Integral Equation Formalism Polarizable Continuum Model Research Articles

Assessing Implicit and Explicit Polarizable Solvation Models for Nuclear-Electronic Orbital Systems: Quantum Proton Polarization and Solvation Energetics.

Accurate simulations of many chemical processes require the inclusion of both nuclear quantum effects and a solvent environment. The nuclear-electronic orbital (NEO) approach, which treats electrons and select nuclei quantum mechanically on the same level, combined with a polarizable continuum model (PCM) for the solvent environment, addresses this challenge in a computationally practical manner. In this work, the NEO-PCM approach is extended beyond the IEF-PCM (integral equation formalism PCM) and C-PCM (conductor PCM) approaches to the SS(V)PE (surface and simulation of volume polarization for electrostatics) and ddCOSMO (domain decomposed conductor-like screening model) approaches. IEF-PCM, SS(V)PE, C-PCM, and ddCOSMO all exhibit similar solvation energies as well as comparable nuclear polarization within the NEO framework. The calculations show that the nuclear density does not leak out of the molecular cavity because it is much more localized than the electronic density. Finally, the polarization of quantized protons is analyzed in both continuum solvent and explicit solvent environments described by the polarizable MB-pol model, illustrating the impact of specific hydrogen-bonding interactions captured only by explicit solvation. These calculations highlight the relationship among solvation formalism, nuclear polarization, and energetics.

Effect of solvent role in electronic properties, band gap, electron injection barrier, charge transport nature, topology studies (ELF, LOL, RDG), and optical properties of azoles for multifunctional applications

The ground state geometries of oxazole compounds, i.e., 3,5-Bis-(4-chloro-phenyl)-7a-methyl-dihydro-oxazolo[3,4-c]oxazole (Compound1) and 3,5-Bis-(4-methoxy-phenyl)-7a-methyl-dihydro-oxazolo[3,4-c]oxazole (Compound2) were optimized using Density functional theory employing B3LYP/6-31G++ level for comparing the geometric parameters (torsion angles, bond angles & bond lengths) with the X-ray crystallographic information. We explored the charge transport nature, wave functional properties, optical and electronic properties of both the oxazoles. The computed geometric parameters are rational to the experimental data. The time-domain TD - B3LYP/6-31G++ & the B3LYP/6-31G++ levels were used to reveal the electronic characteristics and absorption wavelength. Intra-molecular charge transfer was perceived in studied compounds. The IEFPCM (Integral Equation Formalism Polarizable Continuum Model) model was used to calculate the solvation UV spectrum. The effect of various solvents (acetone, acetonitrile, DMF(Dimethylformamide), DMSO (Dimethyl sulfoxide) and methanol) was examined on the excitation energies but solvent polarity has no discernible impact on the wavelengths of absorption. From HOMO-LUMO (Highest Occupied Molecular Orbital – Lowest Unoccupied Molecular Orbital) orbitals with various solvent molecules, band gap energies with the solvation effect are determined. Additionally, through the use of topological analytics like RDG (Reduced Density Gradient), ELF (Electron Localisation Function) & LOL (Localised Orbital Locator), the energy concentration of electrons was elucidated. Furthermore, the outcome of electron-donating cluster (–OCH3) and electron-withdrawing cluster (–Cl) was studied on open-circuit voltage, bandgap alignment, electron coupling constants, excitons dissociation values, ΔGinject – electron injection, LHE-Light Harvesting Efficiency and electron coupling constants (|VRP|).

Solvent effect on the self-association of the 1,2,4-triazole: A DFT study

The self-association of 1,2,4-triazole was studied by the DFT method at the B3LYP/6-311++G(d,p) level in the gas phase, and the most stable dimer and trimer were presented. Based on the integral equation formalism polarizable continuum model (IEFPCM), the effect of solvents such as water and dimethyl sulfoxide (DMSO) on the geometric parameters of molecular complexes (dimer and trimer), atomic charge distribution, molecular electrostatic potential (MEP) surface, and frontier molecular orbitals (FMO) was analyzed. Intermolecular interactions in cyclic and linear complexes were studied using topological analyses (QTAIM, NCI, RDG, ELF, and LOL). IR spectra of 1,2,4-triazole monomer, dimer, and trimer were simulated and compared with experimental results. In self-association, intermolecular hydrogen bonding causes a red shift of the N–H stretching vibrational frequency of 1,2,4-triazole. The solvent effect on the vibrational bands of monomer, dimer, and trimer was analysed.

Probing the water hydrogen-bonding effects on the ground and low-lying excited states of phenanthroline isomers

In this work, the ground and low-lying excited states of a series of phenanthroline isomers (1,10-phenanthroline, 1,7-phenanthroline, and 4,7-phenanthroline) were investigated. Density functional theory (DFT) was used for determining the structural and energetic properties connected to the ground state (such as bond lengths and angles, hydrogen-bond interactions, vibrational frequencies, and relative energies) of each molecule while time-dependent DFT was employed for probing the excited state parameters (excitation energies, oscillator strengths, and structures); both approaches were used in combination with the CAM-B3LYP exchange–correlation functional and the cc-pVTZ basis set. The computations were performed in the gas-phase and water. The effects originating from the interactions with the solvent environment were examined by means of the integral equation formalism polarizable continuum model (IEF-PCM), as well as using a composite solvation model (CSM) through the incorporation of explicit water molecules in combination with IEF-PCM. In terms of relative stability, 1,10-phenanthroline became the most stable isomer when the combined implicit-explicit solvation was taken into account, an interesting behavior that may be assigned to the existence of a chain of hydrogen-bond interactions involving the two explicitly added water molecules and both nitrogen atoms from 1,10-phenanthroline. This feature provided better stabilization to the system when compared to the 1,7-phenanthroline and 4,7-phenanthroline. Taking the 1,10-phenanthroline isomer as an example, all its low-lying singlet excited states were determined to have non-zero oscillator strengths when the CSM was used and, more importantly, one among these states was found as being highly accessible (with oscillator strength = 0.9545). From the comparison with the results obtained using solely the implicit solvation (IEF-PCM results), it is possible to assign the presence of the hydrogen-bond interactions as being an important factor for making such excited state likely to be accessed.

An Experimental and Computational Investigations on the Linear and Nonlinear Optical Characteristics of Novel Chalcone (E)-1-(4-(1H-imidazol-1-yl)phenyl)-3-(1, 5a1-dihydro pyren-1-yl)prop-2-en-1-one

A novel chalcone based pyrene (E)-1-(4-(1H-imidazol-1-yl)phenyl)-3-(1,5a1-dihydropyren-1-yl)prop-2-en-1-one (EIPDP) has been successfully synthesized by Claisen-Schmidt condensation reaction. The molecular structure was optimized using density functional theory (DFT) at B3LYP/ 6-311++G(d,p) basis set. In addition, molecular electrostatic potential (MEP) was obtained to study the intramolecular charge transfer (ICT) by introducing electrophilic and nucleophilic sites on the compound surfaces. Absorption UV-Vis spectra were performed experimentally and theoretically to study the electron transitions of the EIPDP. Further, the excitation states were characterized using the hybrid exchange-correlation functional of Coulomb Attenuated Method-Becke, 3-parameter, Lee-Yang-Parr (CAM-B3LYP) with the Integral Equation Formalism Polarizable Continuum Model (IEFPCM) in Dimethyl sulfoxide (DMSO) solvent at the same basis set. The nonlinear optical (NLO) properties were investigated using Z-scan techniques with continuous wave (CW) laser at 630nm. The NLO findings disclosed that the third-order nonlinear optical parameter (χ 3) for the title compound is in the order of 10−6 esu.

Theoretical insight into the acidity and cooperativity effect of the LLM-105∙(HNO3)2 system.

In order to reveal the nature of the acidity in explosive product, the acidities and cooperativity effects from the intermolecular H-bonding interactions in the LLM-105∙∙∙(HNO3)2 ternary systems were investigated at the B3LYP/6-311 + + G** and M062X/6-311 + + G** levels, with the integral equation formalism polarized continuum model (IEFPCM) based on the self-consistent-reaction-field. The results show that for the ternary systems, the intermolecular H-bonding interactions are stronger than those in the binary complexes, resulting in the lower [H+] concentrations and larger pKa1 values upon the ternary-complex formations. However, there is no obvious correlation between the acidities and cooperativity effects or APT charges of the H atoms involving the H-bonds. Surface electrostatic potential (ESP) and reduced density gradient are used to reveal the nature of the H-bond and acidity. Interestingly, the acidity is closely related to the ESPs of the H atom (VS,H) involving the intermolecular H-bond, but not to the statistical quantities. This is mainly because both acidity and VS,H are the local properties of system, whereas the cooperativity and statistical quantity of ESP are the global property.

A novel copper (II) complex containing pyrimidine-4-carboxylic acid: Synthesis, crystal structure, DFT studies, and molecular docking

A new Cu(II) complex of pyrimidine-4-carboxylic acid was synthesized and characterized through a combination of single-crystal XRD, Ultraviolet-Visible (UV-Vis), and Fourier Transform Infrared Spectroscopy (FT-IR). The Cu(II) complex adopts six-coordinate, distorted octahedral geometry around the Cu (II) center. The ground state geometry of the copper compound was optimized using the Density Functional Theory (DFT) method with unrestricted hybrid density functional B3LYP. The vibrational spectra of the Cu(II) complex and similar molecules were described and compared with calculated data obtained by the DFT/UB3LYP/6–31G(d,p) method. The experimental UV-Vis absorption spectrum was compared to the simulated data using time-dependent (TD)-DFT. The effect of the solvent was carried out using the integral equation formalism-polarized continuum model (IEF-PCM). Global reactivity descriptors (ionization potential, chemical hardness, electron affinity, etc.) were surveyed by using the DFT/UB3LYP and DFT/UCAM-B3LYP methods. The non-linear optical (NLO) parameters of the complex were calculated by using the UB3LYP method with 6–31G(d,p) basis set. Furthermore, the molecular docking study was also performed to display interactions between the B-DNA and the Cu(II) complex.

DFT-GIAO 1H and 13C-NMR Chemical Shifts Calculation of Uncaria longiflora Alkaloids

Recently, the structure elucidation of three new chiral alkaloids, namely isoformosaninol (1), formosaninol (2), and longiflorine (3), isolated from the leaves of U. longiflora var. pteropoda (Miq.) Ridsdale has been reported. Their molecular structures were initially determined by using experimental NMR data, following a systematic method for establishing the absolute configuration of pentacyclic oxindole alkaloids (POAs), and the chemical correlation method based on the known chirality of their precursor, secologanin. Indeed, the integration of the information from experimental and theoretical data can be of fundamental importance for the successful elucidation of the configurational and stereostructural assignments of organic compounds, including natural products. Thus, the present work was conducted to further support the success of this integration by focusing on the NMR data, which is the most critical spectroscopic analysis in the structural elucidation of natural products. The 1H and 13C-NMR chemical shift values for the three alkaloids were calculated using density functional theory-gauge including atomic orbitals (DFT-GIAO) approximation at the B3LYP/6-311+G(d,p) level of theory in integral equation formalism polarizable continuum model (IEF-PCM) concerning to tetramethylsilane (TMS). Statistical error analysis between the experimental and calculated supported an excellent correlation with linearity of higher than 93% and 99% for 1H and 13C-NMR chemical shifts, respectively, for the three alkaloids. The correct correspondences between experimental and calculated data sets were further supported by the mean absolute error (MAE) parameter. The present findings provide insights on the usefulness of integrating experimental and calculated NMR data to ascertain structural elucidation in easing ambiguity. 

Estimation of Dipole Moments of New Coumarin Dye by Experimental and Theoretical Methods

AbstractThe absorption and fluorescence emission spectra of coumarin dye, 4‐((4‐methoxyphenoxy) methyl)‐6‐methoxy‐2H‐chromen‐2‐one (4‐MPMMC) in different polarity solvents are recorded. The effects of solvent polarity on the spectral properties are discussed. It is found that, spectrum peak shifts toward higher wavelength, as the solvent polarity changes. The ground (µg) and excited state (µe) dipole moments are estimated using Lippert's, Bakshiev's, and Kawski‐Chamma‐Viallet's equations. The µe values are found to be higher than µg values for all solvents. This suggests that the dye is more polar in excited state than in ground state. Computational studies are done using Time Dependent Density Functional Theory (TD‐DFT), DFT, and Zindo methods with the help of Gaussian16W; Integral Equation Formalism Polarizable Continuum Model (IEFPCM). Further, the excited state dipole moments are estimated in different solvents and are compared with the experimental results. The reactive centers like electrophilic and nucleophilic sites are identified along with contour action using electrostatic potential (ESP) 3D map using DFT analysis.

Quantum chemical computational studies on 4-(1-Aminoethyl)pyridine

The density functional theory (DFT) method combined with B3LYP and B3PW91 hybrid functional were utilized for geometrical optimization, vibrational frequencies and electronic spectral study. The B3LYP and B3PW91 levels of the time dependent-DFT with 6–311+G(d, p) basis set have been used to determine the highest occupied molecular orbital (HOMO) – the lowest unoccupied molecular orbital (LUMO) energies, absorption wavelengths, and electronic properties (total energy and energy gap) of 4-(1-aminoethyl)pyridine. Global reactivity descriptors like ionization potential, chemical hardness and electron affinity, etc. have been estimated using the B3LYP/6–311+G (d, p) and B3PW91/6–311+G (d, p) methods. The effect of the solvent has been simulated using the integral equation formalism-polarized continuum model (IEF-PCM).

Quantum chemical analysis of hydrogen bonding in pyrrolidone dimers and pyrrolidone–water complexes

The structure of pyrrolidone dimers and hydrogen-bonded complexes of pyrrolidone with water molecules (1–3 molecules in complex) was studied by quantum chemical method on the basis of density functional theory (DFT) using three-parameter hybrid Becky-Lee-Yang-Parr functional and gradient-corrected correlation functional of Perdew, Burke and Ernzerhof (PBE) with D3 version of Grimme dispersion correction, Austin-Frisch-Petersson functional with dispersion correction (APFD) and augmented correlation-consistent polarized valence-only triple-zeta (aug-CC-pVTZ) basis set. The geometrical parameters of hydrogen bonds, binding energies, atomic charges based on Atomic Polar Tensors (APT) and vibrational frequencies were calculated and Natural Bond Orbital (NBO) and quantum theory of atoms in molecules (QTAIM) methods were used. The analysis was carried out for classic H-bonds and C-H…O. The calculations also were made taking into consideration the water medium with the integral equation formalism polarizable continuum model (IEFPCM).

Water hydrogen-bonding effects on the ground and low-lying excited states of dipyridyl isomers

In this work, we examined the ground and low-lying excited states of six dipyridyl isomers (2,2′-dipyridyl, 2,3′-dipyridyl, 2,4′-dipyridyl, 3,3′-dipyridyl, 3,4′-dipyridyl, and 4,4′-dipyridyl), emphasizing the effects that solvation (water) molecules have on properties such as ground state equilibrium structures, relative energies in terms of conformations and transition states (regarding possible cis–trans interconversions), vertical excitation energies (VEs), generalized oscillator strengths (GOS), and excited state structures. Density functional theory (DFT) and its time-dependent formalism (TD-DFT) were used for determining all the ground state and excited state properties, respectively, both being employed with the CAM-B3LYP exchange–correlation functional and the cc-pVTZ basis set. In addition, effects caused by interactions with the solvent environment were probed by means of using two different approaches: i) the integral equation formalism polarizable continuum model (IEF-PCM) and ii) a composite solvation model (CSM) through the incorporation of explicit water molecules in combination with the IEF-PCM. In general, a decrease in the relative energies regarding a given cis/trans counterpart is noticed when solvation is considered independently from the model used; all the dipyridyl cis/trans isomers became (practically) isoenergetical due to dipyridyl-H2O hydrogen-bonding interactions. Moreover, the interconversion barriers were also found to be lowered due to solvation effects. For instance, the energy barrier in terms of interconversion of the trans 2,2′-dipyridyl to the cis 2,2′-dipyridyl was determined as (approximately) 67 % of the corresponding value obtained in the gas-phase. Although no major differences regarding the values of the VEs associated to a bright state are suggested from the comparison between the results obtained for a given isomer through the consideration of solvation and those corresponding determined in the gas-phase, the GOS are all increased when solvation is considered, suggesting an enhancement in the photoabsorption of all the isomers when in presence of solvent. In addition and in contrast to what was seen previously in the case of the gas-phase, 4,4′-dipyridyl presented a bright state among the five lowest-lying excited singlets (accessible at the UVC energy region), which is located at 5.49 eV (with GOS = 0.4465) at the TD-DFT/CAM-B3LYP/cc-pVTZ level of theory in water (IEF-PCM) and at 5.47 eV (with GOS = 0.5331) at the same level of theory with the CSM. Given that no significant change was noticed in the optimized structures for the excited states, it is possible to infer that all the compounds will decompose through photo decomposition (chemical reaction occurring in the excited state) rather than direct photolysis when in solution.

Molecular interaction studies of hydrogen-bonded N-Methyl-2-Pyrrolidone /Ethanol binary mixtures by dielectric relaxation spectroscopy and their temperature dependence

Complex permittivity of the binary mixtures of N-Methyl-2-Pyrrolidone (NMP) with Ethanol (ETH) has been studied in the microwave frequency range at various temperatures. The binary liquid system NMP-ETH is selected to interpret the effect of carbonyl (-CO) group of NMP and hydroxyl group (-OH) of ETH on the volumetric, thermal and dielectric properties. The dipole moment (μ) and relaxation time (τ) is evaluated from Higasi's method and Havriliak-Negami equation. The excess molar volume (VmE), excess permittivity (εE), excess refractive index (nDE), excess inverse relaxation time (1/τ)E are fitted with the Redlich-Kister equation. The results obtained from Polarizable Continuum Model (PCM) and Integral Equation Formalism Polarizable Continuum Model (IEFPCM) solvation theories using DFT methods are correlated with the experimentally determined parameters. The molecular association and chemical stability of the system is interpreted in terms of single-point energy, HOMO-LUMO calculations. The existence of a hydrogen bond within the NMP-ETH system is confirmed from the FT-IR, UV–Vis's spectra.

Spectroscopic characterization and binding interaction of heavy metal onto the surface receptor of the azobenzene: DFT and experimental approach

The azobenzene 1-arylazo-2-naphthol has been synthesized and characterized by elemental analysis, 1H NMR, IR and UV–Vis spectroscopies using both experimental and theoretical methods. The MEP, NPA and FMOs have also been performed at the DFT/B3LYP-D3 level with different solvents in order to investigate the solvent's effect. The energetic behavior of the compound has been examined in the gas phase and in solvent media using the integral equation formalism polarizable continuum model (IEF-PCM). Solvents had sligth significant effect on NPA values whereas both molecules hardness and stability decrease along with increasing of the solvent's polarity. Vibrational and absorption analysis showed no significant azo±hydrazone tautomerism. Theorically, the title molecule calculated in Acetonitrile solvent is the most reactive. The observed red shifts are explained by the large extension of the π conjugated system and the blue shifts confirm the appearance of several tautomeric forms of the studied azo-benzene which lead to a marked improvement in photochemical stability. The cation binding properties of azo benzene as absorption sensor for Cu2+, Mg2+, Ni2+ and Zn2+ cations were reported. The highest adsorption energy in both gas and liquid phase corresponds to the complexes Azoic/Ni2+ then in Azoic/Cu2+ and somewhat in Azoic/Zn2+complex. The lowest adsorption energy is given to Azoic/Mg2+ complex. After cations chemisorption on azoic molecule a bathochromic shift is observed in the optical spectra, particularly for Azoic/Ni2+ complex, which is the proof of interaction between azoic compound and mentioned cations. The electronic proprieties and the vibrational spectra can therefore be used to detect the presence of different cations and the azobenzene shows appropriate properties to constitute good cations (Ni2+ and Cu2+) sensors.

Energy change mechanisms of HMX solute molecules in pure solvents and binary solvent mixtures

The quantum mechanical continuum solvation models have been used to probe into the energy change mechanisms of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) solute molecules in pure solvents and binary solvent mixtures. The relation between the long-range electrostatic energy and the static dielectric constant is determined by the integral equation-formalism polarizable continuum model (IEFPCM). For solvents having hydrogen bonds, the electrostatic interaction is significantly high due to the short-range polarization induced by solute-solvent hydrogen bonding that is unfavorable to crystallization from solution. The non-electrostatic energy has been calculated by the universal solvation model (SMD), which arises from the effects of cavitation, dispersion, and solvent structure (CDS). The calculated interaction energies from different components are discussed in terms of the solvent descriptors, temperature and molecular geometries. The simulation results show that the effects of CDS are important to antisolvent crystallization in dimethyl sulfoxide (DMSO)-alcohol binary solvent mixtures and the energy change mainly originates from the short-range non-electrostatic interaction.

Stabilization of glyphosate zwitterions and conformational/tautomerism mechanism in aqueous solution: insights from ab initio and density functional theory-continuum model calculations.

In this work, a comparative theoretical conformational analysis of the commercially most successful herbicide compound, glyphosate (N-phosphonomethylglycine), has been made at various quantum chemical levels of theory, in the gas phase and aqueous solution, using the integral equation-formalism polarizable continuum model (IEFPCM) and the solvation model density (SMD) approaches. The stable conformers of non-ionized (NE) and ionized or zwitterionic (ZW) neutral forms of glyphosate and the inter-conversions between them are described. Calculations revealed that several NE conformers of glyphosate exist in the gas phase but the zwitterionic form (ZW) is unstable in vacuo at all levels of theory. In aqueous solution, the stabilization of the zwitterion form of glyphosate was unable to be predicted satisfactorily within the equilibrated framework of the IEFPCM polarizable continuum model and using the standard UFF-radii cavity. However, the calculation with the density-based solvation model (SMD) was consistent with the experimental findings and led to the identification of the phosphonate zwitterionic (ZWP) structure as the global minimum energy in aqueous solution. The ZWP ⇋ NE tautomeric equilibrium between the non-ionized and zwitterionic forms of glyphosate was studied in aqueous solution at the SMD-B3LYP-D3/6-311++(2d,2p) level. Zwitterion formation in solution could occur by means of a concerted intramolecular proton transfer from the nitrogen to the oxygen of the phosphonate group. An analysis of the intermolecular mechanism shows that the addition of one water molecule favours the process either thermodynamically or kinetically. The possibility that the tautomerization process of glyphosate via a nonconcerted mechanism with zwitterion carboxylate (ZWC) as the intermediate can be excluded and the ZWP → ZWC proton transfer conversion can be a nearly barrierless process in PES and FES surfaces. comparison with similarly related biologically active systems was made.

Structures of water clusters in the solvent phase and relative stability compared to gas phase

Most of biological and chemical processes occur in aqueous solution. To consider this solvent effects, theoretical investigations including explicit water molecules forming clusters are often considered. These clusters have been extensively investigated in the gas phase to understand their structures, energetics, dynamics, and several other properties. However, their structures, energetics, hydrogen bond networks and many other properties in the solvent phase remained unknown. In this work, we have investigated the effects of solvent on the structures, energetics and hydrogen bond networks of the water clusters from dimer to nonamer. We have explored thoroughly the potential energy surfaces (PESs) of the considered water clusters at classical level to generate initial geometries. The generated geometries have been fully optimized in the solvent phase (represented by a dielectric continuum medium) at the MN15/6-31++G(d,p) level of theory. For the description of the dielectric continuum medium we used the integral equation formalism polarized continuum model (IEF-PCM). The results show that the hydrogen bond network in the solvent phase is different from that in the gas phase due to further interaction with the dielectric continuum medium. Several structures located in the solvent phase are found to be unstable in the gas phase. Nevertheless, we have found that the global minimum structures in both phases have the same shape although their hydrogen bond lengths are different.

Quantum chemical calculation of intrinsic reaction coordinates from trans to cis structure of fluvoxamine

Fluvoxamine is a selective serotonin reuptake inhibitor. Its trans-isomer [(E)-isomer] is pharmacologically active, whereas its cis-isomer [(Z)-isomer] loses its activity. It is a pharmaceutical interest whether the structural change from the (E)-isomer to the (Z)-isomer spontaneously occurs in aqueous solutions without ultraviolet (UV) irradiation. In the present study, the transition state of fluvoxamine was determined by quantum chemical calculation using density functional theory (DFT), and the intrinsic reaction coordinates (IRCs) from the (E)-isomer to the (Z)-isomer were calculated using UB3LYP/6-311++G(d,p) with the integral equation formalism-polarizable continuum model (IEF-PCM). The activation energy of isomerization from the (E)-isomer to the (Z)-isomer was estimated to be 55 kcal/mol. Further, the absorption spectra, the nuclear magnetic resonance chemical shift values, the Raman spectra and the infrared spectra were calculated for the (E) and (Z)-isomers obtained from the reaction coordinate calculation, and these results were in good agreement with the experimental values. The geometrical structures of the (E) and (Z)-isomers proposed in the present study can be used as theoretical models of fluvoxamine for molecular dynamics calculations in future.

Solvent effects on the structures of the neutral ammonia clusters

Understanding the solvation processes is subjected to the understanding of the clusters of the solvent molecule that constitute the solution. The description of proton transfer and ion diffusion processes in ammonia depends on the structures of the ammonia clusters. These structures have been well investigated in the gas phase. Although several processes take place in solution, solvent effects on the structures of molecular clusters have received less attention. In this work, we have investigated the solvent effects on the structures of neutral ammonia clusters from dimer to nonamer. Thus, we generated initial geometries using the bee colony algorithm as implemented in the ABCluster code. The generated geometries have been fully optimized at the MN15/6-31++G(d,p) and ωB97XD/6-31++G(d,p) levels of theory in the dielectric continuum medium. For the description of the dielectric continuum media we used the integral equation formalism polarized continuum model (IEF-PCM).

Predicting novel strong acids of plumbylene at theoretical levels

AbstractWe have reached at new acyclic plumbylenes which show high acidity, via B3LYP, Def2‐TZVP, MP2, and wB97XD functionals. Our scrutinized plumbylenes include dicyclopropaplumbylene (1), dicyclopentaplumbylene (2), dicycloheptaplumbylene (3), and their unsaturated analogs (1’‐3’, respectively). All scrutinized plumbylenes and their corresponding protonated forms, 1H(1’H)‐3H(3’H), appear as minima on their energy surfaces. The conductor‐like polarizable continuum model (CPCM) and integral equation formalism polarized continuum model (IEFPCM) are used to predict the pka values for electrophilic plumbylenes, 1(1’)‐3(3’), in chloroform and water. In most cases, plumbylenes turn out as strong acids for showing relatively high negative pka values. The acidity trend of plumbylenes (pka) appears consistent with their proton affinity (PA), electrophilicity (ω), nucleophilicity (N), Mulliken electronegativity ( ), absolute chemical hardness (ηabs), singlet‐triplet energy gap (ΔEs‐t), and highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) energy gap (ΔEH‐L). Structure 1, with two cyclopropyl groups, turns out as the most acidic specie in chloroform and water.