Self-consistent Reaction Field Research Articles

Calculated Aqueous Reduction Potentials of Neutral and Anionic Halogen Diatomic Molecules.

The free energy of hydration, aqueous, and gas phase electron affinity and aqueous reduction potentials of F2, Cl2, Br2, I2, ClF, BrF, IF, BrCl, ICl, IBr, and their corresponding anions were calculated using an electronic structure approach previously developed for these properties for X• and XO•, where X is a halogen which yielded excellent results. The gas phase electron affinities were calculated at the Feller-Peterson-Dixon level based on complete basis set extrapolation of CCSD(T) results with additional corrections. The agreement with the available experimental data is excellent, and the calculations provide a complete set of reliable electron affinities for these diatomic halogens. The hybrid solvation approach uses single point implicit solvation calculations on gas phase optimized clusters with explicit solvent molecules. The gas phase energy calculations were performed using MP2 and CCSD(T)-F12b for tetramer clusters (four explicit waters) and MP2 for octamer clusters (eight explicit waters). The final redox potentials were obtained at the MP2/aug-cc-pVTZ (aT) with a self-consistent reaction field (SMD) level using the octamer clusters. The aqueous reduction potentials of the neutral diatomic halogens are predicted within 0.06 V of the experiment for diatomic neutrals. The same agreement of 0.06 V is predicted for the redox potential resulting from dissociation electron attachment of the diatomic halogen anions. The current work extends reduction potentials for multiple redox couples for which no experimental data is available, for example, those containing iodine and the interhalogen anions. F2•- is predicted to dissociate for its lowest energy structure in both the tetramer and octamer clusters to form solvated F-, HF, and OH•.

A quantum mechanistic investigation into the unusual reactions of nitrilimine and nitrile oxide with 2,3,4,5-tetraphenylcyclopentadienone.

The theoretical study investigates the [3 + 2] cycloaddition (32CA) reactions between C, N-diphenyl nitrilimine with 2,3,4,5-tetraphenylcyclopentadienone and benzonitrile oxide with 2,3,4,5-tetraphenylcyclopentadienone. Nitrilimines and nitrile oxides are dipoles used in the synthesis of several heterocyclic compounds, including spiropyrazoline oxindoles and isoxazolines. The derivatives of these compounds are found with different biological activities, such as ion channel blockers, anti-inflammatory and anticancer agents as well as antimalarial. Conceptual density functional theory (CDFT) analysis, along with the activation energies of the 32CA reaction between C, N-diphenyl nitrilimine with 2,3,4,5-tetraphenylcyclopentadienone, demonstrates concordance with the empirical findings. The 32CA reaction is found to proceed through a very polar single-step asynchronous mechanism. While deductions from the activation energies of the 32CA reaction between benzonitrile oxide and 2,3,4,5-tetraphenylcyclopentadienone are found to lead to the experimental product, the parr function analysis could not explain the observed chemo- and regioselectivity. This 32CA reaction is also found to proceed through a one-step asynchronous mechanism, though with a non-polar character. The modulation of substituents positioned at the reactive sites of the reactants is found to influence the kinetics, thermodynamics, and CDFT parameters of the two 32CA reactions, consequently impacting the observed selectivities. The 32CA reactions between C, N-diphenyl nitrilimine with 2,3,4,5-tetraphenylcyclopentadienone and benzonitrile oxide with 2,3,4,5-tetraphenylcyclopentadienone have been explored theoretically using the density functional theory method at the hybrid ωB97X-D coupled with the split valence triple-ξ (TZ) basis set as implemented in the Gaussian 09. Solvent effects were taken into account by full optimization of the gas phase geometries through the polarizable continuum model developed within the self-consistent reaction field.

Prediction of Redox Potentials for U, Np, Pu, and Am in Aqueous Solution.

The redox properties of the actinides in aqueous solution are important for fuel production/reprocessing and understanding the environmental impact of nuclear waste. The redox potentials for U, Np, Pu, and Am in oxidation states from 0 up to VII (as appropriate) in aqueous solutions have been predicted at the density functional theory level with the B3LYP functional, Stuttgart small core pseudopotential basis sets for the actinides, and explicit (30H2O molecules)/implicit treatment of the aqueous solvent using the self-consistent reaction field COSMO and SMD approaches for the implicit solvation. The predictions of the structural parameters of clusters incorporating first and second solvation shells are consistent with the available experimental data. Our results are typically within 0.2 V of the available experimental data using two explicit solvation shells with an implicit solvent model. The use of the PW91 functional substantially improved the prediction of the Pu(VI/V) redox couple. The redox couples for An(VI/IV) and An(V/IV) which involve the addition of protons and removal of the actinyl oxygens led to slightly larger differences from an experiment. The An(IV/0) and An(III/0) couples were reliably predicted with our approach. Predictions of the unknown An(II/I) redox potentials were negative, consistent with expectations, and predictions for unknown An(VII/VI), An(III/II), and An(II/0) redox couples improve prior estimates.

Prediction of the pKa's of Hydrated Metal Carbonates and Bicarbonates for Mg, Ca, Mn, Fe, Co, Ni, Cu, and Zn Dications.

The gas- and aqueous-phase acidities of hydrated metal dication carbonates, bicarbonates, and hydroxide complexes M(CO3)(H2O)n for n = 1 to 3, M(HCO3)2, M(HCO3)2(H2O)2, M(HCO3)(OH), and M(HCO3)(H2O)2(OH) for M = Mg, Ca, Mn, Fe, Co, Ni, Cu, and Zn were calculated at the CCSD(T)/aug-cc-pwCVDZ/cc-pwCVDZ level in the gas phase and at the B3LYP/aug-cc-pVTZ/cc-pVTZ(-PP) level with the COSMO self-consistent reaction field (SCRF) method in the aqueous phase. The composite correlated molecular orbital theory G3(MP2) and G3(MP2)B3 methods were used to predict the pKa's of the Mg structures and cis-cis carbonic acid to provide additional benchmarks. Using values scaled to experiment for H2CO3, the pKa's of bicarbonate ligands in group 2 and transition-metal complexes were compared to carbonic acid to gauge the effect of the metal complex on the bicarbonate. The group 2 metal complexes M(HCO3)2 and M(HCO3)(OH) decreased the acidity of the bicarbonate ligands, whereas their dihydrates were even less acidic. The transition-metal di-bicarbonate and bicarbonate hydroxide complexes generally made the bicarbonate more acidic especially when reduction of the metal occurs consistent with electron donation from the ligands; this is accompanied by spin transfer which typically increases in the order Mn < Fe < Co < Ni < Cu. The transition-metal dihydrates were less acidic than carbonic acid. Using values scaled to experiment for hydrated metal dications, the pKa's of water coordinated to group 2 and transition-metal complexes were generally more acidic than the hydrated metal dications, with the exception of Ca bicarbonate dihydrate, Co carbonate, Ni di-bicarbonate dihydrate, and Cu bicarbonate hydroxide di-bicarbonate.

Applicability of self-consistent reaction field (SCRF) method to DFT estimation of hydrogen isotope separation factors in reversible processes

ABSTRACT In earlier quantum chemical calculations of isotope effects, chemical species in the liquid phase were generally treated as existing in the gas phase. In recent years, however, advances in computational programs have made it easier for the self-consistent reaction field (SCRF) method to handle chemical species in the liquid phase, and as a result, it has become easier to apply the SCRF method to isotope effect calculations. This paper concerns the scope of application of the DFT-SCRF method to reversible processes for hydrogen isotope enrichment. It is found that the applicability of the method depends on the type of the intermolecular interaction in the liquid phase and the degree of hydrogen isotope effect (separation factor) on which the process is based. When the magnitude of the isotope effect of the separation system is greater than 10–1, the simple SCRF method is fully applicable; when the magnitude is around 10–2, SCRF with a dimer model, in which the monomer is replaced by a dimer, is applicable for the analysis of the liquid phase with relatively strong intermolecular interactions. Anharmonic correction to the separation factor calculated based on harmonic frequencies may be effective to systems with the liquid phase with weak intermolecular interactions.

Study of Interactions of Nucleoside Anticancer Drugs, Capecitabine and Gemcitabine, with SWNT and BNNT using Molecular and Quantum Mechanical Calculations

Abstract: Using single-wall carbon nanotubes (SWCNTs) and boron nitride nanotubes (BNNTs), this study evaluated the interactions between Capecitabine (CAP) and Gemcitabine (GEM). Molecular mechanics and quantum mechanics were used in the analysis. : The interaction between CP and GM with SWCNTs and BNNTs under various solvents was analyzed using the self-consistent reaction field (SCRF) as a model and DFT as the analytical method. Additionally, the effect of temperature on the stability of the molecule interactions during the experiment was examined. The thermodynamic properties of the title compounds were analyzed based on theoretical calculations. It included the calculation of Frontier Molecular Orbitals (FMOs) and Total Density of States (DOS). In addition to studying the ionization potential (I), we also examined the other molecular properties of the structures, such as electrophilicity (ω), electron affinity (A), chemical hardness (η), and electronic chemical potential (μ). To investigate the interaction between CAP and GEM with SWCNTs and BNNTs, molecular mechanics methods (MM) including AMBER, OPLS, CHARMM, and MM+ force fields, were employed. Monte Carlo simulation techniques were used to calculate the results at different temperatures. : The effects of the liquid phase and mixed solvent media with varying dielectric constants (Water, DMSO, Methanol, and Ethanol) on the interaction between CAP and GEM using the force fields described above were examined in this study. The correlation between data generated by Monte Carlo, Quantum Mechanics, and Molecular Mechanics was demonstrated. There was a striking similarity in the thermodynamic properties and conformer populations of all three materials.

Prediction of Aqueous Reduction Potentials of X•, ChH•, and XO• Radicals with X = Halogen and Ch = Chalcogen.

The aqueous electron affinity and aqueous reduction potentials for F•, Cl•, Br•, I•, OH•, SH•, SeH•, TeH•, ClO•, BrO•, and IO• were calculated using electronic structure methods for explicit cluster models coupled with a self-consistent reaction field (SMD) to treat the aqueous solvent. Calculations were conducted using MP2 and correlated molecular orbital theory up to the CCSD(T)-F12b level for water tetramer clusters and MP2 for octamer cluster. Inclusion of explicit waters was found to be important for accurately predicting the redox potentials in a number of cases. The calculated reduction potentials for X• and ChH• were predicted to within ∼0.1 V of the reported literature values. Fluorine is anomalous due to abstraction of a hydrogen from one of the surrounding water molecules to form a hydroxyl radical and hydrogen fluoride, so its redox potential was calculated using only an implicit model. Larger deviations from experiment were predicted for ClO• and BrO•. These deviations are due to the free energy of solvation of the anion being too negative, as found in the pKa calculations, and that for the neutral being too positive with the current approach.

Theoretical Study of the Photophysical and Photochemical Properties of 1H‐Benzimidazole and 2‐Ethyl‐7‐nitro‐5‐Substituted 1H‐Benzimidazoles

AbstractTheoretical study of the photophysical/photochemical properties of 1H‐benzimidazole and its derivatives was carried out using APFD, B3LYP, CAM‐B3LYP and PBE0 density functionals with 6‐311+G(2d,p) basis set. The effects of ethanol, 1,4‐dioxane, acetonitrile and water was investigated by means of Integral Equation Formalism of the Polarizable Continuum Model (IEPCM) in the framework of Self‐Consistent Reaction Field (SCRF). The results obtained show that S2 state of the 1H‐benzimidazole molecule is more acidic than the S0 state as the N5−H11 bond length increased to ~ 1.01 Å. At B3LYP/6‐311+G(2d,p) level of theory, the excitation energy of 1H‐bensimidazole molecule in ethanol from S0 to the S2 state was calculated to be 273 nm (4.54 eV). The electronic energy for this transition was calculated to be 0.131 a.u. and observed to occur between π→π* orbitals. Calculations with the PBE0, APFD and B3LYP functionals reproduced the experimental dipole moment in 1,4‐dioxane, with values of 4.09, 4.09 and 4.07 Debye respectively. However, the dipole moments of the 2‐ethyl‐7‐nitro‐5‐substituted‐1H‐benzimidazoles were calculated to be higher for electron donating groups (EDGs) than those bearing electron withdrawing groups (EWGs). In addition, the molecular polarizability was observed to increase with decreasing energy gap. Local excitation (LE) and charge‐transfer (CT) were observed to mediate the mechanisms of electronic excitation in 2‐ethyl‐7‐nitro‐5‐substituted‐1H‐benzimidazoles.

Polarization consistent dielectric screening in polarizable continuum model calculations of solvation energies.

A polarization consistent framework, where dielectric screening is affected consistently in polarizable continuum model (PCM) calculations, is employed for the study of solvation energies. The computational framework combines a screened range-separated-hybrid functional (SRSH) with PCM calculations, SRSH-PCM, where dielectric screening is imposed in both PCM self-consistent reaction field (SCRF) iterations and the electronic structure Hamiltonian. We begin by demonstrating the impact of modifying the Hamiltonian to include such dielectric screening in SCRF iterations by considering the solutions of electrostatically embedded Hartree-Fock (HF) exact exchange equations. Long-range screened HF-PCM calculations are shown to capture properly the linear dependence of gap energy of frontier orbitals on the inverse of the dielectric constant, whereas unscreened HF-PCM orbital energies are fallaciously semi-constant with respect to the dielectric constant and, therefore, inconsistent with the ionization energy gaps. Similar trends affect density functional theory (DFT) calculations that aim to achieve predictive quality. Importantly, the dielectric screened calculations are shown to significantly affect DFT- and HF PCM-based solvation energies, where screened solvation energies are smaller compared to the unscreened values. Importantly, SRSH-PCM, therefore, appears to reduce the tendency of DFT-PCM to overestimate solvation energies, where we find the effect to increase with the dielectric constant and the polarity of the molecular solute, trends that enhance the quality of DFT-PCM calculations of solvation energy. Understanding the relationship of dielectric screening in the Hamiltonian and DFT-PCM calculations can ultimately benefit on-going efforts for the design of predictive and parameter free descriptions of solvation energies.

Efficiency of CuCr2O4/Titanium dioxide nanoparticles composite for organic dye removal in aqueous solutions

Semiconductor metal oxide with TiO2 nanoparticles removes hazardous compounds from environmental samples. TiO2 nanoparticles have shown potential as an efficient photocatalyst by being employed as a nano-catalyst for the breakdown of organic contaminants in wastewater samples. To separate substances from contaminated samples, combined UV and visible light irradiation has been used. Sol-gel synthesis was used to produce a copper chromite-titanium nanocomposite, which was then evaluated using analytical methods, such as XRD, BET, DRS-UV, and FT-IR. Using visible light, the photocatalytic activity of a nanocomposite made of CuCr2O4 and TiO2 was investigated for its role in the breakdown of malachite green. The effects of several parameters, including pH change, anions presence, contact time, catalyst amount, concentration variation, and the kinetics of photocatalytic degradation were investigated. The magnitude of transition energy calculated using UV-DRS spectra was found to be 3.1 eV for CuCr2O4−TiO2 nanocomposite. Maximum degradation was observed at pH 7.0. The surface area and pore volume of the co-doped samples of Cr2O4 – TiO2 obtained from BET were found to be 6.1213 m2/g and 0.045063 cm3/g respectively. The average particle size of the catalyst of the nano-catalysts calculated from XRD was found to be 8 nm for TiO2 and 66 nm for TiO2–CuCrO4. The peaks obtained in FTIR between the range of 900-500 cm−1 were due to the presence of an aromatic compound. The binding mechanism of a dye molecule to the surface of CuCr2O4–TiO2 nanocomposite was analysed using quantum chemical calculations with the self-consistent reaction field technique employing integral equation formalism for the polarized continuum method and the UFF atomic radii set.

C-PCM study on the electronic and optical properties of Fe(CO)4B12N12 complexes

We explored solvent effect on the stability, dipole moment, polarizability and first hyperpolarizability of Fe(CO)4B12N12 complexes at MPW1PW91/6-311G(d,p) level of theory. These complexes were considered in the low spin states. The self-consistent reaction field theory (SCRF) based on conductor-like polarizable continuum model (PCM) was employed to illustration of the solvent influences. The relations between the parameters with solvent polarity functions (McRae and Suppan functions) were given. Also, relations of the wavenumbers values of the stretching of carbonyl ligands with the Kirkwood–Bauer–Magat equation (KBM) were provided.

Interaction of Isonicotinic Acid Hydrazide with Carboxylic Acid Anhydrides

There has been presented data on the synthesis of monoamides and cyclic imides which are derivatives of isonicotinic acid hydrazide. Cyclic anhydrides of carboxylic acids (succinic, maleic and phthalic) easily react with the hydrazide of isonicotinic acid with cycle opening, forming isonicotinoylhydrazide of dicarboxylic acids, and under more severe conditions the latter are transformed into cyclic acid imides. The structures of the synthesized compounds were studied using 1H- and 13C-NMR spectroscopy, as well as data from twodimensional COSY (1H-1H) and HMQC (1H-13C) spectra. The values of chemical shifts, multiplicity and integral intensity of 1H and 13C signals in one-dimensional NMR spectra were determined. Homo- and heteronuclear interactions confirming the structure of the studied compounds were established using spectra in the COSY (1H-1H) and HMQC (1H-13C) formats. In the approximation of the density functional B3LYP with a base set of 6-31G(d), the enthalpy of the reactions ΔHr in the absence and in the presence of a solvent — isopropanol (self-consistent reaction field method) were calculated quantum-chemically

Arylene Diimide Derivatives as Anolyte Materials with Two-Electron Storage for Ultrastable Neutral Aqueous Organic Redox Flow Batteries

Arylene Diimide Derivatives as Anolyte Materials with Two-Electron Storage for Ultrastable Neutral Aqueous Organic Redox Flow Batteries

Exploration of the Electronic, Spectroscopic Properties, and Bonding of an Antimalarial Drug of Chromium Arene–Quinoline Half Sandwich Complex in Aqueous Solution: A PCM Investigation

In this paper, using the mPW1PW91 functional, quantum chemical calculations were used to explore electronic, spectroscopic properties and bonding of an antimalarial drug of chromium arene–quinoline half sandwich complex in gas and aqueous phases. The solvent effects were examined using the self-consistent reaction field theory (SCRF) based on the polarizable continuum model (PCM). Reactivity parameters of the complex and chloroquine were compared. The molecular properties of these molecules were related to their biological activity. The studied complex and chloroquine's octanol-water partition coefficient (log P) were calculated and compared. The correlation between molecular hardness and biological activity was illustrated. The temperature dependence of thermodynamic parameters of the complex was investigated. Cr-C bonds in the studied drug were illustrated using NBO and QTAIM analyses.

DFT-analysis of protolytic equivalents of 5-(aryl)-4-(methyl,amino)-1,2,4-triazole-3(2H)-thione

The use of modern computer methods in aspects of quantum chemistry and systematic analysis of their results give an idea of the reactivity of organic compounds, as well as to understand the essence of known experimental data, correct predictions, and quantitative estimates. Undoubtedly, theoretical calculations are useful in solving such an urgent problem of modern chemistry as prototropic equilibria and properties of substances in the gas phase, solutions, and solid-state. The aim of the work – until recently assigned to a theoretical vivification in the infusion of solvents on tautomeric equilibrium and acid-base powers і know more broadly practical stasis in the pharmaceutical industry. Materials and methods. The effect of solvation effects on tautomerism and antitropic properties of 1,2,4-triazole derivatives was studied on the example of model compounds. All calculations were performed using the Gauss-View 6.0.1 molecular link visualization program and Gaussian 98, Gaussian 03 software packages and the use of default convergence criteria. After optimizing the geometry, frequency calculations followed. Thus, the stationary structures are confirmed by checking that all ground states have only real frequencies, and all transition states have only one imaginary frequency. The same method and established basis were used to optimize the geometry. Solvation calculations were performed in the framework of continuous models (D-PCM, C-PCM, IEF-PCM, IPCM, SCIPCM) of discrete and combined models using the Hartree–Fock constraint method, the method of density functional theory B3LYP with basic sets 6-31G (d), 6-31G (d,p), 6-31G++ (d,p), cc-pVDZ, as well as semi-empirical methods in the MOPAC6 package. Results. For the first time, various quantum chemical calculations of solvated model compounds using different approaches and models, variation of the basis in non-empirical calculations, identification of the role of electronic correlation effects, method of geometry optimization, etc. were carried out within the theory of self-consistent reaction field. The main stage of this study was to compare trends in the equilibrium change in the relative stability of tautomeric forms of thione-thiol tautomerism of 1,2,4-triazole-2(3H)-thions in the gas phase and different prototropic solvents due to the possibility of using different models and calculation methods for quality predictions of the effect of solvation on the position of tautomeric equilibrium in compounds of this class. It was found that the selected various solvents according to all used quantum chemical methods and models (D-PCM, C-PCM. IEF-PCM, IPCM, SCIPCM) reduce the difference in the stability of tautomeric forms of the investigated compounds in comparison with the gas phase, while the greatest stabilizing effect is observed in the solvation of NH-tautomers derived from 1,2,4-triazole-2(3H)-thiones. Using all energy parameters (∆Etot, ∆E0, ∆H298, ∆G298) allowed to determine the effect of complexation on the relative stability of tautomeric forms of the studied compounds. The difference in the values of the energy levels of HOMO and LUMO – orbitals indicate the reactivity of the molecule and its activation energy, which indicates the chemical reactivity of the molecule to electronic transport and the manifestation of biological activity with intramolecular charge transfer. Conclusions. For the first time, complex quantum chemical calculations of thione-thiol tautomers of 5-(aryl)-4-(methyl, amino)-1,2,4-triazole-3(2H)-thiones were performed and it was found that prototropic solvents reduce the difference in all models. In the stability of tautomeric forms of the investigated compounds in comparison with the gas phase. The calculated values of electronic correlation models on the hydrogen atom make a significant contribution to the relative stability of tautomeric forms, while the use of polarization functions of quantum chemical methods on hydrogen atoms has practically no effect on the tautomeric equilibrium. From the obtained data it becomes clearer that in the gas phase and aprotic solvents the thione tautomer with the center of NH-acidity is the most stable, and the thiol tautomer of 1,2,4-triazole-3(2H)-thione predominates in the transition to polar proton-donor solvents. The obtained data indicate the possibility of conducting an electrophilic substitution reaction (eg, alkylation) in the form of an anion. The partially negative charge of the Nitrogen atoms of the 1,2,4-triazole ring promotes electrophilic addition reactions. In the thionic form, on the contrary, electrophilic substitution reactions are possible.

Computational investigation of the solvent and temperature effects on the tautomerization of 7-amino-1,3-dioxo-2,5-diphenyl-2,3-dihydro-1H, 5H-pyrazolo[1,2-a][1,2,4]triazole-6-carbonitrile

This research examines the effects of solvent polarity and temperature on the tautomerization of 7-amino-1,3-dioxo-2, 5-diphenyl-2,3-dihydro-1H,5H-pyrazolo[1,2-a][1,2,4]triazole-6-carbonitrile at CAM-B3LYP/6-311G (d,p) level of theory. The selected solvents are n-hexane, diethyl ether, pyridine, ethanol, methanol, and water. The solvent effects have been examined by the self-consistent reaction field theory (SCRF) based on conductor-like polarizable continuum model (CPCM). The solvent effects have been explored on the energy barrier, frontier orbitals energies, and HOMO-LUMO gap. Dependencies of thermodynamic parameters (DG andDH) on the dielectric constants of solvents have also been tested. Specifically, the temperature dependencies of the thermodynamics parameters have been studied within 100-1000 K range. The rate constant of the tautomerism reaction is computed from 300 to 1200 K, in the gas phase.

Stereoselective cycloaddition of biologically active thioindoline with the smallest nanocage in gas phase versus solution via density functional theory

AbstractA fine speculation of enantioselectivity prior to the expensive experimental endeavors is truly one of the ultimate goals of the computational organic chemists. In this survey, we have predicted stereo specificity for hetero Diels–Alder (DA) cycloaddition of (E)‐3‐benzylidene‐indoline‐2‐thione (I) with C20 to give (Ia) as drug delivery in the gas phase and in solution, at density functional theory (DFT)–self‐consistent reaction field (SCRF). The enthalpy difference between liquid (l) and gas (g) phases (∆Hl‐g), as well as activation energy (Eexo≠, Eendo≠) of Ia cycloadduct, appears proportional to the dielectric constant of solvent (ε). In contrast to the above trends, kinetic stability based on ∆EL‐H of Ia, develops in opposite to that of ε. The more stability of Ia is attributed to its H―bonding, and dipole–dipole interaction in water. The energy barrier of exo transition states (TS) is low; hence, cycloaddition is recommended to be of synthetically interest for preparation of asymmetric nano compound. Moreover, the π‐π aromatic stacking among the substituted phenyl ring and C20 (πsubstituted phenyl ring ↔ πC20) has significant effect on destabilization of endo TS. This DA reaction have polar nature according to one‐step mechanism, that comprises an initial hetero‐DA reaction yielding Ia, which experiences a subsequent [3,3] sigmatropic shift to yield the expected formal cycloadduct. This is a consequence of more polar nature of reaction, due to lower nucleophilicity (N), higher electrophilicity (ω), higher maximum electronic charge (ΔNmax), more polarity (μ), and more global electron density transfer (GEDT) of Ia in polar solvents (especially in water) in comparison to gas phase. This polar character is given by the electrophilic character of the C20 dienophile (ω = 5.29 eV) and nucleophilic character of the 1,3‐diene molecule (I) (N = 3.70 eV). Additionally, molecular mechanism of the considered reaction is substantially different from the DA reactions between simple 1,3‐diene and dienophiles.

Towards a transferable nonelectrostatic model for continuum solvation: The electrostatic and nonelectrostatic energy correction model.

In this work, we introduce an electrostatic and non-electrostatic (ENE) correction to the solvation energy based on the Solvent-Accessible Surface Area (SASA) of the solute and the solvent static dielectric constant. The proposed correction was developed for neutral solutes in non-aqueous solvents, considering three different implicit solvation models based on a Self-Consistent Reaction Field treatment of solute-solvent mutual polarization using an Apparent Surface Charge formalism, namely the Integral Equation Formalism of the Polarizable Continuum Model using a continuous surface charge scheme (PCM), the Solvation Model based on solute electron density (SMD), and the generalized Finite-Difference Poisson-Boltzmann (FDPB) model. The proposed correction was parametrized on a diverse training set of 4980 solvation data from the Solv@tum database of experimental solvation energies, and validated on the non-aqueous subset of the MNSOL database comprising 2140 solvation energies. The performances of the proposed ENE models with minimal and extended parameters formulations have been analyzed and the latter variant has been further compared to the widely used Cavity, Dispersion, and Solvent structural effects (CDS) non-electrostatic model originally developed for the SMx family of implicit solvation models. Overall, a very good agreement between the computed solvation energies with the ENE correction and the reference experimental data has been found on both the training and test sets for all continuum solvation models considered. Furthermore, results for the ENE correction are on par with the reference CDS non-electrostatic model for both SMD and FDPB electrostatics, but with the advantage of using a lower number of parameters and thus an improved transferability between different electrostatics treatments.

Solvent effect on cycloaddition of C20 nanofullerene with indoline‐2‐one, at density functional theory

AbstractThe biologically active (E)‐3‐(furan‐2‐yl)methylene‐indoline‐2‐one (I) is studied, in the gas phase, C6H6, C2H4Cl2, EtOH, MeNO2, DMSO, and H2O using the self‐consistent reaction field (SCRF)—density functional theory (DFT). This species has been used in tumor growth, metastasis, and angiogenesis. A mainly interesting issue is the solvent effect on the stability, geometry, and energy of intermolecular hetero‐Diels–Alder cycloaddition of I with C20 to yield drug delivery (Ia). By optimization of adduct (Ia) from gas phase to nonpolar and then polar solvent, the following results is obtained: (1) The trend of thermodynamic and kinetic stability and also polarity seem proportional to the dielectric constant of the used solvent and formation of the hydrogen bonding. (2) In contrast to general belief that the endo isomer appears more stable than exo isomer, here, the exo isomer appears more stable than endo isomer. (3) The exo cycloaddition can be carried out thermally at room temperature and currently hold responsible for regioselectivity. (4) The possibility of endo cycloaddition is favorable by the lowest energy barrier of 4.2 kcal/mol probed in benzene, while the highest energy barrier of 7.3 kcal/mol is estimated in water. (5) Nonbonding electrostatic interaction between the sulfur heteroatom and nanocage, as well as the π–π aromatic stacking, appears to have significant destabilizing effect on the endo isomer. (6) In going from exo transition state (TS) and endo TS to and Ia cycloadduct, the molecular electrostatic potential is changed as a function of shape, size, symmetry, and regioselectivity.

(Trifluorosilyl)methyl 2-methylacrylate: Synthesis, experimental and theoretical studies

The novel stable organosilicon compound containing pentacoordinated silicon atom, named as (trifluorosilyl)methyl 2-methylacrylate, was synthesized and fully characterized including single-crystal X-ray diffraction. The asymmetric unit of the title compound contains two independent molecules, one of which adopting the s-cis configuration and the other has the s-trans configuration with respect to the CO and CC bonds. In the crystal, conformers form cis- and trans-dimeric pairs due to tetrel-bonding interaction and hydrogen bonds CH··· F. Energetic and geometric characteristics for these dimers were calculated by DFT methods at M06-2X/6-311G(d,p) level of theory using QTAIM analysis. The calculations in the polar medium (DMSO) for two dimeric fragments of crystal packing were performed with Onsager self-consistent reaction field method.