Enthalpies Of Solvation Research Articles

Development of Abraham model correlations for enthalpies of solvation of solutes dissolved in N-methylformamide, 2-pyrrolidone and N-methylpyrrolidone

Enthalpies of solution at infinite dilution have been determined for 2-propanol, ethylene glycol, 1,3-butanediol, 1,4-butanediol, phenol, 1-naphthol, 3-nitrophenol, 4-nitrophenol, 4-chlorophenol, and formamide dissolved in N-methylformamide, 2-pyrrolidone, and N-methylpyrrolidone at 298.15 K, as well as for N-methylformamide dissolved in 2-pyrrolidone and N-methylpyrrolidone, based on solution calorimetric measurements. Results of our experimental measurements, combined with published literature data, have been used to derive Abraham model expressions for predicting the enthalpies of solvation of solutes dissolved in the three fore-mentioned amide solvents. Our derived mathematical expressions back-calculated the observed enthalpy of solvation data to within a standard deviation of 3.1 kJ mol−1 or less.

Solvated State of Ethylenediamine in Nonaqueous Solvents, According to Quantum Chemical Data

Quantum chemical modeling is used to study the equilibrium geometric parameters and atomic charges in molecules of ethylenediamine (En) in the free state, methanol (MeOH), acetonitrile (AN), N,N‑dimethylformamide (DMF) and dimethylsulfoxide (DMSO), along with the Gibbs energies and enthalpies of amine solvation in the considered solvents. It is found that the conformational state of En is approximately the same in each solvent. In aprotic solvents, the solvation of En proceeds mainly because of the universal type of interactions between amine molecules and solvent molecules; in methanol, solvation energy of En and the solvate’s stability are determined by both universal and specific types of solute–solvent interactions with the contribution from the universal type of interactions predominating.

Ammonia Solubility, Density, and Viscosity of Choline Chloride–Dihydric Alcohol Deep Eutectic Solvents

In the present work, dihydric alcohols (including 1,4-butanediol, 2,3-butanediol, and 1,3-propanediol) were paired with choline chloride (ChCl) to form deep eutectic solvents (DESs) with the molar ratio of ChCl to dihydric alcohol fixed at 1:3 and 1:4. The solubility of NH3 in these DESs was systematically determined at 303.15, 313.15, 323.15, and 333.15 K under pressures up to 420.0 kPa using the isochoric saturation method and was correlated using the Krichevsky–Kasarnovsky (K–K) equation. The dissolution Gibbs free energy, enthalpy, and entropy changes of NH3 solvation were further calculated according to the temperature dependence of Henry’s constants. Based on the reported CO2 solubility data, the selectivities of NH3/CO2 in DESs used herein were calculated. The density and viscosity data of the DESs were also measured and fitted at a temperature range of 303.15–343.15 K. Overall, the dihydric alcohol-based DESs present quite promising NH3 absorption and separation performance, with a value of 3.0 mol NH3 per kg DES and an NH3/CO2 selectivity of 98 at 303.15 K and 100.0 kPa.

An approach for the calculation of vaporization enthalpies of aromatic and heteroaromatic compounds at 298.15 K applicable to supercooled liquids

An approach for the calculation of the vaporization enthalpies of aromatic and heteroaromatic compounds at T = 298.15 K with accuracy competitive with experiment was proposed. The vaporization enthalpies may be calculated from the solution enthalpies of liquid and solvation enthalpies in benzene. The solution enthalpies of liquids were shown to be constant within a given type of aromatic compounds. For a set of 67 liquid and 41 solid aromatic and heteroaromatic compounds not capable of intermolecular hydrogen bonding, it was experimentally demonstrated that the solution enthalpies of liquids or supercooled liquids in benzene were equal to 1 ± 1 kJ·mol−1. The way to consider intermolecular hydrogen bonding, e.g., in phenol, aniline, pyrrole derivatives, was also proposed. The methods for solvation enthalpy calculation were proposed previously.The calculated and literature vaporization enthalpies values of 415 aromatic and heteroaromatic compounds were compared. Average absolute deviation amounted to 1.3 kJ·mol−1. The proposed approach is especially valuable for calculation of the vaporization enthalpies of low-volatile compounds, including those solid at T = 298.15 K.

Structure and dynamics of aqueous solutions containing poly-(acrylic acid) and non-ionic surfactant pentaethylene glycol n-octyl ether (C8E5): A molecular simulations study

Self-assembly of non-ionic surfactant pentaethylene glycol n-octyl ether (C8E5) in aqueous solution containing anionic polyelectrolyte poly (acrylic acid) PAA was investigated via atomistic molecular dynamics (MD) simulations. The concentration of surfactant (Cs) varied in the range (Cs = 9.6 × 10−4–0.3 M) of dilute to concentrated systems while polymer concentration was in dilute solution condition (i.e. Cp = 0.01 M). Binary and ternary systems show formation of nearly spherical micellar aggregate at low Cs and lamellar aggregates at high Cs. Strong interaction between PAA and C8E5 is observed at low Cs, in agreement with experimental data. PAA chain adsorbs onto the micellar aggregate and wraps around the aggregate. For lamellar phase aggregates PAA chain shows polar interactions with hydrophilic moieties of surfactant, originating from interactions between COOH groups of PAA and CO groups of C8E5. The concentration at which free-micelles form in ternary (polymer, surfactant and water) solution is greater than CMC of the binary surfactant-water system, in qualitative agreement with experimental data. At low Cs the interaction between surfactants and polymer chain is weak and does not perturb chain conformations. The radius-of-gyration Rg of PAA increases with Cs. Interaction of surfactant molecules with water is more cooperative at higher values of surfactant concentration, as evident from the values of solvation enthalpy. Significant hydrogen bonds were observed to occur between polar oxygens and hydroxyl oxygen (O2HA) of PAA. The number of h-bonds between polar oxygens and O2HA of PAA increase with Cs. Hydrogen bonds of PAA with surfactant molecules increases with Cs as the polymer expands at high Cs. Formation of surfactant aggregate is enthalpically favored across the entire range of concentration in binary and ternary solution. Binding of PAA to surfactant aggregate is favorable at higher surfactant concentration. The enthalpy of formation of ternary solution exhibits a transition from unfavorable to favorable which interestingly is driven by the structural transition from spherical micellar to the lamellar phase. This signature for this transition is also seen by conformation change of PAA upon binding to surfactant aggregate.

Enthalpies of sublimation and vaporization of poly-substituted phenols containing intramolecular hydrogen bonds by solution calorimetry method

A simple procedure for calculation of solvation enthalpy of compounds containing intramolecular hydrogen bond was developed. This procedure is based on the assumption that fragments of molecules containing intramolecular hydrogen bonds can be express as one group contribution. The proposed approach was verified by determination of the vaporization/sublimation enthalpies of poly-substituted phenols. Vaporization/sublimation enthalpies were obtained as difference between solution and solvation enthalpies in benzene. Solution enthalpies of thirteen compounds in benzene were measured in the present study. The obtained vaporization/sublimation enthalpies are in good agreement with values available in the literature. This promising result makes the solution calorimetry method preferable for quick estimations of enthalpy of phase transition, especially for explosive or compounds of low volatility.

Novel behavior in a polymer solution: the disappearance of the melting temperature (Tm) and enthalpy change (\u0394Hm) of the solvent

The phase change temperature and enthalpy change as a function of polystyrene (PS) concentration in dimethylformamide through a dynamic heating and quenching process were investigated. Cold crystallization, freezing and melting phenomena in a 10 wt% PS solution were all observed. Cold crystallization and melting phenomena were still observed in a 20 wt% solution. In a 30 wt% solution, all three phenomena disappeared without any solvent enthalpy changes, e.g., enthalpy changes at the melting temperature. The disappearance of both the melting temperature and the melting enthalpy change indicated that all polymer and solvent molecules in the 30 wt% solution existed only in the amorphous phase without any phase changes despite repeated heating and quenching processes. Thus, our results can provide a new approach for gelation through enthalpy changes and can be applied in the fabrication of porous membranes with a narrow distribution.

Dissolving Cellulose in 1,2,3-Triazolium- and Imidazolium-Based Ionic Liquids with Aromatic Anions.

We present 1,2,3-triazolium- and imidazolium-based ionic liquids (ILs) with aromatic anions as a new class of cellulose solvents. The two anions in our study, benzoate and salicylate, possess a lower basicity when compared to acetate and therefore should lead to a lower amount of N-heterocyclic carbenes (NHCs) in the ILs. We characterize their physicochemical properties and find that all of them are liquids at room temperature. By applying force field molecular dynamics (MD) simulations, we investigate the structure and dynamics of the liquids and find strong and long-lived hydrogen bonds, as well as significant – stacking between the aromatic anion and cation. Our ILs dissolve up to 8.5 wt.-% cellulose. Via NMR spectroscopy of the solution, we rule out chain degradation or derivatization, even after several weeks at elevated temperature. Based on our MD simulations, we estimate the enthalpy of solvation and derive a simple model for semi-quantitative prediction of cellulose solubility in ILs. With the help of Sankey diagrams, we illustrate the hydrogen bond network topology of the solutions, which is characterized by competing hydrogen bond donors and acceptors. The hydrogen bonds between cellulose and the anions possess average lifetimes in the nanosecond range, which is longer than found in common pure ILs.

Experimental and thermodynamic analyses of supercritical CO2-Solubility of minoxidil as an antihypertensive drug

A major challenge in the production of micro/nano-sized drug particulates is to understand the solubility behavior of the drug in a supercritical fluid (SCF). In the present study, solubility of Minoxidil, an antihypertensive drug, in SC-CO2 was measured statically under various sets of operating conditions in terms of temperature (308–338 K) and pressure (120–270 bar), leading to solubilities in the range of 0.24 × 10−6 to 3.39 × 10−6. Next, three different approaches were followed to estimate, rather than actually measure, the solubility, where models based on two equations of state (i.e., Soave–Redlich–Kwong (SRK) and Peng-Robinson (PR)) combined with either Wong-Sandler (WS) or van der Waals (vdW2) mixing rules, semi-empirical equations (Méndez-Santiago and Teja (MST), Bartle et al., Chrastil, Kumar and Johnston (K-J)), and the activity coefficient (UNIQUAC and modified Wilson models) were adopted to model the experimental data. The semi-empirical models were proved to be self-consistent upon performing the respective self-consistency tests. Eventually, results were devised to calculate estimates of the vaporization (ΔHvap), solvation (ΔHsol) and total enthalpies (ΔHtotal).

Solvation enthalpy of selected glymes in the mixtures of N,N-dimethylformamide with propan-1-ol or methanol at 298.15 K. The solvent contribution to the solvation enthalpy of glymes

The enthalpies of solution of monoglyme, diglyme, triglyme, tetraglyme, pentaglyme and hexaglyme in N,N-dimethylforamide+propan-1-ol mixtures have been measured at 298.15 K. The preferential solvation process of glymes molecules in the mixtures of N,N-dimethylformamide with methanol or propan-1-ol has been discussed. Then the contribution of DMF, PrOH, and MeOH to the solvation enthalpy of group (–CH2– and –O–) of glymes has been calculated. On the basis of the obtained data, the effect of the structural and energetic properties of the N,N-dimethylforamide+propan-1-ol mixtures on the solution enthalpy of glymes in this mixtures has been analyzed.

Thermodynamic Contribution of Water in Cryptophane Host-Guest Binding Reaction.

A detailed examination of binding thermodynamics is undertaken for the interaction between rubidium ion and a water-soluble cryptophane molecule using isothermal titration calorimetry. The equilibrium-binding quotient for this host-guest pair decreases with increasing product formation. When analyzed with a thermodynamic framework that considers water explicitly in the governing equation, the shift in equilibrium is ascribed to an unfavorable change in the free energy of solvation upon formation of the inclusion complex. A van't Hoff analysis of the binding data, as well as an observation of aggregation between inclusion complexes, suggests that charge-charge interactions between rubidium ion and the phenolate groups of the cryptophane host provide the driving force for association in water that overcomes a large and unfavorable change in solvent enthalpy.

Enhanced absorption separation of hydrofluorocarbon/hydrofluoroolefin refrigerant blends using ionic liquids

The separation of hydrofluorocarbons (HFCs) and hydrofluoroolefins (HFOs) from novel refrigerant blends will become essential to boost the recycling of these compounds and drastically reduce the emission of HFCs, which are powerful greenhouse gases. In this work, the use of ionic liquids (ILs) as solvent media is explored to perform the selective separation of HFC/HFO refrigerant mixtures composed of the HFCs R32 (difluoromethane) and R134a (1,1,1,2-tetrafluoroethane) and the HFO R1234yf (2,3,3,3-tetrafluoropropene). The low-viscosity IL 1-ethyl-3-methylimidazolium thiocyanate, [C2mim][SCN], is selected as separation agent to prove that small and non-fluorinated ILs, with lower hydrogen bonding capability than other ILs, can provide enhanced solubility selectivity and mass transport properties for the selective separation of HFC/HFO refrigerant blends. The phase behavior of IL-refrigerant systems is determined at temperatures between 283.15 and 313.15 K and pressures up to 0.7 MPa. Results are parametrized according to the NRTL activity model and the separation selectivity is assessed in terms of Henry’s law constants, solvation enthalpies and entropies, infinite dilution coefficients, Gibbs free energy of mixing, and ideal and noncompetitive selectivity. Results show superior HFC/HFO solubility selectivity in [C2mim][SCN] compared to other ILs due to unfavorable entropic effects that difficult the solvation of large molecules such as R1234yf.

Regression against Temperature of Gas–Liquid Chromatography Retention Factors. Van’t Hoff Analysis

The present work deals with the precise experimental determination of the gas–liquid chromatography (GLC) retention factors (k) in a sufficiently large temperature range to allow the calculation of the thermodynamic quantities associated with the sorption process. Once isothermal retention factors of three homologous series members of the type H-(CH2)n-Y (Y = CH3, OH, CN) were measured over a temperature range of about 110 K on a low-polar PDMS (HP-1) capillary column and checked for accuracy and precision by “arc plot” representation, the data were analyzed by applying different forms of the van’t Hoff relationship. We compared the linear versus nonlinear van’t Hoff plots representing situations characterized by ΔsolvCp° = 0, ΔsolvCp°≠ 0 = constant, and ΔsolvCp° = f(T), respectively (ΔsolvCp° represents the difference in isobaric heat capacity associated with movement of the analyte between the mobile and the stationary phase). The “logarithmic” and “quadratic” nonlinear van ‘t Hoff equations were shown to be more appropriate than the linear van‘t Hoff equation for determining enthalpy and entropy of solvation. Special attention was devoted to the fitting performance and extrapolation capability of models with nonzero ΔsolvCp°. By several metrics, the quadratic model exhibits better behavior in extrapolations yielding reasonable accuracy for retention time and/or enthalpy of solvation predictions at temperatures located below the experimental range.

Solvation Energy of Ions in a Stockmayer Fluid.

We calculate the solvation energy of monovalent and divalent ions in various liquids with coarse-grained molecular dynamics simulations. Our theory treats the solvent as a Stockmayer fluid, which accounts for the intrinsic dipole moment of molecules and the rotational dynamics of the dipoles. Despite the simplicity of the model, we obtain qualitative agreement between the simulations and experimental data for the free energy and enthalpy of ion solvation, which indicates that the primary contribution to the solvation energy arises mainly from the first and possibly second solvation shells near the ions. Our results suggest that a Stockmayer fluid can serve as a reference model that enables direct comparison between theory and experiment and may be invoked to scale up electrostatic interactions from the atomic to the molecular length scale.

Study of the solvation process of some pyrazole derivatives in three different solvents by solution calorimetry and IR spectroscopy: Unravelling solute-solvent interactions

The study of the relationship between intermolecular interactions present in the solvation process and the magnitude of thermodynamic properties is extended from imidazole to pyrazole derivatives. The enthalpies of solution of pyrazole, 3,5-dimethylpyrazole and 3,4,5-trimethylpyrazole were calorimetrically determined in the solvents water, methanol and acetonitrile. The enthalpy of solution values for the three compounds in the three solvents are endothermic and spontaneous with an increase in entropy. As in the case with imidazole derivatives, the formation of a solution of pyrazole derivatives creates liquids that are more structured thermodynamically. The enthalpy of sublimation for 3,4,5-trimethylpyrazole, which is not available in the literature, was determined by the Knudsen effusion method. The combination of these thermodynamic properties has allowed the corresponding enthalpies of solvation to be obtained for the three pyrazole derivatives in the three selected solvents. With the use of the Pierotti equations and the enthalpies of solvation, the enthalpies of cavity formation were calculated along with the corresponding solute-solvent enthalpies of interaction. The infrared spectra and molecular volumes, as estimated through the electronic density, were used to obtain molecular insights into the solvation sensible sites within the studied solute molecules. The discussion of the solvation process and enthalpies of interaction of the pyrazole derivatives is based on the molecular structural features of solutes, specific intermolecular interactions and protic or aprotic nature of the solvents. The use of any empirical parameters in the discussion of the results was avoided.

Temperature‐dependent vapor–liquid equilibria and solvation free energy estimation from minimal data

AbstractWe present a new strategy to estimate the temperature‐dependent vapor–liquid equilibria and solvation free energies of dilute neutral molecules based on only their estimated solvation energy and enthalpy at 298 K. These two pieces of information coupled with matching conditions between the functional forms developed by Japas and Levelt Sengers for near critical conditions and by Harvey for low and moderate temperature conditions allow the fitting of a piecewise function that predicts the temperature‐dependent solvation energy for dilute solutes up to the critical temperature of the solvent. If the Abraham and Mintz parameters for the solvent and solute are available or can be estimated from group contributions, this method requires no experimental data and can still provide accurate estimates with an error of about 1.6 kJ/mol. This strategy, which requires minimal computational resources, is shown to compare well with other methods of temperature‐dependent solvation free energy prediction.

Effect of Solvent Polarity on Enthalpies of Solvation of Ethylene Oxide Oligomers

The enthalpies of dissolution, ΔsolHm∞, and solvation, ΔsolvHm∞, of ether oligomers CH3O(CH2CH2O)nCH3 (n = 1–4) in ethyl acetate, pyridine, N,N-dimethylformamide, and acetonitrile have been determi...

Updated Abraham model correlations to describe enthalpies of solvation of solutes dissolved in heptane, cyclohexane and N,N-dimethylformamide

ABSTRACT A search of the published chemical and engineering literature found enthalpy of solution data for an additional 71, 39 and 46 organic compounds dissolved in heptane, cyclohexane and N,N-dimethylformamide, respectively. The newly retrieved enthalpy of solution data was converted to enthalpy of solvation values, ΔH solv, using standard thermodynamic relationships. Updated Abraham model correlations were derived for describing gas-to-heptane, gas-to-cyclohexane and gas-to-N,N-dimethylformamide enthalpies of solvation by combining the additional values to our existing heptane, cyclohexane and N,N-dimethylformamide ΔH solv databases. The updated Abraham model correlations for heptane, cyclohexane and N,N-dimethylformamide described the observed ΔH solv values to within overall standard deviations of less than 3 kJ/mole.

Sampling Solvation Free Energy of Electrolytic Solvents with 3D2PT

Interactions between biomolecules and their surrounding solvation environment contribute significantly to their stability and to the driving forces for complex formation and conformational change. However, exploring the impact of solvation on these processes requires a thorough quantification of thermodynamic contributions to changes in the free energy of the system. Microscopic details available in atomistic molecular dynamics simulations allow for the extraction of solvation enthalpies from pair-wise additive protein-water and water-water interactions relative to the bulk solvent. The 3D-2PT method developed in the Heyden lab at Arizona State University complements this information with an analysis of hydration water entropies obtained from an analysis of intermolecular vibrations. Both the solvation enthalpy and entropy are analyzed on three-dimensional grids with 0.5-1.0 Å resolution allowing for direct thermodynamic insights into local hydration sites at the protein-water interface.Here, the original 3D-2PT approach is expanded to include contributions of electrolytes to the solvation enthalpy, entropy and free energy. This is achieved in a mixed resolution approach, which considers the drastic differences in concentration between water (∼55 M) and electrolytes (∼0.15 M) and resulting statistics for local environments. In addition to an analysis of water and ion vibrations in their local coordination environments, the new analysis distinguishes solute-water, solute-ion, water-water, ion-ion and water-ion interactions and their contributions to the solvation enthalpy.

Solvation Thermodynamic Properties of Anionic and Natural Sulfate-Free Surfactant Molecules

Anionic surfactants such as sodium dodecyl sulfate (SDS) and sodium lauryl ether sulfates (SLES) are commonly used to provide the cleansing action in consumer products such as shampoos and body washes. While many are harsh on skin, anionic surfactants provide these products with excellent foaming and lather characteristics that are desired by consumers. Alternatively, sulfate-free natural surfactants, including sugar-based, amino acid-based and plant-based materials, are sustainable and readily biodegradable commodities have excellent skin mildness, yet are difficult to incorporate into personal cleansing formulations because of their impact on formulation stability, thickening and rheology. In order to better understand the origin of these diverse solvation properties which results in diverse mechanisms of micellar self-assembly and dynamics we performed extensive molecular dynamics simulations and free energy calculations on the two types of surfactant molecules. In this study, we have investigated the single surfactant hydration thermodynamic properties, such as solvation entropy, enthalpy, and free energy of SDS, SLES compounds, and sulfate-free Sodium Lauroyl Sarcosinate (SLSar) to look for molecular descriptors that correlate with harshness. If successful such work could provide for rapid screening of new surfactant candidates