Green Chemistry最新文献

Nucleophilic addition to pyridiniums, metal-catalyzed hydrogenation, and cycloadditions constitute a valuable toolbox of modern pyridine dearomatization strategies. Though, in recent years, there have been notable improvements and variations of the canonical Birch reduction to address its notorious safety hazards and poor chemoselectivity, it remains an unexplored mode of reactivity for controlled pyridine dearomatization. Here, we report a simple and safe protocol for the electrochemical Birch carboxylation of pyridines utilizing a sustainable approach and CO₂ as a green C1 building block. This reaction is highly selective for pyridine reduction in the presence of several functional groups incompatible with the canonical Birch reduction and enables direct access to decorated piperidine scaffolds.

The electrosynthesis of H₂O₂via the two-electron oxygen reduction reaction (2e⁻-ORR) is a promising alternative method due to its cost-effectiveness and environmentally friendly nature. Atomically dispersed Co single atoms are considered as the active catalyst for the 2e⁻-ORR, but they still suffer from the strong adsorption of the intermediate *OOH resulting in low selectivity for H₂O₂. Herein, we propose an inter-atomic synergistic strategy by constructing a heteronuclear diatomic catalyst (Co/ZnPc-S-C₃N₄) to optimize the adsorption of *OOH and enhance the performance of H₂O₂ electrosynthesis. In Co/ZnPc-S-C₃N₄, synthesized by a supramolecular strategy through π–π stacking between MPc (M = Co or Zn) and a S-doped C₃N₄ substrate, the incorporation of Zn induces electron transfer from cobalt to zinc constructing an electron-deficient cobalt center, which inhibits the cleavage of the O–O bond in adsorbed *OOH and favors the two-electron ORR pathway. Thus, Co/ZnPc-S-C₃N₄ exhibits more than 95% H₂O₂ selectivity and nearly 100% Faraday efficiency as well as long-term stability in both alkaline and neutral electrolytes, with H₂O₂ yields of 5.35 and 5.45 mol g_cat⁻¹ h⁻¹, respectively, outperforming the reported analogous catalysts. This work provides an effective strategy for the design of heteronuclear diatomic catalysts, making them promising candidates for the 2e⁻-ORR.

Correction for ‘Fluorescent carbon dots from birch leaves for sustainable electroluminescent devices’ by Shi Tang et al., Green Chem., 2023, 25, 9884–9895, https://doi.org/10.1039/D3GC03827K.

Oxygen-doped carbon materials are promising candidates for the electrocatalytic hydrogen evolution reaction (HER). However, optimizing and delineating the roles of specific oxygen-containing functional groups in modulating their catalytic activity remains challenging. Herein, a green and environmentally friendly method involving hydrogen peroxide (H₂O₂) hydrothermal activation of carbonized wood (CW) is employed to regulate and examine oxygen-containing functional groups. Experimental results show that oxygen-doped carbon with a higher proportion of CO species exhibits enhanced electrocatalytic activity in KOH and alkaline seawater. Theoretical calculations further revealed that the CO functional group regulated the electronic structure of defective carbon and improved the electrocatalytic activity of the HER by promoting the dissociation of water. This study presents a green method for modulating oxygen-containing functional groups and offers theoretical insights into their roles, paving the way for designing more efficient oxygen-doped, metal-free carbon-based electrocatalysts for HER.

The catalytic synthesis of aromatic azo compounds via oxidative coupling of anilines still faces great challenges due to the difficulty in controlling product selectivity. In this study, we have pioneered the application of Mo₂C as a pre-catalyst for the selective oxidation of aniline using H₂O₂ to produce azobenzenes and azoxybenzenes. Both experimental and theoretical studies reveal that H₂O₂ induces the formation of Mo oxycarbides (MoC_xO_y) on the surface of Mo₂C during the reaction, which subsequently activates H₂O₂ to generate active sites (Mo⋯O) essential for the oxidative coupling of anilines. Furthermore, the kinetics of the critical conversion from Ph-NH₂ to Ph-NHOH over MoC_xO_y can be adjusted by modulating the solvent, thereby enabling controlled product selectivity between azobenzenes and azoxybenzenes. This work elucidates the structural evolution of Mo₂C to MoC_xO_y in a H₂O₂ system and its catalytic oxidation capabilities, potentially paving the way for broader applications of MoC_xO_y in various oxidation reactions.

Coumarins and their derivatives possess crucial biochemical and pharmaceutical properties. However, the exploration of the coumarin biosynthesis pathways remains limited, restricting their microbial biosynthesis, especially for hydroxycoumarins. In this work, we designed and verified novel artificial pathways to produce a valuable compound 4,6-dihydroxycoumarin (4,6-DHC) in Escherichia coli. Based on the retrosynthesis analysis, multiple routes were designed and verified by extending the shikimate pathway, screening the potential enzymes, and characterizing the enzymes involved. Rare codon optimization and protein engineering strategies were applied to optimize the rate-limiting steps. De novo biosynthesis of 4,6-DHC was achieved using the cheap carbon source glycerol, and the titer can reach 18.3 ± 0.7 mg L⁻¹. Ultimately, inducible regulation of critical pathway genes with a tetracycline-inducible controller yielded a significant boost in 4,6-DHC production, achieving a titer of 56.7 ± 2.1 mg L⁻¹. This research successfully created a microbial platform for 4,6-dihydroxycoumarin production and demonstrated a generalizable strategy for synthesizing valuable compounds.

Previous bioreactor studies achieved high volumetric n-caprylate (i.e., n-octanoate) production rates and selectivities from ethanol and acetate with chain-elongating microbiomes. However, the metabolic pathways from the substrates to n-caprylate synthesis were unclear. We operated two n-caprylate-producing upflow bioreactors with a synthetic medium to study the underlying metabolic pathways. The operating period exceeded 2.5 years, with a peak volumetric n-caprylate production rate of 190 ± 8.4 mmol C L⁻¹ d⁻¹ (0.14 g L⁻¹ h⁻¹). We identified oxygen availability as a critical performance parameter, facilitating intermediate metabolite production from ethanol. Bottle experiments in the presence and absence of oxygen with ¹³C-labeled ethanol suggest acetyl-coenzyme A-based derived production of n-butyrate (i.e., n-butanoate), n-caproate (i.e., n-hexanoate), and n-caprylate. Here, we postulate a trophic hierarchy within the bioreactor microbiomes based on metagenomics, metaproteomics, and metabolomics data, as well as experiments with a Clostridium kluyveri isolate. First, the aerobic bacterium Pseudoclavibacter caeni and the facultative anaerobic fungus Cyberlindnera jadinii converted part of the ethanol pool into the intermediate metabolites succinate, lactate, and pyroglutamate. Second, the strict anaerobic C. kluyveri elongated acetate with the residual ethanol to n-butyrate. Third, Caproicibacter fermentans and Oscillibacter valericigenes elongated n-butyrate with the intermediate metabolites to n-caproate and then to n-caprylate. Among the carbon chain-elongating pathways of carboxylates, the tricarboxylic acid cycle and the reverse β-oxidation pathways showed a positive correlation with n-caprylate production. The results of this study inspire the realization of a chain-elongating production platform with separately controlled aerobic and anaerobic stages to produce n-caprylate renewably as an attractive chemical from ethanol and acetate as substrates.

This study investigated the potential for replacing conventional solvents such as acetonitrile (ACN) and methanol (MeOH) with greener alternatives – ethanol (EtOH) and dimethyl carbonate (DMC) – in chromatographic separations. The aim was to assess whether these environmentally friendly solvents could achieve comparable separation performance while reducing the environmental impact of the analyses. Chromatographic separations were carried out on two different mixtures: non-polar and polar, using three stationary phases with different surface properties (C18, diphenyl and perfluorinated phenyl). The Technique for Order of Preference by Similarity to Ideal Solution algorithm (TOPSIS) was used to select the optimal conditions for ultra-high performance liquid chromatography (UHPLC) separations, integrating multiple criteria, including chromatographic run time, tailing ratios, resolution and solvent-related environmental hazards. The results show that EtOH and DMC can effectively replace traditional solvents without compromising separation performance, confirming that sustainable analytical methods for mixtures of non-polar and polar compounds are achievable with green solvents.

This study presents a novel approach to unlock and enrich branched cutin from tomato peel waste using sudden supercritical water hydrolysis. Cutin, the structural polyester of the plant cuticle, offers exceptional properties for biomaterials developments, however, conventional extraction methods often degrade its intricate three-dimensional network, limiting its potential applications. Utilizing sudden supercritical water hydrolysis (SCWH) with a reaction time of approximately one second, non-cutin components are hydrolyzed while preserving and enriching the native cutin structure. Characterization of the cutin-rich solid revealed the absence of a detectable glass transition temperature or melting point, indicating the maintenance of its native polymeric architecture phenomena typically observed when cutin is isolated as a mixture of monomers. Furthermore, mechanical testing revealed high rigidity under more stringent conditions, with a measured Young's modulus of 0.7 GPa. This rapid and efficient process not only valorizes agricultural and industrial residues but also enables the development of sustainable, bio-based materials. The successful preservation and enrichment of native cutin open new avenues for its application in advanced biomaterials, offering a promising alternative to fossil fuel-derived polymers.

Correction for ‘Efficient separation of oil–phenol mixtures and removal of neutral oil entrainment via an in situ deep eutectic method’ by Wanxiang Zhang et al., Green Chem., 2025, 27, 1145–1156, https://doi.org/10.1039/D4GC05756B.