Thickness-Dependent Charge Transport in Three Dimensional Ru(II)- Tris(phenanthroline)-Based Molecular Assemblies.

We describe here the fabrication of large-area molecular junctions with a configuration of ITO/[Ru(Phen)3]/Al to understand temperature- and thickness-dependent charge transport phenomena. Thanks to the electrochemical technique, thin layers of electroactive ruthenium(II)-tris(phenanthroline) [Ru(Phen)3] with thicknesses of 4-16 nm are covalently grown on sputtering-deposited patterned ITO electrodes. The bias-induced molecular junctions exhibit symmetric current-voltage (j-V) curves, demonstrating highly efficient long-range charge transport and weak attenuation with increased molecular film thickness (ß = 0.70 to 0.79 nm-1). Such a lower ß value is attributed to the accessibility of Ru(Phen)3 molecular conduction channels to Fermi levels of both the electrodes and a strong electronic coupling at ITO-molecules interfaces. The thinner junctions (d = 3.9 nm) follow charge transport via resonant tunneling, while the thicker junctions (d = 10-16 nm) follow thermally activated (activation energy, Ea ∼ 43 meV) Poole-Frenkel charge conduction, showing a clear "molecular signature" in the nanometric junctions.

Evaluation of the Anticancer and Biological Activities of Istaroxime via Ex Vivo Analyses, Molecular Docking and Conceptual Density Functional Theory Computations.

Cancer is a disease that occurs as a result of abnormal or uncontrolled growth of cells due to DNA damage, among many other causes. Certain cancer treatments aim to increase the excess of DNA breaks to such an extent that they cannot escape from the general mechanism of cell checkpoints, leading to the apoptosis of mutant cells. In this study, one of the Sarco-endoplasmic reticulum Ca2+ATPase (SERCA2a) inhibitors, Istaroxime, was investigated. There has been very limited number of articles so far reporting Istaroxime's anticancer activity; thus, we aimed to evaluate the anticancer effects of Istaroxime by cell proliferation assay and revealed the cytotoxic activity of the compound. We further determined the interaction of Istaroxime with topoisomerase enzymes through enzyme activity tests and detailed molecular modeling analysis. Istaroxime exhibited an antiproliferative effect on A549, MCF7, and PC3 cell lines and inhibited Topoisomerase I, suggesting that Istaroxime can act as a Topoisomerase I inhibitor under in vitro conditions. Molecular docking analysis supported the experimental observations. A chemical reactivity analysis of the Istaroxime molecule was made in the light of Density Functional Theory computations. For this aim, important chemical reactivity descriptors such as hardness, electronegativity, and electrophilicity were computed and discussed as detailed.

On point perforating defects in bilayer structures.

This article deals with the issue of perforating point defects (pores) in a bilayer heterostructure composed of striped borophene and graphene. Three types of non-equivalent vacancies of the minimum size are considered. These include a single vacancy and two double vacancies. The study of the properties and stability of the perforating defects in borophene-graphene heterostructures is important given the increasing role of such structures in membranes for water purification, renewable energy generation, and other osmotic applications. Using the DFT method, the atomic configurations and main energy characteristics of the proposed defects are obtained. The results show that the formation of a single boron vacancy on the borophene side of borophene-graphene requires less energy than the formation of a carbon vacancy in graphene. Comparisons between double vacancies in nanoscale materials are unreliable because different reference systems produce the different chemical potentials. The problem of choosing the reference system for reliable calculation of the vacancy formation energies is posed and discussed. Using borophene-graphene as an example, it is shown that the reference system strongly affects the magnitude and sign of the vacancy formation energy. Hydrogenation is tested to stabilize the proposed defects.

Semiempirical Approach to the Fukui Function Analysis of Uric Acid under Different pH Conditions.

Analytic Fukui functions calculated at a first-principles level are combined with experimental pKa values and the calculation of tautomerization energies to obtain the effective regioselectivity of uric acid toward electron-transfer reactions under different pH conditions. Second-order electron binding energies are also computed to determine which of the tautomers is more likely to participate in the electron transfer. A comparison of vertical and adiabatic proton detachment energies allows us to conclude that tautomerization is not mediating deprotonation and that two monoanionic species are of comparable relevance. The main difference between these monoanionic species is the ring that has been deprotonated. Both monoanionic species are produced from a single neutral tautomer and mainly produce a single dianionic tautomer. As a method for the analysis of systems affected by pH such as uric acid, we propose to plot condensed Fukui functions versus pH, allowing us to draw the effect of pH on the regioselectivity of electron transfer in a single image.

A Comparative XPS, UV PES, NEXAFS, and DFT Study of the Electronic Structure of the Salen Ligand in the H2(Salen) Molecule and the [Ni(Salen)] Complex.

A comparative study of the electronic structure of the salen ligand in the H2(Salen) molecule and the [Ni(Salen)] complex was performed using the experimental methods of XPS, UV PES, and NEXAFS spectroscopy along with DFT calculations. Significant chemical shifts of +1.0 eV (carbon), +1.9 eV (nitrogen), and -0.4 eV (oxygen) were observed in the 1s PE spectra of the salen ligand atoms when passing from a molecule to a complex, unambiguously indicating a substantial redistribution of the valence electron density between these atoms. It is proposed that the electron density transfer to the O atoms in [Ni(Salen)] occurred not only from the Ni atom, but also from the N and C atoms. This process seemed to be realized through the delocalized conjugated π-system of the phenol C 2p electronic states of the ligand molecule. The DFT calculations (total and partial DOS) for the valence band H2(Salen) and [Ni(Salen)] described well the spectral shape of the UV PE spectra of both compounds and confirmed their experimental identification. An analysis of the N and O 1s NEXAFS spectra clearly indicated that the atomic structure of the ethylenediamine and phenol fragments was retained upon passing from the free salen ligand to the nickel complex.

Thermal Stability and Vibrational Properties of the 6,6,12-Graphyne-Based Isolated Molecules and Two-Dimensional Crystal.

We report the geometry, kinetic energy, and some optical properties of the 6,6,12-graphyne-based systems. We obtained the values of their binding energies and structural characteristics such as bond lengths and valence angles. Moreover, using nonorthogonal tight-binding molecular dynamics, we carried out a comparative analysis of the thermal stability of 6,6,12-graphyne-based isolated fragments (oligomer) and two-dimensional crystals constructed on its basis in a wide temperature range from 2500 to 4000 K. We found the temperature dependence of the lifetime for the finite graphyne-based oligomer as well as for the 6,6,12-graphyne crystal using a numerical experiment. From these temperature dependencies, we obtained the activation energies and frequency factors in the Arrhenius equation that determine the thermal stability of the considered systems. The calculated activation energies are fairly high: 1.64 eV for the 6,6,12-graphyne-based oligomer and 2.79 eV for the crystal. It was confirmed that the thermal stability of the 6,6,12-graphyne crystal concedes only to traditional graphene. At the same time, it is more stable than graphene derivatives such as graphane and graphone. In addition, we present data on the Raman and IR spectra of the 6,6,12-graphyne, which will help distinguish it from the other carbon low-dimensional allotropes in the experiment.

Anisotropic Carrier Mobility and Spectral Fingerprints of Two-Dimensional γ-Phosphorus Carbide with Antisite Defects.

We apply density functional theory to study carrier mobility in a γ-phosphorus carbide monolayer. Although previous calculations predicted high and anisotropic mobility in this material, we show that the mobility can be significantly influenced by common antisite defects. We demonstrate that at equilibrium concentrations defects do not inhibit carrier mobility up to temperatures of 1000 K. However, defects can change the mobility at high nonequilibrium concentrations of about 10-4 to 10-2 defects per atom. At the low end of this concentration range, defects act as traps for charge carriers and inhibit their mobility. At the high end of this range, defects change the effective carrier masses and deformation potentials, and they can lead to both an increase and a decrease in mobility. We also report the Raman and IR spectra associated with antisite defects. We predict new vibrational modes and shifts of the existing modes due to the defects.

Energy and Electronic Properties of Nanostructures Based on the CL-20 Framework with the Replacement of the Carbon Atoms by Silicon and Germanium: A Density Functional Theory Study.

We consider SinCL-20 and GenCL-20 systems with carbon atoms replaced by silicon/germanium atoms and their dimers. The physicochemical properties of the silicon/germanium analogs of the high-energy molecule CL-20 and its dimers were determined and studied using density functional theory with the B3LYP/6-311G(d,p) level of theory. It was found that the structure and geometry of SinCL-20/GenCL-20 molecules change dramatically with the appearance of Si-/Ge-atoms. The main difference between silicon- or germanium-substituted SinCL-20/GenCL-20 molecules and the pure CL-20 molecule is that the NO2 functional groups make a significant rotation relative to the starting position in the classical molecule, and the effective diameter of the frame of the systems increases with the addition of Si-/Ge-atoms. Thus, the effective framework diameter of a pure CL-20 molecule is 3.208 Å, while the effective diameter of a fully silicon-substituted Si6CL-20 molecule is 4.125 Å, and this parameter for a fully germanium-substituted Ge6CL-20 molecule is 4.357 Å. The addition of silicon/germanium atoms to the system leads to a decrease in the binding energy. In detail, the binding energies for CL-20/Si6CL-20/Ge6CL-20 molecules are 4.026, 3.699, 3.426 eV/atom, respectively. However, it has been established that the framework maintains stability, with an increase in the number of substituting silicon or germanium atoms. In addition, we designed homodesmotic reactions for the CL-20 molecule and its substituted derivatives Si6CL-20/Ge6CL-20, and then determined the strain energy to find out in which case more energy would be released when the framework breaks. Further, we also studied the electronic properties of systems based on CL-20 molecules. It was found that the addition of germanium or silicon atoms instead of carbon leads to a decrease in the size of the HOMO-LUMO gap. Thus, the HOMO-LUMO gaps of the CL-20/Si6CL-20/Ge6CL-20 molecules are 5.693, 5.339, and 5.427 eV, respectively. A similar dependence is also observed for CL-20 dimers. So, in this work, we have described in detail the dependence of the physicochemical parameters of CL-20 molecules and their dimers on the types of atoms upon substitution.

High-Performance Material for the Effective Removal of Uranyl Ion from Solution: Computationally Supported Experimental Studies.

Adsorption is a widely used method for pollution removal and for the recovery of valuable species. In recent years, the use of metal-organic compounds among the adsorbents used in adsorption studies has increased. In this study, the performance of the water-insoluble Fe complex as a metal organic framework (MOF-Fe-Ta) of water-soluble tannic acid, which is not used as an adsorbent in uranium recovery and removal, was investigated. For the characterization of the new synthesized material, Fourier transform infrared, scanning electron microscopy, and X-ray diffraction analyses were performed. The changes in the adsorption process based on various parameters were investigated and discussed. The point of zero charges value of the adsorbent was found as 5.52. It was noticed that the adsorption increases as the pH increases. Analyzing the effect of concentration on adsorption, we determined which model explained the adsorption better. The monolayer capacity of the adsorbent determined in light of the Langmuir model was reported as 0.347 mol kg-1. The Freundlich constant, namely the ß value obtained in the Freundlich model, which is a measure of surface heterogeneity, was found to be 0.434, and the EDR value, which was found from the Dubinin-Raduskevich model and accepted as a measure of adsorption energy, was 10.3 kJ mol-1. The adsorption was kinetically explained by the pseudo-second-order model and the adsorption rate constant was reported as 0.15 mol-1 kg min-1. The effect of temperature on adsorption was studied; it was emphasized that adsorption was energy consuming, that is, endothermic and ΔH was found as 7.56 kJ mol-1. The entropy of adsorption was positive as 69.3 J mol-1 K-1. As expected, the Gibbs energy of adsorption was negative (-13.1 kJ mol-1 at 25 °C), so adsorption was considered as a spontaneous process. Additionally, the power and mechanism of the interaction between studied adsorbent and adsorbate are explained through density functional theory computations. Computationally obtained data supported the experimental studies.

Ab Initio Insight into the Interaction of Metal-Decorated Fluorinated Carbon Fullerenes with Anti-COVID Drugs.

We theoretically investigated the adsorption of two common anti-COVID drugs, favipiravir and chloroquine, on fluorinated C60 fullerene, decorated with metal ions Cr3+, Fe2+, Fe3+, Ni2+. We focused on the effect of fluoridation on the interaction of fullerene with metal ions and drugs in an aqueous solution. We considered three model systems, C60, C60F2 and C60F48, and represented pristine, low-fluorinated and high-fluorinated fullerenes, respectively. Adsorption energies, deformation of fullerene and drug molecules, frontier molecular orbitals and vibrational spectra were investigated in detail. We found that different drugs and different ions interacted differently with fluorinated fullerenes. Cr3+ and Fe2+ ions lead to the defluorination of low-fluorinated fullerenes. Favipiravir also leads to their defluorination with the formation of HF molecules. Therefore, fluorinated fullerenes are not suitable for the delivery of favipiravir and similar drugs molecules. In contrast, we found that fluorine enhances the adsorption of Ni2+ and Fe3+ ions on fullerene and their activity to chloroquine. Ni2+-decorated fluorinated fullerenes were found to be stable and suitable carriers for the loading of chloroquine. Clear shifts of infrared, ultraviolet and visible spectra can provide control over the loading of chloroquine on Ni2+-doped fluorinated fullerenes.

On the Impact of Substrate Uniform Mechanical Tension on the Graphene Electronic Structure.

Employing density functional theory calculations, we obtain the possibility of fine-tuning the bandgap in graphene deposited on the hexagonal boron nitride and graphitic carbon nitride substrates. We found that the graphene sheet located on these substrates possesses the semiconducting gap, and uniform biaxial mechanical deformation could provide its smooth fitting. Moreover, mechanical tension offers the ability to control the Dirac velocity in deposited graphene. We analyze the resonant scattering of charge carriers in states with zero total angular momentum using the effective two-dimensional radial Dirac equation. In particular, the dependence of the critical impurity charge on the uniform deformation of graphene on the boron nitride substrate is shown. It turned out that, under uniform stretching/compression, the critical charge decreases/increases monotonically. The elastic scattering phases of a hole by a supercritical impurity are calculated. It is found that the model of a uniform charge distribution over the small radius sphere gives sharper resonance when compared to the case of the ball of the same radius. Overall, resonant scattering by the impurity with the nearly critical charge is similar to the scattering by the potential with a low-permeable barrier in nonrelativistic quantum theory.

Computer Test of a Modified Silicene/Graphite Anode for Lithium-Ion Batteries.

Despite the considerable efforts made to use silicon anodes and composites based on them in lithium-ion batteries, it is still not possible to overcome the difficulties associated with low conductivity, a decrease in the bulk energy density, and side reactions. In the present work, a new design of an electrochemical cell, whose anode is made in the form of silicene on a graphite substrate, is presented. The whole system was subjected to transmutation neutron doping. The molecular dynamics method was used to study the intercalation and deintercalation of lithium in a phosphorus-doped silicene channel. The maximum uniform filling of the channel with lithium is achieved at 3% and 6% P-doping of silicene. The high mobility of Li atoms in the channel creates the prerequisites for the fast charging of the battery. The method of statistical geometry revealed the irregular nature of the packing of lithium atoms in the channel. Stresses in the channel walls arising during its maximum filling with lithium are significantly inferior to the tensile strength even in the presence of polyvacancies in doped silicene. The proposed design of the electrochemical cell is safe to operate.