Self-consistent Reaction Field Research Articles

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.

Predicting the Mechanism and Products of CO2 Capture by Amines in the Presence of H2O

An extensive correlated molecular orbital theory study of the reactions of CO2 with a range of substituted amines and H2O in the gas phase and aqueous solution was performed at the G3(MP2) level with a self-consistent reaction field approach. The G3(MP2) calculations were benchmarked at the CCSD(T)/CBS level for NH3 reactions. A catalytic NH3 reduces the energy barrier more than a catalytic H2O for the formation of H2NCOOH and H2CO3. In aqueous solution, the barriers to form both H2NCOOH and H2CO3 are reduced, with HCO3- formation possible with one amine present and H2NCOO- formation possible only with two amines. Further reactions of H2NCOOH to form HNCO and urea via the Bazarov reaction have high barriers and are unlikely in both the gas phase and aqueous solution. Reaction coordinates for CH3NH2, CH3CH2NH2, (CH3)2NH, CH3CH2CH2NH2, (CH3)3N, and DMAP were also calculated. The barrier for proton transfer correlates with amine basicity for alkylammonium carbamate (ΔG‡aq < 15 kcal/mol) and alkylammonium bicarbonate (ΔG‡aq < 30 kcal/mol) formation. In aqueous solution, carbamic acids, carbamates, and bicarbonates can all form in small amounts with ammonium carbamates dominating for primary and secondary alkylamines. These results have implications for CO2 capture by amines in both the gas phase and aqueous solution as well as in the solid state, if enough water is present.

Generalizing Continuum Solvation in Crystal to Nonaqueous Solvents: Implementation, Parametrization, and Application to Molecules and Surfaces.

We present an extension of a generalized finite-difference Poisson-Boltzmann (FDPB) continuum solvation model based on a self-consistent reaction field treatment to nonaqueous solvents. Implementation and reparametrization of the cavitation, dispersion, and structural (CDS) effects nonelectrostatic model are presented in CRYSTAL, with applications to both finite and infinite periodic systems. For neutral finite systems, computed errors with respect to available experimental data on free energies of solvation of 2523 solutes in 91 solvents, as well as 144 transfer energies from water to 14 organic solvents are on par with the reference SM12 solvation model for which the CDS parameters have been developed. Calculations performed on a TiO2 anatase surface and compared to VASPsol data revealed an overall very good agreement of computed solvation energies, surface energies, as well as band structure changes upon solvation in three different solvents, validating the general applicability of the reparametrized FDPB approach to neutral nonperiodic and periodic solutes in aqueous and nonaqueous solvents. For ionic species, while the reparametrized CDS model led to large errors on free energies of solvation of anions, addition of a corrective term based on Abraham's acidity of the solvent significantly improved the accuracy of the proposed continuum solvation model, leading to errors on aqueous pKa of a test set of 83 solutes divided by a factor of 4 compared to the reference solvation model based on density (SMD). Overall, therefore, these encouraging results demonstrate that the generalized FDPB continuum solvation model can be applied to a broad range of solutes in various solvents, ranging from finite neutral or charged solutes to extended periodic surfaces.

A comprehensive theoretical analysis of Curtius rearrangement of syn-syn and syn-anti conformers of oxalyl diazide

The complete theoretical study of thermal Curtius rearrangement of syn-syn and syn-anti conformers of oxalyl diazide, in the gas phase and in solution has been established for the first time. The inexplicit solvent effect was taken into account via the self-consistent reaction field (SCRF) method. The gas and solution phases of all optimized geometries of the mentioned conformers associated with the Curtius rearrangement along the concerted and stepwise pathways were reported using the polarized continuum model and non-electrostatic terms from the SMD universal solvation model. The Curtius rearrangement of syn-syn and syn-anti conformers was taken place via concerted and stepwise pathways, respectively. The syn-syn conformer of oxalyl diazide is more stable than the syn-anti conformer in the gas phase and solution, and rearranged to syn-carbonyl azide isocyanate via an exergonic concerted mechanism with a single transition state. Nevertheless, the rearrangement of syn-anti conformer occurred through the two transition states and an intermediate, which the first and second steps are endergonic and exergonic, respectively. Theoretical results point out that the concerted pathway is predominant with 102-106 and 104-105 times faster than the stepwise mechanism in gas phase and solution, respectively. Topological analysis of the electron localization function at the B3LYP/6–311++G (2d,d,p) level of theory indicate that the catastrophe sequence 1-6-C†TSC†F C†C-0 begins with the N4–N5 bond breaking, elimination of nitrogen molecule and increasing of non-bonding monosynaptic attractor on N4 atom, and then changing of topological signature of C2–N4 bond, breaking of C1–C2 bond, and formation of pseudo-radical centers on C1 and C2 atoms. Subsequently, annihilation of pseudo-radical centers on the C1 atom, change of topological signature of C2–N4 and formation of C1–N4 bond were executed. The obtained results of ELF calculations show that the reaction takes place via a concerted mechanism but highly asynchronous process.

Computational Study of Triphosphine-Ligated Cu(I) Catalysts for Hydrogenation of CO2 to Formate.

The catalyzed hydrogenation of CO2 to formate via a triphosphine-ligated Cu(I) was studied computationally at the density functional theory level in the presence of a self-consistent reaction field. Of the four functionals benchmarked, M06 was generally in the best agreement with the available experimentally estimated values. Two bases, DBU and TBD, were studied in the context of two proposed mechanisms in the MeCN solvent. Activation of H2 was explored by using LCu(DBU)+ to form LCuH. Dissociation of a ligand arm results in higher barriers to form the key hydride complex, LCuH. The preferred mechanism passes through a transition state, where the H2 has one H atom interacting with the copper center and the other H atom interacting with the N atom of the base, similar to H2 insertion into a frustrated Lewis pair. There is no significant difference between the choice of a base, DBU or TBD, with respect to the proposed mechanisms. We propose that the experimentally observed differences between DBU and TBD reactivities for this mechanism are due to off-pathway changes.