Preferential Solvation Research Articles

Investigation on florasulam in aqueous blends including solubility, preferential solvation, thermodynamic properties and enthalpy–entropy compensation

The equilibrium solubility of florasulam in solvent mixtures (methanol/ethanol /n-propanol/propylene glycol (PG) + water) was determined experimentally by isothermal saturation method at 278.15 K to 323.15 K under 101.2 kPa. Both high temperature and low water content of solvent promoted the dissolution of florasulam. Under given conditions, the mole fraction of florasulam was greater in (n-propanol + water) than other three solvent mixtures. Besides, the solubility of florasulam was correlated with the Jouyban-Acree (J-A) model and van’t Hoff-Jouyban-Acree (V-J-A) model. The obtained average relative deviations (RAD) and root mean square deviations (RMSD) were no >4.04 % and 1.73 × 10-4. The calculated preferential solvation parameter δx1,3 was used to analyze the preferential dissolution of florasulam between water and alcohols from the molecular perspective. The result is that in the intervals 1 > xmethanol > 0.32, 1 > xethanol > 0.23 and 1 > xn-propanol > 0.19, the florasulam was preferentially dissolved by methanol/ethanol/n-propanol. In other concentration ranges, the florasulam was preferentially dissolved by water. The reason for the special existence of PG + water is that |δx1,3| < 1 × 10-2 and the dissolution of florasulam in it conformed to the uncertainty propagation rather than preferential solvation theory. The parameters (ΔsolHo, ΔsolGo, ΔsolSo, ΔtrGo, ΔtrHo and ΔtrSo) that could reflect the apparent and transfer thermodynamic properties were obtained. It was concluded that the solubility change of florasulam was dominated by entropy and the transfer of florasulam from pure water to mixtures was an exothermic process. Finally, the enthalpy–entropy compensation analysis further studied the mechanism of enthalpy and entropy in the dissolution process.

Bisacodyl in aqueous co-solvent solutions of isopropanol/methanol/ethanol: Solubility modeling, preferential solvation and density functional theory study

At the microscopic level, quantitative analysis of molecular surface was used to highlight the electrostatic properties of acidity/basicity of bisacodyl. The -C = O and -N = groups are the principal targets of electrophilic attack because they have the lowest global electrostatic potentials, ranging from −157.6 kJmol−1 to −144.8 kJmol−1. The Hirshfeld partition analysis-based independent gradient model was used to visually examine the weak interactions between bisacodyl and the solvents, including methanol, ethanol, isopropanol, and water. The isothermal shake-flask method was used to evaluate the bisacodyl solubility in three aqueous co-solvent blends of isopropanol, methanol, and ethanol, under 101.2 kPa. The solubility data of bisacodyl in neat methanol is increased from 5.507 to 44.86 to 10-4 when the temperature rose from 278.15 to 323.15 K, whereas it climbed from 1.134 to 17.94 to 10-4 in neat isopropanol. The solubility variation is mostly caused by solvent–solvent interactions, which are explained by the solubility parameter, and solute–solvent interactions, which are explained by the dipolarity-polarizability of the solute. Three models—the Jouyban-Acree model, the modified van't Hoff-Jouyban-Acree-model, and the modified Wilson model were used to analyze the connection between solubility and experimental temperature and cosolvent composition, producing the largest relative average deviation of 9.41%. At temperatures between 293.15 K and 313.15 K, the preferred solvation of bisacodyl was examined using a method based on inverse Kirkwood-Buff integrals. The preferred solvation parameters of bisacodyl had positive values in the medium and rich concentrations of isopropanol/NMP (taken from a published work)/methanol/ethanol, suggesting that bisacodyl was preferentially solvated by these solvents. A quartic polynomial formulation of the interaction term as a function of the Hildebrand solubility parameter using an EHSA was used to accurately describe the solubility of bisacodyl in the four solutions. The dissolution of bisacodyl was entropy-driven process in all solvent mixtures.

3,4,5-Trimethoxycinnamic acid in aqueous co-solvent solutions of isopropanol/acetone/methanol/ethanol: Solubility, preferential solvation and intermolecular interactions

Quantitative analysis of molecular surface was applied at the microscopic level to emphasize the electrostatic characteristics of acidity/basicity of 3,4,5-trimethoxycinnamic acid (TMCA). The primary sites of electrophilic and nucleophilic assault are the –C=O and >OH groups owing to global maximum and lowest electrostatic potentials of −155.5 kJmol−1 and +185.8 kJmol−1, respectively. Using the independent gradient model based on Hirshfeld partition analysis, the weak interactions between TMCA and solvent were visually inspected. The solubility of TMCA in four co-solvent blends, namely isopropanol + water, methanol + water, acetone + water and ethanol + water, was determined under 101.2 kPa by the isothermal shake-flask technique. As the temperature increased from 278.15 to 323.15 K, the TMCA solubility in neat methanol increased from 66.20 × 10−4 to 942.9 × 10−4; while in neat acetone, it increased from 175.1 × 10−4 to 555.1 × 10−4. Two solubility curves intersect at about 305.8 K. According to the research based on KAT- linear solvation energy relationships, the solvent–solvent interactions are mostly responsible for the solubility fluctuation. The relationship between solubility and experimental conditions was established using three models: the Jouyban–Acree model, the modified Wilson model, and the modified Jouyban–Acree-van't Hoff model, yielding the highest relative average deviation of 9.56 %. A technique based on inverse Kirkwood–Buff integrals was used to investigate the preferential solvation of TMCA at 298.15 K. The preferential solvation parameters of TMCA showed positive values in isopropanol/acetone/methanol/ethanol -medium and -rich compositions, indicating that isopropanol/acetone/methanol/ethanol preferentially solvated TMCA. Dissolution of TMCA in these aqueous cosolvent solutions was an endothermic process.

Exploring the Macroscopic Properties of Humic Substances Using Modeling and Molecular Simulations

Soil organic matter (SOM) is composed of a complex and heterogeneous mixture of organic compounds, which poses a challenge in understanding it on an atomistic level. Based on the progress of molecular dynamics simulations and our efforts to create molecular systems that resemble SOM, in this work, we expanded our knowledge of SOM through the use of humic substances (HSs). Specifically, we studied the standardized samples of HS of the International Humic Substances Society (IHSS). This society provided the elemental and organic composition used as input parameters for our Vienna Soil Organic Matter Modeler 2 (VSOMM2). We modeled and simulated different HS samples from various sources, including soil, peat, leonardite, and blackwater river. In order to compare between different HS, we reduced the organic composition information to two principal components, which are associated principally with the amount of carboxyl and aromatic groups in the HS, denominated as PCacid and PCarom, respectively. We performed a plethora of analyses to characterize the structure and dynamics of the systems, including the total potential energy, density, diffusion, preferential solvation, hydrogen bonds, and salt bridges. In general terms, at the water content value of 0.2, we observed that most properties depend on the carboxyl group protonation state. The Coulombic interactions from this ionic specie and the interaction with cations determine the overall behavior of the studied systems. Furthermore, the type of cations and the pH influence those properties. This study exemplifies the importance of molecular dynamics to explain macroscopic properties from the structure and dynamics of the molecules modeled, such as the interaction network, i.e., hydrogen bonds or salt bridges of molecules presented in the system and their mobility.

Solubility Modeling and Preferential Solvation of Benzamide in Some Pure and Binary Solvent Mixtures at Different Temperatures

Solubility Modeling and Preferential Solvation of Benzamide in Some Pure and Binary Solvent Mixtures at Different Temperatures

Preferential Solvation Study of Rosuvastatin in the {PEG400 (1) + Water (2)} Cosolvent Mixture and GastroPlus Software-Based In Vivo Predictions.

Rosuvastatin (RST) is a poorly water-soluble drug responsible for limited in vivo dissolution and subsequently low oral systemic absorption (poor bioavailability). The mole fraction solubility values of RST in various ratios of binary mixtures "{PEG400 (1) + water (2)}" at 298.15 K were employed to investigate the preferential solvation (PS) of RST (3) by the binary components. Moreover, the GastroPlus program predicted the drug dissolution/absorption rates, plasma drug concentration, and compartmental regional drug absorbed from a conventional tablet as compared to the RST-loaded (PEG400 + water) mixture (at x 1 = 0.5) in healthy subjects (considering the fast condition). Fedors' method was adopted to estimate the values of molar volume (314.8 cm3·mol-1) and Hildebrand solubility parameter (28.08 MPa1/2) of RST. The results of inverse Kirkwood-Buff integrals showed the PS of RST by PEG400 as observed in all studied ratios of the binary mixture. The highest PS value (δx 1,3 = 1.65 × 10-2) for RST by PEG400 was attained at x 1 = 0.5. Finally, the GastroPlus program predicted the maximum dissolution rate [20 mg within 15 min as compared to pure RST (1.5 mg within 15 min)]. Moreover, the program predicted increased in vivo oral absorption (1.2 μg/mL) and enhanced regional absorption (95.3%) of RST from upper segments of the gastrointestinal tract for the RST-loaded PEG400 + water mixture in humans as compared to conventional tablets (87.5% as total regional absorption and 0.88 μg/mL as in vivo absorption). Hence, the present binary system ferrying RST can be a promising strategy to control systemic dyslipidemia after oral or subcutaneous administration.

Composition of the Solvation Shell of the Selected Cyclic Ethers (1,4-Dioxane, 12-Crown-4, 15-Crown-5 and 18-Crown-6) in a Mixture of Formamide with Water at Four Temperatures

The solution enthalpy of 15-crown-5 and 18-crown-6 ethers in the mixture of formamide (F) and water (W) was measured at four temperatures: 293.15 K, 298.15 K, 303.15 K, 308.15 K. The standard molar enthalpy of solution, ΔsolHo, depends on the size of cyclic ethers molecules and the temperature. With increasing temperature, the values of ΔsolHo become less negative. The values of the standard partial molar heat capacity Cp,2o of cyclic ethers at 298.15 K have been calculated. The Cp,2o=f(xW) curve shape indicates the hydrophobic hydration process of cyclic ethers in the range of a high-water content in the mixture with formamide. The enthalpic effect of preferential solvation of cyclic ethers was calculated and the effect of temperature on the preferential solvation process was discussed. The process of complex formation between 18C6 molecules and formamide molecules is observed. The cyclic ethers molecules are preferentially solvated by formamide molecules. The mole fraction of formamide in the solvation sphere of cyclic ethers has been calculated.

Solvation effects on glyphosate protonation and deprotonation states evaluated by mass spectrometry and explicit solvation simulations.

Glyphosate is a widely used herbicide, and its protonation and deprotonation sites are fundamental to understanding its properties. In this work, the sodiated, protonated, and deprotonated glyphosate were evaluated in the gas phase by infrared multiple photon dissociation spectroscopy to determine the exact nature of these coordination, protonation, and deprotonation states in the gas phase. In this context, Natural Bond Orbital analyses were carried out to unravel interactions that govern glyphosate (de)protonation states in the gas phase. The solvent effect on the protonation/deprotonation equilibria was also investigated by implicit (Solvation Model Based on Density and polarizable continuum models) and explicit solvation models (Monte Carlo and Molecular Dynamics simulations). These results show that glyphosate is protonated in the phosphonate group in the gas phase because of the strong hydrogen bond between the carboxylic oxygen (O7) and the protonated phosphonate group (O8-H19), while the most stable species in water is protonated at the amino group because of the preferential interaction of the NH2 + group and the solvent water molecules. Similarly, deprotonated glyphosate [Glyp-H]- was shown to be deprotonated at the phosphonate group in the gas phase but not in solution, also because of the preferential solvation of the NH2 + group present in the other deprotomers. Therefore, these results show that the stabilization of the protonated amino group by the solvent molecules is the governing factor of the (de)protonation equilibrium of glyphosate in water.

The Group Contribution to the Function Derived from Density and Speed-of-Sound Measurements for Glymes in N,N-Dimethylformamide + Water Mixtures.

The density and speed of sound of pentaglyme and hexaglyme in the N,N-dimethylformamide + water mixture at four temperatures are presented. The limiting apparent molar volumes (VΦ,m0=Vm0), the isobaric molar thermal expansion (Ep,m0), the isentropic compressibility (κS), and the limiting partial molar isentropic compression (KS,Φ,m0 = KS,m0) were calculated. Changes in the values obtained from the physicochemical parameters, as functions of composition and temperature, were analyzed in terms of the molecular interactions and structural differentiation of the investigated systems. The hydrophobic hydration process of the studied glymes was visible in the area of high water content in the mixture. The hydration number of glymes in water at four temperatures was calculated and analyzed. The contribution of the -CH2- and -O- group to the functions describing the volume and acoustic properties of the investigated system was calculated. The calculated values of the functions analyzed using the group contribution are in agreement with the values obtained from the experimental data. Thus, such contributions are valuable for wide ranges of data, which can be used to analyze the hydrophobic hydration and preferential solvation processes, as well as to calculate the values of these functions for other similar compounds.

Building a molecular model for ion channel and transporter stability in membranes through a partnership of experiments and computation.

Ion channels and transporters are the molecular gatekeepers of biology, governing the passage of atoms and molecules in and out of cells. They provide essential nutrients for metabolism, eliminate waste, enable cell-to-cell communication and store the potential energy that fuels life. Yet, despite their overwhelming importance, we still lack a physical and molecular understanding of why membrane transport proteins form stable structures that enable their specific functions within the oil-filled environment of the lipid bilayer. Our lack of understanding here is well rationalized by the inherent challenge of measuring equilibrium reactions of membrane protein assembly in membranes, compounded by the complexity of the reaction solvent as a structured lipid bilayer. However, through a combination of novel experimental single-molecule microscopy approaches coupled with coarse-grained and all-atom computational modeling, we can now measure equilibrium constants of protein association in membranes and dissect out the important molecular contributions from the protein and surrounding membrane. Here, I present our results on two systems where reversible binding within membranes can be quantitatively assessed - the homodimeric CLC-ec1 chloride/proton antiporter and the dual-topology homodimeric Fluc fluoride ion channel. By combining experimental and computational studies, we identify a driving force for protein association that arises from state-dependent perturbation of the membrane structure and a mechanism for tuning dimerization stability by altering solvation energetics through preferential solvation. These results provide generalizable mechanisms that drive membrane protein assembly in membranes that are expected to apply to all ion channels and transporters.

Amine Hole Scavengers Facilitate Both Electron and Hole Transfer in a Nanocrystal/Molecular Hybrid Photocatalyst

A well-known catalyst, fac-Re(4,4'-R2-bpy)(CO)3Cl (bpy = bipyridine; R = COOH) (ReC0A), has been widely studied for CO2 reduction; however, its photocatalytic performance is limited due to its narrow absorption range. Quantum dots (QDs) are efficient light harvesters that offer several advantages, including size tunability and broad absorption in the solar spectrum. Therefore, photoinduced CO2 reduction over a broad range of the solar spectrum could be enabled by ReC0A catalysts heterogenized on QDs. Here, we investigate interfacial electron transfer from Cd3P2 QDs to ReC0A complexes covalently bound on the QD surface, induced by photoexcitation of the QD. We explore the effect of triethylamine, a sacrificial hole scavenger incorporated to replenish the QD with electrons. Through combined transient absorption spectroscopic and computational studies, we demonstrate that electron transfer from Cd3P2 to ReC0A can be enhanced by a factor of ∼4 upon addition of triethylamine. We hypothesize that the rate enhancement is a result of triethylamine possibly altering the energetics of the Cd3P2-ReC0A system by interacting with the quantum dot surface, deprotonation of the quantum dot, and preferential solvation, resulting in a shift of the conduction band edge to more negative potentials. We also observe the rate enhancement in other QD-electron acceptor systems. Our findings provide mechanistic insights into hole scavenger-quantum dot interactions and how they may influence photoinduced interfacial electron transfer processes.

Unveiling the effect and correlative mechanism of series-dilute electrolytes on lithium metal anodes

An emerging development direction for electrolytes is the utilization of low-concentration electrolytes (LCE, generally less than 0.5 M) owing to their promising properties such as better wetting ability, reduced costs, and fast electrochemical kinetics, which have been studied in several battery scenarios. However, the direct assessment of LCEs with Li metal anodes has not yet been done, which would provide new insights to high-energy-density rechargeable lithium metal batteries (LMBs). For this purpose, apparent cycling performances of Li metal anode (LMA) in series-diluted (0.1∼1.0 M) ether-based electrolytes are reported in this study with Li||Li and Li||Cu cells, showing the enhanced performances with the concentration increasing. Moreover, the concentration effect and the underlying mechanism are revealed in detail by using coordinated post-mortem analyses and theoretical simulations, demonstrating that the preferential solvent decomposition in LCEs induces the organic-dominant interfacial layer on LMAs. Such layer demonstrates low interface stability, causing poor cycling performance among various current densities in Li half cells. However, comprehensive results also indicate that LCEs are facing a good opportunity because of the fast interfacial charge transfer kinetics originating from the weak solvation nature. This work elucidates the roles of electrolyte concentration on the LMA and uncovers their correlative mechanism of series-diluted electrolytes. It is a certain breakthrough for this timely research to provide a comprehensive perspective for designing novel low-concentration electrolytes.

Solubility and Data Correlation of 2-Bromo-5-hydroxypyrazine in Four Cosolvent Mixtures and Ten Mono-Solvents from 278.15 to 323.15 K

The experimental solubility of 2-bromo-5-hydroxypyrazine dissolved in 10 mono-solvents (methanol, ethanol, isopropanol, N,N-dimethylformamide (DMF), n-propanol, acetonitrile, acetone, ethylene glycol (EG), propylene glycol (PG), water) and cosolvent mixtures of methanol + water, ethanol + water, isopropanol + water, and DMF + water was determined by the isothermal saturation method between 278.15 and 323.15 K at 101.2 kPa. The largest solubility was observed in DMF + 2-bromo-5-hydroxypyrazine for mono-solvent systems and in DMF + water for mixed solvent systems. The Jouyban–Acree model (J–A), van’t Hoff–Jouyban–Acree model (V–J–A), and Apelblat–Jouyban–Acree model (A–J–A) were utilized to correlate the 2-bromo-5-hydroxypyrazine solubility in mixtures, and the Apelblat model, van’t Hoff model, λh model, and Jouyban model were used to correlate the 2-bromo-5-hydroxypyrazine solubility in 10 mono-solvents. The preferential solvation of 2-bromo-5-hydroxypyrazine in mixed solvents was researched by calculation of δx1,3. This study presents insights into modulating the 2-bromo-5-hydroxypyrazine crystallization process and in understanding equilibrium behaviors in different solvents.

Exploring the role of preferential solvation in the stability of globular proteins through the study of ovalbumin interaction with organic additives

&lt;abstract&gt; &lt;p&gt;The impact of denaturing and stabilizing osmolytes on protein conformational dynamics has been extensively explored due to the significant contribution of protein solvation to the stability, function, malfunction and regulation of globular proteins. We studied the effect of two nonspecific organic molecules, urea, which is a conventional denaturant, and dimethyl sulfoxide (DMSO), which is a multilateral organic solvent, on the stability and conformational dynamics of a non-inhibitory serpin, ovalbumin (OVA). A differential scanning microcalorimetry (DSC) experimental series conducted in the phosphate buffer solutions containing 0–30% of additives revealed the destabilizing impact of both urea and DMSO in a mild acidic media, manifested in the gradual decrease of thermal unfolding enthalpy and transition temperature. These findings differ from the results observed in our study of the mild alkaline DMSO buffered solutions of OVA, where the moderate stabilization of OVA was observed in presence of 5–10% of DMSO. However, the overall OVA interaction patterns with urea and DMSO are consistent with our previous findings on the stability and conformational flexibility of another model globular protein, α-chymotrypsin, in similar medium conditions. The obtained results could be explained by preferential solvation patterns. Positive preferential solvation of protein by urea in urea/water mixtures mainly weakens the hydrophobic interactions of the protein globule and eventually leads to the disruption of the tertiary structure within the whole range of urea concentrations. Alternatively, under certain experimental conditions in DMSO/water mixtures, positive preferential solvation by water molecules can be observed. We assume that the switch to the positive preferential solvation by DMSO, which is shown to have a soft maximum around 20–30% DMSO, could be shifted towards lower additive concentrations due to the intrinsic capability of ovalbumin OVA to convert into a heat-stable, yet flexible set of conformations that have increased the surface hydrophobicity, characteristic to molten-globule-like states.&lt;/p&gt; &lt;/abstract&gt;

Evolution of vibrational bands upon gradual protonation/deprotonation of arsinic acid H2As(O)OH in media of different polarity.

This computational work is devoted to the investigation (MP2/def2-TZVP) of the geometry and IR parameters of arsinic acid H2AsOOH and its hydrogen-bonded complexes under vacuum and in media with different polarity. The medium effects were accounted for in two ways: (1) implicitly, using the IEFPCM model, varying the dielectric permittivity (ε) and (2) explicitly, by considering hydrogen-bonded complexes of H2As(O)OH with various hydrogen bond donors (41 complexes) or acceptors (38 complexes), imitating a gradual transition to the As(OH)2+ or AsO2- moiety, respectively. It was shown that the transition from vacuum to a medium with ε > 1 causes the As(O)OH fragment to lose its flatness. The solvent polar medium introduces significant changes in the geometry and IR spectral parameters of hydrogen-bonded complexes too: as the polarity of a medium increases, weak hydrogen bonds become weaker, and strong and medium hydrogen bonds become stronger; in the case of a complex with two hydrogen bonds cooperativity effects are observed. In almost all cases the driving force of these changes appears to be preferential solvation of charge-separated structures. In the limiting case of complete deprotonation (or conversely complete protonation) the vibrational frequencies of νAsO and νAs-O turn into νAs-O(asym) and νAs-O(sym), respectively. In the intermediate cases the distance between νAsO and νAs-O is sensitive to both implicit solvation and explicit solvation and the systematic changes of this distance can be used for estimation of the degree of proton transfer within the hydrogen bond.

Binding of carboxylate and water to monovalent cations.

The interactions of carboxylate anions with water and cations are important for a wide variety of systems, both biological and synthetic. To gain insight on properties of the local complexes, we apply density functional theory, to treat the complex electrostatic interactions, and investigate mixtures with varied numbers of carboxylate anions (acetate) and waters binding to monovalent cations, Li+, Na+ and K+. The optimal structure with overall lowest free energy contains two acetates and two waters such that the cation is four-fold coordinated, similar to structures found earlier for pure water or pure carboxylate ligands. More generally, the complexes with two acetates have the lowest free energy. In transitioning from the overall optimal state, exchanging an acetate for water has a lower free energy barrier than exchanging water for an acetate. In most cases, the carboxylates are monodentate and in the first solvation shell. As water is added to the system, hydrogen bonding between waters and carboxylate O atoms further stabilizes monodentate structures. These structures, which have strong electrostatic interactions that involve hydrogen bonds of varying strength, are significantly polarized, with ChelpG partial charges that vary substantially as the bonding geometry varies. Overall, these results emphasize the increasing importance of water as a component of binding sites as the number of ligands increases, thus affecting the preferential solvation of specific metal ions and clarifying Hofmeister effects. Finally, structural analysis correlated with free energy analysis supports the idea that binding to more than the preferred number of carboxylates under architectural constraints are a key to ion transport.

Solubility modeling, dissolution and solvation thermodynamics, and solute–solvent interactions of diflufenican in aqueous aprotic and protic cosolvents

Electrostatic characteristics of acidity and basicity of the diflufenican molecule were uncovered by examining the Hirshfeld surface and the electrostatic potential surface, respectively. When it comes to nucleophilic and electrophilic assault, the >NH, =O, and -O- groups are where it is at. Diflufenican-solvent interactions were shown using an independent gradient model based on Hirshfeld partition analysis. Under 101.2 kPa, the isothermal saturation technique was used to experimentally obtain the diflufenican solubility in mixtures of isopropanol/methanol + water and ethyl acetate + ethanol across the temperature range from 278.15 to 323.15 K. Diflufenican was more soluble in ethyl acetate + ethanol blends than alcohol + water blends at the same temperature and cosolvent composition. Maximum relative average deviation of 9.57 percent was obtained using the Jouyban-Acree and modified van't Hoff-Jouyban-Acree models of correlation. The literature-reported solubility of diflufenican in ethylene glycol (EG), ethanol, propylene glycol (PG), and N,N-dimethylformamide (DMF) + water, as well as our determined in ethyl acetate + ethanol and methanol/isopropanol + water at 298.15 K, were all investigated using an extended Hildebrand solubility parameter approach. The local mole fractions of diflufenican in the seven solutions were also investigated using the inverse Kirkwood-Buff integrals technique. Preferential solvation of diflufenican by PG, ethanol, DMF, methanol, and isopropanol in aqueous solutions and by ethyl acetate in ethyl acetate + ethanol solutions was observed. Diflufenican in aqueous EG mixes was not preferentially solvated by EG. Results and discussion of the enthalpy–entropy compensation features of dissolution were reached.

The dependence of degree of extraction treatment of diesel distillate from the content of preferential solvent - ionic liquid

One of the perspective directions of the employment of ionic liquids is using them as “green” preferential solvent in the process of extraction treatment of undesirable components (aromatic hydrocarbons, sulfur and resin compounds) from the composition of oil fractions. The process of extraction treatment of ionic liquid of various oil distillates may be reviewed as an alternative traditional method of treatment and additional way in the combination of extraction process with other treatment methods allowing combining the advantages of both methods. The paper presents the results of combined process of extraction treatment of hydraulically cleaned diesel fraction using as an extractant of ionic liquids synthesized based on the vinegar acid dipropyl and dibutilamines. It is shown that during step-by-step extraction treatment of ionic liquid of diesel distillate compared to the one-step process, relatively high degree of dearomatization and desulphurization of crude is achieved. In three-phase extraction treatment of diesel distillate with diropilammonium acetate and dibutillamonium acetate with ionic liquids, relatively high extraction capacity diropilammonium acetate of ionic liquids containing more voluminous cation fragment is specified.

Ursolic Acid and Oleanolic Acid Dissolved in Methanol/Acetone + Water Blends: Thermodynamic Solubility, Intermolecular Interactions, and Solvation Behavior

With the purpose of qualitative characterization of the electrostatic properties of the acidity and basicity of ursolic acid (UA) and oleanolic acid (OA), quantitative analyses of the molecular surface were employed in this contribution. The −OH and −COOH groups on the molecules of OA and UA took precedence over establishing hydrogen bonds with the solvents acetone/methanol/water. In addition, the intermolecular interactions of OA and UA with acetone/methanol/water were investigated using an independent gradient model based on the Hirshfeld partition of molecular density. In solutions of OA/UA dissolved in methanol/acetone/water, attractive interactions, including the hydrogen-bond force and van der Waals (vdW) force, occur. The shake-flask technique was applied to evaluate the equilibrium solubility of UA and OA in acetone + water and methanol + water at 101.2 kPa and elevated temperatures covering from 278.15 to 323.15 K. Solvent–solvent interactions accounted by the solubility parameter of solutions had a significant domination in the variability of solubility magnitudes. The van’t Hoff–Jouyban–Acree, Apelblat, and Jouyban–Acree models revealed a good correlation for the measured solubility, with a relative mean deviation of no more than 7.73%. The Kirkwood–Buff integral approach was utilized to determine the preferred solvation of UA and OA by solvent species. In both the rich- and intermediate-composition regions of methanol/acetone, UA or OA is preferentially solvated with positive preferential solvation parameters by methanol/acetone.

Solubility determination, hansen solubility parameter, solvent effect and preferential solvation of thenalidine in four aqueous binary mixtures

The equilibrium solubility of thenalidine in four solvent mixtures (ethanol + water, n-propanol + water, isopropanol + water, and N,N-dimethylformamide (DMF) + water) was studied using the isothermal saturation method at temperatures ranging from 278.15 to 323.15 K under 101.2 kPa. For the mixed systems, the increase in temperature was positively correlated with an increase in solute dissolution. Besides, the water content in the solvent was also a variable that cannot be ignored in the dissolution results. The solubility data in mixed solvents were correlated and calculated by Jouyban-Acree model (J-A), van’t Hoff-Jouyban-Acree model (V-J-A) and Modified Apelblat-Jouyban-Acree model (A-J-A). The largest values of the relative average deviation (RAD) and the root-mean-square deviation (RMSD) were 4.75 × 10−2 and 0.79 × 10−4, respectively. These values were obtained upon using n-propanol + water and DMF + water, respectively. The Hansen solubility parameter was effective for exploring the dissolution behavior of thenalidine in different solvents considering the interaction between solvent and solute molecules. Furthermore, the solvent effect related to thenalidine dissolution was evaluated through the KAT-LSER model, which indicated that the solute–solvent molecule interactions were critical. Finally, the derivation of the preferential solvation parameters (δx1,3) of thenalidine was achieved by the method of inverse Kirkwood–Buff integrals. For ethanol/n-propanol/isopropanol + water, the thenalidine was preferentially dissolved in ethanol/n-propanol/isopropanol within intervals of 1 > x1 > 0.24, 1 > x1 > 0.19 and 1 > x1 > 0.13, respectively. In contrast, thenalidine dissolved preferentially in water in other intervals. However, for DMF + water, |δx1,3| was less than 1 × 10−2, thus, the preferential solvation theory was not applicable for this system.