Properties Of Aqueous Solutions Research Articles

Functional and Rheological Properties of Vicia faba L. Protein Isolates.

A protein isolate (85.5%) was obtained from the Vicia faba L. seeds. The main protein fraction, typical for the seeds of this plant, was found to be most numerous: Legumin (35 kDa) and Vicilin (45 kDa). The hydrodynamic and surface properties of isolate aqueous solutions were studied with the help of dynamic light scattering, -potential, and tensometry in a wide range of concentrations and pH conditions. Selected functional properties, like foaming and emulsifying abilities, were studied. An increase of water solubility was shown with a raising pH, as well as a water holding capacity (WHC). The protein isolate showed a tendency to decrease the surface tension of water solutions, with high hydrophobicity and a negative charge of the isolate enhancing the foaming and emulsifying properties. The analysis of the concentration and the pH influence on selected functional properties indicated alkaline conditions as favorable for good foaming and emulsifying properties of the isolate and affected on their rheological properties.

Visualization of microwave near-field distribution in sodium chloride and glucose aqueous solutions by a thermo-elastic optical indicator microscope

In this study, a new optical method is presented to determine the concentrations of NaCl and glucose aqueous solutions by using a thermo-elastic optical indicator microscope. By measuring the microwave near-field distribution intensity, concentration changes of NaCl and glucose aqueous solutions were detected in the 0–100 mg/ml range, when exposed to microwave irradiation at 12 GHz frequency. Microwave near-field distribution intensity decreased as the NaCl or glucose concentration increased due to the changes of the absorption properties of aqueous solution. This method provides a novel approach for monitoring NaCl and glucose in biological liquids by using a CCD sensor capable of visualizing NaCl and glucose concentrations without scanning.

Structure, Molecular Interactions, and Dynamics of Aqueous [BMIM][BF4] Mixtures: A Molecular Dynamics Study.

Molecular dynamics simulations with many-body polarizable force fields were carried out to investigate the thermodynamic, structural, and dynamic properties of aqueous solutions of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]). The radial distribution functions exhibit well-defined features, revealing favored structural correlations between [bmim]+, [BF4]-, and H2O. The addition of water is shown to alter ionic liquid structural organizations by replacing counterions in the coordination shells and disrupt the cation-anion network. At low water concentration, the majority of water molecules are isolated from each other and have lower average dipole moment than that in pure water. With increasing hydration level, while [bmim][BF4] ionic network breaks up and becomes isolated ion pairs or free ions in the dilute limit, water begins to form clusters of increasing sizes and eventually forms a percolating network. As a result, the average water dipole moment increases and approaches its bulk value. Water is also observed to have a substantial influence on the dynamics of ionic liquids. At low water content, the cation and anion have similar diffusion coefficients due to the correlated ionic motion of long-lived ion pairs. As the water concentration increases, both ions exhibit greater mobility and faster rotations from the breakup of ionic network. Consequently, the ionic conductivity of [bmim][BF4] aqueous solutions rises with increasing water composition.

Size-Sensitive Thermoelectric Properties of Electrolyte-Based Nanofluidic Systems.

In this work, we investigate the thermoelectric properties of aqueous KCl solutions confined in graphene nanochannels through molecular dynamics simulations. The channel height H ranges from 0.7 to 7.8 nm. It is found that the Seebeck coefficient, Se, and the figure of merit, ZT, of the KCl solution are highly sensitive to H when H is small. For the nanochannel of H = 1.0 nm, Se = 30.6 mV/K and ZT = 4.6 at room temperature, which are superior to most of the solid-state thermoelectric materials. The remarkable thermoelectric properties in small channels are attributed to the flow slip at the channel walls and the mean excess enthalpy density of the solution, which is mainly from the potential energy contribution. The molecular insight promotes the applications of nanofluidic devices for thermal energy harvesting.

Comparative study of pluronic-chitosan and pluronic-guar gum composite thermogels

Triblock copolymers display, in water, a rich phase behavior with changes in temperature and concentration that makes them particularly attractive for many industrial and biomedical applications. In an attempt to develop smart carriers with improved properties, additives such as polysaccharides are often included in the poloxamer formulations. In the present work, we examine and compare the associative properties of concentrated aqueous solutions of pluronic F127 in presence of chitosan and guar gum. Dynamic light scattering was used to analyze the effects of the two polysaccharides on the different self-assembled structures formed within these solutions as a function of temperature from the micellization to the sol-gel transition. The most marked differences between the two systems can be observed above the sol-gel transition, where the analysis of the correlation functions evidenced the presence of three processes: a fast process that represents unimers diffusion, an intermediate process related to individual hydrated micelles, and a slow mode due to the presence of large micellar aggregates. We hypothesize that the different molecular weight and ionic character of the polysaccharides are responsible for the different size of the diffusing entities as well for the nature of the bonds which hold together the extended network between micelles formed above the sol-gel transition.

Radiothermal radiation method for aqueous solutions

For the first time, an ultra-high-sensitivity method for measuring radio-thermal radiation was developed and used in practice in order to establish the difference in the physical properties of aqueous solutions of substances in the millimeter region of the spectrum. The method is used to study the dynamics of the dielectric properties of aqueous solutions depending on the composition of the base substance and its concentration. The dynamics of dielectric properties establishes a one-to-one correspondence between the number and concentration of ions of the dissolved basic substance contained in water and the number of water molecules involved in cooperative interaction, which gives a consistent microscopic picture of ion-water cooperative interactions in the studied aqueous solutions of K2SO4 and Cs2SO4. The density of water molecules perturbed by the ions of the base substance contained in the hydration shell at normal concentrations is proportional to the number of ions, while the transition to weaker solutions leads to the creation of multilayer hydration shells. This means that the number of perturbed water molecules, depending on the number of ions, increases according to a law different from linear. In accordance with the experimental data, the values of the absorption coefficients of aqueous solutions were determined in a wide range of concentrations for alkali metal sulfates. It is noted that alkali metal sulfates have physical properties that generalize the dynamics of dielectric constants depending on the concentration of the base substance. A monotonic increase in the values of the absorption coefficients of solutions with a decrease in the concentration of basic substances in the region of high dilutions was established with individual dynamics for each basic substance, reflecting the total hydration changes in salt solutions. Research has shown that the proposed method for measuring radio-thermal radiation fixes a significant difference in the values of the dielectric constants of aqueous solutions at high dilutions from their values for water.

ВПЛИВ ЕЛЕКТРОМАГНІТНОГО ВИПРОМІНЮВАННЯ МІЛІМЕТРОВОГО ДІАПАЗОНУ НА ОПТИЧНІ ВЛАСТИВОСТІ ВОДИ В РОЗЧИНАХ ГЕМОГЛОБІНУ

The features of the influence of microwave radiation on the optical properties of pure water and water in solutions of hemoglobin in the near infrared range with the aim to characterize the certain structural and dynamic state of water are investigated. The object of the study was the optical properties of distilled water and aqueous solutions of human hemoglobin in the concentration range of 7 and 15 μm and in the temperature range 10–40°C. The optical spectra were recorded by using a BiospecMini spectrophotometer in the wavelength range of 190–1100 nm. In order to increase the accuracy of the analysis of spectral data the spectra were normalized relative to the baseline which was taken as a line that ran parallel to the horizontal axis due to the minimum value of the optical density in the absorption spectrum. The values of the absorption maxima and the optical density were used as the main parameters of the absorption spectra. The B spline function was used to more accurately determine these parameters. Microwave exposures of distilled water and hemoglobin solutions was performed at a wavelength of 7.1 mm with a maximum 100% output power which was calculated to be approximately 24 mW. The dependence of the parameters of the water absorption spectrum in the range of the second overtone of the OH-valence oscillation of the water molecule on temperature is detailed. There were not found statistically significant changes in the distilled water absorption spectrum in the range of the second overtone OH-valence oscillation of the water molecule after one-hour exposure of the microwave EMR. In hemoglobin solutions in this spectral range there is a small but statistically significant increase in absorption. This may indicate on additional EM-induced activation of the libration motions of water molecules and an increase the probability of deformation oscillations that which are manifested in the near IR range in the band of the second overtone of water.

Влияние УФ-излучения на спектральные свойства 2,6-ди(гидроксиметил)-4-метилфенола

The effect of UV radiation on the spectral properties of aqueous solutions of 2,6-di(hydroxymethyl)-4-methylphenol has been studied. Pulsed excilamps based on working molecules: KrCl (222 nm), XeBr (283 nm), XeCl (308 nm) were used as UV radiation sources. The degree of photodegradation depends on the irradiation time, the concentration of the test compound, and the characteristics of the excilamp used for irradiation.

Simulation Study on Structure, Transport Proprerties, and Dielectric Properties of Aqueous Solutions of Bio-Molecules Used in Biofuel Cells

Simulation Study on Structure, Transport Proprerties, and Dielectric Properties of Aqueous Solutions of Bio-Molecules Used in Biofuel Cells

Microwave Dielectric Permittivity and the Relaxation of 1,3-Dioxolane and 2,2-Dimethyl-1,3-dioxolane-4-methanol Aqueous Solutions

Results are presented from measuring the microwave dielectric properties of aqueous solutions of 1,3-dioxolane and 2,2-dimethyl-1,3-dioxolane-4-methanol at seven frequencies in the range of 5–25 GHz and temperatures of 288, 298, and 308 K. The static dielectric constants are considered, along with the times and parameters of activation of the dielectric relaxation process. Differences between hydration-induced changes in water and the effects of interaction between different groups of molecules are established for the solutions of the considered compounds. The dynamics of water molecules in solution is slowed, compared to that in pure water in both cases. It is established that this slowing is due to different molecular mechanisms of interaction between the dissolved species and the tetrahedral network of the H-bonds of the initial water.

Equilibrium States in Aqueous Solutions of Some Ionic Liquids

Abstract—Physicochemical properties of aqueous solutions of a number of proton ionic liquids (electrical conductivity, dissociation parameters, pH, and concentration functions) are determined using specially designed equipment and the techniques of computer resistometry. The correlations between the physicochemical properties of water–organic mixtures and a possible structure of the organic phase are established.

ВПЛИВ ЕЛЕКТРОМАГНІТНОГО ВИПРОМІНЮВАННЯ МІЛІМЕТРОВОГО ДІАПАЗОНУ НА ОПТИЧНІ ВЛАСТИВОСТІ ГЕМОГЛОБІНУ

The biological activity of millimeter electromagnetic radiation (MEMR) has long been known that is the basis for its use in medicine. But the primary biophysical mechanisms of this factor at the molecular level remain poorly understood and debated. Because of it the features of the influence of microwave radiation on the optical properties of water solutions of hemoglobin with the aim to characterize the certain structural state of hemoglobin were investigated in this research. The object of the study was the optical properties of aqueous solutions of human hemoglobin in the concentration range of 7 and 15 μM and in the temperature range 10–40°C. The optical spectra were recorded by using a BiospecMini (Shimadzu) spectrophotometer in the wavelength range of 190–1100 nm. In order to increase the accuracy of the analysis of spectral data the spectra were normalized relative to the baseline which was taken as a line that ran parallel to the horizontal axis due to the minimum value of the optical density in the absorption spectrum. The values of the absorption maxima and the optical density were used as the main parameters of the absorption spectra. The B-spline function was used to more accurately determine these parameters. Microwave exposure of hemoglobin solutions was performed at wavelength of 7,1 mm with power that calculated to be approximately 6mW. This power of electromagnetic radiation corresponds to the conditional limit range between thermal and non-thermal action of this factor. The dependence of the optical properties of hemoglobin in the spectral range of heme absorption on temperature was analyzed and effects of microwave radiation on the optical properties of hemoglobin solutions were considered in frame of hypochromic effects induced by temperature. It was revealed that the parameters of the absorption spectrum of an aqueous solution of hemoglobin depend on temperature. The optical density in the Sore band and the spectral bands of the oxygenated form of hemoglobin decreases upon temperature increase. The observed temperature hypochromic effect is associated with increased protein aggregation. The effect of MEMR leads to a small but statistically significant hypochromism in the spectra of hemoglobin absorption that testifies an increase in protein aggregation under the action of this physical factor which cause the changes in the hydration of protein molecules. This effect depends on the protein concentration and is not detected at low concentrations.

One-pot synthesis and aqueous solution properties of pH-responsive schizophrenic diblock copolymer nanoparticles prepared via RAFT aqueous dispersion polymerization

Well-defined doubly pH-responsive schizophrenic diblock copolymer nanoparticles with tunable isoelectric points are prepared via RAFT aqueous dispersion polymerization using an efficient one-pot protocol.

Examining the Hofmeister Series through Activation Energies: Water Diffusion in Aqueous Alkali-Halide Solutions.

The effect of ions on the properties of aqueous solutions is often categorized in terms of the Hofmeister series that ranks them from chaotropes ("structure-breakers"), which weaken the surrounding hydrogen-bond network to kosmotropes ("structure-makers"), which enhance it. Here, we investigate the Hofmeister series in ∼1 M sodium-halide solutions using molecular dynamics simulations to calculate the effect of the identity and proximity of the halide anion on both the water diffusion coefficient and its activation energy. A recently developed method for calculating the activation energy from a single-temperature simulation is used, which also permits a rigorous decomposition into contributions from different interactions and motions. The mechanisms of the salt effects on the water dynamics are explored by separately considering water molecules based on their location relative to the ions. The results show that water diffusion is accelerated moving down the halide group from F- to I-. The behavior of the diffusion activation energy, Ea, is more complex, indicating a significant role for entropic effects. However, water molecules in the first or second solvation shell of an ion exhibit a decrease in Ea moving down the halide series and Na+ exhibits a larger effect than any of the anions. The Ea for water molecules within the second solvation shell of an ion are modest, indicating a short-ranged nature of the ion influence.

Studies of osmotic and activity coefficient properties of aqueous solutions of triethylammonium formate and triethylammonium glycolate protic ionic liquids at 298.15 K

The triethylammonium-based carboxylate protic ionic liquids (PILs) are called as truly bio-ionic liquids. They can be used as green solvent, additives (biphasic catalysis) and for other considerable effects involving nano-material specially related to biomolecules. In this work, osmotic coefficient (φ) measurements using vapor pressure osmometry technique for aqueous solutions of two PILs, namely, triethylammonium formate [TEAF] (0.01290–0.55988 mol·kg−1) and triethylammonium glycolate [TEAG] (0.00989–0.53176 mol·kg−1) have been reported at 298.15 K. The water activity (aw) and solvent activity coefficient (γ1), mean molal activity coefficient (γ±) of PILs and osmotic pressure (π) of solutions properties in a binary mixture, were determined using experimentally measured φ data. The analysis of osmotic pressure data revealed that the studied PILs are electrolytes in the limit of infinite dilution and yield correct molecular weights as well as show negative values for virial coefficients. The variations of osmotic coefficient and mean molal activity coefficient of studied PILs with concentration indicate positive deviations from Debye-Hückel limiting law similar to that of ammonium ions. Further, Gibbs free energy changes due to mixing (ΔGm) and excess Gibbs free energy changes (ΔGE) for the studied binary systems are estimated. The solute-solute virial coefficient (NB22∗0) for the studied PILs in aqueous solutions were estimated by an application of the McMillan−Mayer theory of solutions. The results indicate that the hydration effect is dominant in PILs through the cooperative H–bonding with water-structure making effect suggesting the significance of hydrophobic hydration as observed in tetraalkylammonium salts and aprotic ionic liquids. A need to study the water molecule splitting at nitrogen charge centre and possible attenuation of water structural effects due to hydrophobic moieties present in the molecule is emphasized.

Ecological Cutting Fluids.

This study deals with metalworking fluids (MWFs). According to DIN 51385, depending on their base, the fluids are divided into oil and water fluids. The oil bases include, among others, mineral, synthetic, vegetable and paraffin oils. This division does not comprise surfactant solutions which can be successfully used in metalworking. Due to the fact that this type of fluid was not qualified, a new type of lubricant based on the aqueous solutions of surfactants has been proposed. Two new notions have been introduced: surfactant working fluids (SWFs) for working fluids and surfactant lubricants (SLs) for all kinds of lubricants as a broader term. The effect of the physicochemical properties of aqueous solutions of sodium lauroyl sarcosinate (SLS), also known as sodium N-dodecanoyl-N-methyl glycinate, on tribological properties determined using a four-ball machine (Tester T-02) (Łukasiewicz Research Network—The Institute for Sustainable Technologies, Radom, Poland) was analyzed. On the basis of aqueous SLS solutions a composition of working fluids was developed and their functional properties were verified by means of tribological and stand tests as well as during operation. The test results obtained clearly indicate that functional properties of 2% solutions of sodium lauroyl sarcosinate with a foam inhibitor (0.05%) and a biocide (0.1%) are comparable to those of a quality commercial hydraulic fluid.

Drug release from hydroxypropylcellulose gels cannot be statistically predicted from their viscometric and initial viscoelastic properties

This study questioned whether rheological properties can predict drug (metronidazole) release from Hydroxypropylcellulose (HPC) platforms. Viscometric and viscoelastic properties of aqueous, alcohols/diols and mixed solvent HPC solutions and gels were determined using viscometry and oscillatory analysis. Drug release was conducted at pH 7.4 under sink conditions. Relationships between rheological parameters and drug release were modelled using multiple linear stepwise regression. Viscometry identified ethanol and water as good solvents for HPC. Diol solvents were predicted to exhibit greater interactions with HPC (COSMO modelling) but possessed lowest intrinsic viscosities. Pentanediol or ethylene glycol prepared gels exhibited greatest elasticity. No relationships were observed between dilute solution properties and initial gel viscoelasticity. Drug release from HPC gels occurred via gel erosion and diffusion. No relationships were observed between initial gel viscoelasticity and drug release and thus, for gel platforms that undergo erosion in aqueous media, drug release cannot be predicted from initial gel viscoelasticity.

ELECTROCHEMICAL PROPERTIES OF AQUEOUS SOLUTIONS OF SODIUM AMINOMETHANESULFONATES

The pH and conductometric study of the electrochemical properties of aqueous solutions (1∙10-4 ÷ 9∙10-3 М) YNHCH2SO3Na (Y = H, CH3, HOCH2CH2, (CH3)3C and C6H5CH2) was carried out. The values of the limiting electrical conductivity were calculated by extrapolation according to Shidlovsky. The activation parameters of the electrical conductivity of the systems “sodium aminomethanesulfonate – H2O” at 293-313 K were obtained.

Review of the Main Factors Affecting the Flotation of Phosphate Ores

The way to successfully upgrade a phosphate ore is based on the full understanding of its mineralogy, minerals surface properties, minerals distribution and liberation. The conception of a treatment process consists of choosing the proper operations with an adequate succession depending on the ore properties. Usually, froth flotation takes place in phosphate enrichment processes, since it is cheap, convenient, and well developed. Nevertheless, it is a complex technique as it depends on the mineral’s superficial properties in aqueous solutions. Aspects such as wettability, surface charge, zeta potential, and the solubility of minerals play a basic role in defining the flotation conditions. These aspects range from the reagents type and dosage to the pH of the pulp. Other variables namely particles size, froth stability, and bubbles size play critical roles during the treatment, as well. The overall aim is to control the selectivity and recovery of the process. The following review is an attempt to add to previous works gathering phosphate froth flotation data. In that sense, the relevant parameters of phosphate ores flotation are discussed while focusing on apatite, calcite, dolomite, and quartz as main constituent minerals.

Dynamic and Static Properties of Aqueous NaCl Solutions at 25°C as a Function of NaCl Concentration: A Molecular Dynamics Simulation Study

We present the result of molecular dynamics (MD) simulations to calculate the molar conductivity Λ m = λ N a + + λ C l − of NaCl in SPC/E water at 25°C as a function of NaCl concentration (c) using Ewald sums employing a velocity Verlet algorithm. It is found that the MD result for Λm with Ewald sum parameter κ = 0.10 Å−1 gives the closest one to the experimental data and that the obtained radial distribution functions g i i (r) with κ = 0.10 Å−1 show a dramatic change with a very deep minimum of g NaCl (r) and, as a result, sharp maxima of g NaNa (r) and g ClCl (r) at the distance 9.95 Å, which indicates a characteristic of ionic atmosphere, the basis of the Debye–Hückel theory of ionic solutions. The static and dynamic properties of NaCl (aq) solutions are analyzed in terms of radial distribution functions, hydration numbers, coordination numbers around Na+ and Cl−, residence times of water around Na+ and Cl−, water diffusion, and ion-ion electrostatic energies to explain the behavior of the molar conductivity Λm of NaCl obtained from our MD simulations.