Solution and Mixing Thermodynamics of Propranolol and Atenolol in Aqueous Media

Based on the van’t Hoff and Gibbs equations, the thermodynamic functions Gibbs energy, enthalpy, and entropy of dissolution, and of mixing of propranolol (PPN) and atenolol (ATN) in water at pH=11.5, were evaluated from solubility values determined at several temperatures. The equilibrium solubility values obtained for ATN were almost three hundred-fold higher than those for PPN. The enthalpies of dissolution were positive for both drugs, whereas the entropies of dissolution were both negative indicating a greater molecular organization after the drugs’ dissolution processes. Otherwise, the entropies of mixing were also negative in both cases indicating mixing-entropy is driving on drugs dissolution processes. The results were discussed in terms of solute-solvent interactions, especially hydrophobic hydration.     

Solubility of naproxen in several organic solvents at different temperatures

By using the van’t Hoff and Gibbs equations the thermodynamic functions Gibbs free energy, enthalpy, and entropy of solution, were evaluated from solubility data of naproxen (NAP) determined at several temperatures in octanol, isopropyl myristate, chloroform, and cyclohexane, as pure solvents. The water-saturated organic solvents also were studied except cyclohexane. The excess free energy and the activity coefficients of the solutes, and the mixing and solvation thermodynamic quantities were also determined. The NAP solubilities were higher in chloroform and octanol with respect to those obtained in cyclohexane. In addition, by using literature values for NAP aqueous solubility, the thermodynamic functions relative to transfer of this drug from water to organic solvents were also estimated.     

Solubility and Thermodynamic Data of Febuxostat in Various Mono Solvents at Different Temperatures

This study examines the solubility and thermodynamics of febuxostat (FBX) in a variety of mono solvents, including “water, methanol (MeOH), ethanol (EtOH), isopropanol (IPA), 1-butanol (1-BuOH), 2-butanol (2-BuOH), ethylene glycol (EG), propylene glycol (PG), polyethylene glycol-400 (PEG-400), ethyl acetate (EA), Transcutol-HP (THP), and dimethyl sulfoxide (DMSO)” at 298.2–318.2 K and 101.1 kPa. The solubility of FBX was determined using a shake flask method and correlated with “van’t Hoff, Buchowski-Ksiazczak λh, and Apelblat models”. The overall error values for van’t Hoff, Buchowski-Ksiazczak λh, and Apelblat models was recorded to be 1.60, 2.86, and 1.14%, respectively. The maximum mole fraction solubility of FBX was 3.06 × 10⁻² in PEG-400 at 318.2 K, however the least one was 1.97 × 10⁻⁷ in water at 298.2 K. The FBX solubility increased with temperature and the order followed in different mono solvents was PEG-400 (3.06 × 10⁻²) > THP (1.70 × 10⁻²) > 2-BuOH (1.38 × 10⁻²) > 1-BuOH (1.37 × 10⁻²) > IPA (1.10 × 10⁻²) > EtOH (8.37 × 10⁻³) > EA (8.31 × 10⁻³) > DMSO (7.35 × 10⁻³) > MeOH (3.26 × 10⁻³) > PG (1.88 × 10⁻³) > EG (1.31 × 10⁻³) > water (1.14 × 10⁻⁶) at 318.2 K. Compared to the other combinations of FBX and mono solvents, FBX-PEG-400 had the strongest solute-solvent interactions. The apparent thermodynamic analysis revealed that FBX dissolution was “endothermic and entropy-driven” in all mono solvents investigated. Based on these findings, PEG-400 appears to be the optimal co-solvent for FBX solubility.     

Triiodide ion formation equilibrium and activity coefficients in aqueous solution

The equilibrium quotient for the formation of triiodide was studied as a function of temperature, 3.8–209.0°C, and ionic strength, 0.02–6.61. The best-fit value for the molal equilibrium constant at 25°C is 698±10 and the corresponding partial molal enthalphy, entropy, and heat capacity of formation are: H^o=–17.0±0.6 kJ-mol^–1, S^o=–0.6±0.3 J-K^–1-mol^–1, and C _p ^o =–21±8 J-K^–1-mol^–1. Activity coefficients of iodine were determined as a function of ionic strength (NaClO₄) at 25°C and conclusions are drawn as to the corresponding ionic strength dependence of the triiodide anion.     

Thermodynamic properties of chloro-complexes of silver chloride in aqueous solution

Available data on the solubility of silver chloride in aqueous solutions of HCl, NaCl, KCl, LiCl, and NH₄Cl, along with potentiometric measurements of the activity of Ag⁺ in aqueous NaCl–NaClO₄ mixtures, have been analyzed to obtain the thermodynamic properties of the (AgCl)⁰, AgCl ₂ ^– , AgCl ₃ ^2– , and AgCl ₄ ^3– complexes. Results obtained include the stability constants of the complexes and 25°C, the virial parameters needed to calculate the activity coefficients of the complexes and the heats of the reactions by which they are formed. These results are sued to calculate tables of recommended values for the solubility of silver chloride in the host solutions as a function of concentration from 0 to 150°C and to make a critical evaluation of the reliability of previously published data.     

Complexation of aluminate anion by bis-tris in aqueous media at 25–50°C

Gibbsite, Al(OH)₃, solubility studies in aqueous NaCl solutions at pH 9 demonstrate that the aluminate anion forms a strong complex with the neutral Bis-tris molecule 2,2-Bis(hydroxymethyl)-2,2,2-nitrilotriethanol, at low temperatures. The logarithm of the molal concentration quotient for the reaction

The influence of pH on phosphatidylcholine monolayer at the air/aqueous solution interface

The measurements of the interfacial tension at the air/aqueous subphase interface as the function of pH were performed. The interfacial tension of the air–aqueous subphase interface was divided into contributions of individuals. A simple model of the influence of pH on the phosphatidylcholine monolayer at the air/hydrophobic chains of phosphatidylcholine is presented. The contributions of additive phosphatidylcholine forms (both interfacial tension values and molecular area values) depend on pH. The interfacial tension values and the molecular areas values for LH⁺, LOH⁻ forms of phosphatidylcholine were calculated. The assumed model was verified experimentally.     

Structure and dynamics at the surface of a concentrated aqueous solution of CsF

A molecular dynamics simulation of a liquid layer of a concentrated CsF solution in water has been performed in order to compare the results with those obtained in an experimental study of our group. The main result of the experiment was the existence of a monolayer of nearly pure water constituting the surface and a homogeneous mixture constituting the bulk of the system. The simulation reveals the same phenomena which can be explained by the circumstance that the ions near the surface mostly keep their first solvation shell intact. The water molecules belonging to these shells and being placed on the vapor side constitute this monolayer. The density profiles of the ions indicate that the Cs ions penetrate further into the surface than the F ions. The orientational structure of the first shell of water molecules around an ion is the same for ions in the surface and ions in the bulk in contrast to the dynamics which is altered. The spectra of the librational motion are shifted to lower frequencies. In addition to that the spectra belonging to libration which involves motion of the dipole moment develop a peak in the low frequency range irrespective of whether the water molecules are bonded to Cs or to F ions. This can be correlated with an overall preferred orientation of the water molecules in the surface which is most pronounced for the dipole moment. The calculation of the diffusion coefficients shows that the top surface layer of nearly pure water is a region of enhanced and extremely anisotropic mobility. The mean residence time of water molecules in the surface in the first shell of an ion is reduced according to the enhanced mobility.     

Study on gamma-ray-induced degradation of polymer electrolyte by pH titration and solution analysis

Degradation process of polymer electrolyte was investigated by pH titration and solution analysis. Perfluorosulfonic acid, which is generally used for fuel cells and sensors, was irradiated with gamma-ray. Irradiated samples were immersed in distilled water, and the suspensions were titrated with NaCl solution while pH was monitored. Initial pH without any sodium ion decreased as increase in absorbed dose, indicating acid release from polymer electrolyte. To identify the chemical structure of dissolved species, solution analysis was performed by ion chromatography, total organic carbon (TOC) analyzer, and inductively-coupled plasma atomic emission spectrometry (ICP-AES). It was shown that proton, sulfide ion, fluorine ion and organic carbon were detected in the solution, and the ratio among these ions and atoms changed depending on the irradiation conditions. It shows that the solution analysis can identify the scission site by irradiation sensitively, and gives useful information for investigation of polymer degradation process.     

Spectroscopic investigation of Rose Bengal/cyclodextrin interactions in aqueous solution: the case of the hydroxypropyl-cyclodextrins

The interaction of Rose Bengal (RB) with hydroxypropyl-α-cyclodextrin (HP-α-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD) and hydroxypropyl-γ-cyclodextrin (HP-γ-CD) has been studied in water and in acetate buffer at pH 4.5 by UV–Vis absorption, fluorescence spectroscopy and Induced Circular Dichroism at 298 K. Evidence of the complex formation between the RB and all HP-CDs have been obtained both in water and in buffer. Binding constants and stoichiometry of RB/HP-CD complexes in water have been determined by applying the modified Benesi-Hildebrand equation to the fluorescence measurements.     

Uncertainties in Determination of pH

 A statistical analysis of multi-point calibration procedure for practical measurement of pH under laboratory conditions is given. The procedure is shown to provide the necessary elements for simple assignment of an uncertainty to a pH measurement – an essential element of quality control. Performance of ordinary least squares regression for prediction of confidence limits is compared to orthogonal regression, inverse regression and Monte Carlo simulations. In case of pH measurement by multi-point calibration procedure, methods considering uncertainties in both axes are found to be statistically more satisfactory than ordinary least squares regression. By analysis of 50 pH calibration data, randomly selected from 250 5-point glass electrode calibrations, it is found that the practical differences, however, are of minor importance. The significance of uncertainty in pH is demonstrated for an example from metal ion speciation in aqueous solution. Received September 20, 1999. Revision April 19, 2000.     

Bacteria transport through goethite-coated sand: effects of solution pH and coated sand content

This study investigated the transport of bacteria through goethite-coated sand, focusing on the effects of solution pH and coated sand content on the transport of Escherichia coli ATCC 11105. The first set of column experiments was performed in columns (length 30 cm, diameter 5 cm) packed with quartz sand coated with goethite in solution having a pH in the range of 6–9. The second was carried out in columns (length 30 cm, diameter 2.5 cm) with varying coated sand contents ranging from 0 to 100%. Results indicate that the bacteria transport in the coated sand was influenced by solution pH. Around pH 6 and 7, bacterial mass recoveries were low at 2.4–6.7% while they were high at 76.3–81.6% around pH 8 and 9. Around pH 8, the positively charged coated sand may convert to being negatively charged, causing an electrostatically repulsive interaction between the coated sand and bacteria, thus effecting a sharp change in the mass recovery. Results also reveal that the mass recovery decreased from 76.7 to 2.7% as the coated sand content increased from 0 to 100%, showing the nonlinear dependency of mass recovery on the content of coated sand. This study demonstrates the importance of the solution pH and coated sand content in the adhesion of bacteria to goethite-coated sand and furthermore contributes to the knowledge of bacterial removal in positively charged porous media.     

Effect of β-cyclodextrin on spectroscopic properties of ochratoxin A in aqueous solution

Ochratoxin A (OTA) is a nephrotoxic mycotoxin produced by several fungal species, mainly Aspergillus ochraceus, A. carbonarius and Penicillium verrucosum. It contaminates many foodstuffs, particularly cereals and their derivatives, coffee, beer, wine and cocoa, and represents a serious health threat both to humans and animals. Spectroscopic properties of OTA solutions depend on the pH, solvent polarity and can be influenced by the presence of cyclodextrins (CDs). In this work, the effect of β-CD on spectroscopic properties of OTA in aqueous solutions has been investigated by means of absorption and steady-state fluorescence at different pHs (range 3.5–9.5). Binding constants of OTA/β-CD inclusion complexes have been determined by applying modified Benesi-Hildebrand equation. A 1:1 stoichiometry of OTA/β-CD complexes has been observed at all tested pHs.     

Solubility of oxygen in aqueous sodium carbonate solution at pressures up to 10 MPa

The solubilities of oxygen in 0.2, 0.5, 0.7 and 1.0 M Na₂CO₃ solution have been measured at 300.15 K and under pressures up to 10 MPa using a magnetically stirred autoclave and a direct sampling technique. The accuracy of apparatus was verified by duplicating the solubility of oxygen in pure water in literature. The experimental data of the solubility of oxygen in aqueous sodium carbonate solution were shown that the solubility of oxygen increases with increasing pressure and decreases with increasing salt concentration due to salting-out effect. The experimentally measured data were satisfactorily compared with the predicted values by our model based on non-primitive mean spherical approximation (MSA) and perturbation theory.     

pH reversible micelle transition of a tertiary amine-based gemini surfactant in aqueous solution

In this work, we prepared a tertiary amide-based gemini surfactant (DSTAPA), which contained two pH-sensitive tertiary amide head groups. Then the molecule state distribution and self-assembly transition of the surfactant in aqueous solution were investigated under different pH conditions. The DSTAPA molecules were on the states of double cationic (DSTAPAH²⁺), single cationic (DSTAPAH⁺), and double tertiary amine groups (DSTAPA) under acidic, neutral, and basic conditions, respectively. With the variation of the molecule states, the sample was water-like below pH of 6.8 and immediately transformed to gel-like fluid between pH of 6.8 and 7.8, then changed to white precipitate with the further increase of pH value. Furthermore, the microstructure and regulation mechanism were investigated by rheological measurements, dynamic light scattering, and cryogenic transmission electron microscopy. The appearance and micelle transitions of the DSTAPA aqueous solution are actually owing to the spherical–worm-like micelle transition, leading to dramatic viscosity increase and hydrogel formation. This transition was completely reversible and repeated for at least three cycles. Finally, a reasonable mechanism of the transition was proposed based on the viewpoints of the molecular states and micelle structures. The DSTAPA aqueous system with pH-reversible property has a great potential application in oil and gas production.     

Solubility Determination,Hansen Solubility Parameters and Thermodynamic Evaluation of Thymoquinone in (Isopropanol + Water) Compositions

This article studies the solubility, Hansen solubility parameters (HSPs), and thermodynamic behavior of a naturally-derived bioactive thymoquinone (TQ) in different binary combinations of isopropanol (IPA) and water (H₂O). The mole fraction solubilities (x₃) of TQ in various (IPA + H₂O) compositions are measured at 298.2–318.2 K and 0.1 MPa. The HSPs of TQ, neat IPA, neat H₂O, and binary (IPA + H₂O) compositions free of TQ are also determined. The x₃ data of TQ are regressed by van’t Hoff, Apelblat, Yalkowsky–Roseman, Buchowski–Ksiazczak λh, Jouyban–Acree, and Jouyban–Acree–van’t Hoff models. The maximum and minimum x₃ values of TQ are recorded in neat IPA (7.63 × 10⁻² at 318.2 K) and neat H₂O (8.25 × 10⁻⁵ at 298.2 K), respectively. The solubility of TQ is recorded as increasing with the rise in temperature and IPA mass fraction in all (IPA + H₂O) mixtures, including pure IPA and pure H₂O. The HSP of TQ is similar to that of pure IPA, suggesting the great potential of IPA in TQ solubilization. The maximum molecular solute-solvent interactions are found in TQ-IPA compared to TQ-H₂O. A thermodynamic study indicates an endothermic and entropy-driven dissolution of TQ in all (IPA + H₂O) mixtures, including pure IPA and pure H₂O.     

Thermodynamic modeling of CO2 and H2S solubilities in aqueous DIPA solution, aqueous sulfolane-DIPA solution, and aqueous sulfolane-MDEA solution with electrolyte NRTL model

A thermodynamic model developed for CO₂ and H₂S solubilities in aqueous MDEA solution is extended to cover CO₂ and H₂S solubilities in aqueous DIPA solution, aqueous sulfolane-DIPA solution, and aqueous sulfolane-MDEA solution. The model makes use of the 2009 version of the electrolyte NRTL model for liquid phase activity coefficient calculations and the PC-SAFT equation of state for vapor phase fugacity coefficient calculations. The NRTL binary parameters for the molecule-electrolyte pairs required for the H₂O-DIPA-CO₂ ternary and the H₂O-sulfolane-DIPA-CO₂ quaternary are regressed against the solubility data of CO₂ in aqueous DIPA solution and aqueous sulfolane-DIPA solution, respectively. The NRTL binary parameters for the molecule-electrolyte pairs required for the H₂O-DIPA-H₂S ternary and the H₂O-sulfolane-DIPA-H₂S quaternary are regressed against the solubility data of H₂S in aqueous DIPA solution and aqueous sulfolane-DIPA solution simultaneously. The NRTL binary parameters for the electrolyte-electrolyte pairs involved in the H₂O-DIPA-CO₂-H₂S quaternary are regressed against the solubility data of the acid gas mixtures in aqueous DIPA solution. Likewise, the NRTL binary parameters for the sulfolane-electrolyte pairs required for the H₂O-sulfolane-MDEA-CO₂ quaternary and the H₂O-sulfolane-MDEA-H₂S quaternary are regressed against the solubility data of the acid gases in aqueous sulfolane-MDEA solution. The predicted enthalpies of acid gas absorption are compared favorably with the literature data available for the H₂O-DIPA-CO₂ system, the H₂O-DIPA-H₂S system, and the H₂O-sulfolane-MDEA-CO₂ system.     

Enthalpies of solution of glycylglycine and diglycylglycine in aqueous alcohols at 298.15 K

The integral enthalpies of solution of glycylglycine and diglycylglycine in water–ethanol, water–n-propanol and water–i-propanol mixtures were measured at 298.15 K and alcohol mole fraction concentrations (x₂) ranging up to 0.3 by calorimetry. The Δ_solH° and Δ_trH° vs. x₂ were found to have extrema. Enthalpic coefficients of pairwise interactions (h_xy) between peptide and alcohol molecules were positive and increased in the series ethanol, n-propanol, i-propanol.     

Molecular imprinting of peptides and proteins in aqueous media

Molecular imprinting has received significant attention in recent years, as it provides a viable method for creating synthetic receptors capable of selectively recognizing specific target molecules. Despite significant growth within the field, the majority of template molecules studied thus far have been characterized by their low molecular weight and insolubility in aqueous systems. In biological systems, molecular recognition events occur in aqueous media. Therefore, in order to create molecularly imprinted polymers capable of mimicking biological processes, it is necessary to synthesize artificial receptors which can selectively recognize their respective target biological macromolecules such as peptides and proteins in aqueous media. In this review, we discuss the challenges associated with the imprinting of peptides and proteins in aqueous media. In addition, we discuss the significant progress which has been made within the field.     

Solubility of gallium(III) oxyhydroxide in aqueous NaCl solutions at 100°C

The hydrolysis-precipitation equilibrium reaction of aqueous gallium(III) solution was investigated in 0–3 mol-kg^-1 NaCl media at low pH at 100°C using a pressure-tight glass vessel. All precipitates were identified as GaOOH. The results were analyzed with a nonlinear least-squares computer program to obtain the solubility product K_so for gallium(III) oxyhydroxide using a single-parameter type of Debye-Hückel equation. The value of log K_so for GaOOH(s) + 3H⁺ ⇆ Ga³⁺ + 2H₂O was -0.60 at 100°C. The solubility product calculated from thermodynamic data was compared with the experimental result.