Chemphyschem最新文献

Ionic liquids are nowadays investigated with respect to their use as electrolytes for high-performance energy storage materials. In this study, we provide a tutorial on how to calculate dynamic properties such as self-diffusion coefficients, ionic conductivities, transference numbers, as well as ion pair and ion cage dynamics, that all play a role in judging the applicability of ionic liquids as electrolytes. For the case of the ionic liquid $\left[C_2{C}_1\mathrm{Im}\right]\left[{\mathrm{NTf}}_2\right]$ , we investigate the performance of different force fields. Amongst them are non-polarizable models employing unity charges, a charge-scaled version of a non-polarizable model, a polarizable model and another non-polarizable model with refined Lennard-Jones parameters. We also study the influence of the system size on the dynamic properties. While all studied force field models capture qualitatively correct trends, only the polarizable force field and the non-polarizable force field with refined Lennard-Jones parameters provide quantitative agreement to reference data, making the latter model very attractive for the reason of lower computational costs.

Zr-based metal-organic frameworks (MOFs) are typically employed in heterogeneous catalysis due to their porosity, chemical and thermal stability, and well-defined active sites. Density functional theory (DFT) is the workhorse to compute their electronic structure; however, it becomes very costly when dealing with reaction mechanisms involving large unit cells and vast configurational spaces. Semiempirical quantum mechanical (SQM) methods appear as an alternative approach to simulate such chemical systems at low computational cost, but their feasibility to model catalysis with MOFs is still unexplored. Thus, here we present a benchmark study on UiO-66 to evaluate the performance of SQM methods (PM6, PM7, GFN1-xTB, GFN2-xTB) against hybrid DFT (M06). We evaluate defective nodes, ligand exchange reactions, barrier heights, and host-guest interactions with metal nanoclusters. Despite some caveats, GFN1-xTB on properly constrained models is the best SQM method across all studied properties. Under proper supervision, this protocol holds promise for application in exploratory high-throughput screenings of Zr-based MOF catalysts, subject to further refinement with more accurate methods.

Here, we used a combination of laser-induced experiments and density functional theory (DFT) calculations to study the mechanism of growth of carbonaceous species on the Mg surface. Experimental observations revealed that the carbon deposit forms upon laser illumination on the Mg surface, with the deposit being clearer and better structured in the presence of 1,3-butadiene (C₄H₆) compared to ethylene (C₂H₄) gas. DFT thermodynamic and kinetic calculations of C₂-C₄ hydrocarbons interaction on low-index Mg(0001) were used to explain this experimental observation. Our results on Mg(0001) showed that the cis isomer of C₄H₆ binds more strongly than its trans isomer via a [4+2] cycloaddition mechanism. We also investigated the adsorption of two units of C₂H₄ and C₄H₆ molecules, as well as the subsequent dehydrogenation stages that produce radical species responsible for chain growth mechanisms. The results showed that free energy change of dehydrogenation of two units of cis-C₄H₆ [i. e. cis-C₈H₁₂] is lower than the dehydrogenation of trans conformer of C₄H₆ and C₂H₄ molecule, indicating that the dehydrogenation of two units of cis-C₄H₆ facilitates the initiation of growth of carbonaceous species on Mg surfaces. Therefore, the DFT calculations pinpoint the origin of the experimental observation of clearer carbon deposits on the Mg surface.

Elucidating the significance of low-energy electrons in the rupture of electron-accepting biomolecules and the process involved in it is crucial in understanding different biochemical processes. Capturing of the incident electron in one of the empty molecular orbitals and the formation of a temporary negative ion (TNI) is considered to be a stepping stone towards the lesion of the molecule. This TNI formation manifests itself as a resonance peak in the cross-sections determined for the electron-molecule interaction. In the present work, we have reported the integral (ICS), differential (DCS), and momentum transfer (MTCS) cross-sections for the elastic scattering of low-energy electrons from the isomers, 2H-pyran and 4H-pyran $\left(C_5{H}_{6}O\right)$ , which are an important structural subunits of polyphenolic compounds. The single-center expansion method has been employed for the scattering calculations. Further, we have used the time delay approach to identify and analyze the resonance peaks. Our results for the ICS and DCS compare well with the data available in the literature. MTCS data for 2H-pyran and 4H-pyran have been reported for the first time. Moreover, we have also identified an extra peak for each molecule, from time delay analysis, which might be a potential resonance.

Since hydrogen is a promising alternative to fossil fuels due to its high energy density and environmental friendliness, water electrolysis for hydrogen production has received widespread attentions wherein the development of active and stable catalytic materials is a key research direction. This article designs a dual transition metal doped functional graphene for hydrogen evolution reaction via density functional theory calculations. Among varied combinations, 16 candidates are screened out that are expected to be stable as reflected by the criterion of formation energy E_f<0 and active due to its free energy of hydrogen adsorption ▵G_H within the window of ±0.3 eV. Considering its feasibility in structural modification and electronic adjustment due to the strong dd orbital couplings, the homogeneous dual-atom moiety delivers improved performance toward hydrogen evolution in comparison with the single-atom counterpart. Owing to the good resistance of electrochemical dissolution, the work figures out the potential combinations of Cu₂C₃N₃, Rh₂C₆, Rh₂C₃N₃ and Rh₂N₆ endowed with the ▵G_H values of -0.03, 0.12, -0.21, and 0.06 eV, respectively, being comparable to the benchmark Pt materials. Therefore, this study provides a new direction for the experimental synthesis of highly active carbon-based electrocatalysts and highlights the well-tuning ability posed by the dual-atom interaction.

Photoluminescence (PL) quenching mechanism and dynamics of carbon nanodots (CNDs) with molecular electron donors and acceptors are investigated by means of time-resolved emission spectroscopy. CNDs are prepared by direct pyrolysis from two different precursors, di-ammonium citrate and tri-ammonium citrate, at two different temperatures, 150 °C and 180 °C, for 40 hours under ambient conditions. Despite the small changes in the pyrolysis temperature, rather significant differences are observed in the structure, PL quantum yield, and hence observation of the important characteristics of PL quenching kinetics in the presence of benzophenone (BP) and dimethoxybenzene (DMB) as an electron acceptor and donor, respectively. Molecular dynamic simulations of CNDs in the presence of molecular quenchers support the spectroscopic data and the photophysical behavior of CNDs, and the distinct PL quenching dynamics are attributed to the hydrogen bonding interaction in the case of BP and the π π-stacking interaction in the case of DMB as PL quenchers.

A halobenzene molecule contains several sites that are capable of acting in an electron-donating capacity within a H-bond. One set of such sites comprise the lone electron pairs of the halogen (X) atoms on the periphery of the ring. The π-electron system above the ring plane can also fulfill this function in many cases. DFT calculations are applied to compare and contrast the propensity of these two site types to engage in such a H-bond within the context of mono, di, tri, tetra, and hexasubstituted halobenzenes. The X atoms chosen for study comprise the full set: F, Cl, Br, and I. It is found that even when the electrostatic potential of the X lone pair is more negative than that above the ring, it is the latter position which is the preferred binding site of HCl in most cases. This preference switches over to the X lone pair only for higher order of substitution, with n=4 or 6. This pattern is explained in large measure by the higher contribution of dispersion when the proton donor is located above the ring.

For a series of cytochrome b5 proteins isolated from various species, including bacteria, animals, and humans, we analyzed the intrinsic strength of their distal/proximal FeN bonds and the intrinsic stiffness of their axial NFeN bond angles. To assess intrinsic bond strength and bond angle stiffness, we employed local vibrational stretching force constants k^a(FeN) and bending force constants k^a(NFeN) derived from the local mode theory developed by our group; the ferric and ferrous oxidation states of the heme Fe were considered. All calculations were conducted with the QM/MM methodology. We found that the reduction of the heme Fe from the ferric to the ferrous state makes the FeN axial bonds weaker, longer, less covalent, and less polar. Additionally, the axial NFeN bond angle becomes stiffer and less flexible. Local mode force constants turned out to be far more sensitive to the protein environment than geometries; evaluating force constant trends across diverse protein groups and monitoring changes in the axial heme-framework revealed redox-induced changes to the primary coordination sphere of the protein. These results indicate that local mode force constants can serve as useful feature data for training machine learning models that predict cytochrome b5 redox potentials, which currently rely more on geometric data and qualitative descriptors of the protein environment. The insights gained through our investigation also offer valuable guidance for strategically fine-tuning artificial cytochrome b5 proteins and designing new, versatile variants.

Graphene quantum dots (GQDs) have emerged as promising materials for electrochemiluminescence (ECL) applications due to their unique optical and electronic properties. In this study, GQDs were synthesized via electrochemical exfoliation of graphite in a constant current density mode, enabling scalable production with controlled size and surface functionalization. GQDs-4 and GQDs-20, synthesized at applied current densities of 4 mA/cm² and 20 mA/cm² to the graphite electrode, respectively, were investigated on roles of surface states and exciplex dominated aggregation-induced emission (AIE) in their ECL performance. GQDs-4 obtained an absolute ECL quantum efficiency of 0.0012 %±0.0002 %. GQDs-20, with a smaller particle size, achieved an absolute ECL quantum efficiency of 0.028±0.002 %, demonstrating high efficiency in converting electrons into photons. While GQDs-4 exhibited minor intensity in PL and ECL, they displayed a similar emission spectrum to GQDs-20 in the ECL process. This finding highlights the significant role of surface states and AIE in influencing the emission properties of GQDs, independent from core-state transitions. These results provide critical insights into the mechanisms governing GQD-based ECL and offer pathways for optimizing these materials for use in biosensing, optoelectronics, and imaging applications. Keywords: Electrochemiluminescence, Graphene Quantum Dots, Exciplex, Surface States, Multi-color Emission.

Electric double layer capacitors (EDLC) require large specific surface area to provide high power density. The generation of pores increases the electrochemical capacitance with more graphitic edge planes exposed to the electrolyte. Conventional theory believes this increasing in capacitance is owed to the increased specific surface area, but our work uncovers another mechanism. DFT calculations discover the commonly seen defect-free zigzag and armchair edges can increase the quantum capacitance (C_Q) due to their high chemical activity. Meanwhile, high chemical activity makes defect-free edges interact with electrolyte molecules more easily, leading to the potential reduce of electrolyte stabilization and the change on the origin mechanism of double layer capacitance (C_D). Additionally, edges with non-hexagonal defects show a better balance between high C_Q and electrolyte stability. Therefore, our discovery proves the preservation of non-hexagonal defects in edge planes through possible temperature controlling in heat treatment is important in reaching high electrochemical properties for EDLC.