Raman spectroscopic study of the conformational order of octadecylsilane stationary phases: effects of electrolyte and pH

This study investigates effects of the electrolyte, of acidic and basic compounds, and of pH on the rotational and conformational order of octadecylsilane stationary phases with surface coverages of 3.09 and 6.45 mol/m². Both phases exhibit an increase in alkyl chain rotational and conformational order in 5–200 mM aqueous electrolyte solutions relative to water. These stationary phases are effectively salted-out of aqueous electrolyte solutions, thereby causing alkyl chain intermolecular interactions to increase with a concomitant increase in alkyl chain order. Although the presence of acidic and basic compounds generally has no effect on the conformational order of either stationary phase as a function of pH, the higher coverage stationary phase does exhibit pH-dependent changes in aqueous solutions of benzoic acid. At pH values below the pK_a of benzoic acid, the conformational order of this stationary phase is unchanged relative to that observed in the same pH solution in the absence of benzoic acid. In light of independent evidence that such monosubstituted aromatics interact with the octadecylsilane stationary phase under these conditions, the absence of a measurable effect on alkyl chain order for these conditions is attributed to benzoic acid self-association at the stationary phase-mobile phase interface. In contrast, at pH values above the pK_a of benzoic acid, slight disordering of the alkyl chains is observed and is attributed to repulsive interactions between retained benzoate anions.Electronic Supplementary Material Supplementary material is available for this article at     

Experimental Study of the Effect of Temperature,Pressure and Concentration on the Viscosity of Aqueous NaBr Solutions

The viscosity of 10 (0.049, 0.205, 0.464, 0.564, 0.820, 1.105, 1.496, 2.007, 2.382, and 2.961 mol ċ kg⁻¹) binary aqueous NaBr solutions has been measured with a capillary-flow technique. Measurements were made at pressures up to 40 MPa. The range of temperature was 288–595 K. The total uncertainty of viscosity, pressure, temperature and composition measurements were estimated to be less than 1.6%, 0.05%, 15 mK, and 0.02%, respectively. The effect of temperature, pressure, and concentration on viscosity of binary aqueous NaBr solutions were studied. The measured values of the viscosity of NaBr(aq) were compared with data, predictions and correlations reported in the literature. The temperature and pressure coefficients of viscosity of NaBr(aq) were studied as a function of concentration and temperature. The viscosity data have been interpreted in terms of the extended Jones–Dole equation for the relative viscosity (η/η₀) to calculate accurately the values of viscosity A- and B-coefficients as a function of temperature. The derived values of the viscosity A- and B-coefficients were compared with the results predicted by the Falkenhagen–Dole theory of electrolyte solutions and calculated with the ionic B-coefficient data. The physical meaning parameters V and E in the absolute rate theory of the viscosity and hydrodynamic molar volume V k were calculated using the present experimental viscosity data. The TTG model has been used to compare predicted values of the viscosity of NaBr(aq) solutions with experimental values at high pressures.     

Adsorption of Some Nitrogen-Containing Compounds and Benzene Derivatives from Aqueous Solutions on Active Carbons

The adsorption from aqueous solutions of benzene derivatives (phenol, benzoic acid, and newly synthesized benzoic acid derivatives containing imidazole heterocycles: hydrazide of 4-(1H-imidazole-1-ylmethyl) benzoic acid and methyl ester of 4-(1H-imidazole-1-ylmethyl)benzoic acid), as well as of imidazole and triazole, on active carbons with various microporous structures is studied. The effect of the nature of adsorbate molecules and the pore sizes of active carbons on the sorption character is analyzed. It is shown that the adsorption from aqueous solutions of the organic derivatives of benzene is determined, on the one hand, by the size of a molecule, and, on the other hand, by its hydration energy.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 3, 2005, pp. 416–420.Original Russian Text Copyright © 2005 by Kharitonova, Krasil’nikova, Vartapetyan, Bulanova.     

Ionization of aqueous toluic acids: Conductance and thermodynamics

Conductivities of aqueous solutions ofortho-, meta-, andpara-toluic acids have been measured for the concentration range 0.1–2 millimolar and at 5° intervals from 5 to 100°C. At each temperature pK _a(m) andA ₀ have been calculated using the paired ion model recently described by Fuoss. Thermodynamic parameters have been calculated for the ionization of each acid, and Walden products for the anions. Results are discussed in terms of contributions to acidity by enthalpy and entropy changes as well as by hydration of the various solute species.     

Conductivity studies of aqueous solutions of stereoisomers of tartaric acids and tartrates. Part II: D-, L-, andmeso-tartaric acids

Conductivity measurements on aqueous solutions of D-tartaric acid, L-tartaric acid, andmeso-tartaric acid were performed in the temperature range 278.15–308.15 K. The equivalent limiting conductivity of the bitartrate anion, λ°(HTar^-), is evaluated with regard to the primary and secondary steps of dissociation of the acids in aqueous solutions by use of the Quint and Viallard equation for unsymmetrical electrolytes.     

Diffusion Coefficients of Three Organic Solutes in Aqueous Sodium Dodecyl Sulfate Solutions

Tracer diffusion coefficients of phenol, toluene, and benzoic acid in aqueous solutions of sodium dodecyl sulfate (SDS) were measured by the Taylor dispersion technique. In addition, the viscosities and densities of the SDS solutions were measured. For phenol and toluene, the effect of micelle formation on the diffusion coefficient is pronounced. When the SDS concentration is below the critical micelle concentration (cmc), the diffusion coefficients are almost independent of the SDS concentration. However, above the cmc there is a rapid decrease in the diffusion coefficients, and the apparent diffusion coefficients of the two solutes are the weighted average of free solute diffusion and the micelle diffusion. A model is presented to describe the diffusion behavior of the two solutes in aqueous micellar solutions of SDS. The interaction between the two solutes and the micelles has been investigated and the fraction of each solute that is solubilized by the micelles is estimated from the measured apparent diffusion coefficient. For benzoic acid, the diffusion coefficient is dependent on the joint contribution of the benzoic acid molecules that are solubilized by the micelles as well as the corresponding benzoate ions. The effect of micelle formation on the diffusion coefficient of benzoic acid is not as pronounced as for phenol and toluene. Copyright 2000 Academic Press.     

Degradable poly(ethylene oxide) hydrogels formed by crosslinking with tert‐butylperoxybenzoate

Poly(ethylene oxide) (PEO, number‐average molecular weight: 2,000,000) was crosslinked by reaction with t‐butylperoxybenzoate in the melt. Upon swelling in water, the resulting hydrogels were acidic and suggested clear evidence of spontaneous hydrolysis that continued over periods of several weeks to give clear and low‐viscosity aqueous solutions of PEO oligomers. In contrast, in neutral media the gels did not show any signs of hydrolysis. As shown by UV, IR, and size exclusion chromatographic analysis, the PEO hydrolysis products consist of benzoic acid and hydroxyl‐ and carboxyl end‐functionalized low‐molecular‐weight PEOs. This is consistent with the acid‐catalyzed hydrolysis of acetal‐, orthoester‐, and similar end‐functionalized PEOs formed by radical coupling of various PEO radicals with benzoate, alkoxy, and other radicals. Titration of the hydrolysis mixtures indicated that the total molar amount of acid exceeds that of the maximum amount of benzoic acid produced during gel formation. However, the amount of benzoic acid equaled this maximum amount. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 520–527, 2003     

Viscosity of Aqueous Solutions of Lithium,Sodium, Potassium,Rubidium and Caesium Cyclohexylsulfamates from 293.15 to 323.15 K

The viscosities of aqueous solutions of lithium, sodium, potassium, rubidium and caesium cyclohexylsulfamates were measured at 293.15, 298.15, 303.15, 313.15 and 323.15 K. The relative viscosity data were analyzed and interpreted in terms of the Kaminsky equation, η _r=1+Ac ^1/2+Bc+Dc ². The viscosity A-coefficient was calculated from the Falkenhagen-Dole theory. The viscosity B-coefficients are positive and relatively large. Their temperature coefficient ∂ B/∂ T is negative or near zero for lithium and sodium salts whereas for potassium, rubidium and caesium salts it is positive. The viscosity D-coefficient is positive. This was explained by the size of the ions, structural solute–solute interactions, hydrodynamic effect, and by higher terms of the long-range Debye-Hückel type of forces. From the viscosity B-coefficients the thermodynamic functions of activation of viscous flow were calculated. The limiting partial molar Gibbs energy of activation of viscous flow of the solute was divided into contributions due to solvent molecules and the solute in the transition state. The activation energy of the solvent molecules was calculated using the limiting Gibbs energy of activation for the conductance of the solute ions. The activation energy of the solvent molecules was then discussed in terms of the nature of the alkali-metal ions and their influence on the structure of water. The limiting activation entropy and enthalpy of the solute for activation of viscous flow were interpreted by ion-solvent bond formation or breaking in the transition state of the solvent. The hydration numbers of the investigated electrolytes were calculated from the specific viscosity of the solutions.     

Accumulation of some metal ions on Bacillus licheniformis

Pure species of Bacillus licheniformis was used to remove ions from aqueous and simulated waste solutions. Metal ion accumulation on B. licheniformis was fast. Maximum uptake occurred at pH 4±0.5 and at 25±3 °C. One gram of dry B. licheniformis was found to accumulate 115 mg cerium, 34 mg copper and 11 mg cobalt from aqueous solutions. The presence of certain foreign ions such as calcium, sodium and potassium decreased the uptake of ions by B. licheniformis, while citrate and EDTA prevent the uptake. Electron microscopic investigations showed that cerium (III), copper (II) and cobalt (II) accumulated extracellulary around the surface wall of B. licheniformis cells. A bio-adsorption mechanism between the metal ions and B. licheniformis cell wall was proposed.     

Viscosity of aqueous solutions of univalent electrolytes from 5 to 95°C

Viscosity measurements of a series of univalent electrolytes in water have been performed with an automatic dual viscometer system, covering the temperature range of 5 to 95°C. Results are discussed in terms of Jones-DoleB andD coefficients. TheB coefficients of the salts are divided into their ionic contributions according toB(K⁺)=B(Cl^–) at all temperatures. On a simple model intrinsic and structural contributions inB are calculated for the different ions. The structural term depends exponentially on the temperature in a unique manner, independent of the ion (except for Li⁺).     

Radiolysis of Aqueous Solutions of Benzoate Ion: A Radiation Chemistry Experiment for Undergraduates

This investigation describes the chemical effects of ionizing radiation on dilute aqueous solutions of benzoate ion. We have composed an experimental procedure that allows undergraduate chemistry students to identify and to quantitatively determine the amount of the products that are produced. The student investigators determine the absorbed dose that a sample receives when exposed to a ⁶⁰Co source, irradiate dilute aqueous solutions of benzoate ion, and analyze the resulting mixture of hydroxybenzoate ions using high-performance liquid chromatography. The radiolysis of dilute solutions of benzoate ion results in the formation of a mixture of ortho-, meta-, and para-hydroxybenzoate ions that are readily separated on a C₁₈ -Bondapak column. By the use of appropriate calibration curves, the yield (G values) of each of the isomers may be determined and compared.This paper was presented at the 15th Biennial Conference on Chemical Education, Waterloo, Ontario, Canada, August 1998 by N. Zevos and at the 26th Northeast Regional Meeting of the American Chemical Society by Evon Powell.     

Apparent molar volume,viscosity <Emphasis Type="Italic">B</Emphasis>-coefficient,and adiabatic compressibility of tetrabutylammonium bromide in aqueous ascorbic acid solutions at <Emphasis Type="Italic">T</Emphasis> = 298.15, 308.15, and 318.15 K

Apparent molar volumes ϕ_ν and viscosity B-coefficients for tetrabutyl ammonium bromide (TBAB) in (0.00, 0.05, 0.10, and 0.15) mol dm⁻³ aqueous ascorbic acid solutions have been determined from solution density and viscosity measurements at temperatures over the range 298.15 to 318.15 K as function of concentration of ascorbic acid solutions. In the investigated temperature range, the relation: ϕ_ν⁰ = a ₀ + a ₁ T + a ₂ T ², have been used to describe the partial molar volume ϕ_ν⁰. These results, in conjunction with the results obtained in pure water, have been used to calculate the standard volumes of transfer Δϕ _ν ⁰ and viscosity B-coefficients of transfer for TBAB from water to aqueous ascorbic acid solutions for rationalizing various interactions in the ternary solutions. The structure making or breaking ability of TBAB has been discussed in terms of the sign of (δ²ϕ_ν⁰/δT ²) _P . An increase in the transfer volume of TBAB with increasing ascorbic acid concentration has been explained by Friedman-Krishnan co-sphere model. The activation parameters of viscous flow for the ternary solutions studied have also been calculated and explained by the application of transition state theory.     

Relative efficiencies of substituted aromatic monocarboxylic acids as eluents in ion chromatographic separation of inorganic and organic anions

The eluent strengths of para, ortho and meta substituted hydroxy-, nitro-, amino- and sulfobenzoic acids in single column ion chromatographic separations of inorganic and organic anions have been evaluated and compared with benzoic acid.o-Sulfobenzoic acid turns out to be a stronger and efficient eluent compared to others for the separation and determination of monovalent (Cl^–, NO ₂ ^– , Br^–, NO ₃ ^– ) and divalent (SO ₄ ^2– , SeO ₄ ^2– , S₂O ₃ ^2– , S₂O ₆ ^2– ) inorganic anions. In addition it also functions as an appropriate mobile phase for the detection and quantification of some substituted benzoate ions in an aqueous medium.     

Physico-chemical properties of some electrolytes in water and aqueous sodiumdodecyl sulfate solutions at different temperatures

The viscosities of some mineral salt viz.; potassium chloride, potassium nitrate, magnesium chloride, magnesium nitrate, at different concentrations have been determined in water and in binary aqueous solution of sodiumdodecyl sulfate (SDS) (0.007 mol · kg⁻¹ and 0.01 mol · kg⁻¹) at different temperatures. The data have been analyzed using Jones–Dole equation and the derivative parameters B and A have been interpreted in terms of ion–solvent and ion–ion interactions respectively. The change of Gibbs free energy of activation , enthalpy of activation , and entropy of activation for viscous flow of the solutions were calculated using Eyring equation, which depicts the mechanism of viscous flow. The structure making/breaking nature of the studied electrolytes has been discussed in the light of first derivative of B-coefficient (dB/dT) over temperatures. Potassium chloride and potassium nitrate acts as structure breaker in water where as all the salts are structure makers in aqueous SDS solutions, i.e. the postmicellar and pre-micellar regions.     

Vapour pressures,enthalpies and entropies of sublimation of <Emphasis Type="Italic">para</Emphasis> substituted benzoic acids

The vapour pressures of six para-substituted benzoic acids were measured using the Knudsen effusion method within the pressure range (0.1–1 Pa) in the following temperature intervals: 4-hydroxybenzoic acid (365.09–387.28) K; 4-cyanobenzoic acid (355.14–373.28) K; 4-(methylamino)benzoic acid (359.12–381.29) K; 4-(dimethylamino)benzoic acid (369.29–391.01) K; 4-(acetylamino)benzoic acid (423.10–443.12) K; 4-acetoxybenzoic acid (351.28–373.27) K. From the temperature dependence of the vapour pressure, the standard molar enthalpy, entropy and Gibbs energy of sublimation, at the temperature 298.15 K, were derived for each of the studied compounds using estimated values of the heat capacity differences between the gaseous and the crystalline phases. Equations for estimating the vapour pressure of para substituted benzoic acids at the temperature of 298.15 K are proposed.     

Partial Molar Volume,Ionization, Viscosity and Structure of Glycine Betaine in Aqueous Solutions

Densities, partial molar volumes, and viscosities of aqueous solutions of betaine have been measured at 5, 10, 15, 20, 25, 30, 37, and 45 °C over the concentration range 0.05 to 5.0 mol⋅L⁻¹. The partial molar volumes show that betaine exists partly as a monohydrate and partly in its anhydrous form. The proportion of the anhydrous form increases with increasing temperature. Also, an associated form of betaine appears in concentrated betaine solutions, possibly with water as a bridging group. The significance of the viscosity B-coefficient is discussed. The signs of B _st, the increment of the viscosity B-coefficients arising from structural changes of water, are negative and the signs of dB/dT, the temperature derivative of B, are positive. These results show that betaine is a water structure breaker especially at lower temperatures, and this effect decreases to insignificance at higher temperatures. The ionization equilibria of betaine were investigated in aqueous 0.5 mol⋅L⁻¹ and 1.0 mol⋅L⁻¹ NaNO₃ at 5, 15, 25, and 37 °C by a potentiometric method. Using the least-square computer program SUPERQUAD, the complex forms are deduced to be betanium BH, bis(betanium) BHB, and bis(betaine) B₂ or bis(betaine)hydrate BH₂OB.     

Determination of pK(a) of acetic and benzoic acids in pyridine

The pK(a)'s of acetic acid and benzoic acid in pyridine as solvent are found to be 10.1 and 9.8, respectively, at 25 degrees . These results are based on measurements of hydrogen ion activities in mixtures of the acids and their tetrabutylammonium salts. Supplementary studies of differential vapour pressure characteristics of solutions of the acids and the acid-salt mixtures, and conductance of tetrabutylammonium benzoate solutions are also incorporated.     

Interactions of DL-serine and L-serine with NaCl and KCl in aqueous solutions

The activity coefficients at 25‡C of DL-serine and L-serine in aqueous solutions of NaCl and KC1 were measured. This study examines the effect of the nature of the cation of the electrolyte on the activity coefficients of the optical-isomers of serine in aqueous solutions for molality of serine up to 0.4 and molality of electrolyte up to 1. An electrochemical cell with two ion-selective electrodes, a cation, and an anion ion selective electrode,vs. a double-junction reference electrode was used to measure the activity coefficients of the electrolyte and the results were converted to the activity coefficients of serine in the aqueous electrolyte solution. The comparison of the results obtained for DL- and L-serine indicates that the two optical isomers have identical interactions with electrolytes in aqueous solutions and that for this amino acid the effect of the cation of the electrolyte is not significant. Comparison of these results with previous measurements for DL-alanine in aqueous solutions of the same electrolytes show the notable effect of the backbone of the amino acid.     

Nucleophilic debenzoylation of p‐nitrophenyl benzoate in cationic micellar media

Pseudo‐first‐order rate constants for the nucleophilic debenzoylation reaction of p‐nitrophenyl benzoate with various hydroxamate ions [RC = ONHO^?] were investigated in aqueous cationic micellar media at pH 7.8 and 27°C. The kinetic rate data of the reaction revealed that the nucleophilic reactivity sequence of these hydroxamate ions is generally benzohydroxamic acid > salicylhydroxamic acid > acetohydroxamic acid. The k_obs value increases upon addition of cationic surfactants to the reaction medium involving interfacial ion exchange between bulk aqueous media and micellar pseudophase. The effect of surfactant head and tail group is discussed. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 106–112, 2010     

Investigations of the Properties of l-Histidine in Aqueous NaCl Solutions at Different Temperatures

Density and viscosity experimental data for l-histidine in NaCl aqueous solutions were obtained at different salt and different amino acid concentrations in the range of temperatures between 293.15 and 323.15 K. The results have been correlated and analyzed in order to evaluate the influence of electrolyte concentration and temperature on the volumetric and viscometric properties of the solutions. The apparent molar volumes and the transfer volumes of l-histidine in aqueous NaCl solutions at different salt and amino acid molalities over entire temperature range were calculated from experimental density data. The viscosity experimental data have been analyzed with Jones–Dole equation and the Falkenhagen (A) and the Jones–Dole coefficient (B) have been calculated in order to evaluate the interactions occurring in the systems. The B viscosity coefficients were found to be positive for all conditions, showing a kosmotropic effect of solutes, indicating an alignment of zwitterions with ions/water dipoles. A comparison of standard partial molar volumes for some amino acids in water and NaCl aqueous solutions shows that they increase with molecular mass and complexity of the lateral side chain of the amino acid.