Effects of H/D-isotope substitution and temperature on the volume characteristics of tetra-n-butylammonium bromide dissolved in methanol and its D-isotopomers

Densities of Buⁿ ₄NBr solutions in MeOH, MeOD, and CD₃OH were measured at salt concentrations of up to 1.5 solvomolality units (nearly 2.63·10^–2 mole fraction) at 278.15, 288.15, 298.15, 308.15, and 318.15 K. The limiting partial molar volumes of Buⁿ ₄NBr dissolved in these alcohols were calculated. The isotope effects in the volume characteristics of the stoichiometric mixture of ions, [Buⁿ ₄N⁺ + Br^–], are mainly due to the vibrational changes in the solvent structure upon deuteration of different molecular fragments. Structural transformations in infinitely dilute solution of Buⁿ ₄NBr in methanol are governed by non-specific solvation of the symmetrical Buⁿ ₄N⁺ cation.     

Effect of H/D isotope substitution on polarizability of methanol molecules

The electron polarizabilities (α₀·10²⁴/cm³ molec.⁻¹) were estimated from the data on refractive indices and molar volumes of H/D isotopomers of methanol at 25 °C using the Lorentz-Lorentz formula: 3.265 (CH₃OH), 3.260 (CH₃OD), 3.235 (CD₃OH), and 3.231 (CD₃OD). A relationship between the isotope effects for α₀ and volume (packing) changes in the structure of liquid methanol induced by deuterosubstitution in the methanol molecule was proposed. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1927–1928, August, 2005.     

Solubility and preferential solvation of acetaminophen in methanol + water mixtures at 298.15 K

The equilibrium solubility of acetaminophen in methanol + water binary mixtures at 298.15 K was determined and correlated with the Jouyban–Acree model. Preferential solvation parameters by methanol (δx_1,3) were derived from their thermodynamic solution properties by means of the inverse Kirkwood–Buff integrals method. δx_1,3 values are negative in water-rich mixtures but positive in compositions from 0.32 in mole fraction of methanol to pure methanol. It is conjecturable that in the former case, the hydrophobic hydration around non-polar groups plays a relevant role in the solvation. The higher solvation by methanol in mixtures of similar cosolvent compositions and methanol-rich mixtures could be explained in terms of the higher basic behavior of this cosolvent.     

Thermodynamic investigations of sublimation, solubility and solvation of [4-(benzyloxy)-phenyl]acetic acid

Temperature dependences of solubility, saturated vapour pressure and crystal heat capacity of [4-(Benzyloxy)phenyl]acetic acid were determined. The solubility of this compound was investigated in n-hexane, buffered water solutions with pH 2.0 and 7.4 and n-octanol. The enthalpy of sublimation and vaporization as well as the fusion temperature were determined. Solvation and solubility processes have been analyzed. The thermodynamics of transfer processes from one buffer to another (protonation process), from buffers to 1-octanol (partitioning process), and from n-hexane to the applied solvents (specific interaction) have been calculated and compared to those of other NSAIDs. The relevant shares of specific and non-specific interactions in the process of solvation have been investigated and discussed.     

Effect of temperature on the H/D-isotope effects in the enthalpy of hydration of tetramethyl-bis-carbamide

The heats of dissolution of tetramethyl-bis-carbamide (the pharmaceutical Mebicarum) in H₂O and D₂O were measured at 288.15, 298.15, and 318.15 K using a sealed microcalorimeter with an isothermal shell. The error of measurements did not exceed 0.2%. The limiting molar enthalpies of dissolution Δ_sol H _n ^∞ and the H/D-isotope enthalpy effects of hydration δΔ_hydr H _n ^∞(H₂O → D₂O) were determined. Different effects of temperature on the pattern of variation of δΔ _hydr H _n ^∞ were found: when T ≤ 315 K, this value is positive and decreases with T, while for T ≥ 315 K, hydration of tetramethyl-bis-carbamide upon replacement of H₂O by D₂O progressively becomes less endothermic. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 715–717, April, 2006.     

Structural Peculiarities of Dioxane Media in H/D Isotope Effects of Water Solvation at 288.15K-318.15K

Using the data of precision densimetry measurements for diluted solutions of H₂O and D₂O in 1,4-dioxane (1,4-DX) at 288.15 K-318.15 K we calculated the limiting partial molar volumes of the H/D isotopomers of water in dioxane and the excess molar volumes of the stated systems. The water molecules dispersed in 1,4-DX form complexes H-bonded into associates whose packing coefficient slightly exceeds that of the structural aggregates in liquid H₂O and D₂O. It is concluded that the structure of 1,4-DX is loosened and concomitantly undergoes volume expansion caused by the water microimpurities. The differentiating temperature effect on the volume solvation effects of H₂O and D₂O in 1,4-DX has been found.Original Russian Text Copyright © 2004 by. E. V. Ivanov, E. Yu. Lebedeva, and V. K. Abrosimov__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 852–861, September–October, 2004.     

Solubility and preferential solvation of some non-steroidal anti-inflammatory drugs in methanol + water mixtures at 298.15 K

The equilibrium solubilities of naproxen (NAP), ketoprofen (KTP), and ibuprofen (IBP) in methanol + water binary mixtures at 298.15 K were determined and the preferential solvation parameters were derived by means of the inverse Kirkwood–Buff integrals (IKBI) method. These drugs are very sensitive to specific solvation effects. The preferential solvation parameters by methanol δx_1,3 are negative in water-rich mixtures but positive in compositions from 0.32 in mole fraction of methanol to pure methanol. It is conjecturable that in the former case the hydrophobic hydration around aromatic rings and/or methyl groups plays a relevant role in the solvation. The higher solvation by methanol in mixtures of similar co-solvent compositions and in methanol-rich mixtures could be explained in terms of the higher basic behaviour of this co-solvent interacting with the hydroxyl group of the drugs. Moreover, drug solubilities were correlated by using the modified nearly ideal binary solvent/Redlich–Kister model obtaining average percentage deviations (APDs) lower than 9.0%.     

氯化钙甲醇溶液中离子溶剂化作用的理论研究

利用红外光谱研究不同温度下CaCl2/甲醇溶液体系的溶剂化作用,结果表明在溶液中CaCl2以离子形式与甲醇发生溶剂化作用,且溶剂化数随温度升高而降低.通过密度泛函理论（DFT）在B3LYP/6-31G＊＊水平下对CaCl2/甲醇溶液中可能存在的配位构型进行结构优化及热力学性质的计算,说明了在CaCl2/甲醇溶液中各种配位构型存在的可能性,得出温度升高热力学数据的变化规律,解释了溶剂化数随温度升高而降低的趋势.进一步对各种可能配位构型的红外吸收频率进行计算并与实验结果进行比较,推断在CaCl2/甲醇溶液中主要存在的配位构型为[CaCl（CH3OH）n]＋和[Cl（CH3OH）n]-.     

Solvent isotope effects on the solubility of argon and pair interactions in aqueous solution of hexamethylenetetramine

The solubilities of gaseous argon in solutions of hexamethylenetetramine (hmta) in H₂O and D₂O were measured at different concentrations, at five temperatures in the range of 283–318 K, and at a partial gas pressure of 101325 Pa by microvolumetry with an accuracy of ≤0.3%. The standard Setchenov coefficients for argon solutions and the thermodynamic parameters of Ar-hmta pairwise interactions were calculated from the data on the solubility. Interactions between hydrated Ar and hmta molecules are characterized by mutual repulsions. The structural states of water in the hydration sphere of hmta and in the bulk of solution are substantially different. Due to the difference in the mechanisms of hydration of hmta and Ar, the addition of the first component leads to a decrease in the solubility of the second component. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No 8, pp. 1389–1394, August, 2000.     

Effect of polymer microstructure on solubility characteristics and interactions

The effect of polymer microstructure on the solubility characteristics and propensity for interactions of polybutadiene (PBD) has been studied by means of the general solvation equation using data reported by Alessi et al. An increase in the vinyl content from 8% to 69% did not affect the propensity of PBD to interact with and n electron pairs and with dipolar — polarisable probes. In contrast, the hydrogen-bond basicity decreased due to steric hindrance from the alkene side group.     

Solubility and preferential solvation of benzocaine in {methanol (1) + water (2)} mixtures at 298.15 K

The equilibrium solubility of benzocaine (BZC) in several {methanol (1) + water (2)} mixtures at 298.15 K was determined. Solubility values are expressed in mole fraction and molarity and were calculated with the Jouyban–Acree model. Preferential solvation parameters of BZC by methanol (δx_1,3) were derived from their thermodynamic solution properties using the inverse Kirkwood–Buff integrals method. δx_1,3 values are negative in water-rich mixtures (0.00 < x₁ < 0.32) but positive in the other mixtures (0.32 < x₁ < 1.00). To explain the preferential solvation by water in the former case, it is conjecturable that the hydrophobic hydration around non-polar groups of BZC plays a relevant role in the solvation. Moreover, the higher solvation by methanol in mixtures of similar cosolvent compositions and methanol-rich mixtures could be explained in terms of the higher basic behaviour of methanol regarding water.     

A morphometric approach for the accurate solvation thermodynamics of proteins and ligands

We have developed a versatile method for calculating solvation thermodynamic quantities for molecules, starting from their atomic coordinates. The contribution of each atom to the thermodynamic quantities is estimated as a linear combination of four fundamental geometric measures of the atomic species, which are defined by Hadwiger's theorem, and the coefficients reflecting their solvation properties. This treatment enables us to calculate the solvation free energy with high accuracy despite of the limited computational load. The method can readily be applied to macromolecules in an all‐atom molecular model, allowing the stability of these molecules' structures in solution to be evaluated. © 2013 Wiley Periodicals, Inc.     

Effect of ion solvation on the diffuse layer structure in mixed electrolytes

A “solvionic” model of a multicomponent electrochemical system (mixed electrolyte) is considered. An ion in the solution is considered as a point charge rigidly fixed inside its solvation shell. The corresponding equations for the diffuse layer on an ideally polarizable electrode are derived, and an effective method of their numerical solution is formulated. The calculations are performed in order to follow the changes in the diffuse layer structure with variations in the electrode charge and electrolyte composition. Far from the zerocharge potential of solution, the dependences of distributions of solution components over the diffuse layer on the electrode charge radically differ from those within the classic Gouy-Chapman theory. Analytical equations (asymptotics at large electrode charges) for concentrations of solvated ions in the plane of their maximum approach and for their “surface excesses” (diffuse adsorption) are determined. Results of numerical calculations for a 0.2 M LiCl + 0.05 M BaCl₂ solution are plotted.     

Solution thermodynamics and preferential solvation of triclocarban in {1,4-dioxane (1) + water (2)} mixtures at 298.15 K

The equilibrium solubility and preferential solvation of triclocarban in {1,4-dioxane (1) + water (2)} mixtures at 298.15 K was reported. Mole fraction solubility varies continuously from 2.85 × 10^–9 in neat water to 2.39 × 10^–3 in neat 1,4-dioxane. Solubility behaviour was adequately correlated by means of the Jouyban-Acree model. Based on the inverse Kirkwood-Buff integrals, preferential solvation parameters were calculated. Triclocarban is preferentially solvated by water in water-rich mixtures (0.00 < x₁ < 0.18) and also in 1,4-dioxane-rich mixtures (0.78 < x₁ < 1.00) but preferentially solvated by 1,4-dioxane in mixtures with similar solvent compositions.     

Equilibrium solubility,preferential solvation and apparent specific volume of sucrose in some {cosolvent (1) + water (2)} mixtures at 298.2 K

Sucrose is the most widely used sweetener in food and pharmaceuticals. Solubility data of this excipient in aqueous cosolvent mixtures is not abundant. Thus, the main objective of this research was to determine and correlate the equilibrium solubility of sucrose in some {cosolvent (1) + water (2)} mixtures at 298.2 K. Cosolvents were ethanol, propylene glycol and glycerol. Shaken flask method was used to determine isothermal solubility. Concentration measurements were performed by means of density determinations. Solubility of sucrose decreases non-linearly with the addition of cosolvent to water. By means of the inverse Kirkwood–Buff method it is shown that sucrose is preferentially solvated by cosolvent in water-rich mixtures but preferentially solvated by water in cosolvent-rich mixtures. Jouyban–Acree model correlates solubility values with the mixtures composition for all cosolvent systems. Moreover, apparent specific volume of sucrose was also calculated from density and compositions.     

Volumetric properties of mixtures of water and methanol H/D-isotopomers between 5 and 45°C

Densities of H/D-isotopomers mixtures of water (H₂O, D₂O) and methanol (CH₃OH, CD₃OH, CH₃OD, and CD₃OD) over the full range of compositions were measured at 5, 15, 25, 35, and 45°C. Results have been used to calculate molar volumes, excess molar volumes, apparent molar volumes, and isotope effects of the mixtures. The volumetric properties are discussed in terms of the structural changes in water-methanol solutions under the influence of isotope substitution.     

Solvatochromism and preferential solvation of Brooker's merocyanine in water–methanol mixtures

The excitation energy of Brooker's merocyanine in water–methanol mixtures shows nonlinear behavior with respect to the mole fraction of methanol, and it was suggested that this behavior is related to preferential solvation by methanol. We investigated the origin of this behavior and its relation to preferential solvation using the three‐dimensional reference interaction site model self‐consistent field method and time‐dependent density functional theory. The calculated excitation energies were in good agreement with the experimental behavior. Analysis of the coordination numbers revealed preferential solvation by methanol. The free energy component analysis implied that solvent reorganization and solvation entropy drive the preferential solvation by methanol, while the direct solute–solvent interaction promotes solvation by water. The difference in the preferential solvation effect on the ground and excited states causes the nonlinear excitation energy shift. © 2017 Wiley Periodicals, Inc.     

碱性热处理对豌豆蛋白结构及溶解性的影响

本文研究了碱性热处理(pH 12+60℃)对豌豆蛋白结构及溶解性的影响.单独碱处理(pH 12)和碱性热处理均不能改变豌豆蛋白的亚级结构,但圆二色谱和内源荧光结果显示两种处理方法能够引起豌豆蛋白的二级和三级结构发生变化.相比单独碱处理,碱性热处理能够更加显著地使豌豆蛋白的折叠结构展开,使原来埋于内部的疏水基团暴露出来,...     

沥青质杂环模型分子间相互作用及溶剂化效应的理论研究

重质油中沥青质组分易发生聚沉形成团簇,严重影响重质油的加工和利用效率,但目前对于沥青质聚沉的研究较少,其机理尚不明确。本文采用理论计算对沥青质杂环模型分子间相互作用和溶剂化效应进行研究,以此为重质油沥青质聚沉现象的研究及聚沉抑制剂的研发提供一定的数据和理论支持。(1)在M062X/6-31G(d)水平上,计算得到了11种由沥青质杂环分子片段组成的二元体系的全优化稳定构型,讨论分析了构型的几何结构、NBO电荷、Mulliken重叠布居、相互作用能和分子轨道能,得到了最稳定的两种构型。(2)在B3LYP/6-31G(d)水平上,运用SMD模型对沥青质大分子在13种溶剂中进行溶剂化效应的建模和理论计算,通过对静电溶剂化自由能(ΔGelec)、非静电溶剂化自由能(ΔGnonelec)、总溶剂化自由能(ΔGsolv)的分析可知,沥青质溶解性大小的关键在于溶剂对它的远程静电作用的大小。