Gibbs Free Energy Of Solvation Research Articles

Tuning the physicochemical properties of the single-walled boron nitride nanotube by covalent grafting of triazolium-based [MTZ][X1–3] (X1–3 = NTf2−, TfO− and BF4−) ionic liquids in the gas phase and solvent media: A quantum chemical approach

Covalent grafting of boron nitride nanotubes (BNNTs) using ionic liquids can effectively adjust their electronic structures, magnetic properties and solubility, and leads to the development of applications of the boron nitride nanotubes. Because of the localization features of the BNNT π electron system, the empty p orbitals of boron sites can be filled by excess electrons, which encourage covalent bonding with an unpaired electron. In the present work, physicochemical characteristics of the (8,0) zigzag boron nitride nanotubes (BNNTs) functionalized by methyl 1,2,4 triazolium [MTZ] [X1–3] (X1–3=NTf2−, TfO−, and BF4−) based ionic liquids (ILs) were explored at the M06-2X/6–31+G(d,p) level of theory. Three different functionalized-NTs (NTMTZ-X1–3) were found on the potential energy surface. Comparison of the corrected binding energies showed that the stability of the complexes decreases in the order of NTMTZ-X2≈NTMTZ-X1>NTMTZ-X3. From the solvation Gibbs free energies, it was predicted that the solubility in water increases upon surface functionalization of the BNNT. A remarkable reduction in the HOMO-LUMO gap was predicted from 7.30eV in BNNT to 2.91eV in [NTMTZ]+, and 3.18, 3.26 and 4.46eV in NTMTZ−X1–3 complexes, respectively. The density of states (DOS) analysis revealed that the covalent functionalization of BNNT with ILs results in the spin polarization and induces spontaneous magnetization. In addition, the charge transfer values, electron density properties, dipole moment, electrochemical windows (ECW), non-covalent interactions (NCI) index, anodic and cathodic stability were also evaluated. The results also showed that complexes formed from the [BF4]− anion have a wider ECW.

Hybrid QSPR models for the prediction of the free energy of solvation of organic solute/solvent pairs.

Due to the importance of the Gibbs free energy of solvation in understanding many physicochemical phenomena, including lipophilicity, phase equilibria and liquid-phase reaction equilibrium and kinetics, there is a need for predictive models that can be applied across large sets of solvents and solutes. In this paper, we propose two quantitative structure property relationships (QSPRs) to predict the Gibbs free energy of solvation, developed using partial least squares (PLS) and multivariate linear regression (MLR) methods for 295 solutes in 210 solvents with total number of data points of 1777. Unlike other QSPR models, the proposed models are not restricted to a specific solvent or solute. Furthermore, while most QSPR models include either experimental or quantum mechanical descriptors, the proposed models combine both, using experimental descriptors to represent the solvent and quantum mechanical descriptors to represent the solute. Up to twelve experimental descriptors and nine quantum mechanical descriptors are considered in the proposed models. Extensive internal and external validation is undertaken to assess model accuracy in predicting the Gibbs free energy of solvation for a large number of solute/solvent pairs. The best MLR model, which includes three solute descriptors and two solvent properties, yields a coefficient of determination (R2) of 0.88 and a root mean squared error (RMSE) of 0.59 kcal mol-1 for the training set. The best PLS model includes six latent variables, and has an R2 value of 0.91 and a RMSE of 0.52 kcal mol-1. The proposed models are compared to selected results based on continuum solvation quantum chemistry calculations. They enable the fast prediction of the Gibbs free energy of solvation of a wide range of solutes in different solvents.

Relative pKa of some anilinium derivatives in methanol, acetonitrile, and tetrahydrofurane solvents

In this study, the relative pKa values of nine anilinium derivatives in methanol (MeOH), acetonitrile (AN), and tetrahydrofurane (THF) solutions were successfully calculated with mean absolute deviations of 0.63, 0.68, and 0.75 pKa units, respectively. To this aim, their gas‐phase basicities were computed using the CBS‐QB3 composite method. Also, conductor‐like polarizable continuum model (CPCM) with UAHF, UAKS and UA0 cavities and SM8 solvation models at HF/6‐31+G(d) level of theory were applied for the calculation of the solvation Gibbs free energies. The obtained results indicate that there is reliable correlation between the experimental and computed pKa values in the studied solutions. Therefore, to extend the pKa database for anilines, correlation equations were used to predict the pKa values in the investigated solvents.

First principles prediction of aqueous acidities of some benzodiazepine drugs

In this study, aqueous acidities of several benzodiazepine (BZD) drugs including Oxazepam, Clonazepam, Nitrazepam, Flunitrazepam, Diazepam, Alprazolam, Estazolam, Temazepam, Medazepam and Bromazepam were successfully computed using two common thermodynamic cycles. To that, calculated gas phase Gibbs free energies at PBE1PBE/6-311+G(d,p) level of theory and computed solvation Gibbs free energies at (CPCM/IEF-PCM: UAKS, UAHF and UA0)/HF/6-31+G(d) levels of theory were combined. The most accurate pKa values were obtained with thermodynamic cycle involving water and using CPCM-UA0 solvation model with MAD = 0.4. Moreover, for the first time, aqueous pKa value of Halazepam was predicted using the best method equal to 3.1.

Solubilities of sulfuryl fluoride in propylene carbonate, tributyl phosphate and N-methylpyrrolidone

The solubilities of sulfuryl fluoride (SO2F2) in propylene carbonate (PC), tributyl phosphate (TBP) and N-methylpyrrolidone (NMP) was measured by isochoric saturation method at the pressure of up to 600 kPa and temperatures ranging from (293.15 to 313.15) K. Results showed that SO2F2 solubility increased with increasing pressure and decreased with increasing temperature in the three solvents, and the dissolution of SO2F2 in the solvents was a physical process. Moreover, Henry’s law constants and thermodynamic properties such as standard Gibbs free energy, enthalpy, and entropy changes of SO2F2 solvation were further calculated according to the experimental solubility data. The solubility of SO2F2 in these three solvents followed the order of TBP > PC > NMP. The results illustrated that TBP possessed the potentiality to capture SO2F2 among the present absorbents due to the relatively large solubility and low absorption enthalpy for SO2F2.

Solvent effect on the electrochemical oxidation of N,N,N′,N′-tetramethyl-1,4-phenylenediamine. New insights into the correlation of electron transfer kinetics with dynamic solvent effects

Electrochemical oxidation of N,N,N′,N′-tetramethyl-1,4-phenylenediamine (TMPD) to its cation radical (TMPD•+) and dication (TMPD++) in various nonaqueous solvents was studied using the cyclic voltammetry technique on a glassy carbon electrode. The variation of the half-wave potentials (E1/2) with the physical properties of the solvents was interpreted using multi-parametric correlation. It is shown that polarity-polarizability index, viscosity and longitudinal relaxation of solvents play an undeniable role in the E1/2 value. The electron transfer rate constants were simulated and analyzed using the MLR regression method to separate the effect of longitudinal relaxation time from other effective parameters according to the Marcus theory. Finally, a new correlation method was developed which involve solvent's Pekar factor, longitudinal and Debye relaxation time, viscosity and relative permittivity. The computational method was used for calculating the standard of the Gibbs free energy of solvation and oxidation process.

Modeling solubility of CO2/hydrocarbon gas in ionic liquid ([emim][FAP]) using Aspen Plus simulations.

The Peng-Robinson equation of state with quadratic van der Waals (vdW) mixing rule model was chosen to perform the thermodynamic calculations in Flash3 column of Aspen Plus to predict the solubility of CO2 or any one of the hydrocarbons (HCs) among methane, ethane, propane, and butane in an ionic liquid 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([emim][FAP]). Bubble point pressure, solubility, bubble point temperature, fugacity, and partial molar volume at infinite dilution were obtained from the simulations, and enthalpy of absorption, Gibbs free energy of solvation, and entropy change of absorption were estimated by thermodynamic relations. Results show that carbon chain length has a significant effect on the bubble point pressure. Methane has the highest bubble point pressure among all the considered HCs and CO2. The bubble point pressure and fugacity variation with temperature is different for CO2 as compared to HCs for mole fractions above 0.2. Two different profiles are noticed for enthalpy of absorption when plotted as a function of mole fraction of gas soluble in IL. Partial molar volume of CO2 decreases with increase in temperature in [emim][FAP], while it is increased for HCs. Bubble point temperature decreases with increase in the mole fraction of the solute. Entropy of solvation increases with temperature till a particular value followed by a decrease with further increase in temperature. Gibbs free energy change of solvation showed that the process of solubility was spontaneous.

A theoretical study on the C30X15Y15 (X = B, and Al; Y = N, and P) heterofullerenes

Using density functional theory calculations, we investigated the stability, solubility, structural, electronic, and optical properties of C30X15Y15 (X=B, and Al; Y=N, and P) heterofullerenes. The C30B15N15 is found to be the most stable heterofullerene with standard formation enthalpy (ΔH°f) of 222.2kcal/mol, followed by C30Al15N15 (ΔH°f=891.6kcal/mol). The relative stability of fullerenes are as follows: BN>C60>AlN∼BP>AlP, indicating that the BN doping makes the C60 more stable. The XY doping process significantly increases and decreases the solubility of C60 fullerene in water and benzene solvents, respectively. The standard Gibbs free energy of solvation (ΔG°solv) of C60 in water is increased from −0.7 to −33.5kcal/mol by AlN doping process. The dopant X atoms are mainly contributed in generation of occupied states but the Y ones largely create the virtual states. Compared to the pristine C60, the electrical conductivity of the XY doped fullerenes are higher, and the order is as follows: AlP>BP>BN∼AlN>>C60. This indicates that the Al atoms destabilize and P ones stabilize the HOMO and LUMO levels, respectively. The optical gap of these fullerenes is smaller than the HOMO-LUMO gap by about 0.44–0.55eV.

Brick by brick computation of the gibbs free energy of reaction in solution using quantum chemistry and COSMO‐RS

The computational modeling of reactions is simple in theory but can be quite tricky in practice. This article aims at the purpose of providing an assistance to a proper way of describing reactions theoretically and provides rough guidelines to the computational methods involved. Reactions in liquid phase chemical equilibrium can be described theoretically in terms of the Gibbs free energy of reaction. This property can be divided into a sum of three disjunct terms, namely the gas phase reaction energy, the finite temperature contribution to the Gibbs free energy, and the Gibbs free energy of solvation. The three contributions to the Gibbs free energy of reaction can be computed separately, using different theoretico‐chemical calculation methods. While some of these terms can be obtained reliably by computationally cheap methods, for others a high level of theory is required to obtain predictions of quantitative quality. To propose workflows which can strike the balance between accuracy and computational cost, a number of benchmarks assessing the precision of different levels of theory is given. As an illustrative example, the low‐temperature hydrogenation reaction of acetaldehyde to ethanol in solvent toluene is shown. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3944–3954, 2017

Predicting hydrophobic solvation by molecular simulation: 1. Testing united-atom alkane models.

We present a systematic test of the performance of three popular united-atom force fields-OPLS-UA, GROMOS and TraPPE-at predicting hydrophobic solvation, more precisely at describing the solvation of alkanes in alkanes. Gibbs free energies of solvation were calculated for 52 solute/solvent pairs from Molecular Dynamics simulations and thermodynamic integration making use of the IBERCIVIS volunteer computing platform. Our results show that all force fields yield good predictions when both solute and solvent are small linear or branched alkanes (up to pentane). However, as the size of the alkanes increases, all models tend to increasingly deviate from experimental data in a systematic fashion. Furthermore, our results confirm that specific interaction parameters for cyclic alkanes in the united-atom representation are required to account for the additional excluded volume within the ring. Overall, the TraPPE model performs best for all alkanes, but systematically underpredicts the magnitude of solvation free energies by about 6% (RMSD of 1.2 kJ/mol). Conversely, both GROMOS and OPLS-UA systematically overpredict solvation free energies (by ∼13% and 15%, respectively). The systematic trends suggest that all models can be improved by a slight adjustment of their Lennard-Jones parameters. © 2016 Wiley Periodicals, Inc.

Hydrogen-Bond Donicity in DMSO and Gas Phase and Its Dependence on Brønsted Acidity.

The hydrogen-bond (HB) donicity of various HB donors, expressed as standard Gibbs free energy of HB formation with chloride ion, was studied experimentally in dimethyl sulfoxide (DMSO) and computationally in DMSO and the gas phase. Acidity and HB donicity data in the gas phase and DMSO have been obtained for 77 HB donors from different compound families. Applicability of two computational methods (SMD and COSMO-RS) for calculation of solvation contribution to reaction free energy in DMSO was evaluated and discussed. The quality of calculated Gibbs free energies of solvation was assessed using the correlation between HB strengths in solvent and in the gas phase. The investigation of the relationships between HB donicity and Brønsted acidity showed that in the gas phase the correlation is good, and within structurally uniform compound groups both acidity and donicity are described well by substituent constants. The same correlation in DMSO is less distinct. Bidentate HB donors are characterized by higher HB donicity than could be expected from their acidity in both media, and therefore, these HB donors have an important advantage in anion binding applications, e.g., in catalysis.

Carbon Dioxide Solubilities and Diffusivities in 1-Alkyl-3-methylimidazolium Tricyanomethanide Ionic Liquids: An Experimental and Modeling Study

The solubility and diffusivity of CO2 in a series of 1-alkyl-3methylimidazolium tricyanomethanide ionic liquids ([Cnmim][TCM] with n = 2, 4, 6, 7, 8; ILs) was studied using a magnetic suspension balance at temperatures ranging from 298 to 353 K and pressures up to 2 MPa. The effects of temperature, pressure, and alkyl chain length on CO2 solubility and diffusivity were examined. The electrolyte PC-SAFT (ePC-SAFT) equation of state was used to describe the solubility of CO2 in the ILs. The Henry’s law constant and the excess properties of solvation (Gibbs free energy, enthalpy, and entropy) were calculated. A series of equations derived from Fick’s second law were evaluated, and a Fourier expansion of Fick’s second law of diffusion was found to be the most suitable model for deriving diffusivities from gravimetric data. The diffusivities range from 10–10 to 10–9 m2·s–1 in the temperature and pressure ranges applied. The activation energies for CO2 diffusion (12–16 kJ·mol–1) were found to be in the range of...

Thermodynamic functions of solvation of benzene in various binary aqueous-organic solvents

Composition dependences of the thermodynamic functions of solvation in various aqueous-organic mixtures are studied. Limiting activity coefficients and solvation Gibbs free energies of benzene in the mixtures of water with acetone, 1,4-dioxane, dimethyl sulfoxide, and tert-butanol with different compositions at 298K were determined. The results were combined with literature data for the enthalpies of solution in these mixtures and known values of thermodynamic functions of solvation of benzene in several other aqueous-organic solvents. We observed general tendencies of nonlinear enthalpy-entropy compensation, preferential solvation, and existence of a critical composition of the mixtures when the maximum of ΔsolvH and the bend in ΔsolvG vs ΔsolvH plot are observed. The nature of both organic cosolvent and solute influences the concentration of water corresponding to this critical composition. For benzene, it lies between 0.75 and 0.95 mole percent of water in all considered systems. In the same range of compositions, extrema of many other properties of aqueous-organic mixtures were observed. It is concluded that at these compositions, solvation in the mixture is characterized with the highest enthalpy cost of reorganization of binary solvent upon insertion of solute molecules and diminishment of the hydrophobic effect.

Development of intermolecular potential models for electrolyte solutions using an electrolyte SAFT-VR Mie equation of state

ABSTRACTWe present a theoretical framework and parameterisation of intermolecular potentials for aqueous electrolyte solutions using the statistical associating fluid theory based on the Mie interaction potential (SAFT-VR Mie), coupled with the primitive, non-restricted mean-spherical approximation (MSA) for electrolytes. In common with other SAFT approaches, water is modelled as a spherical molecule with four off-centre association sites to represent the hydrogen-bonding interactions; the repulsive and dispersive interactions between the molecular cores are represented with a potential of the Mie (generalised Lennard-Jones) form. The ionic species are modelled as fully dissociated, and each ion is treated as spherical: Coulombic ion–ion interactions are included at the centre of a Mie core; the ion–water interactions are also modelled with a Mie potential without an explicit treatment of ion–dipole interaction. A Born contribution to the Helmholtz free energy of the system is included to account for the process of charging the ions in the aqueous dielectric medium. The parameterisation of the ion potential models is simplified by representing the ion–ion dispersive interaction energies with a modified version of the London theory for the unlike attractions. By combining the Shannon estimates of the size of the ionic species with the Born cavity size reported by Rashin and Honig, the parameterisation of the model is reduced to the determination of a single ion–solvent attractive interaction parameter. The resulting SAFT-VRE Mie parameter sets allow one to accurately reproduce the densities, vapour pressures, and osmotic coefficients for a broad variety of aqueous electrolyte solutions; the activity coefficients of the ions, which are not used in the parameterisation of the models, are also found to be in good agreement with the experimental data. The models are shown to be reliable beyond the molality range considered during parameter estimation. The inclusion of the Born free-energy contribution, together with appropriate estimates for the size of the ionic cavity, allows for accurate predictions of the Gibbs free energy of solvation of the ionic species considered. The solubility limits are also predicted for a number of salts; in cases where reliable reference data are available the predictions are in good agreement with experiment.

Evaluating the Free Energies of Solvation and Electronic Structures of Lithium-Ion Battery Electrolytes.

Adaptive biasing force molecular dynamics simulations and density functional theory calculations were performed to understand the interaction of Li(+) with pure carbonates and ethylene carbonate (EC)-based binary mixtures. The most favorable Li carbonate cluster configurations obtained from molecular dynamics simulations were subjected to detailed structural and thermochemistry calculations on the basis of the M06-2X/6-311++G(d,p) level of theory. We report the ranking of these electrolytes on the basis of the free energies of Li-ion solvation in carbonates and EC-based mixtures. A strong local tetrahedral order involving four carbonates around the Li(+) was seen in the first solvation shell. Thermochemistry calculations revealed that the enthalpy of solvation and the Gibbs free energy of solvation of the Li(+) ion with carbonates are negative and suggested the ion-carbonate complexation process to be exothermic and spontaneous. Natural bond orbital analysis indicated that Li(+) interacts with the lone pairs of electrons on the carbonyl oxygen atom in the primary solvation sphere. These interactions lead to an increase in the carbonyl (C=O) bond lengths, as evidenced by a redshift in the vibrational frequencies [ν(C=O)] and a decrease in the electron density values at the C=O bond critical points in the primary solvation sphere. Quantum theory of atoms in molecules, localized molecular orbital energy decomposition analysis (LMO-EDA), and noncovalent interaction plots revealed the electrostatic nature of the Li(+) ion interactions with the carbonyl oxygen atoms in these complexes. On the basis of LMO-EDA, the strongest attractive interaction in these complexes was found to be the electrostatic interaction followed by polarization, dispersion, and exchange interactions. Overall, our calculations predicted EC and a binary mixture of EC/dimethyl carbonate to be appropriate electrolytes for Li-ion batteries, which complies with experiments and other theoretical results.

Thermodynamic description of the solvophobic effect in ionic liquids

The solvophobic effect is a driving force for self-assembly processes that acts in protic molecular organic solvents as well as in both protic and aprotic ionic liquids. It is known to reduce the solubility of apolar compounds and influence the magnitudes of thermodynamic functions of solvation in molecular solvents. In ionic liquids, thermodynamic aspects of the solvophobic effects have not yet been carefully considered. By comparing the relations between the Gibbs free energy and enthalpy of solvation of different compounds, we show that the solvophobic effect in aprotic ionic liquids can be even stronger than in organic solvents forming a network of intermolecular hydrogen bonds, such as formamide and ethylene glycol. The strength of the solvophobic effect expressed in terms of energy contributions is correlated with the average number of ions per unit volume, which is inversely proportional to the molar volume of the liquid. It is shown that the solvophobic effects become stronger when we change the cation or anion of the ionic liquid with another of a smaller size, and can be extremely weak when the cation contains long alkyl chains, but they are a general phenomenon for all ionic liquids.

Understanding SO2 Capture by Ionic Liquids.

Ionic liquids have generated interest for efficient SO2 absorption due to their low vapor pressure and versatility. In this work, a systematic investigation of the structure, thermodynamics, and dynamics of SO2 absorption by ionic liquids has been carried out through quantum chemical calculations and molecular dynamics (MD) simulations. MP2 level calculations of several ion pairs complexed with SO2 reveal its preferential interaction with the anion. Results of condensed phase MD simulations of SO2-IL mixtures manifested the essential role of both cations and anions in the solvation of SO2, where the solute is surrounded by the "cage" formed by the cations (primarily its alkyl tail) through dispersion interactions. These structural effects of gas absorption are substantiated by calculated Gibbs free energy of solvation; the dissolution is demonstrated to be enthalpy driven. The entropic loss of SO2 absorption in ionic liquids with a larger anion such as [NTf2](-) has been quantified and has been attributed to the conformational restriction of the anion imposed by its interaction with SO2. SO2 loading IL decreases its shear viscosity and enhances the electrical conductivity. This systematic study provides a molecular level understanding which can aid the design of task-specific ILs as electrolytes for efficient SO2 absorption.

Theoretical investigation of the solubilization of COOH-functionalized single wall carbon nanotubes in water

The paper discusses the impact of functionalization in understanding the solubility of (n, 0) single walled carbon nanotube (SWCNT) with varying diameters (n=8–16) to increase its dispersion in water with the aide of spin-unrestricted density functional theory (DFT). A finite nanotube model saturated with hydrogen at both ends was functionalized with a carboxylic acid at the sidewall. Functionalization resulted in an enhancement in the solubility of the nanotubes in water which can be explained by the increase in dipole moment as visualized in the HOMO–LUMO surface plots. This behavior depends on the tube diameter marked with saw tooth like periodic features which originated from their different π bonding structures manifested in the electronic band gaps. Furthermore, as the degree of sidewall functionalization increases, the SWCNT sample becomes more soluble as assessed by the calculated Gibbs free energies of solvation.

Solvation of hydrocarbons in aqueous-organic mixtures

We study the solvation of two hydrocarbons, n-octane and toluene, in binary mixtures of water with organic cosolvents. Two polar aprotic cosolvents that are miscible with water in any proportions, acetonitrile and acetone, were considered. We determine the magnitudes of thermodynamic functions of dissolution and solvation at T=298.15K in the mixtures with various compositions. Solution calorimetry was used to measure the enthalpies of solution, and GC headspace analysis was applied to obtain limiting activity coefficients of solutes in the studied systems. For the first time, the enthalpies of solution of alkane in the mixtures with high water content were measured directly. We observed well-pronounced maxima of the dependencies of enthalpies of solvation from the composition of solvent and no maxima for the Gibbs free energies of solvation. Two factors are concluded to be important to explain the observed tendencies: high energy cost of reorganization of binary solvent upon insertion of solute molecules and preferential surrounding of hydrocarbons with the molecules of organic cosolvent. Enthalpy-entropy compensation leads to a steady growth of the Gibbs free energies with increasing water content. On the other hand, consideration of the plots of the Gibbs free energy against enthalpy of solvation clearly shows that the solvation properties are changed dramatically after addition of a rather small amount of organic cosolvents. It is shown that they suppress the hydrophobic effect very effectively even at low concentration, and acetonitrile suppresses the hydrophobic effect less than acetone.

Solubility and thermodynamic properties of sulfuryl fluoride in water

The solubility of sulfuryl fluoride in water was experimentally measured over the pressure from P=(0 to 600)kPa and T=(283.15 to 308.15)K using isochoric saturation method. Results show that SO2F2 solubility increases with increasing pressure and decreases with increasing temperature. Using the experimental solubility data, Henry’s law constants and the thermodynamic properties such as the standard Gibbs free energy, enthalpy, and entropy changes of SO2F2 solvation were obtained. Henry’s law constant based on mole fraction and molality of SO2F2 in water vary from (432.21 to 1052.96)MPa and (7.78 to 18.96)MPa at T=(283.15 to 308.15)K, respectively.