Chemphyschem最新文献

Pt/TiO₂ catalysts show superior catalytic performance for HCHO removal. Unraveling the detailed mechanism of HCHO oxidation on Pt/TiO₂ is of great importance in guiding robust catalyst design. Herein, HCHO oxidation on Pt/TiO₂ (110) surface is studied by using density functional theory calculations. The results show that HCHO adsorbed at the Pt/TiO₂ interface and subsequent successive dehydrogenation formed CO* species. The Pt site acts as the active center for O₂ activation, and there is a positive linear relationship between the electrons accumulated on Pt site with O₂ adsorption energy. To elucidate how the active O* species is produced, the direct OO bond cleavage and hydrogen-assisted OOH bond cleavage are examined. With hydrogen assistance, the activation barrier of OOH bond cleavage is lowered to 0.33 eV, and the reaction is strongly exothermic (–1.48 eV), indicating that the hydrogen-assisted OOH cleavage path is both kinetically and thermodynamically more favorable. The present work provides mechanistic insight into HCHO oxidation on the Pt/TiO₂ (110) surface and useful guidance in catalyst design with high efficiency.

Complex IV of the mitochondrial respiratory chain, or cytochrome c oxidase (CcO), contributes to the proton motive force necessary for ATP synthesis. CcO can slow the formation of reactive oxygen species and is key to physiology and drug development. The exact molecular mechanisms underlying its proton-pumping function remain elusive. The redox state of CcO's metallic cofactors is intimately connected to structural changes and proton pumping via proton-coupled electron transfer. Time-resolved UV/Vis and IR spectroscopy are used to investigate the effects of the electronic backreaction triggered by photolyzing the CO-inhibited 2-electron reduced state, R₂CO, in the aa₃ oxidase from Cereibacter sphaeroides. An intermediate is identified, in which the binuclear center matches the redox state of the catalytic intermediate E (one-electron reduced state), with a rise time of ≈2 μs. The electron transfer induces structural changes that lead to E286 deprotonation, with a time constant of 13 μs. Thus, it is inferred that transient reduction of heme a alone drives E286 deprotonation. E286 is reprotonated with a time constant of 72 ms when CO rebinds. The results support the view that transient heme a reduction in the physiological E state modulates the electrostatic environment, triggering proton transfer toward the proton-loading site.

Electron transport in organic molecules and biomolecules is governed by electronic structure and molecular conformations. Despite recent progress, key challenges remain in understanding the role of intramolecular interactions and three-dimensional (3D) conformations on the electron transport behavior of organic molecules. In this work, the electronic properties of aromatic amide foldamers are characterized that organize into distinct 3D structures, including an extended secondary amide that adopts a trans-conformation and a folded N-methylated tertiary amide that adopts a cis-conformation. Results from single-molecule electronic experiments show that the extended secondary amide exhibits a fourfold enhancement in molecular conductance compared to the folded N-methylated tertiary amide, despite a longer contour length. The results show that extended amide molecules are governed by a through-bond electron transport mechanism, whereas folded amide molecules are dominated by through-space transport. Bulk spectroscopic characterization and density functional theory calculations further reveal that extended amides have a smaller HOMO–LUMO gap and larger transmission values compared to folded amides, consistent with single-molecule electronic experiments. Overall, this work shows that 3D molecular conformations significantly influence the electronic properties of single-molecule junctions.

The mid-infrared (700–2300 cm⁻¹) absorption spectra of three protonated cyanosubstituted polycyclic aromatic hydrocarbons (CN-PAHs), benzonitrile, 2-cyanonaphthalene, and 9-cyanoanthracene, measured by infrared multiple photon dissociation using the free-electron laser Free-Electron Laser for Infrared eXperiments are reported. The frequency of the CN stretch is found to be 2191 ± 10 cm⁻¹ for protonated benzonitrile and 2175 ± 10, and 2140 ± 10 cm⁻¹ for 2-cyanonaphthalene, and 9-cyanoanthracene respectively, showing a clear redshifting of the CN stretch frequency as the size of the aromatic system increases, contrary to neutral cyano-PAHs that show nearly no shift as function of size. Quantum chemical calculations are performed to complement the experimental results at B3LYP/aug-cc-pVTZ level of theory. Density functional theory calculations reproduce the fingerprint region for all three CN-PAHs, although they overestimate the CN stretching vibration frequency. These results likely rule out small protonated cyano-PAHs as major contributors to the unidentified infrared bands observed in space. However, the largest species investigated in this study shows a promising match with the 4.75 μm band.

Degradation studies of the ASnX₃ perovskites to the A₂SnX₆ vacancy-ordered double perovskite form have been well researched, but little is known about how A₂SnX₆ compounds degrade. Herein, a new double perovskite, FA₂SnBr₆ (FA = CH(NH₂)₂), is synthesized and characterized by using X-ray diffraction and X-ray photoelectron spectroscopy. FA₂SnBr₆ is found to crystallize in the P2₁/n monoclinic space group and shows the ability to form single-phase, solid solutions with another double perovskite (NH₄)₂SnBr₆. Solid solutions of ((NH₄)_(1−x)FA_x)₂SnBr₆, where x = 0.03, 0.04, 0.06, and 0.09, are produced, and X-ray radiation damage is investigated to qualitatively and quantitatively uncover degradation mechanisms. Correlation analysis, a new statistical analytical method for X-ray photoelectron spectra, is used to fortify peak fitting models. Comparing shifts in binding energies and relative atomic quantities between two elements constructs phase models from different spectral environments to understand the degradation of these compounds. In each radiation damage experiment, great consideration must be taken to combine the chemistry of the system and the physical process of photoelectron emission with the quantitative phase models formed. Overall, the presence of ammonium in the double perovskite enhances the stability of the compound to X-ray irradiation.

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.