Composition of aqueous solutions containing sodium glycocholate and glycodeoxycholate

Composition and existence range of aggregates formed by sodium glycocholate and glycodeoxycholate contemporary present in aqueous micellar and premicellar solutions were investigated. Solubility measurements of lead (II) glycocholate and glycodeoxycholate give analytical concentration of lead (II) and glycocholate and glycodeoxycholate, respectively. Electromotive force measurements provide the free concentration of hydrogen, sodium and lead (II) ions. Experimental data obtained at 25 degrees C and at three different concentrations of N(CH3)4Cl, used as a constant ionic medium, can be explained by assuming the presence of aggregates of different composition depending on the reagent and ionic medium concentrations. Next to two species containing only glycocholate or glycodeoxycholate, the presence of aggregates formed with the contemporary participation of both bile anions in different ratios was assumed. Species with the hydrogen ion participation are not present in appreciable quantity in the investigated concentration range. As expected, the size of aggregates increases by increasing reagent and ionic medium concentration. Most of the species can be explained with a "core + link" mechanism, where all the glycocholate aggregation numbers are even, while those of glycodeoxycholate are always multiple of three. Analogy and difference with aggregates formed by the two bile anions separately are discussed.     

Small-angle neutron scattering study of sodium cholate and sodium deoxycholate interacting micelles in aqueous medium

Small angle neutron scattering (SANS) measurements of D₂O solutions (0.1 M) of sodium cholate (NaC) and sodium deoxycholate (NaDC) were carried out atT= 298 K. Under compositions very much above the critical micelle concentration (CMC), the bile salt micelle size growths were monitored by adopting Hayter-Penfold type analysis of the scattering data. NaC and NaDC solutions show presence of correlation peaks atQ = 0.12 and 0.1 ?_-1 respectively. Monodisperse ellipsoids of the micelles produce best fits. For NaC and NaDC systems, aggregation number (9.0, 16.0), fraction of the free counterions per micelle (0.79, 0.62), semi-minor (8.0 ?) and semi-major axes (18.4, 31.7 ?) values for the micelles were deduced. Extent of micellar growth was studied using ESR correlation time measurements on a suitable probe incorporating NaC and NaDC micelles. The growth parameter (axial ratio) values were found to be 2.3 and 4.0 for NaC and NaDC systems respectively. The values agree with those of SANS.     

Composition of sodium cholate micellar solutions

To study the composition of sodium cholate solutions, an investigation was carried out at 25 degrees C and in N(CH3)4Cl, as a constant ionic medium, at three different concentrations (W = 0.100; 0.500 and 0.800 mol dm(-3)). Electromotive force measurements of three different galvanic cells, the first involving a glass electrode for hydrogen ions, the second an electrode for sodium ions and the third a lead amalgam electrode, were performed. Independently, lead (II) cholate solubility measurements in the presence of sodium ions were performed, as well. The experimental results obtained from both approaches were explained by assuming the formation of aggregates in cholate and sodium of different composition depending on W and on the cholate concentration. The maximum aggregation found number for cholate was 24 and even aggregation numbers were markedly predominant. Only two species with odd aggregation number were found, but at a low percentage. The assumed species and the relative constants were compared with those found for the other sodium salt of cholanic acids.     

The association of sodium cholate in NaCl and urea solutions

The association of sodium cholate, SC in NaCl and urea solutions at 25 °C has been investigated using laser light scattering and conductivity techniques. The light scattering results show that the mean translational diffusion coefficient, ¯D _h decreases as SC and/or NaCl increase and SC forms secondary aggregates in solutions of high ionic strengths.The addition of urea decreases the equivalent conductance, _eq of SC and a further lowering of _eq occurs as urea concentration increases. This effect becomes more pronounced when urea is substituted by an alkyl group and an additional decrease in _eq is found with increasing alkyl chain and/or concentration. The present results provide the evidence that SC associates progressiveley and ureas decrease the hydrophobic interactions between the solvent and SC monomer resulting in less association in solutions.     

Conductivity and fluorescence studies on the micellization properties of sodium cholate and sodium deoxycholate in aqueous medium at different temperatures: Effect of selected amino acids

In order to add to the existing knowledge of aqueous solution behavior of bile salts in presence of amino acids, the micellization properties of sodium cholate (NaC) (1 to 20) mmol · kg⁻¹, and sodium deoxycholate (NaDC) (0.5 to 10) mmol · kg⁻¹ in 0.1 mol · kg⁻¹ aqueous solution of glycine, leucine, methionine, and histidine have been investigated at different temperatures (293.15 to 318.15) K at intervals of T = 5 K by using conductivity and fluorescence probe studies. The critical micelle concentration (CMC) values have been determined and elucidated in terms of hydrophobicity as well as hydrophilicity of NaC and NaDC in aqueous solution of these additives. Thermodynamic parameters of micellization viz. standard Gibbs free energy (Δ_micG^o), standard enthalpy (Δ_micH^o), and standard entropy (Δ_micS^o) have also been calculated to extract information regarding the nature of micellization of bile salts in aqueous solutions. The (enthalpy + entropy) compensation plots have been interpreted to the contribution of chemical part towards micellization or stability of the micelle formed.     

The phase-separation behaviour of aqueous solutions of polyacrylic acid and its partial sodium salts in the presence of sodium chloride

Phase-separation temperatures have been measured for polyacrylic acid dissolved in aqueous sodium chloride solutions over a range of ionic strengths, degrees of neutralisation, polymer concentrations and molecular weights. The data are used to derive θ-temperatures for this system. The dependence of the θ-points on ionic strength and degree of ionisation is discussed and the results are briefly compared with data for other polyelectrolytes.     

The influence of an electrolyte on micelle formation in aqueous solutions of sodium monoalkyl sulfosuccinates

Critical micelle concentrations were determined by conductometry for the homologous series of sodium monoalkyl sulfosuccinates ROOCCH₂CH(SO₃Na)COONa (R is an alkyl radical, C₁₀–C₁₅) in the presence of sodium chloride. Coefficients of the Corrin-Harkins equation were calculated. It was shown that the formation of micelles began when a certain value of the mean ionic activity of the surface active substance was reached.     

Interaction of sodium cholate with dioctadecyldimethylammonium chloride vesicles in aqueous dispersion

Mixtures of dioctadecyldimethylammonium chloride (DODAC) cationic vesicle dispersions with aqueous micelle solutions of the anionic sodium cholate (NaC) were investigated by differential scanning calorimetry, DSC, turbidity and light scattering. Within the concentration range investigated (constant 1.0 mM DODAC and varying NaC concentration up to 4 mM), vesicle → micelle → aggregate transitions were observed. The turbidity of DODAC/NaC/water depends on time and NaC/DODAB molar concentration ratio R. At equilibrium, turbidity initially decreases smoothly with R to a low value (owing to the vesicle–micelle transition) when R = 0.5–0.8 and then increases steeply to a high value (owing to the micelle–aggregate transition) when R = 0.9–1.0. DSC thermograms exhibit a single and sharp endothermic peak at T_m ≈ 49 °C, characteristic of the melting temperature of neat DODAC vesicles in water. Upon addition of NaC, T_m initially decreases to vanish around R = 0.5, and the main transition peak broadens as R increases. For R > 1.0 two new (endo- and exothermic) peaks appear at lower temperatures indicating the formation of large aggregates since the dispersion is turbid. All samples are non-birefringent. Dynamic light scattering (DLS) data indicate that both DODAC and DODAC/NaC dispersions are highly polydisperse, and that the mean size of the aggregates tends to decrease as R increases.     

Properties of aqueous solution of sodium glycocholate and a nonionic surfactant,and their mixtures

The micellar properties of aqueous binary mixed solutions of sodium glycocholate, NaGC, and octa-oxyethylene glycol mono-n-decyl ether, C₁₀E₈, have been studied on the basis of surface tensions, the mean aggregation number and the polarity of the interior of the micelles. The mean aggregation number, measured by steady state quenching method, decreased with the increase of the mole fraction of NaGC in the mixed system. The polarity of the interior, estimated by the ratio of first and third vibronic peak in a monomeric pyrene fluorescence emission spectrum, suggested that the hydrophobicity of intramicelles increased with the increase of the mole fraction of NaGC in the mixed system. These are considered to be caused by the differences in the chemical structure and the hydrophobic nature between NaGC and C₁₀E₈. The mean aggregation number and the polarity of the interior for each micelle near the CMC in lower total concentration of surfactants showed the tendency approaching those of pure micelle of the nonionic surfactant. This suggests that the ratio of NaGC in the initial micelles in the range of lower total concentration near the CMC is lower than that of the corresponding prepared mole fraction in the mixed system. This lower value was confirmed also from theoretical calculation of the ratio of NaGC at the CMC in the mixed micelle by regular solution treatment of Rubingh in the solution.     

Aggregation number of aqueous sodium cholate micelles from mutual diffusion measurements

With reported values ranging from about 3 to 16, the aggregation number of aqueous sodium cholate micelles is not well established. To provide new information on the aggregation of a bile salt, Taylor dispersion is used to measure the binary mutual diffusion coefficientD of aqueous sodium cholate at concentrations from 0.001 to 0.100 mol-dm^-3 at 25°C. The results are compared with calculatedD values based on the association equilibrium nCholate^- + βnNa⁺ ⇋ (NaβCholate) _n ^(β-1)n wheren is the aggregation number and β is the degree of sodium counterion binding. Fitting the association model to the diffusion data givesn = 3.9±0.6 and β = 0.21 ±0.08. In contrast to the drop inD with increasing concentration of sodium cholate, the diffusion coefficients of sodium dodecylsulfate and other long-chain ionic surfactants increase above the critical micelle region. The ent diffusion behavior of the surfactants is related to changes in the driving forces and mobilities caused by ion association.     

The influence of high-frequency electromagnetic fields on the critical micelle concentration in aqueous solutions of sodium dodecyl sulfate

It was established that the critical micelle concentration in solutions of sodium dodecyl sulfate changed under the action of high-frequency electromagnetic fields (60, 120, and 160 MHz). The thermodynamic functions of micelle formation were calculated. Original Russian Text ? I.E. Stas’, O.P. Mikhailova, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 2, pp. 397–399.     

Effect of temperature on solvation behaviour of diclofenac sodium salt in aqueous glycine and l-proline solutions

Apparent molar volume (V_2,ϕ) and apparent molar isentropic compressibility (K_s,2,ϕ) of diclofenac sodium salt (DSS) drug within the concentration range of (0.001 to 0.008) mol · kg⁻¹ in (0.01, 0.03 and 0.05) mol · kg⁻¹ aqueous glycine and l-proline solutions are computed from the experimental density (ρ) and speed of sound (u) values at T = (293.15 to 313.15) K and atmospheric pressure. Derived parameters such as partial molar properties, transfer partial molar properties, hydration numbers and Hepler’s constant are computed from the data of V_2,ϕ and K_s,2,ϕ. These parameters have been used to understand the effect of temperature on interactions between DSS drug and aqueous glycine/l-proline solution. Furthermore, the structure making and breaking ability of DSS drug in probed solutions are analysed at experimental conditions.     

Particle-macromolecule interactions in aqueous solutions Part 1: Solution and flow behaviour of polyvinylalcohol in an aqueous medium

Summary Shear and concentration dependent flow studies on solutions of a narrow molecular weight fraction of 90.3 % hydrolysed polyvinylalcohol are reported, together with precise density measurements on these same solutions. From the derived flowing volume and partial molar volume values it is concluded that two association processes occur; the first appears similar to micellization of surfactants, the second is association of micellar spheres.

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Zusammenfassung Es wurde die Scher- und Konzentrationsabhängigkeit des Fließverhaltens von Polyvinylalkohollösungen (90,3 % hydrolysiert) mit niedriger Polydispersität untersucht. An den gleichen Lösungen wurden auch Präzisionsdichtemessungen ausgeführt. Aus dem berechneten Fließvolumen und dem partiellen Molvolumen kann gefolgert werden, daß zwei Assoziationsprozesse vorliegen. Der erste davon gleicht der Mizellbildung von Tensiden, der zweite entspricht der Assoziation kugelförmiger Mizellen.

     

Evaporation studies on sodium dehydrocholate aqueous solutions

The evaporation through the air/solution interface of sodium dehydrocholate (NaDHC) aqueous solutions was studied by surface tension and microbalance measurements. The evaporation rate was related to the aggregation processes in the bulk, but not with the adsorption monolayer compactness. Except for very dilute solutions the air/solution interface was saturated by NaDHC molecules, giving rise to a strongly nonideal monolayer. At very low concentration, the adsorbed monolayer behaved as an ideal two-dimensional gas. The results were in agreement with previous research results.     

Many-body effects on structure and dynamics of aqueous ionic solutions

We performed several molecular dynamic studies of metal cations in aqueous solution. The alkali metal ion Li(+) and the first-row transition metal ion Mn(2+) have been chosen as model systems. Two different three-body corrections are proposed to mimic the crucial many-body effects of electrolyte solutions. The correction function, which includes attractive features of the three-body potential, performs considerably better than the purely repulsive interaction function. Structural and dynamic results show that this simple enhancement is able to satisfactorily reproduce experimental and higher-level results for the first hydration shell.     

Structure of aqueous sodium perchlorate solutions

Salt solutions have been the object of study of many scientists through history, but one of the most important findings came along when the Hofmeister series were discovered. Their importance arises from the fact that they influence the relative solubility of proteins, and solubility is directly related to one of today's holy grails: protein folding. In this work we characterize one of the more-destabilizing salts in the series, sodium perchlorate, by studying it as an aqueous solution at various concentrations ranging from 0.08 to 1.60 mol/L. Molecular dynamics simulations at room temperature permitted a detailed study of the organization of solvent and cosolvent, in terms of its radial distribution functions, along with the study of the structure of hydrogen bonds in the ions' solvation shells. We found that the distribution functions have some variations in their shape as concentration changes, but the position of their peaks is mostly unaffected. Regarding water, the most salient fact is the noticeable (although small) change in the second hydration shell and even beyond, especially for g(O(w)***O(w)), showing that the locality of salt effects should not be restricted to considerations of only the first solvation shell. The perturbation of the second shell also appears in the study of the HB network, where the difference between the number of HBs around a water molecule and around the Na(+) cation gets much smaller as one goes from the first to the second solvation shell, yet the difference is not negligible. Nevertheless, the effect of the ions past their first hydration shell is not enough to make a noticeable change in the global HB network. The Kirkwood-Buff theory of liquids was applied to our system, in order to calculate the activity derivative of the cosolvent. This coefficient, along with a previously calculated preferential binding, allowed us to establish that if a folded AP peptide is immersed in the studied solution, becoming the solute, then increasing the salt concentration will make the helix more stable.     

The influence of pressure on ionization equilibria in aqueous solutions

A comparison is made of the abilities of two simple relationships to describe the influence of pressure on ionization constants in aqueous solutions.     

The aromatic amino acid behaviour in aqueous amide solutions

The enthalpies of solution of L-phenylalanine in the mixtures of water with the protein denaturant urea have been measured in the temperature range of 288.15–318.15 K. Using the results of the present research and literature data of free energies, the standard thermodynamic functions of the solute transfer from water to aqueous urea solutions have been estimated in a wide temperature range. The enthalpic, heat capacity, entropic and free energy parameters of the solute-urea pair and triplet interactions have been computed. The amino acid — amide pair interaction was found to be attractive in the temperature range studied due to the favourable enthalpic term. The triplet interaction being slightly repulsive reveals the enthalpic origin also. The examination of the Savage and Wood additivity-of-groups approach does indicate the inapplicability of this scheme to enthalpies and entropies of interaction. It has been found for the first time that the heat capacity of interaction changes its sign at 303 K, i.e. the temperature dependence of enthalpic and entropic parameters passes through the pronounced extrema near the temperature of the minimum of the heat capacity of pure water.