher fat content in the sample enhanced carboxylic acid production. The difference in phenol production between OPMN and OPMNE could be attributed to the presence of potassium. From an environmental point of view, the use of olive pomace wastes could reduce CO2 emissions with further research and by developing experimental processes. © 2020 Society of Chemical Industry.

Valorization of orange bagasse through one-step physical and chemical combined processes to obtain a cellulose-rich material.

BACKGROUND: Orange bagasse (OB) is an agroindustrial residue of great economic importance that has been little explored for the extraction of cellulose. The present study aimed to investigate different combinations of chemical (sodium hydroxide, peracetic acid and alkaline peroxide) and physical (autoclaving and ultrasonication) treatments performed in one-step processes for cellulose extraction from OB and to characterize the materials obtained according to their composition, morphology, crystallinity and thermal stability. RESULTS: The processing yields ranged from 140 to 820 g kg-1 , with a recovery of 720-1000 g kg-1 of the original cellulose. Treatments promoted morphological changes in the fiber structure, resulting in materials with higher porosity, indicating partial removal of the noncellulosic fractions. The use of combined chemical treatments (NaOH and peracetic acid) with autoclaving was more efficient for obtaining samples with the highest cellulose contents. CONCLUSION: Therefore, ACSH (processed by autoclaving with NaOH) was the most effective one-step treatment, resulting in 71.1% cellulose, 0% hemicellulose and 19.0% lignin, with a crystallinity index of 42%. The one-step treatments were able to obtain materials with higher cellulose contents and yields, reducing reaction times and the quantity of chemical reagents employed in the overall processes compared to multistep conventional processes. © 2020 Society of Chemical Industry.

Lignin from oil palm empty fruit bunches: Characterization, biological activities and application in green synthesis of silver nanoparticles.

Lignin was extracted from oil palm empty fruit bunches under four different conditions. The lignin samples were characterized and employed in the green synthesis of silver nanoparticles. Two-dimensional HSQC NMR analysis showed that lignins extracted under more aggressive conditions (3.5% acid, 60 min) exhibited less signals and thus, presented a more degraded chemical structure. Additionally, those lignins obtained under harsh conditions (3.5% acid, 60 min) exhibited higher antioxidant capacity than those obtained under mild conditions (1.5% acid, 20 min). Formation of lignin-mediated silver nanoparticles was confirmed by color change during their synthesis. The surface plasmon resonance peaks (423-427 nm) in UV-visible spectra also confirmed the synthesis of AgNPs. AgNPs showed spherical shape, polycrystalline nature and average size between 18 and 20 nm. AgNPs, in suspension, presented a negative Zeta potential profile. Lignin was assumed to contribute in the antioxidant capacity exhibited by AgNPs. All AgNPs presented no significant differences on the disk diffusion antimicrobial susceptibility test against E. coli. The minimum inhibitory concentration of HAL3-L AgNPs (62.5 µg·mL-1) was better than other physicochemically produced AgNPs (100 µg·mL-1).

Characterization and use of a lignin sample extracted from Eucalyptus grandis sawdust for the removal of methylene blue dye.

A lignin sample was extracted from Eucalyptus grandis sawdust, by the Klason method, and used as adsorbent for the removal of methylene blue (MB) from aqueous solutions. By using a set of complementary analytical tools, the lignin appeared to be constituted of oxygenated functional groups and aromatic moieties, while showing a specific surface area of 20 m2 g-1 and polydisperse particles. Different experimental conditions with various solid to liquid ratio, pH, as well as other external experimental parameters were investigated for the removal of MB by the lignin sample. The experimental adsorption data at the equilibrium were properly fitted by Langmuir model, while adsorption kinetical isotherms were correctly adjusted by the pseudo-second order model. The MB removal by lignin was spontaneous involving physisorption mechanisms leading to a saturation of the adsorption sites with a maximum adsorbed amount of about 32 mg g-1. The data acquired in this study also emphasized the interests to use lignin as potential adsorbent in the light of its properties for the removal of cationic dyes, including MB, with possible recycling and reuse cycles of lignin without any significant loss of its properties.

Valorization of Cork Using Subcritical Water.

Granulated cork was submitted to subcritical water extraction/hydrolysis in a semi-continuous reactor at temperatures in the range of 120-200 °C and with a constant pressure of 100 bar. The influence of temperature on the composition of the cork extracts obtained was assessed-namely, their content of carbohydrates and phenolics. The extraction yield increased with the temperature, and this was associated with the decrease in the dielectric constant of water and the increase in its ionic product. Extracts composed of up to 36% phenolics were obtained at temperatures of up to 120 °C, with an antioxidant activity only two times lower than that of pure gallic acid, but in low amounts. Assays at higher temperatures generated extracts richer in carbohydrates and with a phenolics content of ca. 20 wt.% in comparatively far higher amounts. Neither the amount of suberin nor its structure were affected by the subcritical water treatment.

Ultrasound-assisted alkali-urea pre-treatment of Miscanthus × giganteus for enhanced extraction of cellulose fiber.

Ultrasound-assisted-alkali-urea (UAAU) pre-treatment of miscanthus biomass was investigated for enhanced delignification and extraction of cellulose fiber. The effects of pre-treatment conditions investigated were: sonication time (10.0, 15.0 and 20.0 min), alkali (NaOH) concentration (2.0, 3.5 and 5.0 %, w/v) and urea-concentration (1.0, 1.75 and 2.5 %, w/v) on the delignification and cellulose content. The process parameters were studied and optimized using a response surface methodology (RSM) based on the Box Behnken Design (BBD). From the RSM-BBD analysis, he optimized pre-treatment conditions were 2.1 % NaOH, 1.7 % urea and 15.5-min sonication time with maximal cellulose and lignin contents of 47.8 % (w/w) and 27.5 % (w/w) respectively. The pre-treated samples were further characterized by FTIR, colorimeter, SEM, XRD, and TGA analyses. The UAAU pre-treated samples have higher delignification and cellulose contents than the AU pre-treatment without sonication. Furthermore, the ultrasound process allowed selective removal of lignin without substantially degrading the functionalities of cellulose fiber. The UAAU pre-treated samples exhibited higher thermal stability, fibrillation, crystallinity index and smaller crystallite size.

Characterization of lignans in Forsythiae Fructus and their metabolites in rats by ultra-performance liquid chromatography coupled time-of-flight mass spectrometry.

OBJECTIVES: This study was designed to profile the chemical information of Forsythiae Fructus (FF) and investigate the in-vivo FF-related xenobiotics, especially for lignans. METHODS: Rats were oral administrated of FF and pinoresinol-4-O-glucoside, respectively. Blood and urine samples were collected after ingestion, and xenobiotics was profiled by an UPLC/Qtof MS method. KEY FINDINGS: A total of 19 lignans were identified or tentatively characterized in FF, and 63 lignan-related xenobiotics were found in rat plasma and urine after ingestion of FF. It was found that lignans could be transformed into metabolites by furan ring opening, hydrogenation, demethylation, dehydration and phase II reactions (sulfation and glucuronidation). The whole metabolic behaviour of bisepoxylignan was revealed by evaluating the metabolism of pinoresinol-4-O-glucoside in vivo. It was found that the configuration of C-8/C-8' was retained after furan ring opening and metabolic reactions always occurred at position of C-3/C-4/C-5 or C-3'/C-4'/C-5'. Additionally, other types components in FF and in vivo were also characterized. CONCLUSIONS: This work revealed the in-vivo metabolism of FF, and reported the characteristic metabolic reactions of lignans for the first time. It was also provided the foundation for the further investigation on pharmacodynamic components of FF or TCMs containing FF.

Structural features and antioxidant behavior of lignins successively extracted from ginkgo shells (Ginkgo biloba L).

Ginkgo shells as by-products from Ginkgo biloba L. industries with a remarkable annual output up to now are not fully analyzed and exploited. For the application of ginkgo shells beyond their current roles, structure and antioxidant activity of milled wood lignins successively extracted from two ginkgo shell species were investigated. Results showed lignin in ginkgo shells is abundant in guaiacyl units with the presence of ferulates and p-coumarates and demonstrates a high yield of vanillin (1.47-1.65 mmol/g-lignin) by nitrobenzene oxidation, much higher than general softwoods and hardwoods (0.6-0.9 mmol/g-lignin), which makes ginkgo shells good feedstocks for the production of food and beverage flavoring agent. By increasing the extent of ball-milling (4-8 h), the polydispersity of lignin molecular weight exhibits negligible change, but condensation and aldol interconversion occur to its Cß/C5 structure and end-groups, respectively. Lignin in ginkgo shells also features outstanding antioxidant activity with the optimal radical scavenging index of 6.9, much higher than commercial butyl hydroxyanisole (3.85) and butylated hydroxytoluene (0.29), and the phenolic hydroxyl is demonstrated to dominate this contribution by the analysis of statistical product and service solutions. These results reveal lignin in ginkgo shells shows many unique structural and biological properties for materials.

Lignin Precipitation and Fractionation from OrganoCat Pulping to Obtain Lignin with Different Sizes and Chemical Composition.

Fractionation of lignocellulose into its three main components, lignin, hemicelluloses, and cellulose, is a common approach in modern biorefinery concepts. Whereas the valorization of hemicelluloses and cellulose sugars has been widely discussed in literature, lignin utilization is still challenging. Due to its high heterogeneity and complexity, as well as impurities from pulping, it is a challenging feedstock. However, being the most abundant source of renewable aromatics, it remains a promising resource. This work describes a fractionation procedure that aims at stepwise precipitating beech wood (Fagus sp.) lignin obtained with OrganoCat technology from a 2-methyltetrahydrofuran solution, using n-hexane and n-pentane as antisolvents. By consecutive antisolvent precipitation and filtration, lignin is fractionated and then characterized to elucidate the structure of the different fractions. This way, more defined and purified lignin fractions can be obtained. Narrowing down the complexity of lignin and separately valorizing the fractions might further increase the economic viability of biorefineries.

Horticultural Plant Residues as New Source for Lignocellulose Nanofibers Isolation: Application on the Recycling Paperboard Process.

Horticultural plant residues (tomato, pepper, and eggplant) were identified as new sources for lignocellulose nanofibers (LCNF). Cellulosic pulp was obtained from the different plant residues using an environmentally friendly process, energy-sustainable, simple, and with low-chemical reagent consumption. The chemical composition of the obtained pulps was analyzed in order to study its influence in the nanofibrillation process. Cellulosic fibers were subjected to two different pretreatments, mechanical and TEMPO(2,2,6,6-Tetramethyl-piperidin-1-oxyl)-mediated oxidation, followed by high-pressure homogenization to produce different lignocellulose nanofibers. Then, LCNF were deeply characterized in terms of nanofibrillation yield, cationic demand, carboxyl content, morphology, crystallinity, and thermal stability. The suitability of each raw material to produce lignocellulose nanofibers was analyzed from the point of view of each pretreatment. TEMPO-mediated oxidation was identified as a more effective pretreatment to produce LCNF, however, it produces a decrease in the thermal stability of the LCNF. The different LCNF were added as reinforcing agent on recycled paperboard and compared with the improving produced by the industrial mechanical beating. The analysis of the papersheets' mechanical properties shows that the addition of LCNF as a reinforcing agent in the paperboard recycling process is a viable alternative to mechanical beating, achieving greater reinforcing effect and increasing the products' life cycles.

VS2 and its doped composition: Catalytic depolymerization of alkali lignin for increased bio-oil production.

VS2 spheres and VS2 sheets with doped compositions (Mo, Ag and graphite) were successfully prepared by one-step hydrothermal method and characterized by different techniques including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption isotherms. Catalysts were applied for the depolymerization of alkali lignin. VS2 spheres exhibited lower yield of degraded lignin and bio-oil than those with VS2 sheets and VS2 flowers heated to 250 °C and held for 1.5 h with 2.0 MPa H2. The catalytic depolymerization performance was markedly affected by the dopant in the VS2 sheets, with the highest degraded lignin yield of 81.22%, achieved over 5 wt% Ag-VS2 at 290 °C under 2.0 MPa H2 for 1.5 h, yielding 61.23% bio-oil. The VS2-based catalysts show excellent selectivity in the interruption of the lignin structure and target production of bio-oil. The bio-oil showed that the relevant contents of a phenolic-type compound changes significantly according to the dopant in the VS2 catalyst.

A natural compound (LCA) isolated from Litsea cubeba inhibits RANKL-induced osteoclast differentiation by suppressing Akt and MAPK pathways in mouse bone marrow macrophages.

ETHNOPHARMACOLOGICAL RELEVANCE: Litsea cubeba (Lour.) Pers. has been traditionally used as a folk prescription for treating rheumatic diseases in China. AIM OF THE STUDY: This study aimed to investigate the effects and underlying mechanism of LCA, a new type of dibenzyl butane lignin compound extracted from L. cubeba, on macrophage colony stimulating factor (M-CSF) plus receptor activator of NF-κB ligand (RANKL)-induced osteoclast differentiation in mouse-derived bone marrow macrophages (BMMs). MATERIAL AND METHODS: TRAP staining, TRAP enzyme activity assay and actin ring staining were applied to identify the effects of LCA on osteoclast differentiation. Protein expression of NFATc1, c-Fos and MMP-9, and phosphorylation of p65, Akt, JNK, ERK and p38 in RANKL-induced osteoclasts was determined using western blotting to investigate the underlying mechanism. RESULTS: LCA significantly suppressed RANKL-induced osteoclast differentiation by inhibiting TRAP activity, decreasing the number of TRAP+ multinuclear osteoclasts and reducing the formation of F-actin ring without obvious cytotoxicity in BMMs. Moreover, LCA treatment strongly reduced protein expression of NFATc1, c-Fos and MMP-9, and attenuated the phosphorylation of p65, Akt, JNK, ERK and p38 in RANKL-stimulated BMMs. CONCLUSIONS: LCA ameliorated RANKL-induced osteoclast differentiation via inhibition of Akt and MAPK signalings in BMMs, and may serve as a potential pro-drug for bone destruction prevention.

Methanolysis Fractionation and Catalytic Conversion of Poplar Wood toward Methyl Levulinate, Phenolics, and Glucose.

In the present study, methanolysis of poplar biomass was conducted for the selective transformation of hemicellulose and lignin, which leads to methyl glycosides (mainly C5 glycosides) and lignin fragments in the liquefied products that can be separated according to their difference in hydrophilicity. The distribution of methyl glycosides and delignification was dependent on the presence of acid catalysts and reaction temperatures. The obtained lignin fraction was separated into solid lignin fragments and liquid lignin oil according to their molecular weight distribution. Subsequently, directional conversion of methyl C5 glycosides into methyl levulinate was performed with dimethoxymethane/methanol as the cosolvent. A yield of 12-30% of methyl levulinate yield (based on the methyl glycoside) was achieved under these conditions. The remaining cellulose-rich substrate showed enhanced susceptibility to enzymatic hydrolysis, resulting in a yield of glucose of above 70%. Overall, the described strategy shows practical implications for the effective valorization of biomass.

Characterization and comparison of lignin derived from corncob residues to better understand its potential applications.

Lignocellulosic biomass is regarded as an ideal renewable resource for replacing traditional fossil fuels. Corncob residues (CRs) generated after hemicelluloses pre-extraction of corncobs were potential feedstocks to produce lignin-based products. Three lignin fractions, i.e., dioxane lignin (DL), milled-wood lignin (MWL), and enzymatic mild acidolysis lignin (EMAL), were isolated from CRs and characterized by HPLC, GPC, FT-IR, NMR, and TGA to reveal characteristics of CRs lignin to better understand its potential applications. The results showed that the yield of DL, MWL and EMAL were 12.8%, 14.7% and 15.6%, respectively. The molecular weight of DL, MWL and EMAL were 2001, 5391, and 2629 g/mol, respectively. The EMAL and MWL had similar structural features including guaiacyl and syringyl units, ß-O-4' aryl ether, p-coumaric acids, ferulates, and phenylcoumarans, while the structure of DL was relatively simple. It is expected that this work will provide some useful information for the utilization of CRs in view of biorefinery.

Homolytic and Heterolytic Cleavage of ß-Ether Linkages in Hardwood Lignin by Steam Explosion.

Steam-explosion lignin (SEL) was extracted with ethanol from steam-exploded hardwood (okoumé, Aucoumea klaineana Pierre) pretreated at various severities after neutral or acidic impregnation. The SELs were subjected to structural characterization by 2D HSQC NMR, 31P NMR, and SEC and compared with milled-wood lignin (MWL). A strong decrease in the ß- O-4 content is observed with increasing steam-explosion severity accompanied by a gradual increase in molecular mass. Cα-oxidized S units (S', Hibbert's ketones) were quantified by NMR and used as a marker of the hydrolytic mechanism; naphthol was used as a carbonium-ion scavenger. It has been observed that mixed reactions of hydrolysis and homolysis are involved, but the SEL is mainly cleaved homolytically, favoring recondensation through radical coupling even at low reaction severity. However, acidic preimpregnation of wood prior to steam explosion enhanced the carbonium-ion pathway.