Thermodynamic studies on the interaction of some ureas and salts with micellar triton-X-100 in aqueous solutions

We have determined the enthalpies of solution in the micellar state (ΔH_s) for Triton-X-100 in 1 m aqueous solutions of urea, 1,3-dimethyl urea, tetramethyl urea, sodium chloride and calcium chloride at 298.15 K and 308.15 K. These results were used to evaluate the heat capacities of solution (ΔC_p,s) for Triton-X-100 micelles in these solvent systems. It has been observed that ΔC_p,s values of micellar Triton-X-100 decreases drastically upon transfer from water to these solutions but is positive in all cases. Thus, the heat capacities of transfer of Triton-X-100 micelles (ΔC_p,tr) are negative in all the systems studied. A comparison of the effect of non-electrolytes (ureas) and electrolytes (salts) on the micelle has been presented. The results have been discussed in terms of the relative water-structure-disrupting tendencies of the ureas and the salts.     

Transport studies of multielectrolyte solutions across a sintered disc impregnated with cellulose acetate

Experimental results for the measurement of electroosmotic pressure, electroosmotic velocity and streaming potential for different aqueous solutions of ammonium chloride—ammonium nitrate through a sintered disc impregnated with cellulose acetate at 30°C are reported. The data have been analysed in the light of non-equilibrium thermodynamics. The Onsager reciprocity relation has been found to hold good for all the systems. The efficiencies of electrokinetic energy conversion have also been determined. The maximum values of conversion efficiencies for both the modes of conversion, i.e., electroosmotic flow and streaming potential, have been found to be equal to each other and independent of the applied input forces.     

Effect of concentration polarization on electrodialytic concentrating of dilute NaCl and NH4NO3 solutions

Electrodialytic concentrating of dilute sodium chloride and ammonium nitrate solutions is studied in a wide range of current densities. Using the model of limiting electrodialytic concentrating, based on the experimental data, the transport characteristics of MK-40/MA-40 membrane pair in the above electrolytes and the hydration numbers of these electrolytes were determined. It is found that a degree of concentration polarization has an effect on the main parameters of limiting electrodialytic concentrating: the current efficiency, the water transfer number across the test membrane pair, and the concentration of solution in the concentrating compartment. These parameters determine the effectiveness of concentrating. It is found that the electrodialytic concentrating is most effective at the limiting current due to the lowest electroosmotic permeability of membrane pair and the highest current efficiency.     

Electroosmotic transport of water and aprotic solvent in heterogeneous membranes

Electrosmotic water transport in MK-40, MA-40, and MA-41 electrodialysis membranes before and after their treatment by aprotic solvent solution and electroosmotic permeability of a MK-40/MA-40 membrane couple in water and N,N-dimethyl acetamide were studied for the first time. It is found that N,N-dimethyl acetamide produces practically no effect on the properties of the studied ion-exchange materials and its transport number through the MK-40/MA-40 membrane couple is independent both of the initial lithium chloride concentration in a desalting cell of the concentrator electrodyalizer and its volume fraction in the solution. The initial concentration of lithium chloride in the desalting cell does not affect the transport numbers of water in the studied membrane couple either. However, these depend on the volume fraction of the organic component in the solution and this dependence features an extremum. A method for estimation of electroosmotic permeability of the membrane couple in aqueous-organic solutions of electrolytes is suggested.     

Studies on the electrochemical and permeation characteristics of asymmetric charged porous membranes

Asymmetric charged porous membranes were prepared by imbedding 10% (W/W) ion-exchange resin in cellulose acetate binder. Membrane potential and conductance measurements have been carried out in sodium chloride solutions at different concentrations to investigate the relationship between concentration of fixed charges and electrochemical properties of developed nonselective cation- and anion-exchange membranes. Counterion transport number and permselectivity of these membranes were found to vary due to the presence of ion-exchange resin. The hydrodynamic and electroosmotic permeability of sodium chloride solutions has been studied in order to compute equivalent pore radius. For cation- and anion-exchange membranes good agreement was observed between pore radius values estimated from hydrodynamic and electroosmotic permeability coefficient separately, while for nonselective membranes no correlation was found. Membrane conductance data, along with values of concentration of fixed charges, were used for the estimation of the tortuosity factor, salt permeability coefficient, and frictional coefficient between solute and membrane matrix employing an interpretation by nonequilibrium thermodynamic principles based on frictional forces. Moreover, surface morphological studies of these membranes also have been carried out and the membranes were found to be reasonably homogeneous.     

Electrodeposition of zinc coatings from the solutions of zinc oxide in imidazolium chloride/urea mixtures

To solve the inherent disadvantages in conventional processes for electrodeposition of zinc, it’s necessary to develop more high-efficiency and environmentally friendly electrolytes. In this work, it was found that the dissolution of ZnO was remarkably enhanced in some imidazolium chloride by the addition of urea, and the solubility of ZnO in 1:1 [Amim]Cl/urea mixture was as high as 8.35 wt% at 373.2 K. Electrochemical measurements showed that zinc could be readily electrodeposited from the solutions of ZnO. Bright, dense and well adherent zinc coatings with good purity were obtained from 0.6 M solution of ZnO in 1:1 [Amim]Cl/urea at 323.2 343.2 K. It’s expected that the solutions of ZnO in imidazolium chloride/urea mixtures have the potential to replace the traditional electrolytes, especially toxic zinc chloride-based ones for zinc electroplating, as well as preparation of zinc materials.     

在电解质溶液中测定非电解质溶解度的新方法

提出了一种可以同时测定电解质溶液中非电解质的溶解度和饱和溶液水活度的新方法。该法把等压平衡与传统化学分析统一起来,其优点是：（1）将多元饱和溶液中非电解质溶解度的测定转变为共存离子的溶度测定,避开了对非电解质难于进行精确化学分析的难题;（2）可以同时确定所测饱和体系的水活度。用该法测定了NaCl和KCl溶液中甘露醇的溶解度并与文献值进行了比较,结果表明二者符合得很好。     

Determination of the migration times of flow measurement markers in CEC

The electroosmotic migration times of fructose, water, and phenol have been measured in several solutions. The electroosmotic flow rate was fundamentally dependent on buffer concentration and on the concentration of additives such as sodium chloride; additives such as methanol and sodium dodecylsulfate did not influence the flow rate, yet tetrabutylammonium bromide had a significant effect.     

Specific background electrolytes for nonaqueous capillary electrophoresis

The use of organic solvents or mixture of solvents in capillary electrophoresis is gaining wider attention. The electroosmotic flow mobility of eight organic solvents (acetonitrile, acetone, dimethylformamide, dimetylsulphoxide, propylene carbonate, methanol, ethanol, n-propanol) and of mixtures of several solvents (methanol-acetonitrile, methanol-propylene carbonate, acetonitrile-propylene carbonate) has been studied. The influence of 1,3-alkylimidazolium salts in different solvents on the separation of different analytes has been investigated. Some of these salts have shown usefulness for matrix-assisted laser desorption ionization matrices and off-line analysis of electrophoresis fractions. It also appears that nonaqueous capillary electrophoresis with 1,3-alkylimidazolium salts as background electrolytes is suitable for separation small inorganic ions.     

Salt addition effect on partition coefficient of some phenolic compounds constituents of olive mill wastewater in 1-octanol-water system at 298.15 K

The 1-octanol-water partition coefficient is an important property to measure the hydrophobicity of organic compounds, which has been demonstrated to be a parameter in studying the conformation of biomolecules in aqueous solutions. For biological systems, electrolytes play an important role in thermodynamic properties. The salt addition effect on the distribution of phenolic compounds between water and 1-octanol at 298.15 K has been studied. The phenolic compounds used were vanillic acid, protocatechuic acid, vanillin, tyrosol, cathecol, caffeic acid and syringic acid, and the considered salts were potassium chloride, sodium chloride and lithium chloride. The influence of both the concentration and size of the added salt on the partition coefficient (K _ow) have been considered. This study shows a salting in with the following decreasing order: LiCl > NaCl > KCl. The Gibbs energies of transfer of phenolic compounds (168–1) form chloride solutions to organic phase have been calculated using experimental 1-octanol-water partition coefficients.     

Ion and water transport during lithium chloride concentration from aqueous organic solutions by electrodialysis

The concentration of lithium chloride from aqueous organic solutions with different volume concentrations of N,N-dimethylacetamide (DMAA) was studied experimentally. An extended model of the limiting electrodialysis concentration of electrolytes from mixed media was developed. The model takes into account the osmotic and electroosmotic mechanisms of the transfer of water and organic solvent, as well as the electromigration and diffusion mechanisms of the salt transfer. Using the experimental data and the extended model, we evaluated the transport parameters of the MK-40/MA-40 membrane pair in aprotic solutions of variable compositions and studied how they changed with an increase in the volume fraction of DMAA in a mixed solution. The contribution of each of these mechanisms of ion and water transport to the electrodialysis concentration of electrolyte from aqueous and organic aqueous solutions was determined. Electroosmotic transfer was found to be the main mechanism of the solvent transfer that limits the stage of the electrodialysis concentration of the electrolyte from aqueous and organic aqueous solutions.     

Modulated photophysics of 3-pyrazolyl-2-pyrazoline derivative entrapped in micellar assembly

The photophysical behavior of 3-pyrazolyl-2-pyrazoline derivative (PZ), a newly synthesized biologically active compound has been studied in micellar solutions of anionic sodium dodecyl sulfate (SDS), cationic cetyl trimethylammonium bromide (CTAB) and nonionic p- tert-octylphenoxy polyoxyethanol (Triton X-100, TX-100) micelle using steady state and time-resolved fluorescence spectroscopy technique. Influence of the micelles on the photophysics of PZ has also been investigated using different approaches. The location of the fluorophore PZ in the micelle has been identified by cetyl pyridinium chloride (CpCl) induced fluorescence quenching and micropolarity surrounding that fluorophore in micellar solution. The effect of urea on the steady state fluorescence and relaxation dynamics of the micelle bound probe has also been observed. The results have been interpreted in terms of the model that urea displaces water molecules from the micellar interface and the consequent destabilization leads to the expulsion of the probe molecules from the interfacial region. An attempt has been made to determine probe sensing microviscosities for these micellar microenvironments in the light of average reorientation times of the probe PZ.     

Electroosmotic-capillary penetration in circular microchannels

Electroosmotic forces can be used to promote penetration of electrolytes in microcapillaries. Analytical solutions for the dynamics of penetration are provided. The investigation includes both the electroosmotic and Poiseuille flows. For horizontal microcapillaries, the expression extends the Lucas-Washburn equation to account for the presence of electroosmotic effects. An analytical solution is also obtained for the case where gravity effects come into play.     

以二(三氟甲基磺酰)亚胺锂为基底的室温熔融盐电解质热学及电化学性质的比较研究

制备了一系列二(三氟甲基磺酰)亚胺锂[LiN(SO₂CF3)₂,LiTFSI]与尿素及其衍生物形成的新型室温熔融盐电解质,并对其热学性质及电导率进行了比较研究.受甲基取代基的影响,LiTFSI-甲基脲体系的共熔温度最低,为-38℃.LiTFSI-尿素体系的室温电导率最高,为1.74×10^-4S/cm,50℃电导率为1.24×10^-3S/cm.     

ITSTUDIES ON THE EFFECT OF UREA ON THE COMPATIBILITY OF PMMA/PVC MIXTURES IN DMF BY A DILUTE- SOLUTION VISCOMETRY METHOD

The interaction between poly(methymethacrylate) (PMMA) and poly(vinyl chloride) (PVC) has been studied indilute urea solutions of dimethylformamide (DMF) at 28℃ using a dilute solution viscometry method. The results show thatthe polymer mixtures are compatible in DMF solution in the absence of urea. The influence of urea addition on the degree ofcompatibility of the polymer mixtures has been studied in terms of the compatibility parameters (△b_m and △[η]_m). It wasfound that the compatibility of the polymer mixtures is decreased with increasing urea addition, passing through a minimumat 0.5 M urea.     

Electroosmosis through a Cation-Exchange Membrane: Effect of an ac Perturbation on the Electroosmotic Flow

Electroosmosis experiments through a cation-exchange membrane have been performed using NaCl solutions in different experimental situations. The influence of an alternating (ac) sinusoidal perturbation, of known angular frequency and small amplitude, superimposed to the usual applied continuous (dc) signal on the electroosmotic flow has been studied. The experimental results show that the presence of the ac perturbation affects the electroosmotic flow value, depending on the frequency of the ac signal and on the solution stirring conditions. In the frequency range studied, two regions have been observed where the electroosmotic flow reaches a maximum value: one at low frequencies (Hz); and another at frequencies of the order of kHz. These regions could be related to membrane relaxation phenomena.     

Computational study of urea and its homologue glycinamide: conformations, rotational barriers, and relative interactions with sodium chloride

Conformational behaviors of urea and glycinamide have been investigated using the B3LYP functional with the 6-311+G* and 6-311+G** basis sets. Urea monomers have nonplanar minima at all the levels studied, even in the aqueous phase. In the case of glycinamide, the intramolecular hydrogen bond formed from the amide to the amine is important for stabilizing the global minimum. Bond rotations and nitrogen inversion barriers for glycinamide conformations have also been reported. The DFT calculated results suggest that urea conformers interact preferentially with the {111} surface of sodium chloride and such interactions can be responsible for the change in the habit of sodium chloride. Glycinamide conformers have a lower affinity toward the {111} surface of sodium chloride in water. The pyramidality of nitrogens in urea conformers does not influence the relative trends of interaction energies with sodium chloride surfaces. The mode of interactions predicted at the LDA/PWC/DND level for urea and glycinamide with sodium chloride for both slab and cluster models shows that the amide functionality (-CONH2) interacts with both Na(+) and Cl(-) ions on the {100} surface; however, the carbonyl oxygen of these additives predominantly interacts with the sodium ions on the {111} surface.     

Determination of amino acids, vitamins, and drug substances in aqueous solutions using new potentiometric sensors with Donnan potential as analytical signal

Basic principles of a new potentiometric sensor are considered. Its analytical signal is the Donnan potential at the ion-exchange polymer/studied solution of electrolyte interface. Assessments of potential drops at individual interfaces are presented, same as estimates of diffusion potentials in the electrochemical circuit for measurement of the sensor response. It is shown that the overall contribution of the values of all potentials to EMF of the electrochemical circuit, except for the Donnan potential, at the ion-exchange polymer/studied solution interface are negligibly low as compared to the experimental values of the circuit EMF in the studied systems. Certain regularities of the Donnan potential formation are studied in the systems with the polymers of different structure and solutions containing inorganic ions and organic electrolytes in different ionic forms. The possibility is shown of using a sensor with such an analytical signal as the Donnan potential for assay of amino acids, vitamins, and drug substances in aqueous solutions. The sensor was used as a selective electrode for determination of lysine in aqueous solutions with neutral amino acids in the range of pH 5.0–7.0 and glycine in aqueous alkali solutions in the range of pH 9.00–11.00. The developed sensor is introduced as a cross-sensitive electrode into the array of multisensor systems for multicomponent quantitative analysis of the lysine monohydrochloride, thiamine chloride, novocaine hydrochloride, lidocaine hydrochloride solutions containing potassium and sodium chlorides. The measurement error of electrolytes in aqueous solutions did not exceed 10%.     

Fast separation of DNA sequencing fragments in highly alkaline solutions of linear polyacrylamide using electrophoresis in bare silica capillaries

An optimized procedure for the fast separation of DNA sequencing fragments in short bare fused-silica capillaries filled with highly alkaline solutions of replaceable linear polyacrylamide is presented. High denaturing abilities of the separation media at pH values over 12 are the main reason for their applications in analyses of ssDNA fragments. Moreover, the alkaline solutions of polyacrylamide provide other advantageous properties: three times higher electrophoretic mobility of ssDNA fragments in comparison to those in urea, negligibly low electroosmotic flow in uncoated capillaries, and an adequate stability to a fast alkaline hydrolysis. The separation power of this procedure is enhanced strongly by using monocarboxy poly(ethylene glycol), a terminator for transient isotachophoresis, which eliminates the electromigration dispersion. A high separation efficiency of our system enables to reduce analysis time to several minutes by decreasing the effective lengths of capillaries to 7 cm. A special sample introduction by diffusion is successfully applied. The experimental results demonstrate a potential of the alkaline electrolytes for an implementation in diagnostic sequencing practice.