Boron-doped sulfonated graphitic carbon nitride as a highly efficient catalyst for the production of 5-hydroxymethylfurfural from carbohydrates.

The presence of humins during the conversion of concentrated fructose presents a major obstacle in the large-scale production of 5-hydroxymethylfurfural (HMF) from fructose. Herein, we reported a boron-doped graphitic carbon nitride sulfonated (BGCN-SO3H) as an excellent catalyst for the synthesis of HMF from fructose. The BGCN-SO3H catalyst structures were analyzed using various characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDX), elemental mapping analysis, and Fourier-transform infrared spectroscopy (FT-IR). The BGCN-SO3H catalyst was evaluated for the synthesis of HMF from fructose. We investigated the influence of catalyst performance, including solvent reactions, catalyst loading, substrates, and volume of solvent to optimize reaction conditions. As a result, the yield of HMF was obtained at 88 % within 5 h when using 30 mg of catalyst. The study of catalyst activity involved examining reactions that allowed recovery and reuse. The research findings offer a method for producing HMF with exceptional efficiency using solid catalysts.

Co@NC Chainmail Nanowires for Thermo- and Electrocatalytic Oxidation of 2,5-Bis(hydroxymethyl)furan to 2,5-Furandicarboxylic Acid.

2,5-Furandicarboxylic acid (FDCA) has emerged as an important bio-based furanic compound, which has broad application prospects in renewable energy and materials, especially in the preparation of polyethylene 2,5-furandicarboxylate (PEF). While the  conventional synthesis of FDCA involves oxidation of 5-hydroxymethylfurfural (HMF) as a substitute, the thermal and chemical instability of HMF due to its aldehyde group poses challenges. A more favorable alternative is the utilization of 2,5-bis(hydroxymethyl)furan (BHMF), a non-aldehyde and more stable precursor. This study pioneeringly reports nitrogen-doped-carbon encapsulated cobalt (Co@NC) chainmail nanowires for the thermal and electrocatalytic oxidation of BHMF to FDCA. The Co@NC/NF achieved a 97.9% conversion of BHMF with a 93.3% yield of FDCA  at 1.475 V vs. RHE, whereas thermal catalysis only obtained 14.9% FDCA yield after 10 hours. Kinetic studies indicated that the large electrochemically active surface area and excellent kinetic parameters contribute its superior electrochemical performance. Mechanistic analysis revealed that the migration of inner electrons to the exterior modified the electronic properties of the carbon layer, thereby facilitating the oxidation of BHMF. Furthermore, the in-situ generation of high-valent cobalt species markedly accelerated the BHMF oxidation. This research underscores the potential of carbon-encapsulated metal chainmail catalysts in thermal and electrochemical biomass conversion.

Non-noble metal catalysts for electrooxidation of 5-hydroxymethylfurfural.

2,5-Furandicarboxylic acid (FDCA) is a class of valuable biomass-based platform compounds. The creation of FDCA involves the catalytic oxidation of 5-hydroxymethylfurfural (HMF). As a novel catalytic method, electrocatalysis has been utilized in the 5-hydroxymethylfurfural oxidation reaction (HMFOR). Common noble metal catalysts show catalytic activity, which is limited by price and reaction conditions. Non-noble metal catalyst is known for its environmental friendliness, affordability and high efficiency. The development of energy efficient non-noble metal catalysts plays a crucial role in enhancing the HMFOR process. It can greatly upgrade the demand of industrial production, and has important research significance for electrocatalytic oxidation of HMF. In this paper, the reaction mechanism of HMF undergoes electrocatalytic oxidation to produce FDCA are elaborately summarized. There are two reaction pathways and two oxidation mechanisms of HMFOR discussed deeply. In addition, the speculation on the response of the electrode potential to HMFOR is presented in this paper. The main non-noble metal electrocatalysts currently used are classified and summarized by targeting metal element species. Finally, the paper focus on the mechanistic effects of non-noble metal catalysts in the reaction, and provide the present prospects and challenges in the electrocatalytic oxidation reaction of HMF.

The relationship between the deterioration of frying oil and the generation of hazards during frying.

Deep-fat frying gives food a desirable color and flavor but inevitably leads to oil deterioration and production of hazards. In this study, the simultaneous generation of multiple hazards under different frying conditions was investigated, the deterioration of frying oil was evaluated, and finally, their correlation was analyzed. The results showed that as the temperature of frying chicken wings increased from 150 to 190 °C, the levels of acrylamide (AA), heterocyclic amines (HCAs), and polycyclic aromatic hydrocarbons (PAHs) in the oil also increased proportionally. At 190 °C, the fried potato oil contained the highest AA content of 2.60 mg·kg-1, while the content of HCAs and PAHs was the highest in fried chicken wings oil, with values of 5.06 µg·kg-1 and 5.18 µg·kg-1, respectively. 5-Hydroxymethylfurfural was detected only in fried potato oil. Oil quality deteriorated gradually with increasing frying temperature and heating time, as indicated by increased acid value, carbonyl value, and levels of total polar compounds. Overall, the results indicated hazards were positively correlated with oil deterioration, suggesting that oil deterioration contributed to the generation of hazards. This work links hazards and oil deterioration, which is crucial for improving the quality and safety of fried foods, while reducing negative environmental impacts, and achieving clean production.

Unlocking the anion effect on steerable production of 5-hydroxymethylfurfural.

Homogeneous metal salt catalysts play a pivotal role in industrial production of 5-hydroxymethylfurfural (HMF). Herein, we first proposed the anion effect on steerable production of HMF using metal salts with different anions as catalyst in a biphasic system of tetrahydrofuran (THF)/NaCl aqueous solution (NaCl aq). Notably, the anions affected the catalytic activity of the metal salts, leading to an order of magnitude difference in the HMF yields, i.e., AlBr3（74.0 mol%）> AlCl3 (60.8 mol%) > Al2(SO4)3 (35.2 mol%) > Al(NO3)3 (14.9 mol%). The anion effect on steerable production of HMF could be attributed to the proximity effect and electron tension. Anions form close-range interactions with glucose molecules by proximity effect to promote electron transfer, facilitating the isomerization of glucose to fructose. Besides, anions induce a reduction of the electron cloud density of glucose carbon atoms, generating electron tension that rapidly transforms glucose from the ground state to the transition state, thereby increasing the HMF yield. Based on the revelation of anions effect and evaluation of techno-economic process, we expect to provides theoretical guidance for high-throughput screening of metal salt catalysts in industrial biorefinery.

Unilamellar MnO2 nanosheets confined Ru-clusters combined with pulse electrocatalysis for biomass electrooxidation in neutral electrolytes.

The electrochemical oxidation of 5-hydroxymethylfurfural (HMFOR) in alkaline electrolyte is a promising strategy for producing high-value chemicals from biomass derivatives. However, the disproportionation of aldehyde groups under strong alkaline conditions and the polymerization of HMF to form humic substances can impact the purity of 2,5-furandicarboxylic acid (FDCA) products. The use of neutral electrolytes offers an alternative environment for electrolysis, but the lack of OH- ions in the electrolyte often leads to low current density and low yields of FDCA. In this study, a sandwich-structured catalyst, consisting of Ru clusters confined between unilamellar MnO2 nanosheets (S-Ru/MnO2), was used in conjunction with an electrochemical pulse method to realize the electrochemical conversion of 5-hydroxymethylfurfural into FDCA in neutral electrolytes. Pulse electrolysis and the strong electron transfer between Ru clusters and MnO2 nanosheets help maintain Ru in a low oxidation state, ensuring high activity. The increased *OH generation led to a groundbreaking current density of 47 mA/cm2 at 1.55 V vs. reversible hydrogen electrode (RHE) and an outstanding yield rate of 98.7 % for FDCA in a neutral electrolyte. This work provides a strategy that combines electrocatalyst design with an electrolysis technique to achieve remarkable performance in neutral HMFOR.

Enhancing the Electrocatalytic Oxidation of 5-Hydroxymethylfurfural Through Cascade Structure Tuning for Highly Stable Biomass Upgrading.

Electrocatalytic 5-hydroxymethylfurfural oxidation reaction (HMFOR) provides a promising strategy to convert biomass derivative to high-value-added chemicals. Herein, a cascade strategy is proposed to construct Pd-NiCo2O4 electrocatalyst by Pd loading on Ni-doped Co3O4 and for highly active and stable synergistic HMF oxidation. An elevated current density of 800 mA cm-2 can be achieved at 1.5 V, and both Faradaic efficiency and yield of 2,5-furandicarboxylic acid remained close to 100% over 10 consecutive electrolysis. Experimental and theoretical results unveil that the introduction of Pd atoms can modulate the local electronic structure of Ni/Co, which not only balances the competitive adsorption of HMF and OH- species, but also promote the active Ni3+ species formation, inducing high indirect oxidation activity. We have also discovered that Ni incorporation facilitates the Co2+ pre-oxidation and electrophilic OH* generation to contribute direct oxidation process. This work provides a new approach to design advanced electrocatalyst for biomass upgrading.

Copper-Catalyzed Oxidation of 5-Hydroxymethylfurfural to 2,5-Diformylfuran Assisted by TEMPOL in Liquid Sunlight Methanol.

2,5-Diformylfuran (DFF) is a significant biomass-derived compound with diverse applications in novel furan-based materials, fragrances, fuel additives, and drug synthesis. A pivotal challenge in DFF synthesis is developing a method to produce DFF under mild conditions using sustainable feedstocks. In this study, an affordable 4-hydroxy-2,2,6,6-tetramethylpiperidine (TEMPOL)- assisted Cu(OAc)2 catalytic system for aerobic oxidation reaction of HMF to DFF in liquid sunlight methanol solvent was developed. The effects of parameters such as metal species, catalyst amount, solvent species, ligand structure, and reaction temperature were systematically investigated. The evolution of product distribution in the reaction solution at various times was monitored and analyzed using 1H-NMR spectroscopy. FT-IR and ESI-MS characterizations were employed to integrate experimental findings and elucidate the reaction mechanism. The highest DFF yield of 96% and complete conversion of HMF were obtained. Furthermore, a total DFF yield of 68.6% was achieved from fructose using a two-steps method, demonstrating the potential for scalable production. The establishment of this catalytic system presents a novel approach for the selective preparation of DFF from sustainable feedstocks.

Oxidation of 5-hydroxymethylfurfural into 2,5-diformylfuran on alkali doped Ru/C catalysts. Electron properties of Ruthenium species as descriptor of catalytic activity.

Selective aerobic oxidation of 5-hydroxymethylfurfural into 2,5-diformylfuran has been achieved on alkali doped Ru/C catalyst. Optimization of Ru metal nanoparticles, as well as the nature and amount of the alkali dopant have been performed. The results showed that doping the Ru/C catalyst with controlled amount of potassium increases the catalytic activity, 2.5 fold with respect to the non-doped sample. Spectroscopic studies showed that these differences in activity can be attributed to a different oxidation reaction mechanism associated to the presence of electron rich Ru species in the promoted sample that facilitate the dissociation of O2, while prevents the oxidation of the metal. The Ru/C-K doped catalyst resulted very stable against leaching and metal sintering, being possible the reuse over several consecutive runs. Moreover, the catalyst could be successfully applied to the oxidation of different alcohols.

The variation of acrylamide and 5-hydroxymethylfurfural in tea with different roasting degrees and the effects of tea polyphenols on their formation.

BACKGROUND: Roasting is an essential step in making roasted teas, and its role in producing flavors has been widely studied. However, the variation of potential hazardous compounds during the tea roasting process is still vague. The present study established an effective method based on liquid chromatography-triple quadrupole-tandem mass spectrometry to simultaneously determine the variation of acrylamide (AA), 5-hydroxymethylfurfural (5-HMF), and free amino acids during the tea roasting process. Meanwhile, the effects of several tea polyphenols on the formation of AA and 5-HMF were investigated by a wet-to-dry thermal model reaction. RESULTS: Medium-temperature roasted teas had the highest levels of AA and 5-HMF, with ranges of 0.13-0.15 µg g-1 and 68.72-123.98 µg g-1, respectively. Quantitative results showed that the levels of monosaccharides and amino acids decreased during roasting, which might contribute to the formation of 5-HMF and AA. Meanwhile, the decrease of epigallocatechin gallate (EGCG), epigallocatechin (EGC), and epicatechin (EC) might be related to their inhibitory effects on 5-HMF and AA. Thermal model reaction results showed that EGCG and EC significantly inhibited 5-HMF formation with a decline rate of 33.33% and 72.22%, respectively, mainly by trapping glucose. Gallic acid (GA) also had an inhibitory effect on the formation of AA (decreased by 92.86%) and 5-HMF (44.44%), mainly through impeding the preliminary reaction of asparagine and glucose. CONCLUSION: The roasting temperature determined the levels of AA and 5-HMF in teas. Catechins inhibited the formation of 5-HMF and AA mostly through trapping monosaccharides, while the inhibitory effect of GA was achieved by impeding the reaction. © 2024 Society of Chemical Industry.

Ultra-Dilute SnCl4-Catalyzed Conversion of Concentrated Glucose to 5-Hydroxymethylfurfural in Aqueous Deep Eutectic Solvent.

5-Hydroxymethylfurfural(HMF) is a versatile chemical synthesized from glucose dehydration catalyzed by metal chloride (MClx) in deep eutectic solvents (DESs). However, the low glucose concentration and high catalyst dosage hinder large-scale HMF production. Herein, we report an aqueous DES of tetraethylammonium bromide(TEAB)-glucose for converting concentrated glucose (40 wt%, relative to TEAB) using ultra-dilute SnCl4 (0.25 mol%), achieving a 62% yield of HMF. Ultra-dilute MClx-catalyzed selective conversion of glucose is feasible only when combining SnCl4 with Br-based DES, which is elucidated by density functional theory and molecular dynamic calculations. Using SnCl4 is essential due to its higher glucose isomerization activity than AlCl3 and CrCl3, which can be attributed to its low-barrier coordination with glucose and its barrier-free separation from fructose. Halide anions in DESs strongly interact with glucose, hindering the MClx-glucose coordination and thereby reducing MClx's activity for glucose isomerization. Consequently, Br-based DESs facilitate higher activity of MClx than Cl-based DESs, due to the weaker interaction between halide anion and glucose. In addition, we elucidated the side reactions including condensation, polymerization, and isomerization, and proposed a reaction network. Our findings clarify the differential activity of MClx and the impact of halide anions in DESs on MClx's activity.

Furandicarboxylic Acid (FDCA): Electrosynthesis and Its Facile Recovery From Polyethylene Furanoate (PEF) via Depolymerization.

Replacing fossil fuels with renewable, bio-based alternatives is inevitable for the modern chemical industry, in line with the 12 principles of green chemistry. 2,5-Furandicarboxylic acid (FDCA) is a promising platform molecule that can be derived from 5-hydroxymethyl furfural (HMF) via sustainable electrochemical oxidation. Herein, we demonstrate TEMPO-mediated electrooxidation of HMF to FDCA in ElectraSyn 2.0 using inexpensive commercially available electrodes: graphite anode and stainless-steel cathode, thereby avoiding the often cumbersome electrode preparation. Key parameters such as concentration of HMF, KOH, and catalyst loading were optimized by experimental design. Under the optimized conditions, using only a low amount of TEMPO (5 mol%), high yield and Faradaic efficiency of 96% were achieved within 2.5 hours. Moreover, since FDCA is a monomer of the bio-based poly(ethylene furanoate), PEF, we aimed to investigate its recovery by depolymerization, which could be of paramount importance in the circular economy of the FDCA. For this, a new polar aprotic solvent, methyl sesamol (MeSesamol), was used, allowing the facile depolymerization of PEF at room temperature with high monomer yields (up to 85%), while the cosolvent MeSesamol was recycled with high efficiency (95-100%) over five reaction cycles.

Underexplored food safety hazards of beekeeping products: Key knowledge gaps and suggestions for future research.

These days, a growing consumer demand and scientific interest can be observed for nutraceuticals of natural origin, including apiculture products. Due to the growing emphasis on environmental protection, extensive research has been conducted on the pesticide and heavy metal contamination of bee products; however, less attention is devoted on other food safety aspects. In our review, scientific information on the less-researched food safety hazards of honey, bee bread, royal jelly, propolis, and beeswax are summarized. Bee products originating from certain plants may inherently contain phytotoxins, like pyrrolizidine alkaloids, tropane alkaloids, matrine alkaloids, grayanotoxins, gelsemium alkaloids, or tutin. Several case studies evidence that bee products can induce allergic responses to sensitive individuals, varying from mild to severe symptoms, including the potentially lethal anaphylaxis. Exposure to high temperature or long storage may lead to the formation of the potentially toxic 5-hydroxymethylfurfural. Persistent organic pollutants, radionuclides, and microplastics can potentially be transferred to bee products from contaminated environmental sources. And lastly, inappropriate beekeeping practices can lead to the contamination of beekeeping products with harmful microorganisms and mycotoxins. Our review demonstrates the necessity of applying good beekeeping practices in order to protect honeybees and consumers of their products. An important aim of our work is to identify key knowledge gaps regarding the food safety of apiculture products.

Direct Reductive Amination of HMF to 5-(Aminomethyl)-2-furanmethanol Using Supported Iridium-based Catalysts.

In this work, partial reductive amination of 5-hydroxymethylfurfural (HMF) with gaseous ammonia over iridium supported on γ-Al2O3, TiO2, SiO2 and carbon has been studied. The influence of the support and pressure was investigated in the valorization under mild conditions of HMF to 5-(aminomethyl)-2-furanmethanol (AMFM). The catalysts were characterized by TEM, SEM-EDS, N2 sorption Isotherms, TGA, CO-Chemisorption, TPR, XRD, NH3-TPD, ICP-AES and XPS. The maximum activity and high rates were obtained for all catalytic systems. At 50 minutes of the reaction the Ir/C catalyst achieved 93% of conversion and exhibited the highest yield and selectivity of 92% and 99% respectively, to the desired product 5-(aminomethyl)-2-furanmethanol. The main properties that influence activity and selectivity are related to the amount of iridium on the surface and catalyst acidity. After the third cycle, 63% and 59% of selectivity and yield to AMFM respectively at 93% of conversion were obtained.

Ligand-Hybridization Activates Lattice-Hydroxyl-Groups of NiCo(OH)x Nanowires for Efficient Electrosynthesis.

Electrochemical dehydrogenation of hydroxides plays a crucial role in the formation of high-valence metal active sites toward 5-hydroxymethylfurfural oxidation reaction (HMFOR) to produce the value-added chemical of 2,5-furandicarboxylic (FDCA). Herein, we construct benzoic acid ligand-hybridized NiCo(OH)x nanowires (BZ-NiCo(OH)x) with ample electron-deficient Ni/Co sites for HMFOR. The robust electron-withdrawing capability of benzoic acid ligands in BZ-NiCo(OH)x speeds up the electrochemical activation and dehydrogenation of lattice-hydroxyl-groups (M2+-O-H⇌M3+-O), boosting the formation of abundant electron-deficient and high-valence Ni/Co sites. DFT calculation reveals that the deintercalation proton is prone to establishing a hydrogen bridge with the carbonyl group in benzoic acid, facilitating the proton transfer. Coupled with the synergistic oxidation of Ni/Co sites on hydroxyl and aldehyde groups, BZ-NiCo(OH)x delivers a remarkable current density of 111.20 mA cm-2 at 1.4 V for HMFOR, exceeding that of NiCo(OH)x by approximately fourfold. And the FDCA yield and Faraday efficiency are as high as 95.24 % and 95.39 %, respectively. The ligand-hybridized strategy in this work introduces a novel perspective for designing high-performance transition metal-based electrocatalysts for biomass conversion.

High-Efficiency Solar Transformation of Sugars via a Heterogenous Gallium(III) Catalyst.

Extremely limited research exploring the photocatalytic potential of main group metals, such as aluminum, gallium, and tin, has been undertaken due to their weak light harvesting properties. This study reports the efficient transformation of sugars to 5-hydroxymethylfurfural (HMF) with high yield employing an original heterogeneous photocatalyst comprising a gallium(III) complex immobilized on an alumina support. Under visible light irradiation, the reaction rate of HMF formation is ~143 times higher than the equivalent thermal reaction performed in the absence of light. The turnover number (TON) of the heterogeneous gallium(III) photocatalyst was as high as 1500, which was ca. two orders of magnitude higher than the TON of the homogeneous gallium(III) system. It is proposed that photoirradiation significantly enhances the Lewis acidity of the catalyst by forming a semi-coordination state between gallium(III) and N-donor ligands, enabling the increased interaction of reactant sugar molecules with gallium(III) active sites. Consistent with this, the photoresponsive coordination of the gallium(III) complex and the abstraction of the hydroxy group by the metal under irradiation with visible light is observed by NMR spectroscopy for the first time. These findings demonstrate that efficient photocatalysts derived from the main group elements can facilitate biomass conversion using visible light.

Base-Free Oxidation of HMF to FDCA over Ru/Cu-Co-O·MgO under Aqueous Conditions.

The copper-cobalt metal oxide composite magnesium oxide catalyst loaded with Ru has achieved the aerobic oxidation of 5-hydroxymethylfurfural (HMF) to the bio-based polyester monomer 2,5-furandicarboxylic acid (FDCA) under base-free conditions. Several Ru/Cu-Co-O·MgO catalysts were prepared, with Cu-Co-O being a combination of CuO and Co3O4. The catalyst's activity was boosted by the synergistic interaction between copper and cobalt, as well as an optimal copper-to-cobalt molar ratio. Optimal catalytic activity was observed in the Ru4/Cu1-Co1-O·MgO catalyst, loaded with 4 wt% Ru when copper-to-cobalt molar ratio of 1:1 and magnesium oxide compounding amount of 6 mmol were employed. The inclusion of MgO and the load of Ru not only expanded the specific surface area of the catalyst but also heightened its basicity. Additionally, the presence of loaded Ru improved the catalyst's reducibility at low temperatures. In aqueous solution under oxygen pressure, the conversion rate of HMF achieved 100%, and the yield of FDCA was 86.1%. After five reaction cycles, examining the catalyst and solution revealed that Ru nanoparticles resisted leaching or oxidation, and MgO exhibited only slight dissolution. The green separation of the product was achieved using semi-preparative liquid chromatography, selectively collecting the FDCA-containing solution by exploiting variations in interactions between solutes and the stationary/mobile phases. The subsequent steps involved rotary evaporation and drying, resulting in FDCA powder with a purity exceeding 99%. Notably, this approach eliminated the need to introduce concentrated hydrochloric acid into the system for FDCA separation, providing a novel method for synthesising powdered FDCA.

Ethnobotany, phytochemistry, pharmacology and quality control of Peucedanum decursivum (Miq.) Maxim: A critical review.

ETHNOPHARMACOLOGICAL RELEVANCE: Dried roots of Peucedanum decursivum, a traditional Chinese medicine (TCM), has historically respiratory diseases such as cough, thick phlegm, headache, fever, and gynecological diseases, rheumatoid arthritis, and nasopharyngeal carcinoma. AIM OF THE STUDY: Made an endeavor to evaluate the research trajectory of P. decursivum, comprehensively discern its developmental status, and offer a guideline for future investigations. MATERIALS AND METHODS: A meticulous search of literatures and books from 1955 to 2024 via databases like PubMed, Web of Science and CNKI was conducted, including topics and keywords of " P. decursivum" "Angelica decursivum" and "Zihua Qianhu". RESULTS: P. decursivum and its prescriptions have traditionally been used for treating phlegm-heat cough, wind-heat cough, gastrointestinal diseases, pain relief and so on. It contains 234 identified compounds, encompassing coumarins, terpenes, volatile oils, phenolic acids, fatty acids and derivatives. It exhibits diverse pharmacological activities, including anti-asthmatic, anti-inflammatory, antioxidant effects, anti-hypertensive, anti-diabetic, anti-Alzheimer, and anti-cancer properties, primarily attributed to coumarins. Microscopic identification, HPLC fingerprinting, and bioinformatics identification are the primary methods currently used for the quality control. CONCLUSION: P. decursivum demonstrates anti-asthmatic, anti-inflammatory, and antioxidant effects, aligning with its traditional use. However, experimental validation of its efficacy against phlegm and viruses is needed. Additionally, analgesic effects mentioned in historical texts lack modern pharmacological studies. Numerous isolated compounds exhibit highly valuable medicinal properties. Future research can delve into exploring these substances further. Rigorous of heavy metal contamination, particularly Cd and Pb, is necessary. Simultaneously, investigating its pharmacokinetics and toxicity in humans is crucial for the safety.

The progress of research on vacancies in HMF electrooxidation.

5-Hydroxymethylfurfural (HMF), serving as a versatile platform compound bridging biomass resource and the fine chemicals industry, holds significant importance in biomass conversion processes. The electrooxidation of HMF plays a crucial role in yielding the valuable product (2,5-furandicarboxylic acid), which finds important applications in antimicrobial agents, pharmaceutical intermediates, polyester synthesis, and so on. Defect engineering stands as one of the most effective strategies for precisely synthesizing electrocatalytic materials, which could tune the electronic structure and coordination environment, and further altering the adsorption energy of HMF intermediate species, consequently increasing the kinetics of HMF electrooxidation. Thereinto, the most routine and effective defect are the anionic vacancies and cationic vacancies. In this concise review, the catalytic reaction mechanism for selective HMF oxidation is first elucidated, with a focus on the synthesis strategies involving both anionic and cationic vacancies. Recent advancements in various catalytic oxidation systems for HMF are summarized and synthesized from this perspective. Finally, the future research prospects for selective HMF oxidation are discussed.

Influence of Hydroxycinnamic Acids on the Maillard Reaction of Arabinose and Galactose beyond Carbonyl-Trapping.

Hydroxycinnamic acids, known for their health benefits and widespread presence in plant-based food, undergo complex transformations during high-temperature processing. Recent studies revealed a high browning potential of hydroxycinnamic acids and reactive Maillard reaction intermediates, but the role of phenolic compounds in the early stage of these reactions is not unambiguously understood. Therefore, we investigated the influence of caffeic acid and ferulic acid on the nonenzymatic browning of arabinose, galactose, and/or alanine, focusing on the implications on the formation of relevant early-stage Maillard intermediates and phenol-deriving products. Contrary to previous assumptions, hydroxycinnamic acids were found to promote nonenzymatic browning instead of solely trapping reactive intermediates. This was reflected by an intense browning, which was attributed to the formation of heterogeneous phenol-containing Maillard products. Although, caffeic acid is more reactive than ferulic acid, the formation of reactive furan derivatives and of heterogeneous phenol-containing colorants was promoted in the presence of both hydroxycinnamic acids.