Integral Equation Formalism Polarizable Continuum Model Research Articles

Exploration of the potential energy surfaces of the [formula omitted] clusters: Solvent phase vs gas phase

In the present work, we investigated the potential energy surfaces (PESs) of the structures of the Cu2+ ion in methanol clusters in two different media: gas and solvent phases. The effects of medium polarization by the integral equation formalism polarized continuum model (IEF-PCM) on structural and energetic parameters were examined on the conformers of the Cu2+(MeOH)n=9,10 clusters using the M06-2X/6-31++G(d,p) level of theory. Thus, in the solvent phase, the cluster structures are hexa-coordinated in the global minimum isomer. The study of the temperature dependency shows that the hexa-, and penta-coordinated structures compete with a large predominance of the hexa-coordinate structures with two solvation shells in the solvent phase. The Wiberg bond indices (WBI) analysis of the ionic bond confirms the structural study. In the IEF-PCM solvent compared to the gas medium, Wiberg bond indices of the tetra-, and penta-coordinate conformers are weaker, and the hexa-coordinate conformers in both media are nearly identical. This proves that compared to the solvent phase, the dative bond is stronger in the gas phase. This is supported by the significant difference in the electronic binding energies at saturation found with a single fitting function which are -88.6 and -146.6 kJmol−1 in the solvent and gas phases, respectively.

Revealing the antioxidant properties of alkyl gallates: a novel approach through quantum chemical calculations and molecular docking.

This study investigates the antioxidant potential of alkyl gallates (C1-C10), focusing on the impact of alkyl chain length and solvent polarity on their antioxidant properties. Known for their biomedical relevance in mitigating oxidative stress, alkyl gallates' structure-activity relationships, particularly regarding chain length and environmental factors, still need to be explored. Key thermochemical parameters, including bond dissociation enthalpy (BDE), ionization potential (IP), proton affinity (PA), and electron transfer enthalpy (ETE), reveal that shorter alkyl chains (C1-C4) exhibit superior antioxidant activity. In contrast, longer chains (C5-C10) show reduced effectiveness due to steric hindrance and lower solubility in polar solvents. Molecular docking studies also demonstrated favorable binding interactions with vital biological targets, further reinforcing their antioxidant potential. Quantum chemical calculations were performed using Gaussian 16 with the B3LYP/6-311G(dp) basis set for geometry optimizations. Solvent effects were modeled using the integral equation formalism-polarized continuum model (IEF-PCM). Molecular docking studies were conducted using AutoDockTools 4.2, targeting Tyrosine Kinase Hck, Heme Oxygenase, and Human Serum Albumin to evaluate fundamental binding interactions. These computational methods provided insights into alkyl gallates' chemical reactivity and antioxidant efficiency, allowing for the rational design of more potent antioxidant compounds.

Exploring the impact of heterocyclic bridges for tuning the amplitudes of Nonlinear optical properties under Gas, IEFPCM and COSMO solvent models

Nonlinear optical (NLO) materials are a distinctive class of materials due to their NLO response and wide range of applications. We present a systematic quantum chemical study for designing triphenylamine based derivatives (1Ph to 3PhDTDZ) by modifying central bridge with various size and types of heterocyclic rings. Density functional theory (DFT) method is used to calculate the NLO properties including linear and third-order NLO polarizabilities (α and γ) by using M06-2X functional coupled with the 6-311G** basis set. The calculation results predict that among the designed compounds, 1PhDTDZ has the highest third-order NLO polarizability of 2347.7 x 10−36 esu and lowest transition energy of 1.828 eV. On the other hand, 3PhDTDZ has a greater amplitude (108.5 x 10−24 esu) of static linear polarizability (αiso). We also computed frequency-dependent third-order NLO polarizability values at various laser wavelengths (1500 nm to 1970 nm). This provides valuable information about the complex interaction between light and matter. Dynamic second hyperpolarizability of electro-optic Pockels effect (EOPE effect, (γ (−ω; ω,0,0)) is calculated at 1500 nm laser wavelength with a larger γ-amplitude of 36708.4 x 10−36 esu. The effect of solvent on α and γ has also been the primary focus of this research. An extensive solvation impact has been studied using integral equation formalism Polarizable Continuum Model (IEFPCM) and Conductor-like Screening Model (COSMO). Magnitudes of αiso and 〈γ〉 have shown variation from gas to solvent methods. While among solvents, amplitudes are seen 3.87 % to 11.29 % greater under the effect of COSMO-methanol than PCM-methanol. The Frontier molecular orbital (FMO) studies found a significant decrease in energy band gaps from 5.75 eV to 2.98 eV. Since our systems exhibit remarkable photovoltaic properties, they can be used as dye-sensitized solar cells (DSSCs). Their open circuit voltage (VOC) ranging from 1 eV to 4 eV. Thus, our designed triphenylamine based derivatives with distinct central heterocyclic bridges showcase remarkable efficiency as NLO materials, with additional benefits of exhibiting good photovoltaic properties.

Solvent effects on the structures of the hydrated copper dication clusters

Understanding the solvation process requires an understanding of how the solvent affects the molecular cluster configurations. The current study examined the impact of solvents on the structures of the hydrated Cu2+ cation, as well as the temperature dependence, and the energetics of the hydrated Cu2+ cation clusters from sizes n=1 from n=10 (Cu2+(H2O)n=1−10). The potential energy surfaces (PESs) in the solvent phase (represented by a dielectric continuum medium) at the MP2/6-31++G(d,p) level of computation have been comprehensively investigated. We employed the integral equation formalism polarized continuum model (IEF-PCM) to describe the dielectric continuum medium. It is pointed out that changes in PESs of hydrated copper dication isomers and structural morphologies occur in the continuum medium. Thus, the relative energies are smallest at T=0 K and for the cluster populations of Cu2+(H2O)n=1−10 are modified. Thus, in the solvent phase, the competition between the conformers is more severe than in the gas phase. Furthermore, highly coordinated conformers are more favorable, and favored conformers in the gas phase are disfavored in the solvent phase. The structural investigations are validated by the analysis of Wiberg Bond Index (WBI) at 300 K. In the solvent phase, the WBIs of the most stable isomers are the smallest and the WBIs of axial bonds are lower than those of equatorial bonds. Concerning the energy analysis, the binding energies were predicted for enormous sizes (at saturation) using a fit function. Thus, the new values of the binding energies obtained are -5467.8 and ▪ in the gas and solvent phases respectively. All these observed differences are due to the effects of the implicit solvent.

Theoretical studies for the detailed electronic structure of organotin(IV) derivatives of 4-fluoroanthranilic acid, X-ray structure of n-dibutyltin bis(4-fluoroanthranilate)

The present study describes the detailed DFT-based electronic structure calculations without any symmetry constraints being performed on di- and triorganotin derivatives of 4-fluoroanthranilic acid (AFA), viz. Me2SnL2 (1), n-Bu2SnL2 (2), Me3SnL (3), and Ph3SnL (4) (where L= monoanion of AFA). The structural and atomic charge analysis have confirmed the previously reported our experimental results, i.e. bicapped tetrahedral and distorted tetrahedral geometry for di- and triorganotin derivatives, respectively, and all the complexes 1–4 contain a positively charged central tin atom surrounded by a negatively charged system. The single crystal X-ray structure of complex 2 (n-Bu2SnL2) also suggests that AFA acts as a monoanion and bidentate ligand resulting a bicapped tetrahedral environment around tin. Various population analysis such as Mulliken (MPA), Hirshfeld (HPA), and natural population analysis (NPA) have been employed to calculate the charges at all the atoms. A finite difference approximation method has been used to explain the charge distribution within the studied complexes 1–4 based on the conceptual global and local reactivity DFT-based descriptions, frontier molecular-orbital analysis (FMOA), and molecular electrostatic potential maps (MEP). Further, the conceptual DFT-based global reactivity descriptors and frontier molecular orbital analysis show that the interactions between CT-DNA and complexes 1–4 may be groove binding or electrostatic. The integral equation formalism-polarizable continuum model (IEF-PCM) has been employed to calculate the UV–visible spectra of 1–4 in the solvent field, whereas the same in the gas phase has been obtained with the help of time-dependent DFT (TD-DFT) at the same level of theory. The intramolecular charge distribution in 1–4 has been investigated with the help of natural bond orbital (NBO) analysis. The topological and energetic parameters at the selected bond critical points in the coordination sphere of complexes 1–4 have been calculated using atoms-in-molecules (AIM) theory. The analysis of different kinds of non-covalent interactions (NCI) in complexes 1–4 has also been investigated.

Neighbor effect on conformational spaces of alanine residue in azapeptides

The conformational properties of Alanine (Ala) residue have been investigated to understand protein folding and develop force fields. In this work, we examined the neighbor effect on the conformational spaces of Ala residue using model azapeptides, Ac-Ala-azaGly-NHMe (3, AaG), and Ac-azaGly-Ala-NHMe (4, aGA1). Ramachandran energy maps were generated by scanning (φ, ψ) dihedral angles of the Ala residues in models with the fixed dihedral angles (φ = ±90°, ψ = ±0° or ±180°) of azaGly residue using LCgau-BOP and LCgau-BOP + LRD functionals in the gas and water phases. The integral-equation-formalism polarizable continuum model (IEF-PCM) and a solvation model density (SMD) were employed to mimic the solvation effect. The most favorable conformation of Ala residue in azapeptide models is found as the polyproline II (βP), inverse γ-turn (γ′), β-sheet (βS), right-handed helix (αR), or left-handed helix (αL) depending on the conformation of neighbor azaGly residue in isolated form. Solvation methods exhibit that the Ala residue favors the βP, δR, and αR conformations regardless of its position in azapeptides 3 and 4 in water. Azapeptide 5, Ac-azaGly-Ala-NH2 (aGA2), was synthesized to evaluate the theoretical results. The X-ray structure showed that azaGly residue adopts the polyproline II (βP) and Ala residue adopts the right-handed helical (αR) structure in aGA2. The conformational preferences of aGA2 and the dimer structure of aGA2 based on the X-ray structure were examined to assess the performance of DFT functionals. In addition, the local minima of azapeptide 6, Ac-Phe-azaGly-NH2 (FaG), were compared with the previous experimental results. SMD/LCgau-BOP + LRD methods agreed well with the reported experimental results. The results suggest the importance of weak dispersion interactions, neighbor effect, and solvent influence in the conformational preferences of Ala residue in model azapeptides.

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.