Search Results (46)

We report a computational investigation on the reachability of the molecular similarity index (MSI) approach for predicting the relative drug strength of methylcarbamate derivatives. Traditional MSI values have been obtained by calculating the overlap integral of total electron momentum densities between one molecule and another. Furthermore, we have proposed and tested orbital-specific MSI (OS-MSI) values, obtained by doing the same but with electron momentum densities of a selected molecular orbital (MO) such as the highest occupied MO (HOMO) and the lowest unoccupied MO (LUMO). In the calculations, a Boltzmann-weighted electron momentum density estimated by a theoretical probability distribution of rotamers was used, while the solvation effect was considered using the polarizable continuum model. It is shown that the traditional MSI values as well as the OS-MSI values for the HOMO do not have any correlation with experimental relative toxicity of the methylcarbamate derivatives. In contrast, it has been observed and found that the OS-MSI values for the LUMO exhibit a noticeable correlation with the experimental data. The reason behind this observation is discussed in relation to the drug reaction mechanism of the methylcarbamate derivatives. Full article

The structure, bonding, and properties of diradicals, triradicals, and polyradicals have been investigated using broken symmetry (BS) molecular orbital (MO) and BS density functional theory (DFT) methods, which are regarded as the first steps in the mean-field approach toward strongly correlated electron systems (SCES). The natural orbital (NO) analyses of the BS MO and BS DFT solutions were performed to elucidate the natural orbitals of their occupation numbers, which are used for derivations of the diradical character (y) and several chemical indices for the open-shell molecules under investigation. These chemical indices are also obtained using SCES, the next theoretical step, which uses symmetry-recovered resonating BS (RBS) and multi-determinant methods such as multi-reference (MR) configuration interaction (CI) and MR-coupled cluster (CC) methods that employ the NOs generated in the first step. The nonlinear optical response properties of organic open-shell species were theoretically investigated with several procedures, such as MR CI (CC), the numerical Liouville, and Monte Carlo wavefunction methods, as the third step to SCES. The second-order hyperpolarizability (γ) of diradicals such as a phenalenyl radical dimer were mainly investigated in relation to the generation of quantum squeezed lights, which are used for the construction of the quantum entangled states for quantum optical devices such as quantum sensing and quantum computation. Basic quantum mechanical concepts, such as the Pegg–Barnett quantum phase operator, were also revisited in relation to the design and chemical synthesis of stable diradicals and polyradicals such as optical quantum molecular materials and future molecular qubits materials. Full article

The electronic structures of the first- and second-row homonuclear diatomics, XeF₂, and the weakly bound dimers of nitric oxide and nitrogen dioxide molecules in their ground states are discussed in terms of molecular orbital (MO) theory and, where possible, valence bond theories. The current work is extended and supported by restricted and unrestricted Hartree–Fock (RHF and UHF) self-consistent field (SCF), complete active space SCF (CASSCF), multi-reference configuration interaction (MRCI), coupled cluster CCSD(T), and unrestricted Kohn–Sham (UKS) density functional calculations using a polarized triple-zeta basis. The dicarbon (C₂) molecule is especially poorly described by RHF theory, and it is argued that the current MO theories taught in most undergraduate courses should be extended in recognition of the fact that the molecule requires at least a two-configuration treatment. Full article

The electronic structure characteristics of bilayer graphyne, bilayer graphdiyne, and bilayer graphtriyne were systematically studied using molecular orbital (MO) analysis, density of states (DOS), and interaction region indicator (IRI) methods. The delocalization characteristics of the out-of-plane and in-plane π electrons (i.e., π^out and πⁱⁿ electrons) of these materials were analyzed using the localized orbital locator (LOL). In addition, their responses to external magnetic fields were investigated through anisotropic induced current density (AICD) and isoscalar chemical shielding surfaces (ICSSs) to compare the induced ring currents and magnetic shielding effects, further exploring the aromaticity of the three bilayer materials. The research results indicate that as the number of alkyne groups increases, the aromaticity of the bilayer graphyne structure gradually weakens. Finally, their photophysical properties were studied through TD-DFT calculations. The results show that they exhibit strong localized excitation characteristics. Full article

This study investigates the adsorption characteristics of the pristine MoTe₂ monolayer and the metal atom (Co, V, W, Zr)-modified MoTe₂ monolayer on the hazardous gases CO, CH₃CHO, and C₆H₆ based on the density functional theory. The adsorption mechanism was studied from the perspectives of molecular density differences, band structures, molecular orbitals, and the density of states. Research analysis showed that the changes in conductivity caused by the adsorption of different gases on the substrate were significantly different, which can be used to prepare gas sensing materials with selective sensitivity for CO, CH₃CHO, and C₆H₆. This study lays a reliable theoretical foundation for the gas sensing analysis of toxic and hazardous gases using metal atom-modified MoTe₂ materials. Full article

Oil-immersed transformers play a pivotal role owing to their environmentally friendly characteristics, compact footprint, and cost-effectiveness. Ensuring the online monitoring of oil-immersed transformers is a fundamental measure to ensure the secure and stable operation of modern power systems. In this paper, metal particle cluster-doped SnS is firstly used in the adsorption and sensing of decomposition components (CO, C₂H₂) under fault conditions in oil-immersed transformers. The study comprehensively analyzed band structure, differential charge density, density of states, and molecular orbital theory to unveil the adsorption and sensing mechanisms of target gases. The findings suggest that the modification of metal particle clusters can enhance the surface electronic properties of single-layer SnS. In the regions of metal particle clusters and the gas–surface reaction area, electronic activity is significantly heightened, primarily attributed to the contribution of d-orbital electrons of the metal cluster structures. The modified SnS exhibits adsorption capacity in the following order: Ru₃-SnS > Mo₃-SnS > Au₃-SnS. Additionally, the modified material demonstrates increased competitiveness for C₂H₂, with adsorption types falling under physical chemistry adsorption. Different metal elements exert diverse effects on the electronic distribution of the entire system, providing a theoretical foundation for the preparation of corresponding sensors. The findings in this work offer numerical insights for the further preparation and development of SnS nanosensors, concurrently shedding light on the online monitoring of faults in oil-immersed transformers. Full article

Two ferrocenecarboxylate (fca)-bridged dirhodium (Rh₂) complexes, [Rh₂(fca)₄] (1) and [Rh₂(fca)(piv)₃] (2; piv = pivalate), were prepared through the carboxylate-exchange reactions of [Rh₂(O₂CCH₃)₄(H₂O)₂] and [Rh₂(piv)₄], respectively, with fcaH and characterized by ¹H NMR, ESI-TOF-MS, and elemental analyses. Single-crystal X-ray diffraction analyses of [Rh₂(fca)₄(MeOH)₂] (1(MeOH)₂) and [Rh₂(fca)(piv)₃(MeOH)₂] (2(MeOH)₂), which are recrystallized from MeOH-containing solutions of 1 and 2, revealed that (1) 1(MeOH)₂ and 2(MeOH)₂ possess homoleptic and heteroleptic paddlewheel-type dinuclear structures, respectively; (2) both complexes have a single Rh–Rh bond (2.3771(3) Å for 1(MeOH)₂, 2.3712(3) Å for 2(MeOH)₂); and (3) the cyclopentadienyl rings of the fca ligands in 1(MeOH)₂ adopt an eclipsed conformation, whereas those in 2(MeOH)₂ are approximately 12–14° rotated from the staggered conformation. Density functional theory (DFT) calculations revealed that (1) the electronic configurations of the Rh₂ core in 1(MeOH)₂ and 2(MeOH)₂ are π⁴σ²δ²π*²δ*²π*² and π⁴σ²δ²δ*²π*⁴, respectively; and (2) the occupied molecular orbitals (MOs) localized on the fca ligands are energetically degenerate and relatively more unstable than those on the Rh₂ cores. Absorption features and electrochemical properties of 1 and 2 were investigated in a 9:1 CHCl₃-MeOH solution and compared with those of fcaH and [Rh₂(piv)₄]. Through examining the obtained results in detail using time-dependent DFT (TDDFT) and unrestricted DFT, we found that 1 and 2 exhibit charge transfer excitations between the fca ligands and Rh₂ cores, and 1 shows electronic interactions between ferrocene units through the Rh₂ core in the electrochemical oxidation process. Full article

This review article describes a historical perspective of elucidation of the nature of the chemical bonds of the high-valent transition metal oxo (M=O) and peroxo (M-O-O) compounds in chemistry and biology. The basic concepts and theoretical backgrounds of the broken-symmetry (BS) method are revisited to explain orbital symmetry conservation and orbital symmetry breaking for the theoretical characterization of four different mechanisms of chemical reactions. Beyond BS methods using the natural orbitals (UNO) of the BS solutions, such as UNO CI (CC), are also revisited for the elucidation of the scope and applicability of the BS methods. Several chemical indices have been derived as the conceptual bridges between the BS and beyond BS methods. The BS molecular orbital models have been employed to explain the metal oxyl-radical character of the M=O and M-O-O bonds, which respond to their radical reactivity. The isolobal and isospin analogy between carbonyl oxide R₂C-O-O and metal peroxide LFe-O-O has been applied to understand and explain the chameleonic chemical reactivity of these compounds. The isolobal and isospin analogy among Fe=O, O=O, and O have also provided the triplet atomic oxygen (³O) model for non-heme Fe(IV)=O species with strong radical reactivity. The chameleonic reactivity of the compounds I (Cpd I) and II (Cpd II) is also explained by this analogy. The early proposals obtained by these theoretical models have been examined based on recent computational results by hybrid DFT (UHDFT), DLPNO CCSD(T₀), CASPT2, and UNO CI (CC) methods and quantum computing (QC). Full article

In this work, the adsorption and sensing behavior of Ag-doped MoSe₂/ZnO heterojunctions for H₂, CH₄, CO₂, NO, CO, and C₂H₄ have been studied based on density functional theory (DFT). In gas adsorption analysis, the adsorption energy, adsorption distance, transfer charge, total electron density, density of states (DOS), energy band structure, frontier molecular orbital, and work function (WF) of each gas has been calculated. Furthermore, the reusability and stability of the Ag-doped MoSe₂/ZnO heterojunctions have also been studied. The results showed that Ag-doped MoSe₂/ZnO heterojunctions have great potential to be a candidate of highly selective and responsive gas sensors for NO detection with excellent reusability and stability. Full article

In this article, we delve into the intricate behavior of electronic mechanisms underlying NMR magnetic shieldings $\sigma$ in molecules containing heavy atoms, such as cadmium, platinum, and mercury. Specifically, we explore Pt$X_n^{-2}$ (X = F, Cl, Br, I; n = 4, 6) and XCl${}_2$Te${}_2$$Y_2$H${}_6$ (X = Cd, Hg; Y = N, P) molecular systems. It is known that the leading electronic mechanisms responsible for the relativistic effects on $\sigma$ are well characterized by the linear response with elimination of small components model (LRESC). In this study, we present the results obtained from the innovative LRESC-Loc model, which offers the same outcomes as the LRESC model but employs localized molecular orbitals (LMOs) instead of canonical MOs. These LMOs provide a chemist’s representation of atomic core, lone pairs, and bonds. The whole set of electronic mechanisms responsible of the relativistic effects can be expressed in terms of both non-ligand-dependent and ligand-dependent contributions. We elucidate the electronic origins of trends and behaviors exhibited by these diverse mechanisms in the aforementioned molecular systems. In Pt$X_4^{-2}$ molecules, the predominant relativistic mechanism is the well-established one-body spin–orbit (${\sigma }^{SO\left(1\right)}$) mechanism, while the paramagnetic mass–velocity (${\sigma }^{Mv}$) and Darwin (${\sigma }^{Dw}$) contributing mechanisms also demand consideration. However, in Pt$X_6^{-2}$ molecules, the ${\sigma }^{(Mv/Dw)}$ contribution surpasses that of the $SO\left(1\right)$ mechanism, thus influencing the overall ligand-dependent contributions. As for complexes containing Cd and Hg, the ligand-dependent contributions exhibit similar magnitudes when nitrogen is substituted with phosphorus. The only discrepancy arises from the ${\sigma }^{SO\left(1\right)}$ contribution, which changes sign between the two molecules due to the contribution of bond orbitals between the metal and tellurium atoms. Full article

The electronic and catalytic properties of two-dimensional MoS₂, WS₂, and NbS₂ quantum dots are investigated using density functional theory investigations. The stability of the considered structures is confirmed by the positive binding energies and the real vibrational frequencies in the infrared spectra. The ab initio molecular dynamics simulations show that these nanodots are thermally stable at 300 K with negligible changes in the potential energy and metal–S bonds. The pristine nanodots are semiconductors with energy gaps ranging from 2.6 to 3 eV. Edge sulfuration significantly decreases the energy gap of MoS₂ and WS₂ to 1.85 and 0.75 eV, respectively. The decrease is a result of the evolution of low-energy molecular orbitals by the passivating S-atoms. The energy gap of NbS₂ is not affected, which could be due to the spin doublet state. Molecular electrostatic potentials reveal that the edge sulfur/transition metal atoms are electrophilic/nucleophilic sites, while the surface atoms are almost neutral sites. MoS₂ quantum dots show an interestingly low change in the hydrogen adsorption free energy ~0.007 eV, which makes them competitive for hydrogen evolution catalysts. Full article

The template effect of giant polyoxometalates (POM) shows promising results towards the supramolecular design of hybrid materials suitable for photocatalytic reactions. Here, we demonstrate a novel synthetic approach for covalently grafting the xanthene dye eosin Y (EY) to the nanoscale Keplerate POM {Mo₁₃₂} via an organosilicon linker (3-aminopropyltrimethoxysilane, APTMS) in a homogeneous regime. Using a phase transfer agent, tetrabutylammonium bromide, we solubilize the Keplerate POM modified with six {Si(CH₂)₃NH₂} groups, {Mo₁₃₂}@Si₆, in a series of organic solvents—acetonitrile, acetone, tetrahydrofuran, and dichloromethane—to perform post-functionalization by using an NHS-ester of EY. Both IR and Raman spectroscopy affirm the preservation of the POM’s structure and showcase an amide bond formation between POM and EY in the obtained conjugate {Mo₁₃₂}@Si₆@EY@TBA. Grafting’s success is observed through significant downfield shifting of EY’s aromatic protons’ signals on the ¹H NMR spectrum as compared to the spectra of EY and EY-NHS. The current synthetic approach enables us to exercise precise control of the stoichiometry in the POM-dye conjugates—1:1 for the POM-EY system—as confirmed by elemental analysis. Comprehensive photophysical analysis of {Mo₁₃₂}@Si₆@EY@TBA by means of UV-Vis and steady-state and time-resolved fluorescence measurements points to an existing strong interaction between molecular orbitals of EY and {Mo₁₃₂}, leading to a photoinduced electron transfer, partial fluorescence quenching, and elongation of the excited state’s lifetime. These findings demonstrate that using APTMS as an organosilicon linker in tandem with the Keplerate POM as a nanoscale template can be readily applied as a routine synthetic procedure for grafting various organic dyes or other organic molecules bearing a carboxylic group in their structure to the giant POM surface in a variety of aprotic organic solvents. Full article

This paper investigates the general trends in the structural, electronic, and optical properties of anatase TiO₂ photocatalysts co-doped with transition metals and sulfur. We attempt to rationalize co-dopant selection by employing molecular dynamics and density functional theory calculations. The structural properties of the first-row transition metal co-dopants were determined. TM-TiO₂ and TM/S-TiO₂ were structurally stable, with minimal changes in their lattice parameters, cell volume, density, and XRD profiles relative to pristine TiO₂. However, only Fe and Mn among the first-row transition metals are thermodynamically favorable, i.e., their substitutional energies are lower relative to pristine TiO₂. Intermediate energy levels (IELs) are formed during the co-doping of transition metals and sulfur on TiO₂. In particular, Fe and Co form two IELs between the VBM and CBM, resulting in improved optical properties, especially in the visible-light region, which are mainly attributed to the unsaturated nonbonding transition metal d orbitals and the half-filled Ti–O bonding orbitals. On the other hand, Cu and Ni form three IELs close to each other due to the M–O anti-bond orbitals, half-filled p orbitals of S, and the Ti–S anti-bonding orbitals. These IELs in co-doped systems can serve as “stepping stones” for photogenerated electrons, facilitating easier charge mobility. Among the investigated co-doped systems, Fe/S-TiO₂ was shown to be the most promising for photocatalytic applications. Full article

Titanium and its based alloys are frequently selected for designing biomedical implants and it is thus necessary to study as detailed as possible their corrosion behavior in biological solutions, such as those in the human body environment. In this paper, with the use of molecular orbital calculation, we designed and developed alloys in the Ti-19Mo-xW system (x = 7, 8, 9, and 10 wt%) and investigated the influence of different contents of tungsten on the behavior of Ti-19Mo-xW alloy samples following corrosion in simulated body fluid (SBF). The values of $\overline{Bo}$ (bond order) and $\overline{Md}$ (the metal—orbital energy level) were calculated for each alloy and correlations were established between $\overline{Bo}$ and the content of tungsten. It was found that with the increase in tungsten content, the value of $\overline{Bo}$ increases. Regarding the values of the corrosion resistance in SBF that resulted from the investigated alloys, the Ti19Mo7W alloy is distinguished by the lowest value of the corrosion current density and the lowest corrosion rate. Full article

We measure double differential cross sections (DDCS) of electrons emitted from CH₄ molecules in collisions with 250 keV protons. The projectile ions are obtained from a 400 kV electron cyclotron resonance-based ion accelerator (ECRIA). We study the energy and angular distributions of the electron DDCS. The observed double and single differential and the total cross section are compared with the state-of-the-art continuum distorted wave eikonal initial state (CDW-EIS) model predictions. Two different approaches are used considering the different target descriptions: complete neglect of differential overlap (CNDO) and molecular orbital (MO) approximations. The MO model uses two different scaling parameters (d = 0.7 and 1.0). In the energy distribution of the DDCS, the carbon KLL Auger line is also observed at 240 eV. The single differential cross section (SDCS) and total cross section (TCS) are derived. Both the MO-based CDW-EIS models are in good agreement with the experimental results; however, the CNDO approach overestimates the data. Full article