Chemphyschem最新文献

Oleyl-capped nanoparticles have been used in nonpolar dispersions and can form ordered assemblies, for which an understanding of their interactions from a theoretical perspective is relevant. Long-range comprehensive molecular dynamics runs (1000 ns) are performed on oleyl-capped gold nanoclusters in different environments: hexane as a nonpolar solvent, and ethanol and pentanol as polar solvents. The molecular dynamics results in ethanol medium demonstrate that oleyl-capped nanoclusters tend to form attractive interactions with themselves via hydrocarbon interdigitation of their oleyl ligands, which leads to their aggregation. On the contrary, the attractive interactions between these nanoclusters are compensated by the interactions with hexane molecules, so that the nanoclusters keep separated from each other, leading to stable dispersions. The behavior of pentanol with the oleyl-capped nanoclusters indicates presumably more similarities to hexane, despite of being a polar solvent. These three simulation cases provide an insightful overview about the stabilization effects of oleyl-capped nanoparticles in organic solvents.

Only very soluble electrolytes can form concentrated solutions. Some salts are so soluble that there are less than four water molecules per ion in saturated solution. Ions usually form clusters or networks with more than one counterion in their coordination sphere in these concentrated solutions. Do these ultraconcentrated solutions form because the counterions have high affinity for each other in liquid, or because they have a poor affinity for each other in solids? Here this question is addressed using the valence matching principle of the bond valence model by comparing the charge density mismatch between counterions to their solubility for a series of alkali fluorides, carboxylates, and oxyanions. The solubilities are plotted against the characteristic average bond valence of the alkali, and the lowest solubilities are those where alkali and anion had matching bond valences. Conversely, the highest solubilities are those with poorly matching bond valences. Available ion-pairing constants indicate that the weakest ion-pairs are those with the largest bond valence mismatch, indicating that the large water solubilities occur despite weak ion-pairing rather than because of strong ion-pairing. Therefore, a key characteristic of highly water-soluble salts is that the counterions have mismatched charge densities.

Quantum chemical methods are employed to investigate the complexation of CaX₂ with nNH₃ (X = H, F; n = 1–3). In the presence of CaX₂, NH₃ molecules engage in several types of noncovalent interactions, namely, hydrogen bonding (HB), calcium bonding (CB), and dihydrogen bonding (DHB). The CaX₂:nNH₃ complexes are primarily stabilized by Ca···N interactions, though other noncovalent contacts also contribute in stabilizing or destabilizing different conformers. Closed ring conformers in CaX₂:nNH₃ complexes show high degree of cooperativity together with a consistent increase in Ca···N bond length and decease in H⁺···H⁻/ H⁺···F⁻ bond length with increasing number of NH₃ molecules. Fragment-wise interaction energy analysis indicates that two-body ammonia–metal hydride/fluoride (A_i–CaX₂) interactions dominate the total interaction energy, while nonadditive terms contribute up to ∼10% in certain heterotrimer conformers but diminish as the number of ammonia molecules increases. Vibrational mode automatic relevance determination analysis (VMARD) of CaX₂:nNH₃ complexes shows unequal contributions from atomic motions within the three different bonds in NH₃ molecule, revealing that complexation induces different intermolecular force constants, leading to loss in symmetry of NH₃ molecules. Pronounced redshift of the symmetric NH stretching mode is consistently observed, accompanied by symmetry lowering of the degenerate asymmetric NH stretching mode.

Lead-based halide perovskite solar cells represent a significant advancement in photovoltaic technology, achieving certified power conversion efficiencies of over 27%. However, the toxicity of lead poses a major barrier to widespread commercialization. The demand for environmentally safe alternatives has driven extensive research into Pb-free perovskites. Current efforts include replacing Pb with Sn or Ge; forming double perovskites in which Pb is substituted by a monovalent–trivalent cation pair; and developing chalcogenide perovskites where the B site (ABX₃) adopts tetravalent cations (rather than Pb) to balance the charge. This concept examines the recent progress in developing Pb-free alternatives, revealing fundamental performance bottlenecks, inherent material limitations, and persistent development challenges. Through a comparative assessment of material properties and device performance limitations, this work highlights the underlying dilemma between environmental safety and efficiency in perovskite photovoltaics. The analysis identifies fundamental material constraints that create substantial barriers to simultaneously achieving both objectives.

Histamine is a neurotransmitter, and it is available as protonated state at the physiological conditions. We predicted theoretically the possibility of excited state intra-molecular proton transfer (ESIPT) at the excited state of N-protonated gauche-form histamine in aqueous phase. The proton transfer occurs from the ammonium unit of aliphatic chain to the nitrogen of the imidazole ring. The acidity of aliphatic amine (N14) and basicity of imidazole nitrogen (N8) increase only at the excited state, suggesting the possibility of proton transfer at the excited state. The distance between amine proton and acceptor nitrogen in the imidazole ring becomes closer at the excited state (∼3.23 Å changes to ∼1.86 Å) in aqueous phase, which facilitates proton transfer from the amine group to imidazole nitrogen at the excited state. The energy barrier calculated using the potential energy surface scans suggests the low activation energy (∼5.1 kcalmol⁻¹) facilitating faster reaction. At pre-ESIPT state, protonated histamine (gauche form) absorbs light of ∼219 nm and emits at ∼315 nm in aqueous phase, whereas at post-ESIPT state it emits at ∼407 nm, reflecting a large red-shifted emission due to ESIPT in protonated histamine. Born-Oppenheimer Molecular Dynamics studies detected the timescale of the ESIPT reaction as ∼203 fs for protonated histamine in aqueous phase, which correlates well with the experimental ESIPT time scale for other systems reported in literature.

The aim of the study was the preparation and characterization of organo-mineral fertilizers supporting sustainable development of agriculture. Materials were obtained by the drum granulation in laboratory conditions and by the pan granulation on a semi-industrial plant. On a laboratory scale, three fertilizer formulas NPK 5-10-20, NPK 4-18-23, and NPK 3-10-12 and 60 fertilizer formulations modified with three different organic materials (lignite, peat, and compost), with five levels of their content (5%, 10%, 15%, 20%, and 30%) were prepared. The effect of granulation on a semi-industrial scale was two fertilizer formulas: NPK 5-10-20 and NPK 4-18-23, with three levels of lignite content (10%, 20%, and 30%). In the obtained materials, the granulometric composition, static and dynamic strength as well as the content of macro and micronutrients were analysed. The properties of the produced fertilizing materials were also verified in microbiological experiments. Based on the experiments carried out, it was found that the only formula that met the legal and quality requirements would be the NPK 4-18-23 formula with ≈20% lignite content. It was found that the organic materials used are not a source of microorganisms in the prepared fertilizers, and these fertilizers would meet the requirements of the regulations.

Methanol (CH₃OH) is increasingly used as an alternative marine fuel due to its ability to reduce emissions of CO₂ and particulate matter. However, its application often leads to elevated levels of unburned methanol in the exhaust. Catalytic oxidation is widely considered an effective strategy for eliminating methanol slip. In this article, a series of Cu/SSZ-13 catalysts with different Cu loadings are prepared by the impregnation method. Methanol conversion increased markedly as the Cu loading increased from 2.5 to 10 wt%. The Cu₁₀/SSZ-13 catalyst achieved complete CH₃OH conversion at 225 °C with minimal byproduct formation throughout the tested temperature range. Further increasing the Cu loading to 12.5 wt% resulted in no significant change in either CH₃OH conversion or byproduct yields. Characterization results indicated that the Cu species predominantly existed as CuO nanoparticles dispersed on the external surface of SSZ-13, rather than as framework-incorporated isolated Cu²⁺ ions. CuO is identified as the primary active phase for CH₃OH oxidation. The superior performance of Cu₁₀/SSZ-13 is attributed to its abundant surface-adsorbed oxygen species and high density of basic sites. In situ DRIFTS measurements further revealed that methoxy and formate species are the key intermediates during methanol oxidation over the Cu₁₀/SSZ-13 catalyst.

The Front Cover depicts two ¹³C spins that interact over nanometer-scale distances, thus allowing the number of spins in a cluster to be counted. The thermometer displays the cryogenic temperature used, and the 25 minutes on the clock represent the mixing time needed to enable the nuclei to influence each other over this distance range. The signal was enhanced by dynamic nuclear polarization to achieve this unprecedented mixing time needed to reach nanometer distances. More information can be found in the Research Article by L. B. Andreas and co-workers (DOI: 10.1002/cphc.202500585).

The phase behavior and electrical conductivity of two ionic liquids (ILs) with the same anion (dicyanamide) and different cations (1-ethyl-3-methylimidazolium and 1-butyl-3-methylimidazolium) at different temperatures (including subzero ones) are studied in detail, and the relationship between the phase state and electrical conductivity is shown. It is found that the formation of several crystalline mesophases at temperatures below −10 °C and their successive melting in the range between −10 and 10 °C leads to a curvature of the Arrhenius plot. In this case, two linear sections and an inflection in the temperature dependence of electrical conductivity are interpreted in terms of the phase states of the IL: homogeneous (solid and liquid) and a heterogeneous (mixed) phases, and the activating energy of conductivity E_a(κ) of the solid IL is significantly higher than that of the molten one. The obtained results may be useful in the designing of new electrolytes based on IL used in a wide range of temperatures.

The copper-catalyzed azide–alkyne cycloaddition (CuAAC) reaction is a foundational transformation in synthetic chemistry, owing to its high efficiency and selectivity. In this work, state-of-the-art quantum chemical methods are applied to elucidate the preference for the dinuclear CuAAC mechanism, involving two copper centers, over the mononuclear analog, involving one copper center. Activation strain and Kohn–Sham molecular orbital analyses reveal that the enhanced reactivity of the dinuclear CuAAC mechanism arises not from alleviation of strain in the copper acetylide upon formation of the six-membered metallacycle, as previously proposed, but rather from reduced steric Pauli repulsion between the copper acetylide and the azide. These results provide mechanistic insight into the origin of dinuclear catalysis in the CuAAC reaction.