Several hydride Mn(I) and Re(I) PNP pincer complexes were applied as catalysts for the homogeneous chemoselective hydrogenation of aldehydes. Among these, Mn(PNP-iPr)(CO)2(H) was found to be one ...of the most efficient base metal catalysts for this process and represents a rare example which permits the selective hydrogenation of aldehydes in the presence of ketones and other reducible functionalities, such as CC double bonds, esters, or nitriles. The reaction proceeds at room temperature under base-free conditions with catalyst loadings between 0.1 and 0.05 mol% and a hydrogen pressure of 50 bar (reaching TONs of up to 2000). A mechanism which involves an outer-sphere hydride transfer and reversible PNP ligand deprotonation/protonation is proposed. Analogous isoelectronic and isostructural Re(I) complexes were only poorly active.
In this work, first-principles DFT calculations were performed to investigate the geometric, electronic, and magnetic properties of double perovskite Ba2NaIO6 (BNIO) in the bulk, and thin film form. ...The results showed that bulk BNIO in cubic phase (Fm-3m, #225) has a lattice constant of 8.43 Å, and is a non-magnetic direct band gap (Eg) semiconductor with Eg of 2.22 eV. Three types of cleaved surfaces namely (001), (011), and (111) oriented surfaces were considered here. The stability of the surfaces was examined with surface energy (Es). The Es is found to be 0.06, 0.09, 0.14 eV/Å2 respectively, for (001), (011), and (111) surface, indicating (001) as the energetically most favorable surface. All three surfaces exhibited metallic character, dominated by the splitting of O-p states of the top layer O-atoms. The (001) and (111) surfaces exhibited a magnetic character with magnetic moments of 0.1 and 2.23 μB per formula unit, whereas the (011) surface remained non-magnetic.
•DFT calculations were used to study the electronic properties of Ba2NaIO6 in bulk and thin film..•The (001) surface was found more stable than (011), and (111) surface.•All the selected surfaces exhibited metallic characteristics.•The (001) and (111) surfaces exhibited a magnetic character, whereas (011) remained non-magnetic.
First-principles calculations were employed to investigate the adsorption and diffusion energy of hydrogen (H) in the Ti/Ti3Al binary system, along with the evolution of the interfacial stability ...induced by the presence of H. The penetration energy barrier indicates that H can more easily penetrate the substrate through the Ti/Ti3Al interface. The formation energy of H increases with distance from the interface and the Ti/Ti3Al interface acts as a sink for trapping hydrogen interstitials. When all interstitial sites are completely occupied by H, the cleavage energy along the interface decreases from 1.935 to 1.094 J/m2, suggesting that H doping significantly reduces the strength of the Ti-Ti3Al (01–10) interface. When the area density of H-doping at the interface exceeds 0.37 atoms/Å2, the α-Ti lattice expands. Consistent with experimental observations, this triggers atomic migration and the generation of Ti-hydrides. Further analysis of the atomic structure and Bader charge transfers indicate that the interaction of Ti and H can alter the localized electronic structure of Al, leading to a weakened interface due to loss of interface bond strength. In summary, the theoretical calculations have provided new insights into possible hydrogen embrittlement (HE) mechanism in titanium alloys.
The absorption spectra of polymers derived from ortho, meta and para phenylenediamines (o‐PDA, m‐PDA and p‐PDA) have been simulated combining periodic density functional theory (DFT) calculations ...with time‐dependent DFT simulations. These latter have been carried out on finite clusters embedded in a set of point charges devised to exactly reproduce the electrostatic potential of the periodic chains. The results are compared with those obtained for solvated o‐PDA, m‐PDA and p‐PDA oligomers of increasing sizes extracted from the periodic structures. The electronic transitions involved have been investigated by a qualitative analysis based on isodensity maps completed by a quantitative analysis based on the density‐based index (DCT). For poly‐(o)‐ and poly‐(p)‐ phenylenediamines the agreement with the experimental data is achieved already by modeling solvated dimers whereas the inclusion of long‐range electrostatic effects is mandatory for poly‐(m)‐phenylenediamine highlighting the importance of an accurate treatment of the electrostatic environment when a finite cluster approach is considered.
The combination of periodic density functional theory with time‐dependent DFT calculations carried out on finite clusters embedded in a set of point charges devised to exactly reproduce the electrostatic potential of the periodic chains has been successfully applied to simulate the absorption spectra of a family of polymers.
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•Structural conformers of HPEH were successfully theoretically identified.•Sensitivity and selectivity detection of Hg2+ by HPEH were successfully optimized using the RSM ...approach.•TD-DFT method successfully determined the model of interaction between HPEH and Hg2+.•Chemical phenomena occurred was successfully employed using NCI-RDG and MD simulation.
A new thiosemicarbazone derivative, N-(2-hydroxyphenyl)-2-1-(pyridin-4-yl)ethylidenehydrazinecarbothioamide (HPEH), has been synthesized, characterized, and further developed as a highly selective and sensitive colorimetric chemosensor for Hg2+ recognition in environmental water samples. Structural conformers of HPEH were successfully identified using a combination of the potential energy surface (PES) and time-dependent density functional theory (TD-DFT) methods. The synthesized HPEH was successfully characterized further and analyzed based on its harmonic vibrational frequencies, NMR spectra, and electronic transitions using the DFT approach. Sigma profiles were generated using the COSMO-RS approach to identify a compatible medium for HPEH to act as a chemosensor. The conditions for the highly sensitive and selective detection of Hg2+ by HPEH were successfully optimized using the statistical response surface methodology approach. The optimum sensing of HPEH occurred in an 8:2 v/v DMSO/pH 7.8 solution at a 20:60 μM HPEH/Hg2+ concentration and after a reaction time of 18 min, with statistically significant independent variables (p < 0.05) for all parameters. Under optimal conditions, the lowest Hg2+ concentration detected by HPEH was 3.56 µM, indicating that HPEH can serve as an alternative and comparable probe for the detection of Hg2+ in aqueous systems. Using the optimized results, the interaction between HPEH and Hg2+ in the chemosensor system was successfully modeled, and the model was subsequently used with the TD-DFT, non-covalent interaction-reduced density gradient (NCI-RDG), and molecular dynamics approaches to gain mechanistic insights into the interaction. The results showed that the newly synthesized HPEH, in addition to being cost-effective, could serve as a suitable alternative and comparable chemosensor for Hg2+ recognition in water samples, with the advantages of being efficient, portable, and eco-friendly, and offering rapid analysis without the need of specialized training.
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•The features of H2 adsorption on MoS2 monolayers and nanoribbons were investigated.•For all systems, the H2 adsorption implies minimal changes in the energy bandgap.•The stacked ...complex is most suitable for H2 sensing by its highest adsorption energy.
Density-functional theory calculations are performed to investigate the adsorption of molecular hydrogen onto MoS2 monolayers, armchair nanoribbons, and stacked monolayer-armchair nanoribbon complexes. The van der Waals interaction is explicitly included through the use of three distinct exchange-correlation functionals and a comparison with the use of LDA is made. The adsorption energy, structural properties, band structure are discussed, considering different adsorption sites, nanoribbon dimensions, and H2 concentrations. Recovery time is evaluated for a particular situation where significant adsorption energy is obtained for the monolayer plus nanoribbon complex, -together with a reasonable modification of the electronic structure, in comparison with MoS2 monolayer and free-standing nanoribbons-, pointing at a promising use of this system as a molecular hydrogen sensor.
Platinum is a nearly perfect catalyst for the hydrogen evolution reaction, and its high activity has conventionally been explained by its close-to-thermoneutral hydrogen binding energy (G ∼ 0). ...However, many candidate nonprecious metal catalysts bind hydrogen with similar strengths but exhibit orders-of-magnitude lower activity for this reaction. In this study, we employ electronic structure methods that allow fully potential-dependent reaction barriers to be calculated, in order to develop a complete working picture of hydrogen evolution on platinum. Through the resulting ab initio microkinetic models, we assess the mechanistic origins of Pt’s high activity. Surprisingly, we find that the G ∼ 0 hydrogen atoms are inert in the kinetically relevant region and that the active hydrogen atoms have ΔG’s much weaker, similar to that of gold. These on-top hydrogens have particularly low barriers, which we compare to those of gold, explaining the high reaction rates, and the exponential variations in coverage lead directly to Pt’s strong kinetic response to the applied potential. This explains the unique reactivity of Pt that is missed by conventional Sabatier analyses and suggests true design criteria for nonprecious alternatives.
Although Zn metal has been regarded as the most promising anode for aqueous batteries, it persistently suffers from serious side reactions and dendrite growth in mild electrolyte. Spontaneous Zn ...corrosion and hydrogen evolution damage the shelf life and calendar life of Zn‐based batteries, severely affecting their industrial applications. Herein, a robust and homogeneous ZnS interphase is built in situ on the Zn surface by a vapor–solid strategy to enhance Zn reversibility. The thickness of the ZnS film is controlled via the treatment temperature, and the performance of the protected Zn electrode is optimized. The dense ZnS artificial layer obtained at 350 °C not only suppresses Zn corrosion by forming a physical barrier on the Zn surface, but also inhibits dendrite growth via guiding the Zn plating/stripping underneath the artificial layer. Accordingly, a side reaction‐free and dendrite‐free Zn electrode is developed, the effectiveness of which is also convincing in a MnO2/ZnS@Zn full‐cell with 87.6% capacity retention after 2500 cycles.
Based on the sulfur phase diagram, a dense and robust artificial layer of ZnS is introduced on the surface of Zn metal via an in situ vapor–solid strategy. This ZnS protective layer not only suppresses side reactions by blocking water from the surface of such a Zn electrode in a Zn‐ion battery, but also inhibits Zn dendrite growth by guiding homogenous Zn plating/stripping.
In this article, we investigate the effects of the isoleucine (ILE)N amino acid chain growth, N = 1.0.6, the ILE conformational effect as well as the solvent presence on the electrical and magnetic ...spectroscopic properties when these compounds are in aqueous solution. Computational molecular dynamics simulations were performed to include the solvent medium and generate uncorrelated configurations involving solute‐solvent structures. The charge point model for solvent was used to obtain the results for quantum mechanical calculation, in special DFT calculations, for (ILE)N structures. Our results for the magnetic shielding constant obtained via GIAO‐DFT‐NMR calculations show that there is evidence of a magnetic behavior that characterizes the number of peptide bonds and, therefore, how the N isoleucine polypeptide chain is composed. TD‐DFT results also show an absorption band shift to larger wavelengths indicating a dependence on N growth.
Behavior of spectroscopic properties of isoleucines in water solution by molecular dynamics and quantum mechanics simulations
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