Chemistry - A European Journal最新文献

A resurgence of research surrounding Au(I)-Aryl complexes has led to sustainable methods toward their synthesis, as well as to the expansion of their scope and applications in catalysis, biology, and materials chemistry. The availability of mild synthetic methodologies has facilitated the design and development of Au(I)-Aryl architectures suitable for specific photonic applications, such as Thermally Activated Delayed Fluorescence (TADF) and Room Temperature Phosphorescence (RTP) emitters. The development and application of reliable synthetic methods have increased, yet several synthetic aspects remain to be uncovered. Herein, the synthesis of N-heterocyclic carbene (NHC) Au(I)-Aryl complexes through mild, base-assisted transmetallation of arylboronic acids is further explored, targeting Au(I)-Aryl structures incorporating polyaromatic and triarylborane frameworks, and structural features of relevance to organometallic synthesis, supramolecular chemistry, and luminescence. In addition to the utilization of K₂CO₃ as the mild, cost-effective base of choice, we introduce the use of aqueous ammonia as a novel tool that facilitates transmetallation to gold. The purpose of additional exploration is to discover limitations of the synthetic methods, as well as inherent flaws regarding the design of [Au(NHC)(Ar)] (Ar = Aryl) complexes. Previously undiscovered synthetic limitations are disclosed, along with practical alternatives.

This study presents a systematic comparison of two recycling strategies for molecular catalyst-multiphasic catalyst recycling and organic solvent nanofiltration (OSN)-within a unified reaction system. Molecular catalyzed reactions are vital in chemical production, necessitating efficient recycling of costly catalyst metals. To facilitate a fair comparison, a versatile model reaction system was developed that allows for both monophasic and multiphasic configurations while preserving the integrity of the central hydroformylation process, converting 1-hexene and CO/H₂ syngas to heptanal in both cases.

The growing demand for sustainable and efficient methods for synthesizing fine chemicals has increased interest in innovative approaches for accessing high-quality chiral building blocks, particularly fluoroalcohols, which are relevant for the production of active pharmaceutical ingredients (APIs). This study presents the complete integration of a two-step process in a continuous flow reactor system for the synthesis of (R)-2-fluoro-1-phenylethanol as a reference molecule. To this end, the individual reaction steps and technologies for the decarboxylative fluorination of 3-oxo-3-phenylpropanoic acid in aqueous media, followed by an enantioselective biocatalytic reduction of the prochiral intermediate phenacyl fluoride, were adapted and implemented in a compact laboratory system for performance demonstration. Alcohol dehydrogenase (ADH) from Rhodococcus ruber (RrADH) produced in a plant-derived BY2 cell-free expression system was used as the biocatalyst, which was immobilized via an imine bond on glutaraldehyde-modified silica supraparticles. The immobilized enzymes were used in batch mode for comprehensive kinetic studies of the enantioselective reduction, including evaluations of their operational and storage stability. Excellent enantiomeric excess (> 99.9%) and overall yields of up to 91% were achieved for both synthesis steps. These results are a prerequisite for the targeted and stable use of the enzyme in a continuously operated two-step process, which was achieved by using a serial micro batch reactor (SMBR) setup with a capillary reactor for precise temperature control. This study demonstrates the advantages of combining immobilized biocatalysts with continuous-flow operation for achieving high efficiency and selectivity in the synthesis of chiral fluoroalcohols. The integrated process provides a sustainable and versatile basis for future developments in the green synthesis of fluorinated building blocks relevant to pharmaceutical applications.

A methyl-substituted ladder meta-phenylene macrocycle (MeLMMP) and its corresponding ladder polymer (MeLPMP), a meta-analogue of the well-known ladder-type poly(para-phenylene), LPPP, were synthesized and comprehensively investigated. Both compounds exhibit limited conjugation due to the meta-linked phenylene units, resulting in absorption and emission features shaped by cross-conjugation. Despite having a longer chain, MeLPMP and MeLMMP exhibit nearly identical electronic and photophysical behavior, suggesting that the number of repeat units has minimal influence. MeLPMP exhibits enhanced vibronic resolution compared to MeLMMP due to a broadening of the optical bands of the macrocycle caused by the presence of a mixture of stereoisomers formed during the non-stereoselective ladderization step. A small amount of fluorenone-type keto defects produces a weak emission near 500 nm, more evident in the macrocycle, and introduces radiationless decay pathways that compete with fluorescence. This decay pathway, together with the weak π,π* conjugation in these angular compounds, lowers the fluorescence quantum yield when compared with the linear MeLPPP, while promoting singlet-triplet conversion and phosphorescence. The data indicate the presence of three chromophoric populations: pristine oligo(meta-phenylene) units; units quenched by nearby keto defects; and intramolecular charge-transfer complexes (ICTCs) formed between oligo(meta-phenylene) units and keto defects. These findings clarify the photophysics of meta-phenylene ladder systems, showing that the MeLMMP macrocycle can act as a structural and electronic model for related ladder polymers.

Dearomative addition reactions of indoles represent a prominent strategy for the synthesis of practically valuable indolines. However, implementing this approach typically requires prefunctionalization of the indole precursor with specific groups (e.g., alkynes, alkenes, or ketones) to facilitate the subsequent cyclization-dearomatization step. In this work, we report a three-component, thiol-yne-mediated dearomative vinylation of indoles that circumvents the need for preinstalling reactive fragments into the indole scaffold. The developed photoredox-catalyzed thiol-yne-heteroarene reaction employs Boc-protected indole-3-carboxylates as effective terminating agents for the radical cascade.

Direct modification of native antibodies with affinity peptides remains a significant challenge, primarily because the affinity peptide often stays bound to the antibody and blocks its interaction with key receptors. In this study, we developed tCAP(N3), a novel traceless chemical conjugation method that employs an affinity peptide. tCAP(N3) can be stored for over a year at refrigerated temperature, as it contains an active ester precursor that can be spontaneously activated under neutral conditions. When tCAP(N3) was mixed with a target native IgG, Ac-Lys(N₃)-Gly-Gly was site-selectively transferred onto Lys248, yielding divalently azidated IgG that can be further modified with DBCO compounds. The resulting antibody conjugates retained Fc receptor binding and antigen recognition comparable to the parent IgG.

The development of cost-effective and high-performance electrocatalysts for methanol oxidation reaction (MOR) is essential to promote the hydrogen energy technology. However, most of the electrocatalysts currently used for MOR have drawbacks, such as inefficient reaction kinetics, low tolerance to carbon monoxide poisoning, and unstable performance. Herein, we report a novel hierarchical MOF heterostructure that is made up of Mn-doped ZIF67 and Mn-doped ZIF-L (Mn-ZIF67/L) directly grown on carbon cloth to highly enhance the MOR performance. Such heterostructure integrates flake-like Mn-doped ZIF-L with Mn-doped ZIF-67 nanocrystals, forming a porous core-shell framework with abundant active sites and enhanced charge transportation. More interesting, the Mn-ZIF67/L experiences dynamic reconstruction (Mn-ZIF67/L-ac) that partial phases in CoMn LDHs are transformed into (Co,Mn)OOH during the electrochemical operation in which further boosting the catalytic performance and stability. The electrochemical results demonstrate that Mn-ZIF67/L-ac remarkably improves the MOR performance with the much lower potential of 1.359 V at 10 mA cm^-2, outperforming commercial RuO₂. The electrocatalyst also delivers the high MOR stability of ∼97% retention after 130 h. This work demonstrates a robust strategy for nonnoble-metal electrocatalysts and an efficient route to hydrogen production through MOR-HER coupling.

Formic acid is an attractive hydrogen carrier in terms of hydrogen capacity and safety. Focusing on hydrogen release from formic acid, the developments of catalysts with easy controllability in mild conditions have been desirable. Previous study reported a hybrid catalytic system of enzymes, photosensitizers, and metal nanoparticles for controllable hydrogen production with visible light. However, methyl viologen, which is a toxic compound, was utilized as an electron mediator from photosensitizers to metal nanoparticles. 9-Mesityl-10-methyl acridinium (Mes-Acr⁺) is one of the promising candidates which hold a long-lived charge-separated state for the removal of methyl viologen from the hybrid system to enhance the safety and the catalytic activity. In this work, cyclodextrins (CDs) were employed to form a complex with Mes-Acr⁺ using supramolecular interactions such as ionic and hydrophobic interactions, which improved photocatalytic activity in aqueous solution. This supramolecular photocatalyst was finally applied to photocatalytic hydrogen production with a system of formate dehydrogenase, NAD⁺, Mes-Acr⁺, CD, and colloidal platinum nanoparticles dispersed by polyvinylpyrrolidone. An ultimate yield from formate to hydrogen reached 24% at pH 6.0, indicating a rate-determining step would be electron transfer from Mes-Acr radical to Pt-PVP to reduce protons.

Herein, we are demonstrating an earth-abundant manganese-catalyzed oxidative deamination of linear and branched primary amines to selectively form carboxylic acids and ketones using water as the oxygen atom source. A series of pincer and non-pincer Mn complexes were assessed for these deaminative transformations. A bio-inspired DAFO (4,5-diazafluoren-9-one) ligand-based [(DAFO)Mn(CO)₃Br] complex (Mn-1) was found to be effective for the reaction proceeding under mildly basic aqueous medium, generating NH₃ and H₂ as sole by-products without the requirement of any oxidant. An optimized condition of 5 mol% Mn-1, Na₂CO₃ (1 equiv) at 150°C for 48 h in water/1,4-dioxane mixture furnished 92% of the corresponding benzoic acid from benzylamine. A wide variety of electron-donating and withdrawing para-, meta-, and ortho-substituted benzylamines, including promising hetero and aliphatic linear primary amines, afforded moderate to excellent yield of the desired carboxylate product. We have also examined a few branched primary amines using 5 mol% Mn-1 and catalytic sodium carbonate at 150°C for 48 h, affording good yield of ketones. The reaction was found to be chemo-selective for primary amine moieties over alcohol functionalities. Further, stoichiometric mechanistic investigation and preliminary computational data provide insights into the possible mechanistic steps.

Designing oxygen evolution reaction (OER) electrocatalysts that can reversibly operate as both oxidation and reduction electrodes is key to developing efficient and rechargeable electrochemical energy systems. However, the evolution of nickel active sites between hydroxide and oxyhydroxide phases, and how such transformations can be made reversible under dynamic operating conditions, remains poorly understood. Here, we report a sulfuric-acid-induced surface oxidation strategy that enables both the controlled formation and reversible regeneration of β-NiOOH active sites on free-standing nickel foam electrodes. Moderate H₂SO₄ treatment (1 M) produces an optimized electrode (1.0-Ni) exhibiting superior OER performance, requiring overpotentials (η) of only 218, 348, and 458 mV at 10, 500, and 1000 mA cm^{- 2}, respectively. The enhanced activity originates from sulfuric-acid-induced modulation of Ni sites, which promotes β-NiOOH formation as the catalytically active phase while maintaining structural integrity. Moreover, a buried β-NiOOH-rich layer serves as a structural-memory reservoir, allowing reversible reconstruction of surface β-NiOOH during redox cycling. This reversible behavior enables the same electrode to function as both anode and cathode, relevant to rechargeable zinc-air battery and other bifunctional electrochemical systems. The dual mechanism acid-induced active-site formation and electrochemical regeneration thus provides a scalable strategy for constructing reversible, heteroatom-free nickel electrodes for sustainable energy conversion.