Chemphyschem最新文献

Radiation-induced processes in the aromatic cyano compound benzonitrile have attracted renewed interest since its detection in the interstellar medium in 2018, and recent studies have elucidated dissociative ionization pathways leading to species such as CN^• and HCN, which can play important roles in interstellar chemistry. This work explores negative ion formation from benzonitrile upon electron attachment with mass spectrometry experiments and the most extensive theoretical study to date of the underlying negative ion states and their respective dissociative relaxation pathways. The measurements confirm the previously reported CN^- formation at a collision energy of 3.0 eV as well as formation of the dehydrogenated parent anion and phenyl anion and CN^- formation in the 7-10 eV energy range. Threshold energies for these dissociation channels are reported at the G4(MP2) level of theory for the first time. Furthermore, by using both scattering calculations and bound state techniques, CN^- formation at around 3.0 eV may proceed from a ²B₁, π₄* shape resonance through nonadiabatic coupling with the σ*, CCN state. In the 7-10 eV range, complete active space plus second-order perturbation (CASPT2) calculations suggest strong contributions from core excited π₄* and σ* resonances.

A rigid H-shaped [2]rotaxane shuttle composed by a mechanically interlocked 24-crown-8(24C8) macrocycle on a thread containing two symmetrical benzimidazole (Bzi) stations bound with a central 2,2'-bipyridyl (Bipy) core is addressed in CH₂Cl₂ solution with all-atoms molecular dynamics simulations. The experimentally observed conformational preferences of the 24C8 ring quantitatively characterizing the free-energy landscape driving its reversible translocation over the synthetic Stop-[Bzi-Bipy-Bzi]-Stop thread at room temperature have been reproduced. Also, this analysis to a translationally inactive form in N,N-dimethylformamide (DMF) dilute solution following the coordination of PtCl₂ to the Bipy chelate site is extended. In this respect, in the presence of PtCl₂, the optimized geometry within the density functional theory (DFT) framework is fully characterized in terms of quantum theory of atoms in molecules (QTAIM) descriptors. Converged DFT wavefunctions in a continuum environment are analytically investigated by means of electron density ρ(r), local electronic energy density, H(r), electron localization function (ELF), and delocalization index δ(X,Y) analysis. The derived picture highlights that the contextual presence of supramolecular contacts confining the 24C8 ring over its primary recognition site, and of a planar square (Bipy)-N₂-Pt^(II)Cl₂ coordination environment parallel to the axle should actually be effective in suppressing the shutting movement as hypothesized via ¹H-nuclear magnetic resonance measurements.

Stimulated by recent findings of a beneficial effect of a high-temperature treatment on the activity and selectivity of highly active and selective Ru/TiO₂ catalysts in the CO_x methanation, a detailed study of the dynamic changes in the chemical and structural properties is performed, induced by this treatment and their correlation with the changes in the catalytic performance of the catalyst. These changes are characterized by time-resolved operando X-ray absorption spectroscopy at the Ru and Ti K-edges, together with structural characterization by high-resolution transmission electron microscopy. The observation of differently long times required for the reduction of the oxidic Ru nanoparticles in CO-free CO₂/H₂ gas mixtures (1000 min) and in trace amounts of CO containing CO/CO₂/H₂ gas mixtures (100 min) under reaction conditions (190 °C, atmospheric pressure) correlates very well with the different times required for catalyst activation in these reaction gas mixtures.

Hybrid material architectures emerge as a transformative approach to enhance the performance of gas sensors. This study reports a novel room-temperature ammonia (NH₃) sensor based on a porous zinc oxide nanoflakes (ZnOP) and polymer-dispersed cholesteric liquid crystal (PDCLC) composite. The hybrid design integrates the high surface area and mesoporous architecture of ZnO with the functional interfacial properties of PDCLC, yielding a material system that excels in both response and selectivity. The sensor demonstrates exceptional performance metrics, including a broad detection range (1-100 ppm), a low detection limit of 2.61 ppm, and rapid response and recovery times of 5 and 18 s, respectively. Notably, the sensor exhibits superior selectivity toward NH₃ over other volatile organic gases, attributed to the tailored interaction between ammonia molecules and the PDCLC matrix. Moreover, the synergistic interplay between ZnOP and PDCLC enhances electron transfer dynamics, further improving sensing efficiency. This work underscores the potential of porous ZnOP/PDCLC hybrids as advanced materials for ppm-level NH₃ detection and establishes a robust platform for designing high-performance gas sensors operable at room temperature.

Understanding the mechanism of CO₂ cycloaddition with epoxides under mild conditions is vital for advancing green carbon capture and utilization strategies. This work investigates the catalytic role of a defective ZIF-8 model with Zn-OH-Zn moieties and bromide (Br^-) assistance in promoting the conversion of CO₂ and propylene oxide into propylene carbonate. Density-functional theory calculations reveal that, in the absence of a catalyst, the reaction proceeds through high activation barriers (52.02 kcal mol^-1 and 59.31 kcal mol^-1 for the α and β pathways, respectively). Upon introducing the Zn-OH-Zn site and Br^-, the energy barrier for the rate-limiting ring-opening step is drastically lowered to 14.45 kcal mol^-1, confirming the synergistic effect between Lewis acid/base sites and halide assistance. The calculated reaction energy of -13.89 kcal mol^-1 aligns well with the experimental enthalpy change (-12.64 kcal mol^-1). This study provides molecular-level insights into the cooperative catalytic mechanism and supports defect-engineering strategies for metal-organic frameworks in CO₂ fixation applications.

Upregulation of serine arginine protein kinase 1 (SRPK1), a protein responsible for phosphorylation of Ser-Arg rich residues aimed at SR proteins, is associated with apoptosis, poor survival, etc. Catalytic sites of the kinase proteins are incompetently preserved, causing difficulty in developing competitive inhibitors for ATP binding sites with broad selectivity; hence, search for inhibitor for the ATP binding pocket of SRPK1 is a necessity for medication against carcinogenesis. Natural product database is explored, and six small molecules are identified; having tolerable pharmacokinetics (low blood brain barrier, moderate clearance rate etc.) and quantum chemical properties are checked. Molecular docking study followed by molecular dynamics give insights into the effective interactions at the ATP pocket. Ligands are screened by MM-GBSA/NMA protocol, followed by estimation of unbinding potential of mean force (PMF) using well-tempered metadynamics. Well-tempered metadynamics confirmed unbinding PMF of -23.71 kcal mol^-1 for CNP0199214 and -14.81 kcal mol^-1 for MSC1186 (Lig_ref) to a relative difference in PMF of the screened ligand to be ≈7 kcal mol^-1. A probable gating mechanism is observed for the reference ligand (Lig_ref) at the protein interface resulting multiple minima in PMF, whereas Lig_4 (CNP0199214) exhibits greater affinity toward the active pocket and therefore choice for a potent compound.

This article ventures into the interactions between DNA and theophylline (Th), a biologically active xanthine derivative with pharmacological properties, using in-silico methods. Density functional theory calculations were used to assess the interactions between theophylline and natural nucleobases: adenine (A), guanine (G), cytosine (C), and thymine (T). Different interacting orientations, namely the planar hydrogen-bonded conformations and the vertically stacked geometries between theophylline and nucleobases have been investigated by evaluating the binding energies of the dimeric structures. The strength of hydrogen bonding between theophylline and nucleobases is found to be stronger compared to π-π stacking interactions, and hence, it is unlikely that theophylline would invade the DNA duplex and insert between nucleobases. Classical molecular dynamics simulations have been performed to gauge the interactions between theophylline and a DNA double helix. Theophylline is indeed observed to interact with DNA via hydrogen bonding rather than π-π stacking, keeping the DNA intact and eliminating any potential damage. Therefore, the adverse drug reactions of theophylline do not originate from the perturbation of DNA, and are of different origins. This research lays a solid groundwork and builds a deep understanding for future investigations aimed at studying interactions between theophylline and biomolecules.

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.

Modular synthetic modification to ligand scaffolds of metal complexes provides an approach to rational improvement of existing molecular catalytic systems. A previous report from the Marinescu group has shown that a cobalt phosphino thiolate complex ([Co(triphos)(bdt)]⁺) has excellent selectivity and activity for electrocatalytic CO₂ reduction to formate. Here, a multimetallic analogue, [Co₃(triphos)₃(tht)]³⁺, that is conjugated through a trinucleating dithiolene ligand in the form of triphenylene-2,3,6,7,10,11-hexathiolate is investigated. While voltammetric studies indicate enhanced current densities under similar conditions to [Co(triphos)(bdt)]⁺, electrolysis and ultraviolet-visible spectroscopy results suggest significant catalyst degradation and overall moderate faradaic yields.

Halide perovskite (HP) versatility for optoelectronic and electrochemical applications is mainly due to their ability to engineer cation mixtures at the A-site within the ABX₃ stoichiometry. Acetamidinium (AC⁺) is a common cation used in these mixed compositions, but its effects on the material's properties have not been addressed in detail. In this work, prototypical methylammonium lead iodide (MAPbI₃) compositions partially substituted with AC⁺ are synthesized and analyzed for structural, electrical, optoelectronic, and stability properties. Results reveal a solubility limit of around 10% AC⁺, lower than encountered in the literature, with slight effects on the phase transition temperatures. As expected, substitution with AC⁺ significantly reduces electronic conductivity and I-V hysteresis but only marginally increases the bandgap energy. Contrary to literature results, light-accelerated degradation tests show that AC⁺ incorporation does not significantly enhance the materials' stability. Among several reasons, this might be related to weak interactions between AC⁺ cations and the inorganic framework. This study establishes the effects of AC⁺ substitution in halide perovskites and provides insights into optimizing A-site compositions for optoelectronic and electrochemical applications.