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.     

Aggregation of sodium dodecyl sulfate in aqueous sodium chloride solutions

Summary Aqueous solutions of sodium dodecyl sulfate with added sodium chloride (0–0.3 mol kg^–1) were studied at 298.2 K in order to calculate the molar standard free energy of micelle formationG _m . The following properties were measured: (i) aggregation number by membrane osmometry, (ii) counter-ion binding and sodium ion activities by electromotive force, (iii) critical micelle concentration by electromotive force and fluorescence spectrophotometry. The results indicate thatG _m . is independent of the NaCl concentration.     

Photooxidative decomposition of sodium dodecyl sulfate in aqueous solutions

Kinetic features and the mechanism of photooxidative decomposition of sodium dodecyl sulfate in an aqueous solution under the action of pulsed short-wavelength UV light with a continuous spectrum upon introduction of hydrogen peroxide was studied.     

On the modeling of calcium sulfate solubility in aqueous solutions

The electrolyte–NRTL model used in a previous work (B. Messnaoui, T. Bounahmidi, Fluid Phase Equilibr. 237(1–2) (2005) 77–85), was extended for modeling of α-hemihydrate and gypsum solubilities in the complex system Ca²⁺–H⁺–SO₄²⁻–HSO₄⁻–H₂PO₄⁻–H₃PO₄–H₂O, at wide range of temperature and P₂O₅ concentration. The chemical equilibrium constant was evaluated as function of temperature according to the Gibbs–Helmholtz equation. The temperature dependence was taken into account in the expression of the standard state heat capacity of ionic, molecular and cristalline salts species. The standard-state heat capacity of Ca²⁺at 298.15 K is calculated to be 27.30 J mol⁻¹ K⁻¹. It is also shown that the experimental data agree with the predicted values of gypsum and anhydrite solubilities in water, at high temperature, by using only the values of parameters ${\tau }_{{\text{H}}_2\text{O}-(\text{C}{\text{a}}^{2+},\text{S}{{\text{O}}_4}^{2-})}$, ${\tau }_{(\text{C}{\text{a}}^{2+},\text{S}{{\text{O}}_4}^{2-})-{\text{H}}_2\text{O}}$ which were calculated, at 298.15 K from data of gypsum solubilities in phosphoric acid solutions.     

Amino acid hydration in aqueous magnesium and sodium sulfate solutions

We study the partial volumes of amino acids in aqueous magnesium and sodium sulfate solutions, which have a different effect on the structure of water, and calculate the structural parameters of hydrated complexes of NH ₃ ⁺ and COO^? groups: hydration numbers and water volumes inside and outside the hydration shell. The hydration numbers are given as a sum of the contributions of the interactions in the ternary (water-salt-amino acid) and binary (water-salt) systems.     

十二烷基聚氧乙烯硫酸钠胶束体系的流变性质研究

用流变学方法研究了无机电解质KBr存在时,阴离子表面活性剂十二烷基聚氧乙烯(3)硫酸钠(SDES)水溶液中胶束的生长和结构。通过测量体系的稳态剪切粘度(η)和应力(σ)关系,得到零剪切粘度(η0)、复合粘度(|η^*|)、动态模量[储能模量(G')和损耗模量(G")、平台模量(G0)、结构松驰时间(τ)等流变学参数,并应用Cox-Merz规则和Cole-Cole图,发现在SDES/KBr体系中可以形成蠕虫状胶束网络结构,体系为假塑性流体,偏离Maxwell模型,具有非线性粘弹性,没有单一的结构松驰时间。     

Interaction of hydroxyapatite with sodium chondroitin sulfate and calcium chondroitin sulfate in an aqueous phase

The suspension pH at a given concentration of hydroxyapatite (HAP) decreased with the concentration of calcium chondroitin-6-sulfate (CaChs), whereas it increased with the concentration of sodium chondroitin-6-sulfate (Na2Chs). The former effect is due to the increase in the concentration of H+ by ion exchange between H+ on the surface of HAP and Ca2+ of CaChs, and the latter is due to the protonation of phosphate ion (Pi) released from the surface of HAP. The absorbed amount of chondroitin-6-sulfate anion (Chs) by HAP was higher with CaChs than with Na2Chs over the concentration range examined. The equilibrium concentration of Pi decreased with increasing concentration of added CaChs because the concentration of free Ca2+, which dissociates from CaChs, regulates the free concentration of Pi through the restriction of the solubility product of HAP (Ksp). In contrast, that in the presence of Na2Chs increased with increasing concentration of added Na2Chs owing to the anion exchange between Chs and Pi of the HAP surface. The total concentration of Ca2+, which was released from HAP into the solution phase, increased after passing through a minimum with increasing concentration of added Na2Chs. That is, the concentration of Ca2+ free from Chs decreased with an increase in the concentration of released Pi owing to the restriction of the solubility product, whereas that of Ca2+ bound by Chs increased with increasing concentration of added Na2Chs through the ion exchange of Na+ with Ca2+. It was confirmed by the dialysis method that the value of Ksp was almost constant around 10, although HAP dissolves incongruently in the presence of Na2Chs.     

Hydrophobic interactions between polymethacrylic acid and sodium laureth sulfate in aqueous solutions

The role of hydrophobic interaction in the development of associative processes is demonstrated, based on the concentration dependences of the viscosity and pH of binary solutions of polymethacrylic acid as an anionic polyelectrolyte and sodium laureth sulfate as an anionic surfactant. It is found that the inflection point on the dependence of the difference between the pH values of binary solutions of polymethacrylic acid and sodium laureth sulfate on the polyelectrolyte concentration is a criterion for determining the predominant contribution from hydrophobic interaction, as is the inflection point on the dependence of pH of individual solutions of polymethacrylic acid on the polyelectrolyte concentration.     

IR study of aqueous metal perchlorate solutions

Aqueous solutions of Mn(II), Co(II), Ni(II), and Zn(II) perchlorates, and for comparison, Mg(II) and Ca(II) perchlorates, have been studied by IR spectroscopy using HDO as an indicator. The investigations were carried out over the entire available concentration range of these salts. Computer deconvolution of the measured spectra demonstrates the effect of metal cations on the HDO molecules.     

Sodium sulfate solubilities in high temperature aqueous sodium chloride and sulfuric acid solutions—predictions of solubility,vapor pressure,acidity, and speciation

Experimental measurements of the solubility of sodium sulfate in aqueous solutions containing both sodium chloride and sulfuric acid in the temperature range 250 to 374°C are reported. These measurements have been combined with previous data on the solubility of sodium sulfate in water, in aqueous sodium chloride, and in sulfuric acid solutions to produce a comprehensive model describing the solubility of sodium sulfate in such solutions. Calculations and predictions of solubility, vapor pressure, boiling point elevation, acidity, and speciation are presented. This model is of fundamental interest in itself and also is of importance because the precipitation of sodium sulfate may be a contributing factor in enhancing crevice corrosion in metals exposed to high-temperature water containing chloride and sulfate ions as impurities.     

Thermodynamics of aqueous sodium sulfate

The activity coefficient of saturated aqueous Na₂SO₄ is calculated from the properties of the solid and the infinitely dilute solution as well as the solubility. These values are compared with those given by the equation of Rogers and Pitzer which is based on the measured dependence of heat capacity upon molality together with other solution properties at low temperature. Excellent agreement is found from 30 to 280°C. Consequently the equation of Rogers and Pitzer is given an extended range of validity to saturated molality and to 280°C. The trend of solubility with temperature is discussed in relation to the C_p of solution.     

Investigation of the state of 8-hydroxyquinoline in aqueous sodium dodecyl sulfate solutions

The influence of sodium dodecyl sulfate on the dissociation of protonated 8-hydroxyquinoline in aqueous solutions is investigated by potentiometric titration at 293 K. The constants of direct binding of 8-hydroxyquinoline with the monomers and micelles of sodium dodecyl sulfate are determined by the computer simulation of the most probable processes. The role of electrostatic and hydrophobic interactions in the studied system is discussed.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 2, 2005, pp. 231–234.Original Russian Text Copyright © 2005 by Ramenskaya, Vladimirova.     

Study of mixed micellar aqueous solutions of sodium dodecyl sulfate and amino acids

Thermodynamic properties of sodium dodecyl sulfate (SDS) in micellar aqueous solutions of L-serine and L-threonine were determined by fluorescence spectroscopy and dynamic light scattering techniques. The values of Gibbs free energy, enthalpy and entropy of the process of micelle formation were calculated using the critical micelle concentration and degree of dissociation. Changes in critical micelle concentration of SDS with the addition of amino acids were examined by both conductivity and pyrene I ₁/I ₃ ratio methods at different temperatures. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interaction of SDS with amino acids. The aggregation behavior of SDS was explained in terms of structural changes in mixed solutions. The data on dynamic light scattering suggest that size of SDS micelles was influenced by the presence of amino acids.     

Destruction of sodium lauryl sulfate in its aqueous solutions by contact glow discharge treatment

Degradation of the anionic surfactant sodium lauryl sulfate (C₁₂H₂₅SO₄Na, SLS) in its aqueous solutions with concentrations of 0.02–1.1 mmol/L acting as a liquid cathode of atmospheric-pressure dc discharge in air at a discharge current ranging within 20–100 mA has been studied. The products of degradation in the liquid phase have been identified, and the kinetic characteristics of their formation at an initial SLS concentration of 5 × 10^?3 g/L (～0.02 mmol/L) and a discharge current of 40 mA have been determined.     

Conductance of aqueous sodium decyl sulfate solutions and the nature of hydration of the decyl sulfate anion

A study is made of the temperature and concentration dependences for conductance of aqueous sodium decyl sulfate solutions. The nature of hydration of the decyl sulfate anion is discussed within the theories proposed by Samoilov, Gurikov, and Krestov. An analysis is performed of the influence of the hydration type on the critical micelle concentration. The analysis suggests that an increase in temperature stimulates micelle formation given that hydration is negative.     

Solubility and solubility constant of barium sulfate in aqueous sodium sulfate solutions between 0 and 80°C

The solubilities of barium sulfate in aqueous solutions of sodium sulfate were studied at ionic strengths from 0.0005 to 0.02 mol-kg^–1 and at 0, 20, 40, 60, and 80°C. The solubility data were used to calculate the solubility constants using an extrapolation method. The solubility constant obtained were in good agreement with literature data. The mean activity coefficients of barium sulfate in aqueous solutions of sodium sulfate were also studied.     

Potentiometric behaviour of the copper electrode in aqueous copper(II) perchlorate solutions containing sodium chloride

It is demonstrated that the copper metal electrode corrodes in the presence of copper(II) ions in solution. A model based on mass balance can properly describe the experimental results. In the presence of copper(II) ions the copper electrode responds to copper(I), indicating that the electrode potential corresponds to a mixed potential.