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.     

Estimation of the volumetric water content in chrysanthemum tissues

Summary A method of estimating water in a neutron image was developed for cold neutron radiography, where the scanning method was applied to the plant sample at a beam port. The spectrum of the cold neutron beam as well as the effective cross section of water was determined to estimate the water thickness in chrysanthemum tissues. The resolution and contrast of the cold neutron radiography were sufficient for the estimation of the water thickness of fine veins in the chrysanthemum leaves. However, volumetric water content was overestimated when the sample shapes were cylindrical. This phenomenon can be explained by the reduction of the effect of neutron scattering from the sample when it is cylindrical.     

Synthesis of thiiranes from oxiranes in water using polymeric cosolvents

Poly(vinylamine) (PVA) and poly(allylamine) (PAA) were prepared and used as polymeric cosolvents. Oxiranes were converted efficiently to the corresponding thiiranes under mild reaction conditions in water with ammonium thiocyanate (NH₄SCN) using these polymeric cosolvents. The polymeric cosolvents are reusable.     

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%.     

Solubility and preferential solvation of indomethacin in 1,4-dioxane + water solvent mixtures

The solubilities of indomethacin (IMC) in 1,4-dioxane + water cosolvent mixtures were determined at several temperatures, 293.15–313.15 K. The thermodynamic functions: Gibbs energy, enthalpy, and entropy of solution and of mixing were obtained from these data by using the van’t Hoff and Gibbs equations. The solubility was maximal in 0.95 mass fraction of 1,4-dioxane and very low in pure water at all the temperatures. A non-linear plot of ΔH_soln ° vs. ΔG_soln ° with negative slope from pure water up to 0.60 mass fraction of 1,4-dioxane and positive beyond this up to 0.95 mass fraction of 1,4-dioxane was obtained. Accordingly, the driving mechanism for IMC solubility in water-rich mixtures is the entropy, probably due to water-structure loss around the drug non-polar moieties by 1,4-dioxane, whereas, above 0.60 mass fraction of 1,4-dioxane the driving mechanism is the enthalpy, probably due to IMC solvation increase by the co-solvent molecules. The preferential solvation of IMC by the components of the solvent was estimated by means of the quasi-lattice quasi-chemical method, whereas the inverse Kirkwood-Buff integral method could not be applied because of divergence of the integrals in intermediate compositions.     

Origin of the magic numbers of water clusters with an excess electron

Electron-bound water clusters [e(-)(H(2)O)(n)] show very strong peaks in mass spectra for n=2, 6, 7, and (11), which are called magic numbers. The origin of the magic numbers has been an enigma for the last two decades. Although the magic numbers have often been conjectured to arise from the intrinsic properties of electron-bound water clusters, we attributed them not to their intrinsic properties but to the particularly weak stability of the corresponding neutral water clusters (H(2)O)(n=2,6,7, and (11)). As the cluster size increases; this nonsmooth characteristic feature in stability of neutral water clusters is contrasted to the smooth increase in stability of e(-)-water clusters. As the magic number clusters have significant positive adiabatic electron affinities, their abundant distributions in atmosphere could play a significant role in atmospheric thermodynamics.     

NMR studies of preferential solvation of sodium cation in mixtures of N-methylformamide with water and some nonaqueous solvents

Sodium-23 NMR chemical shifts and linewidths have been measured for 0.1M NaClO₄ in binary mixtures of N-methylformamide (NMF) with a series of other solvents, as a function of the solvent mole fraction. The relative solvent composition at the isosolvation point, the mid-value of the Na-23 chemical shift between those measured in the respective pure solvents, reveals preferential solvation of the sodium cation in many cases. The isosolvation composition correlates well with the relative solvating abilities of the two solvents-as characterized by their donicities-provided that the cation-solvent interactions are of the hard-hard type and that they are not complicated by interionic interactions. The variation in the electric field gradient around the sodium nucleus, as the composition of the solvent changes, results in broadening of the resonance line. Maximum broadening occurs close to the solvent mole fraction corresponding to the isosolvation point.     

Ammoniated solvation of excess electrons on molecular surfaces

As previously asserted, we have proposed a set of hypothetical molecular surfaces that possessed an extended hydrogen‐bonded network on one of the sides and hydrogen atoms on the opposite side. The uneven distribution of the OH groups (which increases the total dipole moment of the system) coupled to the partial positive charge of the hydrogen atoms creates charge pockets capable of trapping excess electrons. In this work we consider the ability of ammonia (NH₃) in solvating excess electrons in charge pockets on molecular surfaces. The anions are stable with respect to vertical electron detachment, and serve as another example by which electrons can be solvated on molecular surfaces. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

A Gas-phase study of the preferential solvation of Mn2+ in mixed water/methanol clusters

The kinetic shift that exists between two competing unimolecular fragmentation processes has been used to establish whether or not gas-phase Mn(2+) exhibits preferential solvation when forming mixed clusters with water and methanol. Supported by molecular orbital calculations, these first results for a metal dication demonstrate that Mn(2+) prefers to be solvated by methanol in the primary solvation shell.     

Abnormal viscosimetric behavior of homopolymers in mixed solvents and preferential solvation

It is shown that the applicability of the Stockmayer–Fixman–Burchard plot is much more limited in the case of solvent–precipitant mixtures than in the case of pure solvents. The observed deviations can be explained by taking into account the variation of preferential solvation as a function of the molecular weight of the polymer. More precisely the average density of the segments in the region occupied by the coiled molecule seems to be the parameter governing both changes in viscosity and in preferential solvation.     

A procedure for predicting sorption equilibrium in ternary polymer systems from Flory–Huggins binary interaction parameters and the inversion point of preferential solvation

A procedure has been developed, based on the Flory–Huggins theory as generalized by Pouchlý, which permits the calculation of preferential (λ) and total (Y) sorption coefficients from previous information on the binary interaction parameters, χ, χ, and g₁₂(?₁₀) and on the mixture composition at which the sign of λ inverts. The expressions obtained were applied to 10 cosolvent polymer systems for which experimental values of λ and Y are known. Practically in all the studied systems, the theoretical predictions are in fair accordance with the experimental data.     

Predictability of properties in ternary n-alkane/butanone/poly(dimethylsiloxane) systems from flory-huggins binary interaction parameters and inversion point in preferential solvation

An empirical procedure has been developed, based on the Flory-Huggins theory as generalized by Pouchlý, which permits the calculation of preferential sorption coefficient, λ, and the total sorption term, Y, from previous information on the binary interaction parameters, χ_13′⁰, χ₂₃⁰ and g₁₂(φ₁₀) and of the mixture composition at which the sign of λ inverts. The obtained expressions were applied to seven cosolvent polymer systems, n-alkane/butanone/poly(dimethylsiloxane), for which experimental values of λ and Y are known. In all the studied systems, the theoretical predictions are in fair accord with the experimental data.     

Relation between preferential solvation and intrinsic viscosity of polymers in solvent mixtures

Preferential solvation and intrinsic viscosity measurements are reported for three systems: polystyrene + benzene + methanol, polystyrene + carbon tetrachloride + methanol, and poly(2-vinylpyridine) + ethanol + cyclohexane. Plots of the coefficient of preferential solvation λ′ as a function of variation of the segment density Δ_ρ for a given ternary system, give a single curve for a large range of molecular weight and solvent mixture composition. This correlation between λ′ and Δ_ρ is verified in previously published data.     

Determination of primary and secondary solvation numbers and binding constants based on the shift of a proton-transfer equilibrium resulting from hydrogen bonding solvation

We show how the shift in the equilibrium constant K _PT for formation of a proton-transfer adduct in a non-interactive solvent, upon addition of a second, hydrogen-bonding solvent S reveals the nature of the hydrogen bonding solvation process. Data are analyzed for the pentachlorophenoltriethylamine proton-transfer equilibrium in cyclohexane solvent, under-going solvation by the acidic alcohols, 2,2,2-trichloroethanol and 1,1,1,3,3,3-hexafluoro-2-propanol. K _PT vs. [S] data are fitted to a binding isotherm corresponding to two-stage solvation of both the adduct and the free amine. Stoichiometries and binding constants for both primary and secondary solvation of both solvated species are determined as adjustable parameters. Best fits correspond to both the adduct and free amine under-going primary solvation by one alcohol molecule (presumably at the oxygen and nitrogen lone-pairs, respectively) followed by secondary solvation by one to nine additional alcohol molecules, with binding constants ranging from 2100 M^–1, for primary solvation of the adduct by hexafluoro-2-propanol, down to 7 M^–1, for secondary solvation of the amine by trichloroethanol. We speculate that the secondary solvation numbers represent average sizes of hydrogen-bonded alcohol chains, nucleated by the enhanced basicity of the primary-solvation alcohol.     

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.     

Unified concept of solubilization in water by hydrotropes and cosolvents

In the present work hydrophobic dyes, i.e. disperse red 13 (DR-13; (2-[4-(2-chloro-4-nitrophenylazo)-N-ethylphenylamino]ethanol) and Jaune au gras W1201 (1H-indene-1,3(2H)-dione,2-(2-quinolinyl)), are solubilized in water with the help of different additives: acetone and 1-propanol as typical cosolvents, sodium xylene sulfonate (SXS) as a representative of a classical hydrotrope, sodium dodecyl sulfate (SDS) as a typical surfactant, and finally some "solvosurfactants" [ propylene glycol monoalkyl ether derivatives (CiPOj: i = 1, j = 1 and 3; i = 3, j = 1 and 2; i = 4 and tertio-butyl, j = 1) and 1-propoxy-2-ethanol (C3EO1)]. These solvosurfactants are short amphiphiles that do not form well-defined structures in water such as micelles. For all additives an exponential increase in the solubilizations of the two studied hydrophobic dyes was observed when their concentrations in water were increased. Except for the SDS solution, no difference in the overall shapes of the solubilization curves (dye solubility against additive concentration) was found. All the studied molecules were classified according to their hydrotropic efficiencies, i.e., their abilities to solubilize a hydrophobic, sparingly soluble compound in water. The volume of the hydrophobic parts of the studied additives, roughly evaluated by simple calculations, was found to influence strongly the hydrotropic efficiency; i.e. the larger the hydrophobic part of the additive, the better the hydrotropic efficiency. By contrast, the hydrophilic part carrying a charge or not is of minor importance. Taking the hydrophobic part of the molecules as the key parameter, the water solubilization efficiency of cosolvents, hydrotropes, and solvosurfactants can be described in a coherent way.     

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.