Chemphyschem最新文献

The dearomatization of electron-poor indoles was investigated through the addition of lithiated ester or ketone enolates. Nitro-substituted indoles undergo 1,4-addition to afford the dearomatized products, after smooth hydrolysis. Indoles bearing an α-ketoamide group show a more complex reactivity, undergoing either 1,2- or 1,4-addition, depending on the steric hindrance of the amide group. The regioselectivity of the latter is buttressed by DFT calculations.

Excited electronic states of fenchone, thiofenchone, and selenofenchone are characterized and assigned with different gas-phase spectroscopic methods and ab initio quantum chemical calculations. With an increasing atomic number of the chalcogen, increasing bathochromic (red) shifts are observed, which vary in strength for Rydberg states, valence-excited states, and ionization energies. The spectroscopic insight is used to state-resolve the contributions in multiphoton photoelectron circular dichroism with femtosecond laser pulses. This is shown to be a sensitive observable of molecular chirality in all studied chalcogenofenchones. This work contributes new spectroscopic information, particularly on thiofenchone and selenofenchone. It may open a perspective for future coherent control experiments exploiting resonances in the visible and near-ultraviolet spectral regions.

Methanol synthesis typically occurs using syngas (CO, CO₂, and H₂) over Cu/ZnO/Al₂O₃ catalyst. However, this process involves a lot of ambiguities related to the nature of active site, the relative role of CO and CO₂, the importance of metal-support interaction and the true source of C in methanol. Motivated by these challenges, it is computationally studied UiO-68 supported N-heterocyclic carbene-based coinage metal hydrides (NHC-M(I)-H) as single-atom catalysts for methanol synthesis, focusing specifically on CO hydrogenation as a simplified and efficient route. The study confirms that NHC-Cu(I)-H can catalyze methanol synthesis with CO as the only C source. Hence, it can eliminate CO₂ from the reaction mixture which will otherwise complicate product separation due to water formation. Moreover, methanol synthesis from CO is more hydrogen-efficient and energy saving compared to that from CO₂. The calculated activation barrier of methanol synthesis from CO over UiO-68 supported NHC-Cu(I)-H catalyst is lower than those reported for methanol synthesis from CO₂ over various Cu-surfaces and nobel metal-based catalysts. Overall, the study demonstrates that CO hydrogenation over UiO-68 supported NHC-Cu(I)-H is not only a viable and efficient route for methanol production but also provides an attractive alternative to traditional Cu/ZnO/Al₂O₃-based systems.

Gas-phase structural, energetic, and thermal properties of the [Be(NH₃)₁₆]² cluster are investigated by using the MP2/6-311++G** level of theory. The relative stability of isomers is explained evidencing the long-range electrostatic interactions and the spatial arrangement of NH₃ ligands around Be²⁺ cation. The computed isomers binding strength and energies values are compared with that with beryllium cation coordinated from n =  1–6 ligands. A fitting approach yields an asymptotic binding energy of –32.2 kcal mol⁻¹. Clustering energies suggest a compact and strongly bound first solvation shell, with weaker, secondary interactions beyond four to five ligands. The cluster thermal behavior is probed through temperature-dependent solvation enthalpies (ΔH) and free energies (ΔG) in gas phase. Results show that ΔG slightly decreases with temperature, while ΔH increases, emphasizing the role of entropy in thermal stabilization. Finally, Quantum Theory of Atoms in Molecules analysis reveals the coexistence of Be²⁺N coordination bonds and a network of NH…N hydrogen bonds. These cooperative noncovalent interactions significantly enhance both structural and energetic stability.

This review has kinetically investigated the electrophilic attack of 3-aminothiophene 1 by a series of para-substituted benzenediazonium cations 7a–7h in 50% H₂O-50% Me₂SO at 20 °C using stopped-flow spectrophotometry. No kinetic isotope effect is observed with the 2-deuterio-3-aminothiophene, confirming that the rate-determining step is a carbon-based electrophilic aromatic substitution (S_EAr) at the C–2 position. The Hammett plot with σ_p values shows nonlinearity due to electron-donating substituents. However, a linear relationship is obtained using the Yukawa–Tsuno equation, highlighting the resonance contribution via the r(σ_p⁺ − σ_p) term. An excellent linear correlation (R² ≈ 0.9968) is observed between log k₁ and the experimental electrophilicity parameter E of the diazonium cations, as defined in the Mayr–Patz equation, allowing the determination of the carbon nucleophilicity parameters of 3-aminothiophene: N = 9.37 and s_N = 1.18. Importantly, a strong linear relationship is established between N and the Hammett σ⁺ constants for 3-substituted 3-aminothiophenes (R² = 0.9763), described by the equation: N = 6.72 – 2.01 σ⁺. This correlation not only demonstrates the pronounced enaminic behavior of 3-aminothiophenes but also enables the prediction of N values for unmeasured analogs, confirming that substituent–π-system interactions govern nucleophilic reactivity via a hyper-ortho electronic effect.

Persistent photocurrent (PPC) has significant advantages and is used in technologies like photodetectors, optical memory devices, neural networks, and anticounterfeiting systems. Many materials, including II–VI and III–V semiconductors and halide perovskites, are known to show PPC. Quaternary chalcogenides like Cu₂ZnSn(S/Se)₄ (CZTS) and CuInGa(S/Se)₂ (CIGS) also exhibit PPC due to antisite defects. However, some ternary chalcogenides, which are impurity phases of these quaternary materials, are easier to synthesize in a pure phase. These ternary chalcogenides, such as Cu₂SnS₃ (CTS), are gaining attention as lead-free alternatives due to their nontoxicity, stability, and simple synthesis methods. In this study, PPC in Cu₂SnS₃ nanoparticles is reported. High-resolution transmission electron microscopy revealed stacking faults in CTS nanoparticles that directly cause the PPC. These defects within the bandgap region trap the photoexcited charge carriers, resulting in delayed photoresponses. The effect of ligand exchange of the CTS nanoparticles on their PPC behavior is further studied. Photoconductivity is enhanced by 10³ times due to the ligand exchange. Additionally, the delay time is slightly affected by different passivating ligands, suggesting that surface passivation can partially control the defect states.

Endohedral metallofullerenes (EMFs) are a unique class of hybrid molecules formed by encapsulating metal atoms within carbon cages (fullerenes), giving rise to distinctive properties that differ from empty fullerenes. Extensive research has focused on optimizing the synthesis, extraction, isolation, and characterization of EMFs, along with investigating their physicochemical properties and potential applications in areas such as electronics, photovoltaics, biomedicine, and materials science. Here, the use of a laser vaporization source combined with ion mobility and mass spectrometry is demonstrated to characterize and isolate EMF structures, enabling further investigation of their gas-phase chemical properties. This approach is illustrated through a comparative study of the reactivity of empty carbon cages and calcium EMFs in the nucleophilic addition of pyridine.

The control of electron transfer pathways in transition metal complexes is crucial for developing next-generation molecular devices and photocatalysts. Herein, the electronic structure and charge delocalization mechanisms in trinuclear trans-[(NC)₅Fe$$(μ-CN)Ru$$(L)₄(μ-NC)Fe$$(CN)₅]⁴⁻ complexes (L = pyridine, 4-methoxypyridine) using complementary X-ray spectroscopic techniques at the Ru L₃-edge are investigated. By combining 2p3d and 2p4d resonant inelastic X-ray scattering spectroscopy with quantum mechanics/molecular mechanics simulations and time-dependent density functional theory-based X-ray calculations, the modulation of the X-ray spectral features as a function of the ligand architecture and solvent environment are probed. Analysis of the experimental data reveals that ligand field interactions systematically tune charge distribution across the metal-cyanide backbone. A novel pre-edge feature arising from Fe-Ru d-d coupling that directly correlates with the near IR metal-to-metal charge transfer transition energies is identified. These findings aid in establishing the design principles for developing multimetallic complexes with tailored electronic coupling.

This study investigates the production of carbon adsorbents from agricultural precursors (caraway and fennel seeds) using microwave-assisted activation with sodium carbonate, aiming to develop cost-effective materials for wastewater treatment. The prepared carbons exhibited specific surface areas of 25–26 m² g⁻¹ and predominantly acidic surface functional groups. Their adsorption performance is evaluated for the removal of methyl red (MR) and methylene blue (MB), with maximum adsorption capacities of 32–39 mg g⁻¹ for MR and 68–91 mg g⁻¹ for MB. Adsorption follows pseudo-second-order kinetics, while thermodynamic analysis confirms that the process is spontaneous and endothermic. Compared with conventional activation methods, the proposed microwave-assisted route reduces processing time and energy demand. These results demonstrate that microwave-assisted sodium carbonate activation of agricultural residues is a promising strategy for producing sustainable sorbents applicable to organic dye removal in real wastewater systems.

Fluorescent proteins are capable of photoinduced electron transfer, and this property has vast application potentials for chemistry, green catalysis, sustainable energy supply, etc. However, the detailed mechanism, the boundaries, and the maximum possible output reduction potentials remain elusive. Herein, three different metal ions of various reduction potentials are applied to examine their interaction with fluorescent protein PsmOrange through X-ray crystallography and spectrometry. PsmOrange is an irreversible photo-switchable fluorescent protein that's easily oxidized, causing obvious alterations including cleavage of peptide chain, red-shift of fluorescence, and color change. It's shown here that electron transfer from the chromophore to bound metal ions leads to quenching of fluorescence, which causes neither redox damage to the chromophore, nor breakage of peptide chain, nor red-shift of fluorescence, as suggested by structures and spectrophotometry. The perseverant nature of fluorescent proteins promises limitless possibilities to exploit. The reducing power decreases as the distance from the chromophore increases, setting up natural boundaries for the utilization of electrons transferred from fluorescent proteins. The mechanism uncovered here has profound implications for the employment of fluorescent proteins for practical application purposes.