Correspondence between Spectral-Derived and Viscosity-Derived Local Composition in Binary Liquid Mixtures Having Specific Interactions with Preferential Solvation Theory

Local interactions between unlike molecules (1-2) in solution are commonly measured with spectroscopy and used to estimate local composition. Herein, a viscosity model based on preferential solvation (PS) theory is developed for aqueous and nonaqueous binary liquid mixtures containing a dipolar aprotic solvent that provides local composition considering the hydration or solvation shell around complex (1-2) molecules. Spectral-derived and viscosity-derived local composition distributions showed similar trends with bulk composition, and their correspondence is attributed to characteristics of the hydration or solvation shell. Viscosity-derived local compositions were consistent with literature molecular simulations, whereas spectral-derived local composition distributions contained artifacts. The PS viscosity model is also applicable to nonpolar-polar mixtures for which self-association occurs, and it can be used to estimate solvent mixture dipolarity/polarizability. Since the PS viscosity model only requires bulk viscosity, it may provide a means to estimate microviscosity or the solvent environment around biomolecules.

Preferential solvation bromophenol blue in water-alcohol binary mixture

In this study, the perichromic behavior of bromophenol blue (BPB) in various binary solvent mixtures was investigated. The binary mixtures considered were comprised of water and methanol (MeOH), ethanol (EtOH), n-propanol (n-PrOH), isopropanol (iso-PrOH) or t-butanol (t-BuOH). The investigation of a preferential solvation model that considers the addition of small quantities of alcohol to water in the presence of bromophenol blue (BPB) is described in this paper. The data obtained were employed to study the preferential solvation (PS) of the probe. It was observed that with increases in the molar fraction of water the spontaneity of the system decreases. This can be explained by the high solubility of BPB in ethanol, with ∆G > 0 at higher wavelengths (region rich in water with violet solution) and ∆G < 0 at lower wavelengths (region rich in alcohol with yellow solution). The pK of the binary mixture changed in all solvents and for all ratios, and the higher the water ratio is the lower the pK_In will be. In binary mixture, an increase in the hydrogen bond acceptor (HBA) nature of the solvents tested resulted in a bathochromic effect on the absorption band of BPB (Δλ = 12 nm). All of the data obtained showed a good nonlinear fit with the mathematical model (SD ≤ 6.6 × 10^-3), suggesting that BPB has other potential applications besides its use as a pH indicator.

Investigation of Solvent Effects on the Reaction of 1-Fluoro-2,4-Dinitrobenzene with Aniline in Molecular-Molecular and Ionic Liquid–Molecular Solvent Mixtures

The solvent effects on the reaction of 1-fluoro-2,4-dinitrobenzene with aniline was studied in various compositions of molecular-molecular solvent mixtures and molecular solvent-2-hydroxyethylammonium formate mixtures as media containing an ionic liquid. A mounting trend with the mole fraction of water in aqueous solution of alcohols up to a maximum at a mole fraction of 0.9 with respect to water was found, but a mild decrease with the mole fraction of ethyl acetate in methanol–ethyl acetate mixtures. A similar increasing trend was observed with increasing methanol, ethanol, 2-propanol and dimethylsulfoxide content in the mixtures containing the ionic liquid. Solvent effect investigations based on linear free energy relationship confirm that polarity has a major effect in molecular-molecular solvent mixtures, whereas polarity and hydrogen–bond acceptor ability were the dominant factors on reaction rate in molecular-ionic solvent mixtures. A nonlinear free energy relationship based on the preferential solvation hypothesis showed differences between the microsphere solvation of the solute and the bulk composition of the solvents. In these mixtures, the intermediate of the reaction was preferentially solvated by the ionic liquid.

Changes in the SNAr reaction mechanism brought about by preferential solvation

For model S_NAr reactions in mixtures of acetonitrile and water, we found preferential solvation in favor of the aqueous phase.

Preferential solvation and solvation shell composition of free base and protonated 5, 10, 15, 20-tetrakis(4-sulfonatophenyl)porphyrin in aqueous organic mixed solvents

The solvatochromic properties of the free base and the protonated 5, 10, 15, 20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) were studied in pure water, methanol, ethanol (protic solvents), dimethylsulfoxide, DMSO, (non-protic solvent), and their corresponding aqueous-organic binary mixed solvents. The correlation of the empirical solvent polarity scale (E(T)) values of TPPS with composition of the solvents was analyzed by the solvent exchange model of Bosch and Roses to clarify the preferential solvation of the probe dyes in the binary mixed solvents. The solvation shell composition and the synergistic effects in preferential solvation of the solute dyes were investigated in terms of both solvent-solvent and solute-solvent interactions and also, the local mole fraction of each solvent composition was calculated in cybotactic region of the probe. The effective mole fraction variation may provide significant physico-chemical insights in the microscopic and molecular level of interactions between TPPS species and the solvent components and therefore, can be used to interpret the solvent effect on kinetics and thermodynamics of TPPS. The obtained results from the preferential solvation and solvent-solvent interactions have been successfully applied to explain the variation of equilibrium behavior of protonation of TPPS occurring in aqueous organic mixed solvents of methanol, ethanol and DMSO.

Solvent Polarity, Hydrogen-Bonding and Solvophobicity Effects on the Nucleophilic Substitution of Benzenesulfonyl Chloride with Aniline in Aqueous and Non-Aqueous Solutions of Methanol

The reaction between benzensulfonyl chloride and aniline was studied in various compositions of methanol with ethyl acetate, propan-2-ol and water at 25° C. Second-order rate coefficients of this reaction were determined; those in pure solvents were in the order of water > methanol >propan-2-ol> ethyl acetate. Rates decreased sharply with the mole fraction of ethyl acetate in methanol- ethyl acetate mixtures and showed an increasing trend with water content in methanol-water mixtures. Linear free energy relationship regressions showed that the polarity, hydrogen-bond donor ability and hydrophobicity of the media were the main factors affecting the reaction rate coefficient.

Use of a Solvatochromic Probe for Study of Solvation in Ternary Solvent Mixture

Solvation characteristics of 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridino)phenolate in completely miscible ternary solvent mixtures (viz., methanol + acetone + water, methanol + acetone + benzene, and methanol + chloroform + benzene) have been studied by using an electronic spectroscopic procedure. The transition energy (E) corresponding to the charge-transfer band maximum of the solute in a ternary solvent mixture differs significantly from the average E-values in the component solvents weighted by the mole fraction of the solvents. A two-phase model of solvation has been invoked to explain the results. The excess or deficit of solvent components in the local region of the solute molecule over that in the bulk has been estimated using the knowledge of solvation in binary solvent mixtures.

Pyridinium N-phenolate betaine dyes as empirical indicators of solvent polarity: Some new findings

Solutions of the zwitterionic betaine dye 4-(2,4,6-triphenylpyridinium-1-yl)-2,6-di- phenylphenolate are solvatochromic, thermochromic, piezochromic, and halochromic. That means the position of its longest-wavelength intramolecular charge-transfer absorption band depends on solvent polarity, solution temperature, external pressure, and the nature and concentration of added salts. The extraordinarily large negative solvatochromism of this standard betaine dye has been used to establish UV/vis spectroscopically an empirical scale of solvent polarity, called ET(30), respectively ETN scale, meanwhile known for many organic solvents and solvent mixtures. In this review, the solvatochromic properties of some new hydrophilic and lipophilic betaine dyes with better solubility in water (respectively, nonpolar solvents), as well as some recent applications of these betaine dyes in various fields of interest [e.g., microheterogeneous (micellar) and polymer solutions, chemical sensors, as well as surface polarity of silicas, aluminas, and cellulose derivatives] are described.

Role of hydroxyl concentrations in solvatochromic measures of solvent polarity of alcohols and alcohol–water mixtures—evidence that preferential solvation effects may be overestimated

For single solvents, primary alcohols and water, there is a good linear correlation (r = 0.994) between the solvent polarity index ET(30) and the molar concentration of OH groups (or 1000/Vm, where Vm is the solvent molar volume). The corresponding correlations for alcohol-water mixtures are plots vs. the sum of molar concentrations of alcohol and water, alternatively expressed as plots of ET(30)vs. volume fraction. Our quantitative treatment is an extension of recent theoretical and experimental results. In contrast, previous studies of alcohol-water mixtures have relied on plots of ET(30)vs. mole fraction, and have overestimated the effect of preferential solvation of solvatochromic dyes by the more hydrophobic alcohols.

Study of the preferential solvation of some betaine dyes in binary solvent mixtures

The preferential solvation (PS) in mixed binary solvents, e.g. dichloromethane/acetonitrile, dichloromethane/methanol, acetonitrile/water has been studied by monitoring the charge transfer band of some betaine dyes. Since PS accounts for dielectric as well as specific interactions while dielectric enrichment only for the former, it was shown that in the case of dichloromethane/methanol, hydrogen bonding precedes dielectric enrichment whereas in the case of acetonitrile/water the inverse is true.