Binary Aqueous-organic Solvent Research Articles

Comments on “Study on 2-amino-4-chloro-6-methoxypyrimidine in four binary solvent mixtures: Solubility measurement, calculation, preferential solvation and extended Hildebrand solubility parameter approach analysis”

A polemic is given regarding the apparent Gibbs energies of dissolution reported by Huang and Yao for 2-amino-4-chloro-6-methoxypyrimidine dissolved in four binary aqueous-organic solvent mixtures at the harmonic mean temperature. Our reanalysis of the authors’ experimental mole fraction solubility data yielded positive values, rather than negative values, for the apparent Gibbs energies of dissolution.

Catalytic Oxidation of Ethylene in Solutions of Palladium(II) Cationic Complexes in Binary and Ternary Aqueous Organic Solvents

Catalytic Oxidation of Ethylene in Solutions of Palladium(II) Cationic Complexes in Binary and Ternary Aqueous Organic Solvents

The Colorimetric Signaling of Water Content by a Deprotonated Schiff Base in some Aprotic Organic Solvents

AbstractA simple Schiff base, (E)‐2‐[1‐{2‐(2,4‐dinitrophenyl)hydrazono}ethyl]phenol (Hdph) and its deprotonated form, (E)‐1‐(2,4‐dinitrophenyl)‐2‐{1‐(2‐hydroxyphenyl)ethylidene} hydrazine‐1‐ide (dph) have been synthesized and characterized by various physicochemical and spectroscopic techniques. Their structures have also been determined by single‐crystal X‐ray crystallography. The dph has been utilized as a colorimetric probe for the signaling of water content in some water‐miscible aprotic organic solvents (acetonitrile and tetrahydrofuran). The dph reveals a pronounced colorimetric behavior in response to the variation of water content in these solvents. Significant changes in UV‐visible absorption spectra permit a ratiometric analysis of the signaling behavior. The spectral changes are pronounced for the water content of less than 10 %, which is suitable for the application of dph as a receptor for the determination of water content in binary aqueous organic solvents having lower water content. The limit of detection (LOD) for water content in acetonitrile and tetrahydrofuran is calculated as 0.20 % and 0.28 %, respectively.

The impact of mixed solvents on the complexation thermodynamics of Eu(III) by simple carboxylate and amino carboxylate ligands

To gain insight on the role of mixed solvents on the thermodynamic driving forces for the complexation between trivalent f-elements and organic ligands, solution phase thermodynamic parameters were determined for Eu(III) complexation with 2-hydroxyisobutyric acid (HIBA) and 2-aminoisobutyric acid (AIBA) in mixed methanol (MeOH)-water and N,N-dimethylformamide (DMF)-water solvents. Included in this study were the determination of mixed solvent autoprotolysis constants (pKs) as well as the thermodynamic formation constants: log β, ΔG, ΔH, and ΔS, for ligand protonation and Eu(III)-ligand complexation utilizing potentiometry and calorimetry techniques. The results presented are conditional thermodynamic values determined at an ionic strength of 1.0M NaClO4 and a temperature of 298K. It was found that moving from an aqueous solution to a binary aqueous-organic solvent affected all solution equilibria to some degree and that the extent of change depended on both the type of mixed solvent and the ligand in each study. The ability to understand and predict these changes in thermodynamic values as a function of solvent composition provides important information about the chemistry of the trivalent f-elements.

Commentary on “Measurement and correlation of solubility of 1,3,5-trioxane in binary solvents from (288.15 to 328.15) K”

Combined Nearly Ideal Binary Solvent/Redlich-Kister (CNIBS/R-K) equations reported by Li and coworkers [J. Mol. Liq. 234 (2017) 469–480] for calculating the solubility of 1,3,5-trioxane in four binary aqueous-organic solvent mixtures do not describe the solute's observed solubility in the water mono-solvent. Failure of the published CNIBS/R-K expressions result because the authors did not measure the aqueous solubility of 1,3,5-trioxane. No aqueous solubility data were included in the regression analyses used in determining the numerical values of the equation coefficients. New CNIBS/R-K equations are derived by combining the measured solubility determined by Li and coworkers with previously published solubility data for 1,3,5-trioxane in water taken from the chemical literature.

Intriguing Tautomerism of Lumichrome in Binary Aqueous Solvent Mixtures: Implications for Probing Microenvironments.

The water-assisted tautomerism of lumichrome (LC) in binary aqueous-organic solvent mixtures exhibits intriguing spectroscopic features. An especially striking and novel observation is the occurrence of an induction period or lag time for the evolution of the isoalloxazine form of LC from the excited alloxazine form. It is inferred that the observed lag time provides an overview of the changing H-bond network of the surrounding water molecules, at various compositions of the mixed solvent systems. The unique spectral changes for the water-assisted tautomerization of LC, along with the observed lag times, can offer exciting prospects for the use of LC as a promising site-specific probe, to examine complex aqueous microenvironments and active biological systems.

Determination of Abraham model solute descriptors and preferential solvation from measured solubilities for 4-nitropyrazole dissolved in binary aqueous-organic solvent mixtures

ABSTRACTAbraham model solute descriptors are determined for 4-nitropyrazole based on published solubility data for 4-nitropyrazole dissolved in binary aqueous-methanol and aqueous-ethanol solvent mixtures at 298.15 K. The calculated solute descriptors enable the solubility of 4-nitropyrazole to be estimated in more than 80 different organic solvents. Also calculated from the published solubility data are the preferential solvation parameters, obtained from the inverse Kirkwood–Buff integrals, for describing the solvent distribution around the dissolved 4-nitropyrazole solute molecule.

Thermodynamic functions of solvation of benzene in various binary aqueous-organic solvents

Composition dependences of the thermodynamic functions of solvation in various aqueous-organic mixtures are studied. Limiting activity coefficients and solvation Gibbs free energies of benzene in the mixtures of water with acetone, 1,4-dioxane, dimethyl sulfoxide, and tert-butanol with different compositions at 298K were determined. The results were combined with literature data for the enthalpies of solution in these mixtures and known values of thermodynamic functions of solvation of benzene in several other aqueous-organic solvents. We observed general tendencies of nonlinear enthalpy-entropy compensation, preferential solvation, and existence of a critical composition of the mixtures when the maximum of ΔsolvH and the bend in ΔsolvG vs ΔsolvH plot are observed. The nature of both organic cosolvent and solute influences the concentration of water corresponding to this critical composition. For benzene, it lies between 0.75 and 0.95 mole percent of water in all considered systems. In the same range of compositions, extrema of many other properties of aqueous-organic mixtures were observed. It is concluded that at these compositions, solvation in the mixture is characterized with the highest enthalpy cost of reorganization of binary solvent upon insertion of solute molecules and diminishment of the hydrophobic effect.

A thermodynamic study of reactions of amino acids with crown ethers in nonaqueous media as examples of guest—host molecular complex formation

Our findings and the literature data on the effect of binary aqueous organic solvents on the enthalpy and entropy of molecular complexation reactions of 18-crown-6 with glycine, D, L-alanine, and L-phenylalanine and on the stability of the resulting complexes were reviewed. The relationships between the thermodynamic parameters of the complexation reactions and the reactant solvation were analyzed to reveal the key factors that are crucial for the stability of the complexes and the increasing exothermicity of the processes under study in water—ethanol, water—DMSO, and water—acetone. The changes in the stability of 18-crown-6 complexes with amino acids were assumed to be predicted from the Gibbs energy changes in the transsolvation of the amino acids. This criterion was proposed as a basic thermodynamic parameter for estimating the changes in the stability of 18-crown-6 complexes with peptides and ammoniumtype cations (structurally related to amino acids) when the composition of the binary aqueous organic solvent is varied.

The structural effect of some 1,3,4-oxadiazoles and 1,2,4,5-tetrazines on their thermodynamic characteristics of adsorption from aqueous organic solutions on phenyl-bonded silica gel

The thermodynamic characteristics of adsorption of substituted 1,3,4-oxadiazoles and 1,2,4,5-tetrazines from aqueous organic solutions on phenyl-bonded silica gel were determined in the Henry region via the method of high-performance liquid chromatography. The influence of the structure of the studied compounds on their thermodynamic characteristics of adsorption from binary aqueous organic solvents of different natures was examined. The correlation dependences of the standard differential molar changes in the Gibbs energy, enthalpy, and entropy of adsorption on the van der Waals surface area and reduced dipole moment of molecules of the examined compounds were found. The main factors in optimization of the separation techniques and adjustment of the adsorption selectivity of phenyl-bonded silica gel were determined under conditions of reversed-phase high-performance liquid chromatography.

Effects of Organic Solvents on the Barrier Properties of Human Nail

The effects of organic solvent systems on nail hydration and permeability have not been well studied. The objectives of the present study were to investigate the effects of binary aqueous organic solvent systems of ethanol (EtOH), propylene glycol (PPG), and polyethylene glycol 400 (PEG) on the barrier properties of nail plates. 3H–water, 14C–urea, and 14C–tetraethylammonium ions were the probes in the nail uptake and transport experiments to study the effect(s) of organic solvents on nail hydration and permeability. Gravimetric studies were also performed as a secondary method to study nail hydration and the reversibility of the nail after organic solvent treatments. Both ungual uptake and transport were directly related to the concentration of the organic solvent in the binary systems. Partitioning of the probes into and transport across the nail decreased with an increase in the organic solvent concentration. These changes corresponded to the changes in solution viscosity and the barrier properties of the nail. In general, the effects for PPG and PEG were more pronounced than those for EtOH. Practically, these results suggest that organic solvents in formulations can increase nail barrier resistivity. © 2011 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 100:4244–4257, 2011

Composition, Structure, and Mobility of Water−Acetonitrile Mixtures in a Silica Nanopore Studied by Molecular Dynamics Simulations

To investigate the effect of the nanoscale confinement on the properties of a binary aqueous-organic solvent mixture, we performed molecular dynamics simulations of the equilibration of water-acetonitrile (W/ACN) mixtures between a cylindrical silica pore of 3 nm diameter and two bulk reservoirs. Water is enriched, and acetonitrile is depleted inside the pore with respect to the bulk reservoirs: for nominal molar (~volumetric) ratios of 1/3 (10/90), 1/1 (25/75), and 3/1 (50/50), the molar W/ACN ratio in the pore equilibrates to 1.5, 3.2, and 7.0. Thus, the relative accumulation of water in the pore increases with decreasing water fraction in the nominal solvent composition. The pore exhibits local as well as average solvent compositions, structural features, and diffusive mobilities that differ decidedly from the bulk. Water molecules form hydrogen bonds with the hydrophilic silica surface, resulting in a 0.45 nm thick interfacial layer, where solvent density, coordination, and orientation are independent of the nominal W/ACN ratio and the diffusive mobility goes toward zero. Our data suggest that solute transport along and across the nanopore, from the inner volume to the interfacial water layer and the potential adsorption sites at the silica surface, will be substantially different from transport in the bulk.

Micellization of Cetyl Triphenyl Phosphonium Bromide Surfactant in Binary Aqueous Solvents

AbstractThe effect of the different binary aqueous organic solvents viz. 1,4‐dioxane, acetonitrile, dimethylsulfoxide, ethylene glycol, and methanol, on the micelle formation and thermodynamics of a cationic surfactant cetyl triphenyl phosphonium bromide has been studied conductometrically at 298–318 K. From the conductivity data critical micelle concentration, degree of counter ion dissociation (α) and thermodynamic parameters of micellization have been determined. It is observed that micellization tendency of the surfactant decreases in the presence of binary aqueous solvents. The entropies of micellization are all positive, and they compensate the enthalpies of the process.

Determination of itraconazole and hydroxyitraconazole in human serum and plasma by micellar electrokinetic chromatography

The electrokinetic separation of the hydrophobic antimycotic drug itraconazole (ITC) and its major metabolite, hydroxyitraconazole (HITC), by a binary aqueous–organic solvent medium containing sodium dodecylsulfate, by microemulsion electrokinetic chromatography (MEEKC) and by micellar electrokinetic chromatography (MEKC) was studied. The results suggest that the first approach is difficult to apply and that there is no substantial difference between separations performed using MEEKC and MEKC modified with n-butanol. The simpler MEKC method is more than adequate and was thus employed for the analysis of ITC and HITC in human serum and plasma. Separation was achieved in plain fused-silica capillaries having a low-pH buffer (pH 2.2) with sodium dodecyl sulfate micelles and reversed polarity. The addition of 2-propanol and n-butanol enhanced analyte solubility and altered the selectivity of the separation by influencing the magnitude of the electrophoretic component in the separation mechanism. Under optimised conditions and using head-column field-amplified sample stacking, an internal standard, ITC and two forms of HITC could be separated in under 9 min, with detection limits less than 0.01 μg/mL. Analysis of samples from patients currently prescribed ITC revealed a different HITC peak area ratio to that of the standards, suggesting a stereoselective component of ITC metabolisation. Comparison of MEKC data with those of a HPLC method employed on a routine basis showed excellent agreement, indicating the potential of this approach for therapeutic drug monitoring of ITC.

Influence of organic solvent on the behaviour of camphor and α-pinene enantiomers in reversed-phase liquid chromatography systems with α-cyclodextrin as chiral additive

Reversed-phase liquid chromatography has been applied in order to gain insight into the α-cyclodextrin (α-CD)–solute complexation process, which occurs in the aqueous mobile phases containing a secondary achiral modifier. The model compounds tested were (±)-camphor and (±)-α-pinene. Methanol, ethanol, and 1 or 2-propanol were used as secondary modifiers. Retention factors and enantioseparation factors have been determined on a RP 18 stationary phase as a function of the α-CD concentration, secondary modifier content, and temperature changes. The shortest retention and the best separation of studied compounds were achieved for aqueous–methanol eluents. Apparent stability constants in various binary aqueous–organic solvent mixtures have been evaluated for α-CD complexes of camphor enantiomers. Using the competition concept, values for the stability constants in pure water have been calculated. It has been found that: (1) the quotient of the stability constants for both enantiomers, denoted as absolute enantioselectivity E, always remains constant at a fixed value ( E≅1.9), which may indicate that the complex composition does not change, (2) only the first step in the complexation process is altered by changing the solvent, which does not seem to affect the separation of the enantiomers, (3) the remarkable enantioselectivity that is observed results from the second step in the complexation process, (4) enthalpy changes are much more favourable for camphor–α-cyclodextrin complex formation than for the transfer of camphor to the stationary phase, which means that complexation dominates over adsorption and retention is shorter at lower temperatures, (5) the difference in free energy changes of complexation (ΔΔ G) between the enantiomers of camphor is about 1.5 kJ/mol at 20°C.

Determination of flufenamic and mefenamic acids in pharmaceutical preparations using organized media

The fluorescence properties of flufenamic (FF) and mefenamic (MF) acids were obtained in aqueous and binary aqueous–organic solvents with and without α- and β-cyclodextrins (CDs). In addition, the spectral behaviour of the model compounds in aqueous micellar systems of ionic and non-ionic surfactants were investigated. It was shown that, in aqueous acidic solutions, the investigated analytes were better incorporated in CDs (FF) and micelles (FF and MF). The luminescence emissions from the analytes were found to be greatly enhanced by surfactants. The fluorescence of analyte–surfactant system was quenched by increasing amounts of organic solvents. The changes in the dissociation constants of FF and MF in solutions of anionic and non-ionic surfactants (sodium dodecyl sulfate (SDS) and Triton X-100, respectively) were studied spectrofluorimetrically. The fluorescence intensity enhancements in CDs media relative to aqueous solution ranged from 1.3 to 1.6. Sensitive micellar-enhanced spectrofluorimetric methods for the determination of FF and MF were developed, with ranges of application down to ng ml −1 level. The linear dynamic ranges and relative standard deviations were reported. The methods were applied satisfactorily to the determination of both compounds in pharmaceutical preparations with recoveries of 98–101%.

Solvent Effects on Chemical Processes. 11. Solvent Effects on the Kinetics of Decarboxylative Dechlorination of N-Chloro Amino Acids in Binary Aqueous—Organic Solvents

The phenomenological theory of solvent effects is extended to chemical reaction rates and is tested against experimental data on the decarboxylative dechlorination of N-chloroalanine and N-chloroleucine at 25°C in binary aqueous–organic solvent mixtures. The organic cosolvents studied were methanol, ethanol, l-propanol, 2-propanol, ethylene glycol, propylene glycol, acetonitrile, and dioxane. Reaction rates increased in all cosolvent systems. The kinetic solvent effects could be quantitatively described by the theory, and the parameters of the theory (solvation exchange constants K1 and K2 and cavity surface area parameter ΔgA‡) were found to possess magnitudes reasonable for the physical significance assigned to them. In particular, the ΔgA‡ value is consistent with a recent measurement of the volume of activation ΔV‡ of the reaction.

Solvent Effects on Chemical Processes. 10. Solubility of α-Cyclodextrin in Binary Aqueous-Organic Solvents: Relationship to Solid Phase Composition

□ The equilibrium solubility at 25 °C of α-cyclodextrin was measured in several binary aqueous-organic solvent mixtures, the organic cosolvents being methanol, 2-propanol, ethylene glycol, and acetone. Solubility maxima were observed as the solvent composition was varied from pure water to pure cosolvent. The maximum in methanol systems was hardly detectable, but it was very pronounced in 2-propanol and acetone, and two maxima were seen in the ethylene glycol system. Karl Fischer analysis of the solid phase isolated from 2-propanol/water equilibrium systems showed that α-cyclodextrin hexahydrate is the stable form in water, whereas a solid phase containing three water molecules per molecule of α-cyclodextrin is the stable form in the presence of 2-propanol. The appearance of a solubility maximum in this system, and by extension presumably in the other cosolvent systems, is attributed to the existence of more than one stable solid phase of α-cyclodextrin.

Solvent effects on chemical processes. 9. Energetic contributions to the complexation of 4-nitroaniline with α-cyclodextrin in water and in binary aqueous-organic solvents

Abstract The phenomenological theory of solvent effects partitions the free energy change of a process into contributions from solvent-solvent interactions (the general medium or solvophobic effect), solvent-solute interactions (the solvation effect), and solute-solute interactions (the intersolute or intrasolute effect). This approach is applied to complex formation between α-cyclodextrin and 4-nitroaniline in water and many aqueous-organic solvent mixtures; the organic solvents were methanol, ethanol, 2-propanol, ethylene glycol, dimethylsulfoxide, acetonitrile, and acetone. Complex stability constants were measured spectrophotometrically. The parameters of the phenomenological model were extracted by nonlinear regression or by graphical analysis. It is observed that there are two classes of cosolvents, distinguished by their polarity. If the pure solvent has log P < −0.3 (where P is the 1-octanol/water partition coefficient), the system behaves “normally,” with parameter values typical of nonelectrolyt...

Comments concerning solvent effects on chemical processes. Part 7. Quantitative description of the composition dependence of the solvent polarity measure ET(30) in binary aqueous–organic solvent mixtures

A recently published two-step solvational model for mathematically describing the spectral properties of the Dimroth–Reichardt betaine dye ET in binary aqueous–organic solvent mixtures is critically examined in the light of fundamental spectroscopic principles. The published spectroscopic method is found to be inconsistent with the Beer–Lambert relationship with regard to absorption additivity in solutions containing multiple light-absorbing solvational chromophores. Two alternative data treatments are presented for describing the spectral properties of the ET betaine dye. The first treatment is consistent with both the Khossravi–Connors–Skwierczynski two-step solvational model and fundamental spectroscopic principles. The second treatment assumes that only a single solvational chromophore is present in solution, and the observed absorption wavelength shift is described using the nearly ideal binary solvent (NIBS) model.