Properties Of Aqueous Solutions Research Articles

Coarse-Grained Force Field for Polyethylene Oxide and Polyethylene Glycol Aqueous Solutions Based on a Polarizable Water Model

A new, accurate and transferable coarse-grained (CG) force field (FF) for polyethylene oxide (PEO) and polyethylene glycol (PEG) aqueous solutions based on a polarizable CG water (PCGW) model is developed in this work. A PCGW bead, which represents four water molecules, is modeled as two charged dummy particles connected by two constrained bonds to a central neutral particle; a PEO or PEG oligomer is modeled as a chain with repeated middle beads (PEOM) representing diether groups and two terminal beads (PEOT or PEGT) of a different type compared to PEOM. To describe nonbonded van der Waals interactions, a piecewise Morse potential with four tunable parameters is used. The force parameters are automatically and rigorously optimized by a meta-multilinear interpolation parameterization (meta-MIP) algorithm to simultaneously match multiple thermodynamic properties, including the density, heat of vaporization, vapor-liquid interfacial tension, and solvation free energy of the pure PEO or PEG oligomer bulk system as well as the mixing density and hydration free energy of the oligomer/water binary mixture. Additional thermodynamic and structural properties for longer PEO and PEG polymer aqueous solutions, such as the self-diffusion coefficient, radius of gyration, and end-to-end distance, are predicted to test the accuracy and transferability of this new CG FF. Based on the PCGW model, the presented FF optimization algorithm and strategy can be extended to more complex polyelectrolytes and surfactants.

Micellar and solubilizing properties of rhamnolipids.

We studied the micellar and solubilizing properties of aqueous solutions of unfractionated rhamnolipids produced by Pseudomonas aeruginosa. We used nuclear magnetic resonance (NMR) diffusometry, dynamic light scattering, and conductometry to measure the critical micelle concentration (CMC) of rhamnolipid solutions and determined the effective hydrodynamic radii of rhamnolipid monomers and micelles. Based on selective measurements of the self-diffusion coefficients of molecules, performed by NMR diffusometry, the solubilizing properties of rhamnolipids were studied depending on their concentration in solution; aromatic hydrocarbons, benzene, toluene, ethylbenzene, and para-xylene were taken as solubilizates. On the basis of the measurement results, we estimated the distribution coefficient of the solubilizate between the micellar (solubilized) and free (in the aqueous phase) states and the solubilizing capacity of rhamnolipid micelles.

Effect of anions and cations on the self-assembly of ionic liquid surfactants in aqueous solution

Ionic liquid surfactants have shown increasing promise for substituting the traditional amphiphiles due to their flexible tunability and superior physicochemical properties. However, the effect of cationic structure and anion type on the surface properties of ionic liquid surfactants remains unclear. Herein, four ionic liquid surfactants [C12mim][BF4], [PyC12][Br], [C12mim][Br] and [PyC12][BF4] with the same alkyl side chain length were designed and synthesized. Their surface properties, such as micelle-free energy (ΔGmθ), surface tension reduction efficiency (ПCMC), and adsorption efficiency (pC20), and the influence of the type and structure of the anion and cation on their micellar physicochemical properties in aqueous solution were discussed according to the data. The proposed approach demonstrates that the critical micelle concentration (CMC) is determined by combining electrostatic and hydrophobic effects. When the anion is BF4−, the ionic liquid has a lower CMC, and BF4− has a superior hydrophobic effect, which allows the ionic liquid to form micelles more easily. In addition, the ionic liquid of tetrafluoroborate has higher interfacial activity (larger pC20) at the same temperature and its aqueous solution has lower surface tension, making it a more desirable surfactant. All four types of ionic liquids have negative values of ΔGmθ, implying that micelle formation is a spontaneous process. The surface activity of imidazolium- and pyridinium-based ionic liquids was slightly different from the critical micelle concentration under the same anion and carbon chain length. Imidazole and pyridine have highly similar hydrophobic and electrostatic effects, and the cation may not be the most critical factor affecting the surface properties.

Phase Equilibria and Thermodynamic Properties of Phases in the H2O–Gd(NO3)3 System

Solid–liquid equilibria in the system H2O–Gd(NO3)3 were measured from –20 to 70°C using the isothermal saturation method. The Pitzer–Simonson–Clegg thermodynamic model was implemented to obtain the temperature dependence of Gd(NO3)3⋅6H2O solubility constant, to calculate salt solubility and to construct a phase diagram of the system from eutectic point to hydrate melting. Thermochemical properties of gadolinium nitrate aqueous solutions, such as dilution enthalpies and heat capacities, were assessed also. The model has shown to be reliable for phase equilibria calculation from –35 to 90°C and from 0 up to ~15 mol % of salt as well as the thermodynamic properties of Gd(NO3)3 aqueous solutions at room temperature and around it.

The aqueous supramolecular chemistry of crown ethers.

This mini-review summarizes the seminal exploration of aqueous supramolecular chemistry of crown ether macrocycles. In history, most research of crown ethers were focusing on their supramolecular chemistry in organic phase or in gas phase. In sharp contrast, the recent research evidently reveal that crown ethers are very suitable for studying abroad range of the properties and applications of water interactions, from: high water-solubility, control of Hofmeister series, "structural water", and supramolecular adhesives. Key studies revealing more details about the properties of water and aqueous solutions are highlighted.

End‐group controlling aqueous solution properties in star‐shaped poly(2‐hydroxyethyl acrylate) and poly(2‐hydroxyethyl acrylate)‐b‐poly(N‐isopropylacrylamide) polymers

AbstractStar‐shaped poly(2‐hydroxyethyl acrylate) (PHEA)6 polymers were synthesized using hexafunctional chain transfer agent (CTA) trithiocarbonate type via reversible addition‐fragmentation chain transfer (RAFT) polymerization. The (PHEA)6 polymers with dodecyl chain‐end were non‐water soluble. As the molecular weight increased, the polymers could disperse in water, forming large aggregates with a DH of 1027 to 525 nm. On the contrary, the (PHEA)6 polymers with the carboxylic acid group at the chain‐end were completely soluble in water. Then, (PHEA)6 polymers were chain extended with N‐isopropylacrylamide (NIPAM) to obtain poly(2‐hydroxyethyl acrylate)‐b‐poly(N‐isopropylacrylamide) (PHEA‐b‐PNIPAM) block copolymers. The dodecyl group strongly affects the aqueous solution properties of the copolymers even with a high PNIPAM content. Copolymers with dodecyl chain‐end were insoluble or partially soluble in water, forming large aggregates (0.5 mg/ml in distilled water). The copolymers with carboxylic acid end‐group were totally water soluble. The thermo‐responsive phase behavior of the star‐shaped block copolymers was studied, and for this purpose, it was necessary to remove the RAFT group containing the dodecyl tail. The intense turbidity observed in the aqueous dispersions of the corresponding copolymers made it challenging to determine the LCST accurately. The copolymers with a carboxylic end group were evaluated as is.

Engineering chitosan into fully bio-sourced, water-soluble and enhanced antibacterial poly(aprotic/protic ionic liquid)s packaging membrane

The design and facile preparation of water-soluble and eco-friendly polymer packaging membrane materials is a fascinating research topic, particularly in terms of the increasing concerns on potential microplastics pollution in ecosystem. In this study, taking advantages of the structural features of chitosan (CS) and betaine hydrochloride (BHC), fully bio-sourced and water-soluble poly(aprotic/protic ionic liquid)s (PAPILs) were successfully designed and prepared through the reaction of the amino groups in CS and carboxyl groups in BHC. The structure and thermo-properties of the PAPILs were elucidated by a series of characteristic methods. The rheological properties of the PAPILs aqueous solutions were also investigated. Moreover, water-soluble PAPILs membrane with a smooth surface morphology and a tensile strength of 62.9 MPa was successfully prepared. The PAPILs membrane also exhibited satisfactory biocompatibility, excellent antibacterial activities and high oxygen barrier property. Together with these outstanding material performance and functionality, as a “proof of concept”, the potential use of the PAPILs membrane as water-soluble packaging material for laundry detergent capsule and pesticide was preliminarily demonstrated. These findings provide significant insights for the design of sustainable and functional packaging materials by using natural resources.

Micelle Formation of Dodecanoic Acid with Alkali Metal Counterions.

Alkali series with different atomic numbers affect the physicochemical properties of aqueous solutions. The micellar properties of aqueous solutions of dodecanoate as surfactants were measured by changing the counterions (C12-Na, C12-K, C12-Rb, and C12-Cs). A plot of Krafft temperature vs. alkali metal atomic number showed a downward convex curve, with its minimum temperature (20°C) in the C12-K system. By contrast, a plot of the critical micelle concentration (CMC) vs. alkali metal atomic number exhibited an upward convex curve with the maximum CMC (25.6 mmol L-1) at C12-K. Furthermore, the minimum surface tension (γ min ) of the solution at the CMC increased with increasing atomic number (C12-Na ≈ C12-K < C12-Rb < C12-Cs). The size of the dodecanoate micelles decreased with increasing atomic number. The ionization degree of the micelles also increased with increasing atomic number of the alkali metal. Small-angle X-ray scattering (SAXS) measurements revealed that alkali dodecanoate micelles formed spherical to ellipsoidal structures. In addition, micelles from the shell region showed large electrostatic repulsion, judging from the shape of the spectrum in the higher Q -1 region. From the measurement results of the solubilization of naphthalene into the micelles, the size of the micelles corresponded to the maximum solubilization quantity of naphthalene.

Relationship between the major parameters of warm-blooded organisms' life activity and the properties of aqueous salt solutions

&lt;abstract&gt; &lt;p&gt;We are devoted to the physical analysis of the habitat area of warm-blooded organisms – humans and many mammals. For this purpose, the establishment of equilibrium distribution of carbon dioxide in aqueous solutions of salts in contact with atmospheric air starting from some time is investigated. More precisely, the relaxation time of carbon dioxide, as a function of temperature and pH, is investigated. It is found that the pH-relaxation time &lt;italic&gt;τ&lt;sub&gt;S&lt;/sub&gt;&lt;/italic&gt; is a very nontrivial function of temperature, pH values, and NaCl salt concentration. It was assumed that the minimum value of pH relaxation time corresponds to the optimal rate of physical processes in living matter. Using this selection principle and our experimental data, we have shown that the optimal temperature for human and mammalian life activity is close to &lt;italic&gt;T&lt;sub&gt;o&lt;/sub&gt;&lt;/italic&gt; ≈ 37 °C. The lower and upper temperature limits for their possible activity are close to &lt;italic&gt;T&lt;sub&gt;l&lt;/sub&gt;&lt;/italic&gt; ≈ 30 °C and &lt;italic&gt;T&lt;sub&gt;u&lt;/sub&gt;&lt;/italic&gt; ≈ 42 °C, respectively. The optimal value of &lt;italic&gt;pH&lt;/italic&gt;&lt;sub&gt;o&lt;/sub&gt;, determined by the same selection principle, also becomes true if supplemented by the influence of albumin and other proteins.&lt;/p&gt; &lt;/abstract&gt;

New insights into the protein stabilizing effects of trehalose by comparing with sucrose.

Disaccharides are well known to be efficient stabilizers of proteins, for example in the case of lyophilization or cryopreservation. However, although all disaccharides seem to exhibit bioprotective and stabilizing properties, it is clear that trehalose is generally superior compared to other disaccharides. The aim of this study was to understand this by comparing how the structural and dynamical properties of aqueous trehalose and sucrose solutions influence the protein myoglobin (Mb). The structural studies were based on neutron and X-ray diffraction in combination with empirical potential structure refinement (EPSR) modeling, whereas the dynamical studies were based on quasielastic neutron scattering (QENS) and molecular dynamics (MD) simulations. The results show that the overall differences in the structure and dynamics of the two systems are small, but nevertheless there are some important differences which may explain the superior stabilizing effects of trehalose. It was found that in both systems the protein is preferentially hydrated by water, but that this effect is more pronounced for trehalose, i.e. trehalose forms less hydrogen bonds to the protein surface than sucrose. Furthermore, the rotational motion around dihedrals between the two glucose rings of trehalose is slower than in the case of the dihedrals between the glucose and fructose rings of sucrose. This leads to a less perturbed protein structure in the case of trehalose. The observations indicate that an aqueous environment closest to the protein molecules is beneficial for an efficient bioprotective solution.

Influence of a CO2-switchable additive on the surface and foaming properties of a cationic non-switchable surfactant.

Switchable materials in general and CO2-switchable materials in particular are of great interest in environmental research. The replacement of common non-switchable materials (solutions, solvents, surfactants, etc.) with their switchable counterparts has a great potential to make processes more environmentally friendly by enhancing reusability and circularity and thus reducing energy costs and material consumption. Inspired by this, the present work deals with the surface and foaming properties of aqueous solutions of a non-switchable surfactant in presence of a CO2-switchable additive. A 1 : 1 and a 1 : 5 (molar ratios) mixture of the non-switchable surfactant C14TAB (tetradecyltrimethylammonium bromide) and the CO2-switchable additive TMBDA (N,N,N,N-tetramethyl-1,4-butanediamine) were investigated. It was found that surface properties, foamability, and foam stability can be changed by switching the additive with CO2 as a trigger. This observation can be explained by the fact that TMBDA is surface active in its unprotonated, i.e. neutral form, which disturbs the tight packing of the surfactant molecules on the surface. As a consequence, foams generated with surfactant solutions containing the neutral TMBDA are less stable than their TMBDA-free counterparts. On the other hand, the switched diprotonated additive is a 2 : 1 electrolyte with hardly any surface activity and thus does not affect surface and foam properties.

Процессы молекулярного переноса в жидкостных питательных средах дрожжевой и пивной отраслях промышленности. Часть 3. Исследование теплофизических свойств водных растворов мелассы и концентрата пивного сусла

Thermophysical properties of aqueous solutions of molasses and beer wort concentrate with different dry matter content in a wide range of temperature changes were investigated. Seven samples of aqueous solution of beet molasses with an initial dry matter concentration of 77.7 wt.% and seven samples of beer wort concentrate with an initial dry matter concentration of 81 wt.% were studied. The temperature variation range was 10–70℃ with a discreteness of 10℃. Thermal conductivity, specific heat capacity, and thermal diffusivity of the initial solutions were determined by unsteady plane source and differential scanning calorimetry methods. Numerical values of the above-mentioned thermal constants for aqueous solutions of beet molasses in the range of dry matter mass concentrations n of from 16 to 70% at the temperatures of from 293 to 353 K and of beer wort concentrate in the range of dry matter mass concentrations of from 10.2 to 72.4% at temperatures from 284 to 342 K have been experimentally established. Graphical dependences of heat capacity, thermal conductivity, and thermal diffusivity of these parameters on temperature are given. Design equations of the required parameters are obtained, which are of interest both from the point of view of fundamental science on the development of the theory for liquid state of matter, and from the applied point of view of engineering calculations and design of biotechnological equipment.

The evolution of solvation symmetry and composition in Zn halide aqueous solutions from dilute to extreme concentrations.

The emergence of cation-anion species, or contact ion pairs, is fundamental to understanding the physical properties of aqueous solutions when moving from the ideal, low-concentration limit to the manifestly non-ideal limits of very high solute concentration or constituent ion activity. We focus here on Zn halide solutions both as a model system and also as an exemplar of the applications spanning from (i) electrical energy storage via the paradigm of water in salt electrolyte (WiSE) to (ii) the physical chemistry of brines in geochemistry to (iii) the long-standing problem of nucleation. Using a combination of experimental and theoretical approaches we quantify the halide coordination number and changing coordination geometry without embedded use of theoretical equilibrium constants. These results and the associated methods, notably including the use of valence-to-core X-ray emission spectroscopy, provide new insights into the Zn halide system and new research directions in the physical chemistry of concentrated electrolytes.

Multiscale investigation of viscoelastic properties of aqueous solutions of sodium alginate and evaluation of their biocompatibility.

In order to get better knowledge of mechanical properties from microscopic to macroscopic scale of biopolymers, viscoelastic bulk properties of aqueous solutions of sodium alginate were studied at different scales by combining macroscopic shear rheology (Hz), diffusing-wave spectroscopy microrheology (kHz-MHz) and Brillouin spectroscopy (GHz). Structural properties were also directly probed by small-angle X-ray scattering (SAXS). The results demonstrate a change from polyelectrolyte behavior to neutral polymer behavior by increasing polymer concentration with the determination of characteristic sizes (persistence length, correlation length). The viscoelastic properties probed at the phonon wavelength much higher than the ones obtained at low frequency reflect the variation of microscopic viscosity. First experiments obtained by metabolic activity assays with mouse embryonic fibroblasts showed biocompatibility of sodium alginate aqueous solutions in the studied range of concentrations (2.5-10 g L-1) and consequently their potential biomedical applications.

Binaphthanol-derived emitters with aggregation-induced emission, acidochromic and chiral optical properties

The development of chiral organic fluorescent molecules has attracted broad attention for their various optical applications. In this work, four pairs of chiral fluorescent molecules based on binaphthanol structure have been designed and synthesized. These molecules show blue fluorescent emission in organic solvents with good fluorescent quantum yields and large Stokes shifts. The molecules with benzoxazole moiety display aggregation-induced emission effect in methanol/water solutions, while molecules with quinazolinone moiety show aggregation-caused quenching properties. Moreover, compounds with quinazolinone moiety exhibit acidochromic properties in aqueous solution with different pH values, and their emission intensity are significantly enhanced in strongly acidic conditions. The chiral molecules generally have good circular dichroism intensity. Their R- and S- enantiomers show mirror-imaged circular dichroism curves. Further studies reveal that compound with mono quinazolinone moiety has specific aggregation-induced circular dichroism enhancement properties. This work provides a new strategy for obtaining chiral BINOL-based fluorescent molecules with unique optical properties.

Calculation of Dynamic Properties of Drug-Added Aqueous Solutions with T1 T2 Relaxation Times

The development of modern spectroscopic methods has facilitated and accelerated structure analysis. The NMR method is the most popular way to perform structural analysis of compounds with very complex structures.D2O is a solvent that is frequently used in NMR analysis of both chemical molecules and many biological molecules such as drugs, proteins, and enzymes. In this paper, the study of residual water in proton drug-added protein solutions was carried out via NMR relaxation. The spin-lattice (T1) and the spin-spin relaxation (T2) times of residual water in drug-added protein solutions were studied depending on temperature by Avance Bruker 400 MHz 1H-NMR Spectrometer, and activation energies (Ea) and rotational correlation times (τ0 and τc) have been determined for T1 and T2 relaxation times.

The Synthesis of ZnMn2O4 by Glycine Nitrate Combustion and an Examination of Its Electrochemical Properties in Aqueous Solutions of ZnCl2 and NaNO3

The Synthesis of ZnMn2O4 by Glycine Nitrate Combustion and an Examination of Its Electrochemical Properties in Aqueous Solutions of ZnCl2 and NaNO3

Influence of ice formation on the dynamic and thermodynamic properties of aqueous solutions

Influence of ice formation on the dynamic and thermodynamic properties of aqueous solutions

Synthesis and dilute aqueous solution properties of cationic antistatic surfactant functionalized with hydroxyl and ether groups

Abstract Polyester fibers tend to generate and accumulate electrical charges under friction and induction. This significantly affects the production and use process and even poses the risk of electric shocks and fire. Quaternary ammonium salt surfactants with a positive charge can be adsorbed on negatively charged polyester fibers and have excellent antistatic properties. Therefore, we have synthesised a cationic antistatic surfactant functionalised with hydroxyl and ether groups: N-hexadecyl-N,N-dimethyl-N-butanoxy glycerol ether ammonium chloride (HDBGA). The structure was characterized by 1H NMR, FTIR and ESI/MS. The excellent properties of HDBGA in aqueous solution were investigated by measuring the Krafft point (TK), surface tension, conductivity, and steady-state fluorescence. Also antistatic tests were carried out. The results show that the TK of HDBGA is below 0 °C indicating that it can still be applied in cold water. The new quaternary ammonium compound could effectively decrease the surface tension of aqueous solution to 31.28 mN m−1, where the critical micelle concentration (CMC) at 298.15 K was 3.83 × 10−4 mol L−1. In addition, the static electricity and static half-life values of the polyester cloths treated with the HDBGA solutions were also measured, as well as the effects on the fabric properties. The product exhibited excellent antistatic properties and satisfactory wash resistance, and the fabric fibers were not damaged.

Assessment of the robustness of MIL-88A in an aqueous solution: Experimental and DFT investigations

The stability of metal organic frameworks (MOFs) in a water-rich environment is a topic of significant importance, especially for adsorption and water purification applications. MIL-88A containing iron ions and fumaric acid ligands, was synthesized through a water-based viable strategy. The robustness of MIL-88A in aqueous solutions was studied experimentally, through evaluating the chemical, thermal, and hydrolytic stability of this compound by varying the conditions and properties of aqueous solutions. Different characterization techniques were employed to explore the features of the synthesized MIL-88A such as XRD, SEM, FTIR, TGA, UV–vis DRS, zeta potential, and MP-AES measurements. The electronic structure was studied on a model nanocrystal with density functional theory (DFT) calculations. The MIL-88A structure was drastically affected in basic medium as confirmed by the characterization techniques used. MIL-88A became completely amorphous upon exposure to boiling water. The hydrolytic stability results showed that MIL-88A loses gradually its structural integrity in each water cycle.