Chemistry - A European Journal最新文献

Noncovalent halogen bonding, particularly the three-center four-electron (3c-4e^-) [N⋯X⋯N]⁺ motif, represents a critical tool in supramolecular chemistry and materials science. While I⁺-based systems are well-studied, this review focuses on the emerging and highly functional [N⋯Br⋯N]⁺ motif and its application in halogen-bonded organic frameworks (XOFs). The authors comprehensively summarize the synthetic strategies required to overcome the instability of the Br⁺ species, including halogen bond network spatial constraint, cation substitution, ligand exchange, and precise anionic regulation. Structural analysis reveals that the shorter N⋯Br bond length (2.07 Å) and stronger electron-deficient characteristics of the Br⁺-bridge provide unique functional advantages. This structural superiority translates to enhanced performance in applications such as selective alcohol oxidation and highly efficient photocatalytic H₂O₂ production, where XOFs(Br) materials consistently outperform their I-analogues and molecular precursors. Furthermore, it also highlights the potential of XOFs(Br) in biomedical fields, including superior antimicrobial activity and applications in photothermal therapy. This work confirms the significant potential of the [N⋯Br⋯N]⁺ motif to drive future innovation in controllable functional materials, paving the way for the design of stable Br⁺-bridged XOFs for catalysis, precision medicine, and others.

Asymmetric transition metal catalysis represents the most reliable method for the chiral induction in organic scaffolds and to synthesize a wide array of valuable 3D-molecules. However, accessing both enantiomers of the chiral molecules from a catalyst(s) having the same chirality through ingenious stereo-control has remained a highly demanding task. Herein, we disclose the catalytic enantiodivergent synthesis of 3-vinylphthalides from arylcarboxylic acids and cyclopropenes, an efficient surrogate for vinylcarbenes. Through engineering the chiral cyclopentadienylrhodium(III) catalysts, both enantiomers have been achieved with excellent yield and enantioselectivity via regioselective C─H bond functionalization using a weakly coordinating directing group and asymmetric [4+1]-annulation. Experimental and computational investigations revealed the mechanism of the oxidative annulation and enantiodetermining ring-opening isomerization of cyclopropenes, which is governed by the stereoselective cleavage of the C─C bond. The present study opens a new avenue in asymmetric C─H bond functionalization and allows access to both enantiomers of the target molecules without altering the chirality of the ligand.

New series of triazole/pyrazole and tetrazole/triazole/pyrazole ligands were synthesized and coordinated with various transition metals to yield a diverse library of 14 complexes. All compounds were fully characterized by elemental analysis, mass spectrometry, powder X-ray diffractometry, and a range of spectroscopic techniques (¹H NMR, ¹³C NMR, FT-IR, and UV-visible diffuse reflectance). The crystal and molecular structures were elucidated via single-crystal X-ray diffraction, and their supramolecular features were explored through Hirshfeld surface analysis. The ⁵⁷Fe Mössbauer and magnetic SQUID measurements confirmed the high-spin nature of the Fe^II complex 1. In the three human cancer cell lines, most metal complexes are somewhat more cytotoxic than the inactive ligands, with Co(II) complexes 2 and 8 being the most potent in two of the cell lines (with IC₅₀ values in the two-digit micromolar range). Overall, this study highlights how blending tetrazole/triazole/pyrazole ligands with transition metals can lead to coordination compounds with potential in anticancer research, as a proof of concept. These results add valuable insight to the expanding field of metal-based therapeutics and could help guide the development of next-generation, more effective agents.

Herein, we report the Rh-catalyzed [2 + 2 + 2] cycloaddition of linked bis(diynes) Ar-C≡C-C≡C-(CH₂)₃-C≡C-C≡C-Ar with quinones for the rapid and efficient assembly of rigid structures containing bis(arylethynyl)naphthoquinones or anthraquinones using microwave radiation. The photophysical properties of the products were investigated, including absorption, emission, transient absorption (TA) spectroscopy, and singlet oxygen luminescence studies. However, the quinones did not exhibit photoluminescence or detectable singlet oxygen luminescence. Computational analysis via density functional theory (DFT) was performed to elucidate the electronic and structural factors influencing their behavior. Moreover, reductive methylation of one of the bis(arylethynyl)naphthoquinones (3aa) generated the fluorescent bis(methoxy) naphthalene derivative 4aa (Φ_f = 0.53). However, 4aa underwent photooxidation in air under sunlight via reaction with ¹O₂, which it sensitized, leading to ring opening of the bis(methoxy)arene ring.

Catalytically converting 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) underpins renewable, bio -based plastics, yet designing metal-efficient catalysts remains challenging. Here, we combine alloy and support effects by anchoring AuPd alloy nanoparticles on 2D covalent organic frameworks (COFs). Rationalizing alloy composition and COF functionality yielded Au₆₇Pd₃₃/TTATP, which converted HMF → FDCA in water using atmospheric O₂ mild conditions, delivering >99% FDCA yield, stable reusability, a turnover number (TON) of ∼100 at HMF/metal = 100, increasing to 518 at 600 (86.4% yield). High performance stems from alloy-support synergy that (i) partitions function (Au: HMF dehydrogenation; Pd: O₂ activation) and (ii) matches adsorption-desorption (TTATP enriches HMF yet releases FDCA; alloy surfaces moderate HMF binding and avoid the strong FDCA adsorption of Pd alone), thereby enhancing metal atom efficiency.

Eumelanin is a bio-pigment with remarkable photoprotective properties, whose function is tied to its complex supramolecular organization. Although hydrogen bonding and π-π interactions are recognized as key forces in shaping its architecture, their individual contributions remain poorly defined. Among its molecular precursors, the canonical monomer 5,6-dihydroxyindole (DHI) is notable for forming extensive hydrogen-bonded networks that stabilize supramolecular assemblies. To clarify how hydrogen bonding influences supramolecular topology in eumelanin precursors, we investigate selectively methylated derivatives of DHI, examining how subtle modifications to hydrogen-bonding motifs alter crystal packing, intermolecular arrangements, and optical properties. Single-crystal structures reveal that O-methylation (DMI) changes hydrogen-bonding dimensionality yet preserves helical assemblies, whereas full O- and N-methylation (DMI-Me) suppresses hydrogen-bonding, giving rise to zigzag arrangements dominated by van der Waals forces. Solid- and solution-state NMR measurements independently confirm the differences in the hydrogen-bonded assemblies. Complementary electronic spectroscopy shows that noncovalent architectures of the eumelanin derivatives exhibit pronounced excitonic coupling between neighboring chromophores. Electronic structure calculations support these observations, demonstrating that coupling originates primarily from Coulombic interactions, with minimal contributions from charge transfer. By linking molecular substitution to packing motifs and excitonic interactions, this work establishes hydrogen bonding as a design element for directing supramolecular order and emergent optoelectronic behavior in eumelanin-inspired materials.

Accurate monitoring of adenosine triphosphate (ATP)-the universal energy currency of cells-is essential for elucidating cellular metabolism and disease progression. However, the high basal concentration of intracellular ATP (1-10 mM) and variable probe uptake during imaging have hampered the development of reliable fluorescent sensors. Although DNA aptamer-based probes provide excellent selectivity, conventional turn-on designs often lack internal calibration, and Förster resonance energy transfer-based ratiometric probes typically exhibit limited signal changes. We report a ratiometric DNA duplex sensor comprising a Cy5-labeled ATP aptamer and a thiazole orange (TO)-labeled exciton-controlled hybridization-sensitive fluorescent oligonucleotide (ECHO) probe. Upon ATP binding, the aptamer structure switches and releases the reporter strand, resulting in a pronounced decrease in TO fluorescence while the Cy5 signal remains constant. Rational insertion of a polythymidine spacer effectively suppressed undesired TO-to-Cy5 energy transfer, enabling a reliable ratiometric Cy5/ECHO readout. The sensor operates robustly across physiological ATP concentrations, exhibits high nucleotide selectivity and satisfactory serum stability, and shows minimal cytotoxicity. Live-cell flow cytometry and confocal imaging further confirmed that cancer cells displayed significantly higher Cy5/ECHO ratios than normal fibroblasts. This internally self-calibrating aptamer sensor thus provides a powerful platform for intracellular ATP imaging and cancer diagnostics.

In this work, we disclose that β-allyl cycloalkenones can serve as effective bisvinylogous precursors through in situ generation of trienalcohol intermediates under Brønsted acid catalysis. This strategy enables a direct and highly diastereoselective δ,ε-regioselective remote bisvinylogous initiated formal [4+2] cycloaddition of β-allyl cycloalkenones with ortho-quinone methides (o-QMs). In this process, β-allyl cycloalkenones act as dienophiles while o-QMs function as diene precursors, providing efficient access to naphthopyran derivatives with excellent selectivity. Additionally, the asymmetric variant was also investigated using a BINOL-derived chiral Brønsted acid, thereby extending the utility of this method toward enantioselective synthesis.

Fungal unspecific peroxygenases (UPOs) have emerged as powerful catalysts for diverse oxidation reactions. While previous studies have predominantly focused on their native mono(per)oxygenase activity, their full catalytic potential remains underexplored. Herein, we demonstrate that the intrinsic peroxidative activity of UPOs can be effectively leveraged for the straightforward synthesis of benzoxazole compounds. Using the unspecific peroxygenase from Agrocybe aegerita, a broad range of ortho-patterned phenolic substrates were efficiently converted into high-value benzoxazoles with conversions of up to 99% under the neat reaction conditions. The enzyme exhibited superior catalytic performance compared to the well-established horseradish peroxidase. Mechanistic studies demonstrated that phenoxyl radicals generated by UPO's intrinsic peroxidase activity are essential for benzoxazole formation. This work not only presents a mild and efficient synthetic route to benzoxazoles but also expands the known reactivity and oxidative chemistry of UPOs.

Phenylethanoid glycosides (PGs), featuring a phenylethanoid glucoside core, exhibit diverse biological activities, notably neuroprotective effects. However, PGs bearing the susceptible 2'-O-acetyl group remain scarcely explored owing to their limited natural occurrence and the difficulty of preserving esters during synthesis. Herein, we describe the synthesis of such PGs, keeping the 2'-O-acetyl group intact via a remote DPPA-directed glycosylation strategy. The 2-(diphenylphosphinoyl)acetyl (DPPA) group ensures high stereocontrol through hydrogen-bonding in glycosylation, and can be selectively removed under mild Mg(OMe)₂-promoted conditions. This approach enables streamlined access to both acetylated and non-acetylated PGs, including cistanosides E, G, and H, as well as the proposed structure of lophanthoside A. The developed method provides a general platform for constructing PGs bearing acyl groups and supports further investigation of their bioactive mechanisms.