Theoretical Chemistry Accounts最新文献

Structures of pyridinium-based ionic liquids containing 1-methylpyridinium [MP]⁺, 1-ethylpyridinium [EP]⁺ and 1-propylpyridinium [PP]⁺ with halide anions (X) where X = Cl⁻, Br⁻ and I⁻ were studied using density functional theory and the most stable structures of these ionic liquids were compared. Then electronic and structural properties were extracted for the desired liquids. The results show that in the most stable conformers, in these ILs, Cl⁻ and Br⁻ anions prefer to be placed almost in the plane of the pyridinium ring, while I⁻ prefers the position almost vertical to the plane of the pyridinium ring. In order to investigate the hydrogen bonds between molecules by atoms in molecules (AIMs) and natural bonding orbital (NBO) were studied. The calculated thermodynamic functions show that the interaction of the cation–anion pair in ionic liquids containing Cl⁻ and Br⁻ anions is greater than I⁻, and these interactions decrease with the increase in the atomic weight of the halide. Molecular orbital theory has also been used to calculate quantities related to their stability and activity. Also, ionic liquids containing iodine anion have a high dipole moment compared to ionic liquids containing chloride and bromide. The results of this study show that the properties of Any ILs can be controlled by choosing the appropriate anions.

Evaluating the effects of a solvent on the properties of a solute molecule is important to understand its behavior in a solution of that solvent; this, in turn, is important because most reactions—including all the reactions in biological systems—occur in solution. In its most common definition, aromaticity is a property of molecules with delocalized electrons in a ring. It significantly influences their behavior and, therefore, it is important to evaluate the effects of a solvent on it. The most powerful magnetic criterion to estimate aromaticity considers magnetically induced current densities in the ring. The present work applies this approach to adducts of hydroxybenzenes with explicit water molecules. Hydroxybenzenes are selected as the simplest aromatic systems capable of forming solute–solvent hydrogen bonds with water molecules. Hydroxybenzenes without consecutive OH groups are selected to avoid the influence of intramolecular hydrogen bonds between OHs. Current densities are calculated focusing on the aromatic rings, and the effect of the solvent is highlighted by the density changes caused by the presence of the water molecules attached to the hydroxybenzene molecule. The results show that the strength of the ring current decreases as the number of OH groups in the molecule increases. The strength does not change greatly in the adducts with respect to the isolated molecules: the change extent and direction depend mostly on the arrangement of water molecules around the central molecule. The current density maps show that the water molecules may also be involved in the current flow.

We studied intramolecular noncovalent bonds in organogermanium or organosilicon cyclic esters of tris(2-hydroxyalkyl)amines called silatranes and germatranes. We have shown that the N…Si and N…Ge interactions, well known as hypervalent or transannular bonds, can be rightfully categorized as the strong tetrel bonds (TtB). In the wide set of silatranes and germatranes, the TtB strength is under the influence of the Y substituent at Tt atom in the N…Tt–Y fragment and the features of crystalline environment. We have disclosed the quantitative trends in electronic features of N…Tt tetrel bonds and demonstrated the applicability of criteria based on the positions of extremes in electron density and electrostatic potential along the line between N and Tt atoms to compare the strength of the N…Si and N…Ge tetrel bonds. An important observation is that the dependence of gap width on bond lengths is not linear for silatranes. In order to solve this problem we have analyzed the features of total static potential. The gap between positions of extremes in electrostatic and total static potentials is wide for the weak tetrel bonds and narrow for the strong ones.

Avenanthramides (AVs) are the phytochemicals found in cereals exclusively in oats. These are widely known natural substances that have antioxidant properties. The free radical deactivation potential of the eight AVs against five reactive species has been studied in physiological pH. At physiological pH, the radical quenching processes were studied using the sequential proton loss followed by electron transfer (SPLET) from the phenolic hydroxyl groups. Using density functional theory (DFT) computations, theoretical studies have been carried out in the gas phase and aqueous solution at M06-2X/6-31 + G (d,p) level of theory. The free radical scavenging ability of the studied AVs was analyzed by using conceptual density functional theory-based parameters and electrostatic potential analysis. By examining the hydrogen atom and electron affinities of each reactive species, the relative destructive potential of each has been compared. The electron transfer capabilities between the studied compound and reactive species were identified by utilizing the ionization energy and electron affinity plots. Additionally, by calculating the redox potentials and equilibrium constants for the entire process in the aqueous solution, the viability of scavenging the free radical species by selected AVs (both in neutral and mono-deprotonated) has been investigated. From the analysis, the neutral as well as the mono-deprotonated form of AVs are found to scavenge ^•OH and ^•OOH, and ^•NO₂ radicals effectively, while they are inefficacious toward the O₂^•‾ and ^•NO radicals.

Graphical Abstract

Transition metals can enhance the electronic attributes of tungsten oxides. In this study, we focused on W₂O_n (n = 1–6) clusters as a representative examples of tungsten oxide clusters with varying oxygen concentrations. The structures and electronic properties of the TMWO_n (TM = Mn–Ni) clusters have been calculated using first-principles. The ground-state TMWO_n clusters share some structural similarities with the ground-state W₂O_n (n = 1–6) clusters. The W–O bonds of the TMWO₂ (TM = Fe–Ni) clusters are significantly distorted into a triangular structure. The NiWO_n (n = 1–2) and CoWO_n (n = 3–5) clusters display greater thermodynamic stability than other TMWO_n clusters. Among the TMWO_n clusters, the W₂O₄, W₂O₆, MnWO, MnWO₃, MnWO₆, FeWO, FeWO₄, FeWO₆, CoWO, CoWO₆, NiWO₂, NiWO₅ clusters are more kinetically stable. Furthermore, the amount of charge transfer between the TM atoms and W₂O_n clusters increases from 0.050 |e| to 1.066 |e| as the number of oxygen atoms increases. The 4s orbital electrons of the TM atoms for the TMWO_n clusters are partially transferred to the neighboring O atoms.

The derivatives of 1,2,4- triazole have attracted great attention among medicinal chemists due to their wide range of biological activity, good pharmacodynamic and pharmacokinetic profiles, and low toxicity, that necessitates the development of various synthesis methods and a comprehensive study of their reaction mechanisms. A detailed investigation of possible pathways for formation of new spiro-condensed [1,2,4]triazolo[1,5-c]quinazolines, that combine two structural domains with different biological properties, was performed by computational study at the SMD/B3lyp/6-31+G(d) theory level. The mechanism of interaction between [2-(3-hetaryl-1,2,4-triazol-5-yl)phenyl]amine and cyclohexanone in methanol involves three main processes: formation of carbinolamine by addition of an amine to double bond C=O, elimination of a water molecule, and intramolecular cyclization leading to formation of spiro compounds. Results show increase in reactivity of reactants during acid-catalyzed reaction compared to uncatalyzed one. The nature of the heterocyclic substituent on the triazole ring has little effect on the reaction energy, while the mechanism is unchanged.

In this work, the geometrical, optical, and phosphorescence properties of four complexes with general formula [dRpypy—C(OCH₃)R′—dRpypy]Pt, with Pt-1 (R = F, R′ = methyl), Pt-2 (R = F, R′ = hexyl), Pt-3 (R = methoxy, R′ = methyl) and Pt-4 (R = methoxy, R′ = hexyl), were studied using the B3PW91 and TD-B3PW91 methods. The effect of the double substitution R and R′ on the electronic properties of the four complexes has been investigated. Replacing the two fluorine atoms with the two methoxy groups modifies the shape of the UV–vis spectra and red shift the phosphorescence spectra, while the substituents on the linker R′ do not induce changes in both absorption and phosphorescence spectra. Normal modes involved in the vibronic structure were identified and analyzed using adiabatic Hessian approaches according to the Franck–Condon approximation. The computed phosphorescence wavelengths agree with the observed ones and indicate that the fluorinated complexes exhibit a bright light blue color, while the methoxy complexes display a light spring green color. Further, temperature effects on simulated phosphorescence spectra were studied.

The fission products brought about by the growth of nuclear energy is increasing, and their radioactivity will seriously jeopardize human health and pollute the environment. The recycling of radioactive materials has become a problem that needs to be solved nowadays. In this paper, we simulate the adsorption behaviors of typical fission products Cs, Sr, and Co on the surface of WS₂ based on first-principle study. 3 × 3 supercell is selected by convergence test and calculate and compare the parameters of adsorption sites, adsorption energy, and charge transfer. At the microelectronic level, we analyze the interactions of WS₂ with the three nuclides in detail. In addition, the effect of temperature on the adsorption rate of each nuclide on the WS₂ surface is further evaluated by empirical equations. The results show that fissionable metal nuclides tend to be located at the top of the metal atoms of two-dimensional transition metal sulfides (top site of the W atom of WS₂), and Co, moreover, has a much larger adsorption energy than that of Cs and Sr due to its binding to W in a form similar to covalent bonds. Moreover, under high temperature conditions, WS₂ is more favorable for selecting Co and separating it from Cs and Sr. WS₂ is expected to be an excellent material for the separation and recovery of radionuclide Co.

The ESPA (Electronic Structure, Principles and Applications) conference is organized every two years in Spain. It brings together international specialists in theoretical and computational chemistry to present and discuss the latest advances in this field. The first edition was held in Madrid in 1998, and then, subsequently, in San Sebastián, Sevilla, Valladolid, Santiago de Compostela, Palma de Mallorca, Oviedo, Barcelona, Badajoz, Castellón, and Toledo. The 12th edition of the conference could not be held in 2020 due to the covid epidemic, and it was held in Vigo from June 21 to 24, 2022. This special issue assembles a collection of articles from presentations given at the conference.

The E (otimes) e Jahn–Teller (JT) effects associated with the lowest excited degenerate electronic states (S(_1) and S(_2)) of [6]-, [8]- and [10]cycloparaphenylene dications are studied to unravel their size-dependent optical properties. A model Hamiltonian within the linear vibronic coupling approach is adapted to generate the JT-split potential energy surfaces. Computed JT stabilization energy follows the trend: [6]CPP(^{2+}) < [8]CPP(^{2+}) > [10]CPP(^{2+}). Theoretical absorption spectral features are generated using the wavepacket simulations within the reduced- and full-dimensional framework. These simulations reproduce the size-dependent absorption spectral broadening where the broadening increases with the increase in CPP ring size. The near-degeneracy of JT-split states (S(_1) and S(_2)) indicates a possible fluorescence emission from both the states in these molecules.