Chemistry - A European Journal最新文献

The photosynthesis of hydrogen peroxide (H₂O₂) from O₂ and H₂O using solar energy offers a sustainable alternative to conventional processes. However, the H₂O₂ yield is lowered because the H₂O₂ is decomposed by the photocatalysts that are typically used. In this study, porphyrin-containing organosilica photocatalysts were developed for efficient H₂O₂ production. The as-synthesized photocatalysts successfully convert O₂ and H₂O into H₂O₂ upon irradiation with visible light. Organosilica with the optimal number of porphyrin sites exhibit H₂O₂ production rate of 108 µmol·L^-1·h^-1, which is 1.8-times higher than that of the precursor porphyrin ligand. Decomposition of H₂O₂ by the photocatalysts was negligible. Photoluminescence measurements revealed that the incorporation of an optimal number of porphyrin sites into the organosilica significantly enhanced the photocatalytic activity for H₂O₂ production because of the suppression of aggregation-induced quenching. The mechanistic study revealed that H₂O₂ production over the porphyrin-containing organosilica photocatalysts occurred predominantly via a direct two-electron oxygen reduction reaction pathway involving singlet oxygen and photogenerated electrons. These findings open new avenues for efficient photocatalytic production of H₂O₂ and have significant implications for the design of advanced silica-based photocatalytic materials.

Precise control over interlayer stacking in two-dimensional (2D) materials is a powerful strategy for modulating functional properties. Yet how racemic assemblies of enantiopure layers influence the full spectrum of AA, AB, and ABC stacking patterns has remained unexplored. Here, we uncover this missing link with a family of cationic 2D metal-organic frameworks, MOF-CC-2(X), built from a propeller-chiral, tris-triazole click-cage ligand (CC-2), and Ag(I)-triazole coordination. The ligand's dual 1,3,5-triphenyltriazine faces offer orthogonal π-surfaces that respond to the identity and interactions of charge-balancing anions (X = PF₆ ^-, OTf^-, NO₃ ^-). Systematic anion substitution directs the formation of eclipsed AA, paired AABBCC, or fully alternating ABC stacking, further assisted by modulation of π···π interactions. In particular, the solvated NO₃ ^- anions disrupt triazine stacking and reduce interlayer cohesion, enabling exfoliation into ultrathin nanosheets (≤ 5 nm) that preserve chiral registry between homochiral layers. These positively charged, π-rich nanosheets show rapid, selective uptake of sulfonated dyes in water, demonstrating Langmuir-type adsorption and excellent recyclability. This study establishes (1) counteranion identity as a primary driver of stacking in 2D MOFs, (2) racemic layer chirality as a structural design element, and (3) propeller cages as versatile modules for programmable exfoliation and water remediation.

Bimetallic cooperation is a defining feature of many enzymatic and synthetic catalytic systems, where short metal-metal separations enable cooperative substrate activation. Synthesis of complexes wherein two distinct metal centers are placed in close proximity is challenging and typically requires the use of nonsymmetric ligand environments. Here, we report the synthesis, structural characterization, and electronic analysis of heterobimetallic complexes supported by a symmetric PNNP ligand. A mononuclear Ru(II) complex serves as a modular platform for the stepwise construction of RuRu, ZnRu, and CoRu assemblies. The resulting heterobimetallic ZnRu and CoRu complexes adopt closely related architectures. Upon deprotonation, ligand dearomatization induces a pronounced contraction of the metal-metal distance, underscoring the unique ability of the PNNP scaffold to geometrically tune bimetallic cores. Density Functional Theory (DFT) combined with Quantum Theory of Atoms in Molecules (QTAIM) analysis reveals that the CoRu complex features a metallophilic interaction between the two metal centers, whereas the ZnRu analogue lacks such an interaction. Taken together, this study demonstrates that the symmetric PNNP ligand is a versatile platform for assembling heterobimetallic complexes and that controlled ligand deprotonation offers a straightforward route to modulate metal-metal separations and electronic communication within these systems.

Whereas a dinuclear pathway applies to the monooxygenation of phenols by the type 3 copper enzyme tyrosinase, a mononuclear pathway has been identified for the same reaction in corresponding small-molecule systems. DFT calculations of five copper model complexes reveal that the latter mechanism is energetically feasible, identifying all intermediates, and transition states. The mechanism closely resembles the biosynthesis of the topaquinone (TPQ) cofactor in the enzyme amine oxidase (AO), though the latter process is not catalytic. Additionally, it is shown that the hydroxo-quinone complex formed after the hydroxylation step further converts into a copper-geminal diolate species, which is confirmed by MS/MS experiments using isotope labeling with ¹⁸O₂.

An iridium-catalyzed linear-selective sp³ C─H alkylation of N-methylamides with alkenes was developed using bulky, electron-deficient diphosphite ligands. The reaction accommodates N-methylacetamide derivatives bearing diverse substituents and a range of terminal alkenes. Mechanistic studies were conducted to gain insights into the reaction pathway. Internal alkenes can also be used via in situ consecutive alkene isomerization. Selective sp³ C─H functionalization was achieved even in the presence of competing sp² C─H bonds.

A thermally activated delayed fluorescence (TADF) emitter consisting of a triarylamine (TAA) donor and a 1,4-dicyanobenzene (DCN) acceptor moiety was characterized by femtosecond UV-Vis and near infrared (NIR) spectroscopy. The combination of the two techniques allows to probe spectral changes of the emitter in a range extending from 350 to 1600 nm. With the approach, low-lying higher singlet excitations (S_n≥2) contributing to intersystem crossing via spin vibronic mechanisms can be located energetically. Due to the charge transfer (CT) character of the S₁ state, the transition energies S₁→S_n≥2 are strongly solvent dependent as experiments on TAA-DCN dissolved in cyclohexane, toluene, 1,2-dimethoxyethane, and acetonitrile indicate. The experiments also hold information on dielectric and vibrational relaxation ensuing S₁ excitation.

Carbonyl olefination reactions have become essential to organic chemistry since Wittig's report on the first reaction of this kind using a phosphorus ylide. While the reaction mechanism of the Wittig olefination is well understood the same cannot be said about the related silicon analogue, the Peterson olefination. Both an open chain, betaine like intermediate and a cyclic 1,2-oxasiletanide intermediate have been discussed since Peterson's original publication, with little evidence for the cyclic intermediates. Herein we present the synthesis and characterization of several stable cyclic Peterson olefination intermediates synthesized via the reaction of an α-silyl carbanion with various ketones. The α-silyl carbanion is stabilized by three pentafluoroethyl groups at the silicon atom. Furthermore, it bears a carbanion stabilizing phenyl group α to the carbanion.

Prodrugs of nucleotides with aminoacidyl esters as one of the two masking groups of the phosphate are successful molecular constructs for making nucleosidic antivirals bioavailable. Still, some of those '"ProTide" prodrugs have a strong bias to exert their antiviral activity in liver cells, with little activity in nonhepatic tissues. Here, we show that the alcohol residue of the alaninyl esters of two established antivirals has a strong effect on the activity against RNA viruses with pandemic potential. This was first shown for remdesivir (REM), for which a cycloheptyl residue gave 50% inhibition against four different viruses at ≤110 nM concentration. With the cyclobutyl derivative of bemnifosbuvir (BEM), nanomolar EC₅₀ values against dengue virus were measured in a range of cell lines, including cells with much lower metabolic activity than hepatocytes, without significant cytotoxicity up to 50 µM. These findings show how easily activity can be improved and broadened across different tissues through seemingly minor changes in ProTide structure. Our results may instruct the design of new antivirals with broad activity against RNA viruses to increase pandemic preparedness.

Large Stokes shift (LSS) fluorescent proteins, characterized by significant energy gaps between absorption and emission, are invaluable for biological imaging. While most reported LSS systems rely on photoacidic chromophores undergoing excited-state proton transfer (ESPT), photobasic variants have remained underexplored. Here, we construct an LSS complex by incorporating the photobasic fluorophore FR-1V into an engineered rhodopsin mimic hCRBPII mutant M1. Through ultrafast spectroscopy, we reveal pH-dependent ESPT dynamics: at pH 8, ESPT occurs as a single kinetic process ( $\tau$ = 1.8 ps), whereas at pH 11, it proceeds via two distinct processes ( $\tau$ = 1.0 ps, $\tau$ = 13 ps). To reconcile transient absorption spectroscopy (TAS) and time-correlated single-photon counting (TCSPC) results, we hypothesized pH-dependent heterogeneity in the hydrogen-bonding networks of the ground-state Schiff base. Molecular dynamics simulations further support this model, revealing two distinct conformational states: One with stable water-bridged hydrogen-bond networks that facilitate ESPT, and another lacking such networks where proton transfer is structurally impeded. These findings establish a mechanistic framework for pH-responsive biosensors and advance the understanding of protein-chromophore interactions in photobasic systems.

Neutrophil elastase (NE) plays a crucial role in tissue injury and immune regulation across a broad range of inflammation-associated diseases, and changes in its activity provide informative readouts for disease stratification and treatment monitoring. However, current assessments based on biofluids and histology are largely sample-dependent and static, limiting in vivo spatial localization and longitudinal tracking, and often failing to distinguish enzymatic activity from expression levels. In this review, we summarize recent advances in noninvasive in vivo molecular imaging of NE. Specifically, we outline NE-responsive and NE-targeted probes and tracers across near-infrared fluorescence imaging, photoacoustic imaging, and positron emission tomography (PET), while briefly covering representative chemiluminescence strategies as an adjunct modality. We highlight key probe design and signal-transduction strategies and synthesize representative in vivo applications in lung inflammation, cardiovascular inflammation, tumor immunology, and gastrointestinal inflammation.