Topological transformation of the phase diagram of the potassium nitrate-water-<Emphasis Type="Italic">n</Emphasis>-butoxyethanol ternary system

Phase equilibria and critical phenomena in the potassium nitrate-water-n-butoxyethanol ternary system were studied by the visual polythermal method over the temperature range 10–150°C. In this system, the boundary binary liquid system is characterized by the presence of a closed stratification region. The temperature of the formation of a critical tie line of monotectic equilibrium (18.3°C) and solution compositions corresponding to the critical solubility points at various temperatures were determined. The n-butoxyethanol distribution coefficients between the aqueous and organic phases of the monotectic state were calculated at eight temperatures. n-Butoxyethanol salting out from aqueous solutions by potassium nitrate increased as the temperature grew. The generalized scheme of topological transformations of salt-binary solvent ternary system phase diagrams with salting out was substantiated and augmented.     

Phase equilibria and critical phenomena in the potassium perchlorate-water-<Emphasis Type="Italic">n</Emphasis>-butoxyethanol ternary system

Phase equilibria and critical phenomena in the potassium perchlorate-water-n-butoxyethanol ternary system, where the boundary liquid binary system is characterized by the presence of a closed stratification region, were studied by the visual-polythermal method over the temperature range 40–150°C. The temperature of the formation of the critical monotectic equilibrium tie line (141.0°C) and temperature dependences of the compositions of mixtures corresponding to the critical solubility points of the stratification region over the temperature ranges 47.7–130.3 and 141.0–150.0°C were determined. The isotherms of phase states constructed at 10 temperatures were used to reveal the topological transformation of the phase diagram of the ternary system depending on temperature. At low concentrations (up to 5.8 wt %), potassium perchlorate had a salting in action on heterogeneous water-n-butoxyethanol mixtures. The solubility of the salt increased as the temperature grew, and, above 141.0°C, potassium perchlorate had a salting out action. The salting out of n-butoxyethanol from aqueous solutions by potassium perchlorate grew stronger as the temperature increased.     

Phase equilibria and critical phenomena in the cesium nitrate-water-diethylamine ternary system

Phase equilibria and critical phenomena in the cesium nitrate-water-diethylamine ternary system were studied by the visual-polythermal method over the temperature range 60–150 °C, where the boundary binary liquid system was characterized by stratification with a lower critical solution temperature (LCST). The introduction of cesium nitrate into the water-diethylamine system decreased the LCST of this system from 146.1 to 69.3°C and lowered the mutual solubility of the components. The diethylamine distribution coefficients between the aqueous and organic phases were calculated for monotectic equilibria at various temperatures. The salting out of diethylamine with cesium nitrate grew stronger as the temperature increased. The conclusion was drawn that the isotherms of the phase states of the system substantiated the generalized scheme of topological transformations of phase diagrams for salt-binary solvent ternary systems with salting out. The salting out effects of cesium and potassium nitrates on the water-diethylamine binary system were compared.     

Phase equilibria and critical phenomena in the rubidium nitrate-water-acetonitrile system

Phase equilibria and critical phenomena were studied from -5 to 120°C in the rubidium nitrate-water-acetonitrile system, in which the liquid binary subsystem is characterized by liquid-liquid phase separation with an upper critical solution point (UCSP), using a visual polythermal method. We found that rubidium nitrate has a salting out effect on water-acetonitrile solutions and causes them to demix at any temperature in the specified range. Acetonitrile distribution coefficients between aqueous and organic monotectic phases were calculated for various temperatures. The minimum value was observed for 20.0°C. Six isothermal phase diagrams of the system were plotted to verify a fragment of the global scheme of the topological transformation of phase diagrams for salt-binary solvent ternary systems with salting out. The salting out effects of potassium, rubidium, and cesium nitrates on water-acetonitrile mixtures were comparatively analyzed.     

Phase equilibria and critical phenomena in the cesium nitrate–water–pyridine ternary system

The solubilities of components, phase equilibria, and critical phenomena in the cesium nitrate–water–pyridine ternary system are studied in the 5–100°C temperature range by the visual–polythermal method. Cesium nitrate is found to exhibit a salting-out effect at temperatures above 79.9°C causing phase separation in homogeneous water–pyridine solutions. The temperature of formation of the critical monotectic tie line (79.9°C) and the compositions of solutions corresponding to the liquid–liquid critical points at three temperatures are determined. The pyridine distribution coefficients between the aqueous and organic phases of the monotectic state at 85.0, 90.0, and 100.0°C are calculated. Their values demonstrate that salting-out of pyridine from aqueous solutions by cesium nitrate increases at higher temperatures. The plotted isotherms of phase diagrams confirm the fragment of the scheme of topological transformation of the phase diagrams of salt–binary solvent ternary systems with salting-in and salting-out phenomena.     

Topological transformation of a phase diagram for the sodium nitrate-water-isopropanol ternary system

Phase equilibria and critical phenomena in the sodium nitrate-water-isopropanol ternary system, where a boundary binary liquid system shows no immiscibility over the entire temperature range of its liquid state, were studied in the range from 5 to 90°C using a visual polythermal method. The formation temperature of a monotectic critical tie-line was determined to be 6.1°C, and the solution compositions corresponding to critical solution points at various temperatures were determined. Isopropanol partition coefficients between the aqueous and organic phases of monotectic equilibrium were calculated for seven temperatures. The isopropanol salting out from aqueous solutions by sodium nitrate was shown to be enhanced by rising temperature. Isothermal phase diagrams of the title system were constructed to verify a fragment of the general scheme of topological transformations of phase diagrams for salt-binary solvent ternary systems with salting out.     

The salting out action of alkali metal nitrates on the water-diethylamine binary system

The results of a polythermal study of the salting out action of alkali metal (Na, K, and Cs) nitrates on the water-diethylamine binary system characterized by stratification with a lower critical solution point (LCSP) were comparatively analyzed. Alkali metal nitrates experiencing homoselective solvation in aqueousorganic solvents were found to decrease the LCSP of this binary system, that is, have a salting out action. A decrease in the radius of the cation in the series CsNO₃-KNO₃-NaNO₃ decreased the temperature of critical tie line formation in the monotectic state of salt-water-diethylamine ternary systems (69.3, 48.1, and 22.9°C, respectively). In all ternary systems, first and foremost in the system with potassium nitrate, the effect of diethylamine salting out from aqueous solutions grew stronger as the temperature increased. The conclusion was drawn that, among the salts studied, sodium nitrate had the strongest salting out effect at 22.9–88.4°C, and potassium nitrate, at 88.4–150.0°C.     

Phase Equilibria and Critical Phenomena in the Potassium Nitrate-Water-Diethylamine Ternary System

Phase equilibria and critical phenomena in the potassium nitrate—water—diethylamine ternary system were studied by the visual polythermal method over the temperature range 40–150°C. The corresponding boundary binary liquid system was characterized by stratification with the lower critical temperature of solution. The introduction of potassium nitrate into the water—diethylamine system lowered its lower critical temperature of solution from 146.1 to 48.1°C and decreased the mutual solubility of the components. The diethylamine distribution coefficients between the aqueous and organic monotectic equilibrium phases at various temperatures were calculated. The effect of the salting out of diethylamine from aqueous solutions under the action of potassium nitrate was found to strengthen as the temperature increased. The constructed isotherms of the phase states of the system substantiated the generalized topological scheme of the transformation of phase diagrams of salt-binary solvent ternary systems with salting out.     

Topological transformation of the phase diagram for the ternary system cesium nitrate-water-acetonitrile

In the ternary system cesium nitrate-water-acetonitrile, in which liquid-liquid phase separation with an upper critical solution point (UCSP) exists in the liquid binary subsystem, was studied in the range from ?5 to 120°C using visual polythermal analysis. Liquid-liquid phase separation in the ternary system is observed above 96.0°C and below 2.8°C. Acetonitrile distribution coefficients between the aqueous and organic phases of monotectic equilibrium were calculated for various temperatures. Phase isotherms of the system confirm the general scheme of the topological transformation of phase diagrams in salt-binary solvent ternary systems with salting out.     

Topological transformation of the phase diagram of a potassium perchlorate-water-tetrahydrofuran ternary system in the temperature range of 40 to 140°C

Phase equilibria and critical phenomena in a potassium perchlorate-water-tetrahydrofuran ternary system are studied by visual polythermal means in the range of 40 to 140°C; the solubility diagram of the liquid subsystem is characterized by the presence of isolated binodal curve. The temperature of formation for the critical node of the monotectic state (107.3°C) and the dependences of the composition that corresponds to the critical points of solubility in the delayering field vs. temperature in the ranges of 70.3 to 107.3°C and 137.1 to 140.2°C are determined. The topological transformation of the investigated ternary system’s phase diagram upon a change in temperature is studied using isothermal sections of the system’s temperature concentration prism, plotted at nine temperatures. It is found that potassium perchlorate has only a salting-in effect on mixtures of water and tetrahydrofuran at temperatures below 107.3°C; at higher temperatures, it has both a salting-in and a salting-out effect, depending on its concentration and the composition of mixed solvent. It is shown that potassium perchlorate’s effect of salting tetrahydrofuran out of aqueous solutions grows slightly with an increase in temperature.     

Phase equilibria and salting-out effects in a cesium nitrate-triethylamine-water system at 5–25°C

Phase equilibria and critical phenomena in a cesium nitrate-water-triethylamine system in which the constituent binary liquid system is stratified at the lower critical solution temperature (LCST) is studied in a range of 5–25°C by the visual polythermal method. It is found that introducing cesium nitrate into the water-triethylamine system leads to a slight reduction in the LCST (from 18.3 to 16.3°C) and to a decrease in the mutual solubility of the components. The distribution coefficients of triethylamine between aqueous and the organic phases of the monotectic state at different temperatures are calculated. It is found that the salting-out of triethylamine from aqueous solutions by cesium nitrate increases with rising temperature. The results of the salting-out effect of sodium, potassium, and cesium nitrates on a water-triethylamine binary system are compared.     

Peculiarities of phase transformations in aqueous isopropanol solutions

Peculiarities of phase transformations in aqueous isopropanol solutions are studied in the range from room temperature to −15°C. It is found that solution cooling results in the formation of macroaggregates with regular geometrical shapes, which are dispersed in the liquid phase and directedly move in the field of a temperature gradient. In aqueous isopropanol solutions with concentrations of 10–30 vol %, the aggregates are formed at temperatures of −10 to −15°C. The average aggregate size is several millimeters. Under the action of a temperature gradient, the aggregates move to the region of higher temperatures. At temperature gradients of 1–2 K/cm, the aggregate velocity is 1–2 mm/s. The characters of the motion and interaction of aggregates are very sensitive to the temperature distribution in a solution. After the aggregate motion ceases, crystallization of the liquid phase that initially is outside of the aggregates is observed.     

Phase equilibria and critical phenomena in a sodium nitrate-water-diethylamine ternary system

The phase equilibria and critical phenomena in a sodium nitrate—water—diethylamine ternary system were studied by the visual polythermal method at 10—150°C, where the frontier binary liquid system is characterized by delamination with the lower critical solution temperature (LCST). The introduction of sodium nitrate into the water—diethylamine system led to a significant decrease (from 146.1 to 22.9°C) in the LCST of the system and the mutual solubility of its components. The coefficients of the distribution of diethylamine between the water and organic phases of the monotectic equilibrium at different temperatures were calculated. The effect of the salting-out of diethylamine by sodium nitrate from aqueous solutions increased with temperature. The constructed isotherms of the phase states of the system confirmed the general scheme of the topological transformation of the phase diagrams of the salt—binary solvent ternary systems with salting-out. The results of the salting-out action of sodi um, potassium, and cesium nitrates on the water—diethylamine binary system were compared.     

Topological transformation of the phase diagram of the lithium nitrate-water-acetonitrile ternary system within the range of −20 to 50°C

Phase equilibria and critical phenomena in the lithium nitrate-water-acetonitrile ternary system were studied by a visual polythermal method within the range of ?20 to 50°C. In this ternary system, the constituent liquid binary system is characterized by phase separation with an upper critical solution temperature. It was found that the ternary system undergoes phase separation at temperatures below 0.7°C. In the phase diagram within the range of ?1.1 to 0.7°C, a closed phase separation region with two critical points was revealed. The temperature of the formation of the critical tie line of the monotectic state the solid phase of which is the crystalline hydrate LiNO₃ · 3H₂O was determined (?18.7°C). Depending on the concentration, lithium nitrate has both salting-in and salting-out effect on aqueous acetonitrile mixtures. The plotted isothermal sections of the temperature-concentration prism of the system at fifteen temperatures showed the pattern of the topological transformation of its phase diagram with varying temperature.     

Comparing the salting-out effects of alkali-metal nitrates on the water-isopropanol system

The salting-out effects of sodium, potassium, and cesium nitrates on the water-isopropanol system, which is homogeneous throughout its liquid-state temperature range, are compared at different temperatures. The alkali-metal nitrates, which undergo homoselective solvation in aqueous-organic solvents, exert a salting-out effect on aqueous isopropanol. As the crystallographic radius of the cation decreases in the order CsNO₃-KNO₃-NaNO₃, the monotectic critical tie line temperature for the salt-water-isopropanol system decreases (79.0, 47.2, and 6.1°C, respectively). In each ternary system, the salting-out effect on isopropanol strengthens with an increasing temperature, particularly in the system containing sodium nitrate. Among the salts examined, the strongest salting-out effect between 6.1 and 90.0°C is produced by sodium nitrate.     

Structure of water-glycine solutions in saturated and near-saturated regions according to compressibility data

Ultrasonic velocity and density values are measured for aqueous solutions containing 2.00 mol.%, 4.00 mol.%, and 5.00 mol.% glycine in a temperature range of 15–65°C, 5.50 mol.% glycine (20–65°C), and 6.00 mol.% glycine (25–65°C). Adiabatic compressibilities (κ_S) and molar adiabatic compressibilities (K_S) are calculated. The values of κ_S and K_S decrease monotonically with an increase in glycine concentrations up to saturation at all the temperatures. The temperature dependences of κ_S and κ_S have minima that are typical of water and aqueous solutions; the positions of the minima depend on the glycine concentration. The temperature coefficients of the molar compressibility, ∂K_S/∂T, change their signs from negative to positive at lower temperatures (by approximately 10 deg) than ∂κ_S/∂T.     

Physicochemical characterization of a novel surfactant peptide containing an arginine cation and laurate anion

 A novel surfactant peptide consisting of an arginine cation with laurate anion has been synthesized, purified and characterized. The critical micellar concentration (cmc) of peptide in aqueous solutions has been determined using spectroscopic techniques and is found to increase from 0.06 to 0.11 mM with increasing temperature (15–45 °C). Cmc is also determined in the presence of salts like NaCl, KCl and sodium acetate and it is found that these electrolytes hinder aggregation with a significant increase in the case of sodium acetate. The aggregation number of the surfactant peptide has been determined using fluorescence quenching measurements and is observed to decrease from 14 to 6 with increasing temperature (15–45 °C). The standard free energy change (ΔG ⁰ _m) and standard enthalpy change (ΔH ⁰ _m) of the peptide aggregate are found to be negative with a small positive value for standard entropy change (ΔS ⁰ _m). The peptide aggregate seems to undergo phase transition above 50 °C as observed from UV–vis and fluorescence spectroscopy. From pyrene binding studies, it is shown that the interior dielectric constant increases from 5.08 at 34 °C to 8.77 at 50 °C and further decreases with increase in temperature indicating a phase change at 50 °C. Also, the ratio of excimer intensity to monomer intensity, which is a measure of microviscosity of the aggregate, decreases with increase in temperature with a change at 50 °C indicating a phase change. Received: 14 February 1997 Accepted: 13 August 1997     

Thermodynamics of the conversion of aqueous glucose to fructose

The thermodynamics of the conversion of aqueous glucose to fructose has been investigated using both heat conduction microcalorimetry and high pressure liquid chromatography (HPLC). The reaction was carried out in both aqueous Tris/HCl buffer and in aqueous phosphate buffer in the pH range 7–8 using the enzyme glucose isomerase and the cofactors CoCl₂ and MgSO₄. The temperature range over which this reaction was investigated was 298.15–358.15 K. We have found that the enthalpy of reaction is independent of pH over the range investigated. A combined analysis of both the HPLC and microcalorimetric data leads to the following results at 298 15 K:ΔG° = 349 ± 53 J mol^-1, ΔH° = 2.78 ± 0.20 kJ mol^-1, and ΔC _p ^° = 76 ± 30 J mol^-1 K^-1. The stated uncertainties are based upon an analysis of both the random and systematic errors inherent in the measurements. Comparisons are made with literature data. The percent conversion of glucose to fructose has been calculated for the temperature range 300–373.15 K.     

Salting out of triethylamine from aqueous solutions by potassium nitrate

By visual-polythermal method in the range 5–25°C we studied phase equilibria and critical phenomena in a ternary system potassium nitrate-water-triethylamine, where its component, binary liquid system, is stratified at the lower critical solution temperature.     

Long term stability of organic selenium species in aqueous solutions

Long term stability of organic selenium compounds (selenocystine, selenomethionine, trimethylselenonium ion) has been studied over a one year period for 2 analyte concentrations: 25 and 150 μg/L Se, at pH 4.5 in the dark, under different storage conditions: temperature of –20°C, 4°C, 20°C, 40°C; in Pyrex, Teflon, or polyethylene containers; in an aqueous matrix or in the presence of a chromatographic counter ion (pentyl sulfonate at 10^–4 mol/L concentration). Light effects have also been tested. The stability of the selenium species was monitored by HPLC-ICP/MS. Storage conditions can drastically alter the stability of organic selenium species. Organoselenium compounds were shown to be stable in the dark over a one year period in an aqueous matrix at pH 4.5 in Pyrex containers at both 4°C and 20°C. Pyrex vials exposed to natural sunlight at room temperature resulted in a steady decrease of the selenoamino acid concentration. Teflon containers caused losses of less than 25% at both 4° C and 20° C in the dark. However, polyethylene vials presented, at all temperatures tested, a rapid decrease of the TMSe⁺ concentration. The stability of the Se species studied did not show significant differences between 4° C and 20° C in any container material used. Storage of solutions at 40° C led to slight differences between the Pyrex and Teflon containers. However, polyethylene presented a drastic decrease of the three species over time at this higher temperature. Solutions frozen at –20° C in polyethylene vials did not stabilize the TMSe⁺ signal. Finally, concentrations and matrices of the samples did not significantly affect the stability of the species. Received: 15 July 1996 / Revised: 14 July 1997 / Accepted: 18 July 1997