Chemistry - A European Journal最新文献

Epoxidation of ethylene to produce ethylene oxide (EO) is a vital heterogeneous catalytic chemical process in industry, as EO is an important intermediate for the synthesis of fine chemicals including ethylene glycol, ethoxylates, plastics and polyester. EO is commercially produced by the silver-catalyzed partial oxidation of ethylene with air or oxygen. However, it remains challenging to understand its chemical behavior under reaction conditions. To overcome this challenge, a series of catalysts with well-defined structures have been developed. The present review is devoted to summarizing the recent advances in the exploitation of novel catalytic materials for the epoxidation of ethylene, such as metal nanoparticles, clusters, single atoms, and bimetal. The role of promoters in selectivity enhancement will be discussed. A deep understanding of the active species, oxygen species, active structures, activity-structure relationship, and mechanisms contributing to epoxidation process are highlighted. The integration with other advanced technologies such as electrocatalytic and photocatalytic is also reviewed. Finally, the current challenges and future prospects are provided so as to give guidance for the design of efficient catalysts for heterogeneous epoxidation of ethylene to EO, and to improve the fundamental understanding of the underlying catalytic chemistry.

Dynamic liquid crystalline polymers (dLCPs) incorporate both liquid crystalline mesogens and dynamic bonds into a single polymeric material. These dual functionalities impart order-dependent thermo-responsive mechano-optical properties and enhanced reprocessability/programmability enabling their use as soft actuators, adaptive adhesives, and damping materials. While many previous works studying dynamic LCPs utilize dynamic covalent bonds, metallosupramolecular bonds provide a modular platform where a series of materials can be accessed from a single polymeric feedstock through the variation of the metal ion used. A series of dLCPs were prepared by the addition of metal salts to a telechelic 2,6-bisbenzimidazolylpyridine (Bip) ligand endcapped LCP to form metallosupramolecular liquid crystal polymers (MSLCPs). The resulting MSLCPs were found to phase separate into hard and soft phases which aids in their mechanical robustness. Variations of the metal salts used to access these materials allowed for control of the thermomechanical, viscoelastic, and adhesive properties with relaxations that can be tailored independently of the mesogenic transition. This work demonstrates that by accessing phase separation through the incorporation of metallosupramolecular moieties, highly processable yet robust MSLCP materials can be realized. This class of materials opens the door to LCPs with bulk flow behavior that can also be utilized as multi-level adhesives.

Methane dry reforming reaction offers an attractive route to simultaneously convert two kinds of greenhouse gases into clean fuels and high valuable chemicals. Nevertheless, the inactivation of nickel-based catalysts due to sintering and coking in dry reforming has severely limited its industrial application. In this study, we proposed a step-by-step strategy to prepare a series of bimetallic xCu-Ni/SiO2 catalysts derived from phyllosilicate precursors. The optimized catalyst shows exceptional performance, with no deactivation during the 50-hour stability test, and the CH4 and CO2 conversion were 88.8% and 94.0%, respectively. This was attributed to the synergistic catalysis of Cu-Ni alloy, effectively inhibits coke formation. Additionally, the distribution of copper species between nickel species inhibited the mobility and enlargement of nickel particles and thus enhanced the resistance to sintering. The preparation strategy offers valuable insights for designing and preparing of highly efficient and stable bimetallic catalysts under high-temperature conditions.

The arylpyridylmethylamine motif is a privileged scaffold in drug discovery. However, rapidly creating these valuable molecules with structural diversity by directly leveraging readily available, yet simple chemical feedstocks remains a challenge. Herein, we describe a versatile and modular photochemical method for the straightforward construction of arylpyridylmethylamine skeleton utilizing widely accessible starting materials, including amines, aldehydes, and pyridines. This multicomponent coupling proceeds under very mild conditions without the need for any transition-metal catalysts, photocatalysts, and acid additives and displays a broad substrate scope and excellent functional-group tolerance. The potential utility of this methodology in pharmaceutical development is demonstrated through late-stage modification of pharmaceutically relevant compounds, concise synthesis of bioactive compounds, and rapid construction of pyridyl analogue of drug molecules. Combined experimental and computational studies unveiled that this reaction proceeds through radical-radical cross-coupling between persistent pyridylphosphonium radicals and α-amino radicals.

The article describes stepwise oxygenation of the aldimine functions at the backbone of N,N'-bis(pyridin-2-ylmethylene)naphthyl-1,5-diimine (L) in non-interconvertible L-bridged isomeric diruthenium(II)-acac complexes [{RuII(acac)2}2(µ-L)] (cis-1a/trans-1b, acac=acetylacetonate, DFT calculated DEcis-trans = 440 cm-1) via dioxygen activation.. It leads to the formation of the corresponding carboxamido bridged [{RuIII(acac)2}2(µ-Ld2-)] (cis-1ad/ trans-1bd; d denotes doubly-oxygenation) with the concomitant metal oxidation. However, L in doubly oxidized (RuIIIRuIII) congeners i.e. [{RuIII(acac)2}2(µ-L)](ClO4)2 (cis-[1a](ClO4)2/trans-[1b](ClO4)2) as well as electron poor metal fragments derived [{RuII(bpy)2}2(µ-L)]4+ [2](ClO4)4 (bpy=2,2'-bipyridine) and [{RuII(PPh3)2(CO)(H)}2(µ-L)]2+ [3](ClO4)2  failed to undergo the aforestated oxygenation process on purging O2 even at elevated temperature due to the absence of necessary electron exchange between ruthenium and L (i.e. RuII-L-RuII«RuIII-L·--RuII) to initiate the oxygen activation step. Besides structural and spectroscopic characterization of the complexes, oxygenation processes were further monitored through electrochemical, EPR and kinetic experiments in conjunction with DFT calculations, which highlighted mechanistic insights into the reaction sequence.

Short amyloidogenic oligopeptides (APRs) are proposed as early macromolecules capable of forming solvent-separated nanosystems under prebiotic conditions. This study provides experimental evidence that APRs, such as the aggregation-prone oligopeptide A (APR-A), can undergo mutational transitions to form distinct variants, and convert to APR-B, either amyloid-like or water-soluble and non-aggregating. These transitions occur along a spectrum from strongly amyloidogenic (pro-amyloid) to weakly amyloidogenic (anti-amyloid), with the mutation sequence order playing a key role in determining their physicochemical properties. The pro-amyloid pathway facilitates heterogeneous phase separation, leading to amyloid-crystal formation with multiple polymorphs, including the first class 3 amyloid topology. By mapping these transitions, we demonstrate the potential co-evolution of water-soluble miniproteins and insoluble amyloids, both of which could have been pivotal in early bio-nanosystem formation. These insights into amyloid modulation provide a crucial step toward understanding amyloid control mechanisms.

The interaction between apical membrane antigen 1 (PfAMA1) and rhoptry neck protein 2 (PfRON2) is crucial for Plasmodium falciparum red blood cell invasion, making it a key target for anti-malarial drug development strategies. Here, we report the chemical synthesis of PfAMA1 domain-I (PfAMA1-DI) in both linear and backbone-circularized forms, employing a six-segment convergent synthesis approach exploiting one-pot chemistries and solubilizing tags. The chemically synthesized linear PfAMA1-DI construct exhibited incomplete disulfide bond formation during folding, likely due to increased terminal flexibility in the absence of domain-II. To address this, we employed backbone cyclization of the large 180-residue polypeptide chain, with 3-residue linker sequence, as a unique strategy to conformationally restrict its termini and facilitate correct disulfide bond formation. Introducing a multipurpose affinity and solubility tag to the cyclicPfAMA1-DI construct further improved the folding yield by mitigating aggregation. The predicted structure using ColabFold-Alphafold2 indicated that PfRON2 ligand binds within the hydrophobic groove of the cyclicPfAMA1-DI construct similar to the native interactions. These findings underscore the potential of large protein backbone cyclization to stabilize protein structure, offering a compelling strategy for the chemical synthesis of otherwise unstable protein domains with broad applications in miniature protein engineering.

Design of semiconducting materials with facile control of charge transport and the nature of charge carriers is essential for realizing niche applications with organic electronics. Described herein are the synthesis, crystal structure, and analysis of the electronic properties of a four-stage redox amphoteric S-heterocyclic s-indacenodifluorene 6, including the study of its ambipolar charge carrier mobility (μh and μe) in organic field-effect transistor (OFET) devices. Despite being electron-rich, our investigation revealed reversible reduction potentials for 6 in the cyclic voltammetry, which is attributed to the recovery of locally aromatic thiophene and cyclopentadienyl anion units upon electron injection for the two antiaromatic S-heterocyclic as-indacene units in accordance to the Glidewell-Lloyd rule of aromaticity. In line with this, we observed an interesting thermal tunability of the nature of charge carriers from p-type to balanced ambipolar to n-type charge transport with reasonable semiconductor mobility in all regimes of transport. This behaviour is correlated with the modification of the transport levels upon annealing of the semiconductor and possible increase in the extent of π-electron delocalization with temperature. This proof-of-concept tunability of the nature of charge transport indicates the efficacy of our molecular design.

This article presents the synthesis and characterization of a series of robust high-valent organometallic nickel complexes stabilized by a functionalized PC(sp³)P pincer ligand. Notably, the nickel center, covalently confined within the three-dimensional ligand framework, exhibits predictable coordination and redox behavior, coupled with remarkable stability across oxidation states +2, +3, and +4. These states were found to interconvert via one-electron transfer reactions. Among these complexes, the Ni(III)-PC(sp³)P species was identified as an efficient catalyst for the mild and selective hydrosilylation of alkenes, operating through a non-oxidative mechanism that, in some cases, leads to the formation of vinyl silanes and polysilylated products. We demonstrated that, contrary to a widely accepted concept, high-valent metals can serve as viable candidates for hydrogenation catalysts.

A series of Ir(III) complexes, [Ir(C^N)2(en)]+ (where C^N = 2-phenyl-benzo[d]thiazolyl cyclometalating ligand; en = ethylene diamine), are reported with structural variation via a substituent (H, Me, OMe, Cl, OCF3) at the coordinated phenyl ring.  The complexes were soluble in aqueous buffer, with solubility limits correlating inversely with the predicted logP. The complexes display efficient visible absorption at 400-500 nm (e ~ 5000 M-1 cm-1) due to charge-transfer transitions and are triplet emitters in aerated buffer (lem = 529-540 nm; lifetimes up to 0.763 ms; Fem £ 12 %). Each complex was investigated, via computational and biophysical experiments, in the context of DNA binding. According to UV-visible titrations, the cationic complexes bind to DNA with apparent affinities ranging from 6´104 to 5´105 M-1 with apparent binding site sizes between 0.4 and 1.0 base pairs.Isothermal titration calorimetry (ITC) showed that complexes [Ir(L1-3)2(en)]Cl bind to DNA in two types of binding sites, viz. a high affinity (107-108 M-1) binding site with characteristics of major groove binding and a low affinity binding site (105 M-1)  with characteristics of non-specific binding to negatively charged DNA, with binding supported by hydrophobic interactions between complexes.