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We hypothesized that compounds containing ether linkages within their backbone structures, when exposed to hydroxyl radicals (•OH), can generate ultra-weak photon emission (UPE) as a result of the formation of triplet excited carbonyl species (3R=O*). To evaluate this hypothesis, we investigated the UPE of four compounds, each at a final concentration of 185.2 µmol/L: EGTA (ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid), a potent chelator of divalent cations, and three crown ethers—12-crown-4, 15-crown-5, and 18-crown-6—containing two, four, five, and six ether bonds, respectively. •OH was generated using a modified Fenton reagent—92.6 µmol/L Fe2+ and 2.6 mmol/L H2O2. The highest UPE was recorded for the Fe2+–EGTA–H2O2 (2863 ± 158 RLU; relative light units), followed by 18-crown-6, 15-crown-5, and 12-crown-4 (1161 ± 78, 615± 86, and 579 ± 109 RLU, respectively; p < 0.05), corresponding to the number of ether groups present. Controls lacking either H2O2 or Fe2+ exhibited no significant light emission compared to the buffer medium. These findings support the hypothesis that ether bonds, when oxidatively attacked by •OH, undergo chemical transformations resulting in the formation of 3R=O* species, the decay of which is associated with UPE. In crown ethers exposed to Fe2+-H2O2, the intensity of UPE was correlated with the number of ether bonds in their structure.

Purity, morphology, and structural characterization of synthesized deep eutectic solvent (DES)-lignins (D6h, D9h, D12h, D18h, D24h) extracted from willow (Salix matsudana cv. Zhuliu) after treatment with a 1:10 molar ratio of choline chloride and lactic acid at 120 °C for 6, 9, 12, 18, and 24 h were carried out. The purity of DES-lignin was ~95.4%. The proportion of hydrogen (H) in DES-lignin samples increased from 4.22% to 6.90% with lignin extraction time. The DES-lignin samples had low number/weight average molecular weights (1348.1/1806.7 to 920.2/1042.5 g/mol, from D6h to D24h) and low particle sizes (702–400 nm). Atomic force microscopy (AFM) analysis demonstrated that DES-lignin nanoparticles had smooth surfaces and diameters of 200–420 nm. Syringyl (S) units were dominant, and total phenolic hydroxyl content and total hydroxyl content reached their highest values of 2.05 and 3.42 mmol·g−1 in D12h and D6h, respectively. β-Aryl ether (β-O-4) linkages were eliminated during DES treatment.

Lignin depolymerized phenolic compounds and biofuel precursors are ideal value-added products for lignin residues generated in biorefineries and modern paper pulp facilities. Hydrogenolysis of lignin is an efficient depolymerization method for the production of carbon-neutral sustainable fuels and platform chemicals. Lignin is underutilized due to its complex structure, mainly because of its complex interunit linkage crosslinks such as α-O-4, β-O-4, 4-O-5, and β-5. This paper centers on the hydrolysis reaction of three major ether bonds (α-O-4, β-O-4, 4-O-5) in lignin and lignin model compounds based on different catalysts for hydrogenative degradation and catalytic systems. The methods and strategies to inhibit the condensation reactions are summarized. In particular, density functional theory calculation of the reaction pathways are combined with isotopically labeled reaction pathways to deeply analyze the hydrogenation degradation mechanism of biomass and further improve the yield of monophenols during the hydrogenation degradation of lignin. Finally, a brief summary of the challenges and prospects of lignin hydrogenation degradation is proposed.

Lignin depolymerized phenolic compounds and biofuel precursors are ideal value-added products for lignin residues generated in biorefineries and modern paper pulp facilities. Hydrogenolysis of lignin is an efficient depolymerization method for the production of carbon-neutral sustainable fuels and platform chemicals. Lignin is underutilized due to its complex structure, mainly because of its complex interunit linkage crosslinks such as α-O-4, β-O-4, 4-O-5, and β-5. This paper centers on the hydrolysis reaction of three major ether bonds (α-O-4, β-O-4, 4-O-5) in lignin and lignin model compounds based on different catalysts for hydrogenative degradation and catalytic systems. The methods and strategies to inhibit the condensation reactions are summarized. In particular, density functional theory calculation of the reaction pathways are combined with isotopically labeled reaction pathways to deeply analyze the hydrogenation degradation mechanism of biomass and further improve the yield of monophenols during the hydrogenation degradation of lignin. Finally, a brief summary of the challenges and prospects of lignin hydrogenation degradation is proposed.

Polymer‐based film capacitors with ultrafast rates are extensively used in modern electronics and electric power systems. Dielectric polymers typically exhibit a low dielectric constant, while their energy density at elevated temperatures is limited by drastically increased conduction. To address this challenge, it is reported that proton irradiation enables concurrently enhanced dielectric constant and energy storage properties at high temperatures. The combined atomic force microscopy‐infrared spectroscopy and first‐principles calculations reveal that proton irradiation facilitates local rotation of ether bonds in aromatic polymers, producing greatly increased local polar states leading to markedly improved polarizability while preserving dense chain packing. Consequently, an ultrahigh discharged energy density of 6.9 J cm −3 with an efficiency > 95% is achieved in irradiated poly(ether imide) at 150 °C, exceeding current dielectric polymers and nanocomposites. The results suggest an alternative postprocessing method toward rational design of high‐performance dielectrics for capacitive energy storage.

Depolymerizing lignin to produce high-value chemicals has garnered increasing attention. Given the complex structure of real lignin, the cracking efficiency of β-O-4 linkages and the selectivity of depolymerization products are significantly lower than those of lignin model compounds. Meanwhile, the relationship between the structure of lignin and the β-O-4 linkage cracking was ignored. In this work, to well address the issue, three real lignins (corncob lignin (CL), pinus massoniana lignin (PML), and eucalyptus lignin (EL)) were employed to discuss the impacts of special ether bonds in lignin on the β-O-4 linkage cracking in the no-additional-hydrogen catalytic system mediated by a CoNi2@BTC catalyst. The lignin depolymerization results showed that the ether bonding structure in the lignin significantly impacted the cracking of β-O-4 linkages and selectivity of the final products, resulting in a great difference among their intermediates. Notably, the methoxy groups in the real lignin greatly inhibited the further hydrogenation of phenolic compounds, resulting in the accumulation of abundant methoxy-substituted phenolic compounds and a low yield of cycloalkanes (12.37% to 14.06%). To deeply discuss the β-O-4 linkage cracking in the lignin depolymerization, degradation experiments with coexisting ether bond compounds were performed, and the activation energy was employed to quantitatively evaluate the impacts of other ether bonds on the β-O-4 linkage cracking. The results revealed that multiple ether bonds (α-O-4, 4-O-5, and methoxy group) significantly increased the activation energy (from 236% to 373%) of β-O-4 linkages, resulting in the evident decline in the β-O-4 model compound. In addition, the degradation of the methoxy-substituted β-O-4 model compound (GG) demonstrated that the methoxy-substituted aromatic ring products were resistant to further hydrogenation, resulting in the accumulation of methoxy-substituted aromatic ring products in the depolymerization of real lignin. All the findings will provide a novel perspective for the targeted high-value utilization of real lignin in chemical production.

In this work, the one-pot catalytic reductive fractionation of C-lignin in castor shell powders to efficiently provide catechyl monomers was achieved by tandem metal triflate and Pd/C catalysis. The optimized Pd/C + In(OTf)3 combination performed best and provided a 66.9 mg·g−1 yield of corresponding aromatic monomers with the catechol selectivity as high as 95.4%. For the promotion effect of the Lewis acid species, the mechanism studied indicated that the introduction of In3+ could significantly promote the C–O bond cleavage in the LCC to release the C-lignin fragments from the solid lignocellulose and simultaneously accelerate the cleavage of the critical Cα/β–OAr linkage bond in C-lignin to release catechol monomers. In addition, performance differences highlight the cooperation and function-matching effect between the hydrogenation metals and the Lewis ion species, which can promote the high-value utilization of forestry and agricultural residues in chemical synthesis.

In this work a novel method for synthesis of 1,8-dihydroxynaphthalene melanin was presented, as well as the physicochemical properties, molecular structure, and characteristics of the pigment. The proposed synthesis protocol is simple and cost-effective with no enzymes or catalysts needed. The final product is not adsorbed on any surface, since the pigment is the result of autooxidation of 1,8-dihydroxynaphthalene. Performed analyses revealed that the solubility, optical and paramagnetic properties are typical for melanins, and in the EPR spectra an unusual hyperfine structure was observed. The molecular structure of the pigment consists of three different layers forming polar and non-polar surfaces. Additionally, the presence of ether bonds presence was revealed. The developed method creates new opportunities for melanin research and eliminates the need to extract melanins from biological samples, which often lead to structural changes in isolated melanins, which undermines the reliability of analyses of the properties and structure of these polymers. On the other hand, the ubiquity of melanins in living organisms and the diversity of their biological functions have let to the growing interest of researchers in this group of pigments. The analyses carried out show that the obtained synthetic DHN polymer can be considered as a model DHN-melanin in mycological studies and material research.

Hydrogel features can be designed and optimized using different crosslinking agents to meet specific requirements. In this regard, the present work investigates the physico-chemical features of cellulose-based hydrogels, designed by using different epoxy crosslinkers from the same glycidyl family, namely epichlorohydrin (ECH), 1,4-butanediol diglycidyl ether (BDDE), and trimethylolpropane triglycidyl ether (TMPTGE). The effect of the crosslinker’s structure (from simple to branched) and functionality (mono-, bi- and tri-epoxy groups) on the hydrogels’ features was studied. The performances of the hydrogels were investigated through the gel fraction, as well as by ATR-FTIR, DVS, SEM, DSC, and TG analyses. Also, the swelling and rheological behaviors of the hydrogels were examined. The advantages and limitations of each approach were discussed and a strong correlation between the crosslinker structure and the hydrogel properties was established. The formation of new ether bonds was evidenced by ATR-FTIR spectroscopy. It was emphasized that the pore size is directly influenced by the crosslinker type, namely, it decreases with the increasing number of epoxy groups from the crosslinker molecule, i.e., from 46 ± 11.1 µm (hydrogel CE, with ECH) to 12.3 ± 2.5 µm (hydrogel CB, with BDDE) and 6.7 ± 1.5 µm (hydrogel CT, with TMPTGE). The rheological behavior is consistent with the swelling data and hydrogel morphology, such as CE with the highest Qmax and the largest pore size being relatively more elastic than CB and CT. Instead, the denser matrices obtained by using crosslinkers with more complex structures have better thermal stability. The experimental results highlight the possibility of using a specific crosslinking agent, with a defined structure and functionality, in order to establish the main characteristics of hydrogels and, implicitly, to design them for a certain field of application.

To elucidate the effects of polysaccharides, cellulose, water-soluble xylan (WXY), galactoglucomannan (GGM) and xyloglucan (XG) on lignification in vitro, artificial polysaccharide matrices were prepared from a combination of cellulose and hemicelluloses, and dehydrogenation polymer (DHP) was synthesized from coniferyl alcohol in the presence of the matrices by using horseradish peroxidase (HRP). Prior to DHP formation, interactions between cellulose and hemicelluloses were investigated with equilibrium adsorptions of the hemicelluloses on bacterial cellulose (BC) films and with quartz crystal microbalance with dissipation technique (QCM-D) to determine their adsorption on cellulose nanofibers (CNFs). Both analyses showed that the order of adsorption amounts was XG > GGM > WXY. The QCM-D experiments also suggested that HRP strongly interacted with cellulose rather than hemicelluloses. The amount of DHP generated in the XG-BC matrix was the largest among the prepared matrices, and XG facilitated the formation of 5–5′ interunitary linkages. Thus, XG must be involved in the lignification in primary wood cell wall. On the other hand, the amount of DHP in the GGM-BC matrix was the smallest, indicating that GGM hampered lignification.Graphic abstract