Chemphyschem最新文献

This work presents a detailed comparative analysis of C-H activations catalyzed by three different Fe(IV)O porphyrinoid complexes. The study considers the usual heme porphyrin (complex I) as the base compound, porphyrazine (complex II), which is obtained by replacing carbon with nitrogen at the meso position, and phthalocyanine (complex III), which is obtained through the peripheral benzoannulation of porphyrazine. The main focus here is to explore the impact of bridging groups and peripheral functionalization in heme systems on reactivity. Chloride is used as the axial ligand for all complexes and dihydroanthracene (DHA) is used as the substrate. Factors such as distortion energy and different electron acceptor orbitals significantly affect the overall reactivity. The effect of substitution on quantum mechanical tunneling, using H/D kinetic isotope effect studies, is also included. The results reveal a fascinating reactivity order: meso nitrogen substitution enhances reactivity, while additional benzo-annulation hinders reactivity, leading to the order complex II >complex I >complex III. In comparison to the usual model compound I, which is Fe(IV)O-porphyrin π cation radical with an -SH axial ligand, complex II was found to be more reactive. The electron affinity of the Fe(IV)O complexes and the dissociation energy of the forming Fe(IV)O-H bond aligns with observed reactivity trend. These findings support the use of accessible iron frameworks derived from porphyrin in C-H activation processes.

Herein, we propose a purely-organic donor-acceptor (D-A) molecular triad, with a light-absorbing polarized molecular wire (PMW) used as a central linkage, as a proof of concept for the possible future applications of the D-PMW-A arrangement in molecular photovoltaics. This work builds upon our earlier study on the PMW unit itself, which proved to be highly promising for the ultrafast photogeneration of free charge carriers. Quantum-chemical calculations performed for the D-PMW-A triad at a semi-empirical level of theory reveal a large electric dipole moment of the system, and show strong charge-transfer (CT) character of its lowest-energy excited electronic states, including the S1, which favours efficient dissociation of an exciton initially formed upon the absorption of light. The confirmation for this effect was found with nonadiabatic molecular dynamics simulations, revealing an ultrafast relaxation from higher, bright excited states to S1, completed on a subpicosecond timescale. The architecture of the proposed molecular triad enables its electronic coupling to the surrounding environment through chemical bonds, or noncovalent stacking interactions, which might open way for synthesis of a new class of D-PMW-A efficient molecular organic photovoltaic materials.

Cerium oxide, or ceria, (CeO2) is one of the most studied materials for its wide range of applications in heterogeneous catalysis and energy conversion technologies. The key feature of ceria is the remarkable oxygen storage capacity linked to the switch between Ce4+ and Ce3+ states, in turn creating oxygen vacancies. Changes in the electronic structure occur with oxygen removal from the lattice. Accordingly, the two valence electrons can be accommodated by the reduction of support cations where the electrons can be localized in empty f states of Ce4+ ions nearby. Quantifying the different oxidation states in situ is crucial to understand and model the reaction mechanism. Beside the different techniques to quantify Ce3+ and Ce4+ states, we discuss the use of X-ray Raman Scattering (XRS) spectroscopy as an alternative method. In particular, we show that XRS can observe the oxidation state changes of cerium directly in the bulk of the materials under realistic environmental conditions. The Hilbert++ code is used to simulate the XRS spectra and quantify accurately the Ce3+ and Ce4+ content. These results are compared to those obtained from in situ X-ray Diffraction (XRD) collected in parallel and the differences arising from the two different probes are discussed.

Earlier scanning tunneling microscopy (STM) studies have shown that nitrogen forms square c(2x2) islands on Cu(100) surfaces, the assembly of which depends on coverage. Recent calculations have revealed that adatom-adatom interactions are compatible with the formation of square c(2x2) islands. The pair distribution of these islands is a topic of the current investigation. In addition, the domain structure of islands found recently in STM experiments is discussed and explained using two types of island interactions. The potential used for the interaction between N square islands on copper is a combination of previous ab initio calculations and an updated mesoscopic interaction scheme. The 2D-BGY integral equation is extended to handle binary objects like two different types of islands. It is solved for up to a quarter island coverage using a numerical recursion algorithm. Coverage beyond half is accessible with island vacancy symmetry. The calculation predicts the formation of ordered island assemblies with increasing coverage. These results reasonably explain the previous experimental observations. The handling of binary objects also seems to be applicable to assemblies of two adatom types as found in catalysis. The assumptions and limitations of the model are discussed and open questions are formulated.

Computations based on density functional theory are carried out to examine the mechanism of photocatalytic oxidation of methane to methanol with H2O2 as oxidant and water as co-catalyst over anatase TiO2 (101) surface. The reaction proceeds with hydrogen abstraction from methane followed by the formation of surface methoxy species, which is reduced to methanol. We compare the reaction energetics for C-H dissociation in the presence and absence of surface defect, but find no discernible impact of O-vacancy on methane oxidation. In comparison, hydroxyl produced as a result of H2O2 or H2O photo-decomposition dramatically reduces the barrier for CH3-H bond cleavage. The reaction proceeds further by the reduction of surface methoxy group and is the rate-limiting step for methanol formation. Additionally, we find that methyl can also react with water to form methanol with a considerably lower barrier, suggesting an active involvement of water for methanol formation. We also study the role of water as a co-catalyst and observe significant reduction in barriers, facilitated by alternate pathway for proton transfer. The reaction pathways presented provide valuable in- sights into the mechanism of methane oxidation in the presence of H2O2 as oxidant and demonstrate the rate-enhancing role of water for these steps.

Metal nanoparticles sensitize cancers to radiotherapy however their mechanisms of action are complex. The conceptual inspiration arose from theories of physical dose deposition but various chemical and biological factors have also been identified. Interpretation of data has been limited by challenges in measuring true DNA damage compared to DNA damage repair factors. Here, we applied a new assay, STRIDE, for the first time to measure DNA double strand breaks (DSBs) in 4T1 cells as a model of triple negative breast cancer exposed to gold nanoparticles and radiation, and compared this to the common γH2AX assay for DSB repair. The STRIDE assay showed no increase in DSB detection 15 mins after irradiation for cells containing nanoparticles compared to cells without. Gold nanoparticles led to prolonged detection of DSBs after irradiation and delayed the DSB repair. The data show no evidence of increased radiation dose deposition with nanoparticles, but rather enhanced radiobiological effects resulting from nanoparticles which includes disruption of the recruitment of essential DDR machinery, thereby impairing DNA repair processes.

Sulfide solid electrolytes have potential in practical all-solid-state batteries owing to their high formability and ionic conductivity. However, sulfide solid electrolytes are limited by the generation of toxic hydrogen sulfide and conductivity deterioration upon moisture exposure. Although numerous studies have investigated the hydrolysis degradation induced by "moisture," the influence of "atmospheric gases" during moisture exposure has not been extensively investigated despite the importance for practical fabrication. Therefore, in this study, we investigated the impact of atmospheric gases during moisture exposure on an argyrodite-type Li₆PS₅Cl via electrochemical impedance spectroscopy, X-ray diffraction, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. The electrolyte powder was exposed to various atmospheric gases, namely Ar, Ar+500 ppm CO₂, O₂, and O₂+500 ppm CO₂, with moisture at a dew point of -20 °C, and H₂S gas generation was monitored. As a result, the amount of H₂S gas did not depend on the atmospheric gases. However, the atmospheric gases had a significant effect on the decrease in conductivity. Spectroscopic analyses revealed that CO₂ facilitates the formation of carbonates and that O₂ promotes the formation of phosphates and sulfonates. The formation of these compounds leads to surface degradation, which further decreases the conductivity.

The emergence of new SARS-CoV-2 variants of concern (VOC) is a propulsion for accelerated potential therapeutic discovery. SARS-CoV-2's main protease (Mpro), essential for host cell viral replication, is a pre-eminent druggable protein target. Here, we perform extensive drug re-profiling of the comprehensive Excelra database, which compiles various under-trial drug candidates for COVID-19 treatment. For mechanistic understanding, the most promising screened-out molecules with targets are subjected to molecular dynamics (MD) simulations. Post-MD analyses demonstrate Darunavir, Ponatinib, and Tomivosertib forming a stable complex with Mpro, characterized by less fluctuation of Cα atoms, smooth and stable root-mean-square deviation (RMSD), and robust contact with the active site residues. Likewise, they all have lower binding free energy with Mpro, demonstrating strong affinity. In free energy landscape profiles, the distances from His41 and Cys145 exhibit a single energy minima basin, implying their preponderance in proximity to Mpro's catalytic dyad. Overall, the computational assessment earmarks promising candidates from the Excelra database, emphasizing on carrying out exhaustive biochemical experiments along with clinical trials. The work lays the foundation for potential therapeutic interventions in treating COVID-19.

Manganese-based compounds have the characteristics of high theoretical capacity, low cost and stable performance, thus become a research hotspot for cathode materials of zinc-ion batteries (ZIBs). However, in the process of charging and discharging, it is accompanied by problems such as structural collapse and low conductivity, which resulted in severe capacity degration during cycles. In this paper, a kind of Zn²⁺ doped MnO₂ hollow cube cathode material (Zn-MnO₂) was prepared by self-sacrificing template method. The Zn²⁺ doped in MnO₂ crystals can induce oxygen vacancies in the structure, thereby improving the structural stability ion diffusion coefficient and electrical conductivity of the material. After 100 cycles at 0.3 A g^-1, the high specific capacity of 281.2 mA h g^-1 is still maintained. Through ex-situ XPS and ex-situ XRD tests, the mechanism of charge-discharge process was discussed. The results show that the storage mechanism of Zn-MnO₂ is H⁺ and Zn²⁺ insertion/removal and Mn³⁺/Mn²⁺ two-electron reaction pathway. The total state density (TDOS) and partial state density (PDOS) of Zn-MnO₂ and MnO₂ further demonstrated that the doping of Zn2+ enhanced the electron conductivity and is beneficial to the electron transfer during the electrochemical reaction.

The conjoint application of the voltammetry of immobilized particles (VIMP) methodology and the Mott-Schottky analysis (MS) of impedance data to studying metal corrosion patinas is described. The study is applied to copper and bronze objects exploiting the semiconducting character of cuprite and other copper corrosion products. A simplified theoretical modeling of MS analysis at microparticulate deposits extracted from metal corrosion layers attached to graphite electrodes is provided. The proposed model compensates for the disturbing effect of the regions of the basal electrode directly exposed to the electrolyte. Alternative models accounting for the variation of the density of charge carriers with depth are tested as well as the correlation between VIMP and MS data with reasonably satisfactory results.