Search Results (496)

A thermoreversible dynamic covalent network was constructed in recycled polyethylene terephthalate (RPET) via Diels–Alder (DA) chemistry to enhance mechanical performance, reprocessability, and self-healing. Furan-functionalized RPET (RPET-3F) was first prepared from maleated RPET (RPET-MA), followed by crosslinking with bismaleimide (BMI) at different feed ratios. FTIR spectra confirmed the successful grafting of furan groups and the formation of DA adducts. With increasing BMI content, the gel fraction and crosslink density increased substantially, whereas the swelling ratio decreased, indicating the progressive development of a three-dimensional network. RPET-3F-2B showed the highest network integrity among all samples. DSC analysis revealed a distinct retro-DA dissociation peak at 143 °C and a recrosslinking peak near 124 °C, confirming the thermal reversibility of the DA network. Owing to the optimized network structure, RPET-3F-2B exhibited the best mechanical properties and excellent reprocessability, retaining stable performance after three hot-pressing cycles. After repeated reprocessing, its tensile strength remained 74% higher than that of RPET-MA, while the elongation at break was still improved by about 10%. Moreover, the sample showed efficient thermally induced self-healing at 150 °C, with surface cracks nearly disappearing after 4 h. These results demonstrate that DA chemistry offers a promising route to the high-value reutilization of RPET into recyclable, multifunctional polymer materials. Full article

Thermosets are widely used in engineering applications due to their high mechanical strength, thermal stability, and chemical resistance; however, their permanently crosslinked networks also limit repair, reshaping, and recycling. Dynamic covalent chemistry offers a route to addressing these limitations through the incorporation of reversible bond exchange into thermoset networks. A range of dynamic thermosets has been developed based on transesterification, Diels–Alder reactions, imine exchange, disulfide metathesis, boronic ester exchange, and siloxane equilibration, enabling self-healing, reprocessing, welding, and closed-loop recycling. This review examines representative dynamic thermosets in terms of exchange mechanisms, network topology evolution, and macroscopic response. By correlating molecular exchange processes with network-level mechanics and macroscopic performance, this review identifies design principles for dynamic thermosets with improved sustainability and processing compatibility. Full article

Self-healing materials have attracted increasing attention as a strategy to enhance durability, extend service life, and reduce maintenance in advanced material systems. Among these, cellulose-based self-healing materials represent a sophisticated intersection between sustainable macromolecular chemistry and adaptive materials science. This review provides a synthesis of recent advancements in the field, systematically categorizing materials derived from cellulose raw materials. We evaluate the fundamental chemical strategies employed to achieve autonomous repair, distinguishing between extrinsic mechanisms—utilizing cellulose-based micro/nano-capsules to sequester healing agents—and intrinsic mechanisms governed by dynamic covalent chemistry (Schiff-base, boronic ester, Diels–Alder) and supramolecular interactions (hydrogen bonding, metal–ligand coordination, and host–guest assemblies). The analysis highlights how cellulose’s hierarchical structure and abundant surface functionality are leveraged to overcome the traditional trade-off between mechanical toughness and healing efficiency. Particular emphasis is placed on the transition from simple structural hydrogels to sophisticated multifunctional systems. These include ultra-stretchable strain and pressure sensors for e-skin applications, biocompatible and injectable matrices for chronic wound management and stem cell delivery, and advanced anti-freezing eutectogels for performance in extreme environments. Furthermore, we explore the integration of cellulose into traditional sectors, such as self-healing concrete utilizing microbe-induced calcification and smart, eco-friendly coatings for corrosion protection. Finally, we discuss critical challenges, including environmental stability, scalability, and the development of standardized evaluation protocols, providing a roadmap for the next generation of bio-derived, sustainable and intelligent materials. Full article

The root bark of Morus alba L. is commonly used as a natural antioxidant; however, its active constituents and underlying molecular mechanisms remain unclear. In this study, a bioactivity-guided isolation approach was employed to identify antioxidant substances from the root bark of Morus alba L. and to investigate their protective effects against oxidative damage in HaCaT cells. Using techniques such as silica gel column chromatography and semi-preparative HPLC, combined with NMR and HR-ESI-MS analysis, 22 compounds were isolated and identified from the dichloromethane extract of Morus alba L. root bark, including Diels–Alder adducts, flavonoids, and benzofurans. Among them, compounds 1 and 2 are new compounds, while compounds 12 and 16 were isolated from this plant for the first time. Bioactivity screening revealed that Kuwanon A (compound 17) exhibited significant cytoprotective effects in an H₂O₂-induced HaCaT cell injury model, effectively scavenging intracellular reactive oxygen species (ROS), restoring mitochondrial function, and enhancing the activities of antioxidant enzymes such as SOD and GSH. Further studies indicated that H₂O₂ induced ferroptosis in HaCaT cells, characterized by abnormal Fe²⁺ levels, lipid peroxidation, and elevated levels of pro-inflammatory cytokines (IL-1β, IL-6, TNF-α). Kuwanon A significantly ameliorated these pathological changes. Consistently, ELISA and Astral DIA quantitative proteomics analyses demonstrated that Kuwanon A specifically upregulates the expression of the sulfurtransferase NFS1, thereby promoting the expression of the core antioxidant enzyme GPX4 and the iron storage protein ferritin-H, collectively inhibiting ferroptosis. This study elucidates that Kuwanon A is a key active component responsible for the antioxidant and anti-inflammatory effects of Morus alba L. root bark, and its mechanism is closely associated with regulating the NFS1-mediated ferroptosis defense pathway. Full article

Alzheimer’s disease (AD) is a common neurodegenerative disorder linked to cholinergic dysfunction, with butyrylcholinesterase (BChE) being a key therapeutic target for moderate–severe AD. Cortex Mori Radicis, a traditional Chinese medicinal herb, is rich in Diels–Alder adducts with potential neuroprotective effects; here, eighteen Diels–Alder adducts (four new: morusalbanol B–E, 1–4) were isolated and identified from its 80% ethanol extract. Their cholinesterase inhibitory activities were assessed via Ellman’s method, with enzyme kinetics and molecular docking performed for active compounds. Most compounds showed selective BChE inhibition, with kuwanon X (14) being the most potent (IC₅₀ = 2.3 μM). morusalbanol B (1), cathayanon A (8), and kuwanon G (12) acted as noncompetitive inhibitors, while Morusalbanol C (2) and kuwanon X (14) were mixed competitive inhibitors. Molecular docking suggested that potent inhibitors occupied the BChE active pocket via hydrogen bonds, π-π stacking, and hydrophobic interactions with Trp82, His438, and Phe329. MD simulations and MM-GBSA binding free energy analysis further verified that all three representative complexes (1, 8, and 14) achieved favorable thermodynamic and structural stability, with binding driven primarily by van der Waals forces. Residue decomposition revealed that Trp82 and Phe329 served as core binding hotspots for all tested inhibitors. Structure–activity analysis indicated that a cis-trans methylcyclohexene configuration, shorter aliphatic ester chains, and more prenyl groups enhanced BChE inhibition. This study provides new lead compounds and a systematic molecular mechanism basis for developing novel anti-AD BChE inhibitors from natural products. Full article

This review summarizes current knowledge on naturally occurring pristimerin-pristimerin triterpenoid dimers, a rare and structurally diverse class of secondary metabolites reported mainly from Celastraceae species. Known dimers are compiled with emphasis on botanical sources and key architectural features, including the variety of interunit linkages, regio- and stereochemical diversity, and distinct isomeric forms (including atropisomerism). Major advances in structure elucidation and structural revisions are discussed, highlighting the role of modern spectroscopic tools—particularly 2D NMR methods and chiroptical techniques—in resolving connectivity and absolute configuration, and in correcting several earlier assignments. Proposed biosynthetic scenarios are outlined, focusing on the reactivity of the quinone-methide motif and its interconversion with 2,3-diketone forms, as well as (hetero) Diels-Alder-type processes; selected biomimetic studies are summarized as supportive evidence for these pathways. A critical overview of available biological data indicates that many pristimerin dimers display limited activity in common antimicrobial and cytotoxicity assays when compared with monomeric congeners, which may point to alternative ecological roles or storage/transport functions in planta. Finally, key knowledge gaps and future directions are identified, including improved isolation coverage, rigorous synthetic/biomimetic work, and broader pharmacological screening beyond standard panels. Full article

The influence of steric hindrance caused by the dienophiles on the stereoselectivity of cycloadditions of 2H-pyran-2-ones with maleimides was investigated in this study. It was found that sufficiently bulky N-substituents on the maleimides (such as N-triphenylmethyl) can cause the cycloaddition to proceed differently than expected, thus yielding asymmetric exo,endo-bicyclo[2.2.2]octenes instead of the commonly obtained symmetric exo,exo products. Furthermore, the incorporation of an N-triphenylmethyl group, which induces highly diastereoselective formation of asymmetric exo,endo adducts and can later be easily removed under acidic conditions, can be described as an example of an efficient exo,endo-diastereoselective auxiliary. Full article

Natural products from plants have played an important role in cancer and neurodegenerative diseases. In this context, the root bark of Maytenus chiapensis (Celastraceae) was investigated to examine its chemical constituents and potential biological activities. Chromatographic separation of the root bark extract yielded a new Diels–Alder adduct (morenine) formed by a triterpenophenolic moiety derived from tingenone and a bicyclic guaiane-type sesquiterpene linked through a 1,4-dioxane bridge. In addition, eight previously reported Diels–Alder adducts—retusonine and cheiloclines A–D and F–H—were isolated, together with their biosynthetic precursors, the quinone-methide triterpenoids (QMTs) pristimerin and tingenone. Structural elucidation was achieved through detailed 1D and 2D NMR spectroscopic analyses. The adducts were tested for cytotoxicity against six cancer cell lines (A549, SW1573, MIA PaCa-2, T-47D, HeLa, and WiDr cell lines), showing moderate-to-low activity compared with their precursors. Continuous live cell imaging identified apoptosis and vacuole formation as the main modes of action of pristimerin in SW1573 cells. Moreover, acetylcholinesterase inhibition assays revealed that cheiloclines B–D, F, and H exhibited up to 50% inhibition. These findings reinforce the potential of Celastraceae species as a source of unique and complex compounds and enhance our understanding of their therapeutic potential. Full article

Traditional Chinese prescriptions are characterized by complex chemical constituents and wide variations in constituent content, which pose a substantial challenge to their comprehensive characterization. As a classic traditional Chinese prescription known for its heat-clearing and detoxifying properties, Huangqintang Decoction (HQD) is composed of Scutellariae Radix, Paeoniae Radix Rubra, Glycyrrhizae Radix et Rhizoma, and Jujubae Fructus. In this study, we developed an off-line two-dimensional liquid chromatography that addressed the limitations of traditional analysis of unfractionated extracts, such as restricted peak capacity, which often obscured trace components. By coupling with ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF/MS), this study successfully performed rapid identification or characterization of the complete chemical profile of HQD. Notably, beyond high-throughput identification, this approach leveraged characteristic fragment ions and reversed-phase chromatographic behaviors to differentiate some isomers of flavonoid glycosides and triterpenoid saponins, demonstrating its depth in structural identification. Flavonoid glycoside isomers were distinguished by diagnostic neutral losses, while flavanones and chalcones were characterized by retro-Diels–Alder (RDA) and β-rearrangement, respectively. Isomers of triterpenoid saponins were inferred from aglycone-specific pathways alongside RDA cleavages. Ultimately, a total of 192 compounds were identified, including 88 flavonoids, 80 triterpenoids, 7 monoterpene glycosides, 3 fatty acid amides, 3 phenylethanoid glycosides, 4 coumarins, 3 saccharides, 1 organic acid, and 3 others. This study demonstrated that the off-line two-dimensional liquid chromatography analysis strategy significantly enhanced chromatographic resolution and expanded the coverage of trace components. It presented an effective strategy for comprehensive compound identification in complex traditional Chinese medicine prescriptions. Full article

Dynamic covalent bonds are commonly used to maintain the self-healing properties of polyurethanes and facilitate resource recycling. However, relying on a single type of dynamic covalent bond often makes it difficult to effectively regulate both mechanical and self-healing properties across a wide temperature range. In this study, a self-synthesized chain extender containing disulfide bonds was introduced into a polyurethane system, leading to the development of a novel dual-dynamic covalent bond self-healing polyurethane (SSDA-PU). Innovatively, this SSDA-PU demonstrates self-healing properties across a wide temperature range. The successful synthesis of the chain extender and the incorporation of both disulfide bonds and Diels–Alder (DA) bonds were confirmed using FTIR and Raman spectroscopy. The physical characteristics and self-healing performance were comprehensively evaluated through multi-scale testing and characterization, including thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), hardness testing, mechanical tensile tests, and self-healing experiments. The underlying synergistic self-healing mechanism was subsequently elucidated. Findings showed that a higher R-value (isocyanate index) in SSDA-PU leads to over-crosslinking, while an R-value of 1.7 achieves the best overall mechanical performance, with tensile strength and elongation at break reaching 21.1 MPa and 755.17%, respectively. Additionally, SSDA-PU demonstrated the capacity for multiple healing cycles, with an initial self-healing efficiency of 90.38%, which remained notably high at 59.21% even after three damage-healing cycles. Importantly, SSDA-PU exhibited healing capabilities even at relatively low temperatures. Cracks in SSDA-PU can be effectively repaired through the synergistic action of disulfide bond exchange, hydrogen bond dissociation, and thermally reversible DA reactions. SSDA-PU also shows excellent recyclability, offering valuable insights for the practical engineering application of functional polyurethanes. Full article

The formation of recyclable polyethylene materials is significantly limited by traditional crosslinking methods, which involve solvent-heavy processes and permanent chemical bonds that cannot be undone. Herein, we report an environmentally friendly and scalable approach to construct a thermo-reversible polyethylene network (PE-g-DA) via solvent-free, one-step melt processing based on furan–maleimide Diels–Alder (D–A) dynamic covalent chemistry. Furan-functionalized polyethylene was dynamically crosslinked with bismaleimide during melt mixing, fully compatible with conventional polyolefin processing techniques. FTIR spectroscopy, temperature-dependent solubility, and differential scanning calorimetry collectively confirm the reversible formation and dissociation of D–A adducts, enabling thermal switching of the network structure. Equilibrium swelling experiments based on the Flory–Rehner model indicate that the crosslink density can be precisely controlled by varying the bismaleimide content. As a result, PE-g-DA exhibits significantly enhanced tensile strength while maintaining high ductility at moderate crosslink densities. Notably, the dynamic network allows efficient thermal reprocessing, with recycled samples retaining approximately 93% and 80% of their original tensile strength after the first and second reprocessing cycles, respectively. Moreover, intrinsic thermal self-healing behavior is directly visualized by scanning electron microscopy at 120 °C. This work demonstrates that combining dynamic Diels–Alder chemistry with solvent-free melt processing offers a practical and sustainable route to recyclable, reprocessable, and self-healable polyethylene materials with clear potential for large-scale industrial production. Full article

Guanidines are structurally unique, highly basic, nitrogen-containing organic compounds with strong hydrogen-bonding ability and biological activity, providing valuable functionality in medicinal chemistry, organocatalysis, and materials science. Among modern strategies for assembling guanidine-containing molecules, cycloaddition reactions have emerged as powerful tools due to their efficiency, stereoselectivity, and ability to rapidly build molecular complexity. Recent innovations have expanded cycloaddition methodologies for generating guanidine functionalities, incorporating guanidine-containing substrates, and using guanidine-based catalysts. This review summarizes these advances and highlights the current trends in guanidine-related cycloaddition chemistry. Full article

A method for the preparation of 3-substituted azafluorenones is presented. Condensation of ninhydrin with thiomethylamidrazone gives a triazine from which 3-thiomethyl-4-azafluorenone is produced after Diels–Alder cycloaddition with norbornadiene followed by two retro-Diels–Alder cycloreversions. Oxidation of the sulfide to the sulfone allows for nucleophilic substitution at the 3-position. Using different amidrazones can give other substituents at the 3-position directly. The photophysical properties of the azafluorenones are characterized and compared with computational calculations. Compounds with a substituent bearing an n-donor group show significant fluorescence. The n-donor group is prominent in the HOMOs in these systems, whereas in the compounds with weak emission, it is not. The El Sayed rules for intersystem crossing do not explain the emission intensity ordering of these compounds. Full article

The cycloaddition reaction is one of the most common reactions in organic chemistry. It has been applied in various fields. Herein, we focus on the application of cycloaddition reactions in investigating biological molecules and materials using magnetic resonance techniques. To facilitate magnetic resonance studies such as electron paramagnetic resonance (EPR) spectroscopy and paramagnetic nuclear magnetic resonance (NMR) spectroscopy, there is often a requirement to attach spin labels and paramagnetic tags to the system of interest. The cycloaddition reaction is one of the ways to tether these spin labels and paramagnetic tags. In this review, we highlight the applications of various cycloaddition reactions such as the Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) reaction, the strain-promoted azide–alkyne cycloaddition (SPAAC) reaction and the Diels–Alder reaction in the interdisciplinary field of magnetic resonance studies of biomolecules, including proteins, nucleic acids, carbohydrates, lipids and glycans, as well as materials. Full article

Click chemistry is highly valued in the design of polymeric biomaterials due to its ability to generate complex structures and localized surface modifications. However, prominent mechanisms in click chemistry, such as copper-catalyzed azide-alkyne cycloaddition (CuAAC), are inefficient for the synthesis and/or modification of biomaterials because they present significant limitations for in vivo applications. The presence of residual copper in the material is toxic and requires extensive purification, increasing production costs and hindering scalability and availability for in vivo applications. To overcome these limitations and ensure the safety and biocompatibility of materials, biorthogonal reactions such as strain-promoted azide-alkyne cycloaddition (SPAAC) have been developed. Thiol-ene/thiol-yne and Diels–Alder mechanisms are also relevant for the formation of robust polymer networks with specific characteristics and attractive advantages for generating biocompatible materials. These reactions not only improve cell integration and reduce fibrosis in in vivo applications but also enable the creation of functional structures for tissue regeneration. This review provides a comprehensive analysis of advances in the synthesis of biomaterials for tissue regeneration using hydrogels designed via click chemistry, as well as the various mechanisms and structural considerations. Full article