Showing papers in "Journal of Solution Chemistry in 2007"

Cyclic Voltammetric Studies of Ferrocene in Nonaqueous Solvents in the Temperature Range from 248.15 to 298.15 K

Abstract: In the present work the oxidation of ferrocene, Fe(C5H5)2, to the ferrocenium cation, Fe(C2H5)2 +, was examined in the solvents acetonitrile (ACN), acetone (ACE), N-methylformamide (NMF), N,N-dimethylformamide (DMF), N,N-dimethylacetanide (DMA), 3-pentanone (PEN), dimethyl sulfoxide (DMSO) and dichloromethane (DCM) over the temperature range from 248.15 to 298.15 K using the technique of cyclic voltammetry. The anodic (E pa) and the cathodic (E pc) peak potentials, as well as the corresponding anodic (i pa) and cathodic (i pc) peak currents, were obtained at different scan rates (0.02, 0.05, 0.08 and 0.10 V ·s–1). The half-wave potentials (E 1/2) of the Fe(C2H5)2 +/Fe(C5H5)2 couple in the investigated solvent media have been evaluated. The diffusion coefficients (D) have been calculated using the Randles-Sevcik equation. The effects of changing the scan rate, the temperature and properties of the solvent medium such as viscosity and donor number on the electrochemical behavior of ferrocene have been examined.

Influence of the cation on the solubility of CO2 and H2 in ionic liquids based on the bis (trifluoromethylsulfonyl )imide anion

Abstract: Experimental values for the solubility of carbon dioxide and hydrogen in three room temperature ionic liquids based on the same anion—(bistrifluoromethylsulfonyl)imide [Ntf2]—and three different cations—1-butyl-3-methylimidazolium, [C4mim], 1-ethyl-3-methylimidazolium, [C2mim] and trimethyl-butylammonium, [N4111]—are reported between 283 and 343 K and close to atmospheric pressure. Carbon dioxide, with a mole-fraction solubility of the order of 10−2, is two orders of magnitude more soluble than hydrogen. The solubility of CO2 is very similar in the three ionic liquids although slightly lower in the presence of the [C2mim] cation. In the case of H2, noticeable differences were observed with larger mole fraction solubilities in the presence of [N4111] followed by [C4mim]. All of the mole-fraction solubilities decrease with increasing temperature. From the variation of Henry’s law constants with temperature, the thermodynamic functions of solvation were calculated. The precision of the experimental data, considered as the average absolute deviation of the Henry’s law constants from appropriate smoothing equations, is always better than ±1%.

Density and Refractive Index for Binary Systems of the Ionic Liquid [Bmim][BF4] with Methanol, 1,3-Dichloropropane and Dimethyl Carbonate

Abstract: Refractive indices at 298.15 K and densities in the temperature interval 293.15 to 318.15 K were determined at atmospheric pressure over the whole composition range for the binary systems [Bmim][BF4]+(methanol, or 1,3-dichloropropane, or dimethyl carbonate). Due to the high viscosity of the samples, which would produce a wrong density if a classical vibrating-tube densimeter were used, a densimeter was employed that automatically corrects the data for the viscosity effect. Because at room temperature some [Bmim][BF4]+dimethyl carbonate mixtures showed partial immiscibility, liquid-liquid equilibrium was determined for this system. Excess molar volumes and deviations of refractive index from linear mixing behavior were calculated from the experimental data.

Study of the Volumetric Properties of the Aqueous Ionic Liquid 1-Methyl-3-pentylimidazolium Tetrafluoroborate

Abstract: This paper reports the densities of aqueous solutions of the ionic liquid (IL) 1-methyl-3-pentylimidazolium tetrafluoroborate ([pmim][BF4]) that were measured from 278.15 to 343.15 K, at intervals of 5 K, using an Anton Parr model DMA 4500 oscillating U-tube densitometer. The apparent molar volume, φVB, and the partial molar volume of [pmim][BF4], \(\bar{V}_{\mathrm{B}}\) , were calculated. The values of the apparent molar volume, φVB, were fitted to Pitzer’s model for volumetric properties by the method of least-squares, which allowed the partial molar volume of the IL at infinite dilution, \(\bar{V}_{\mathrm{B}}^{\mathrm{o}}\) , and Pitzer’s parameters, βM,X(0)V and βM,X(1)V, to be obtained. The small standard deviations of the fits show that Pitzer’s model is also appropriate for representing the volumetric properties of aqueous solutions of the ionic liquid [pmim][BF4].

Partial Molar Volumes and Refractions of Aqueous Solutions of Fructose, Glucose, Mannose, and Sucrose at 15.00, 20.00, and 25.00 °C

Abstract: The partial molar volumes and refractions of aqueous solutions of fructose, glucose, mannose and sucrose were determined at 15.00, 20.00 and 25.00 °C over a wide concentration range. A model is proposed to describe the deviations of the partial molar volumes at higher concentrations from those at infinite dilution. In addition, the partial molar volumes of the sugars at infinite dilution were fit to quadratic relations in temperature.

Li+ Transport Mechanism in Oligo(Ethylene Oxide)s Compared to Carbonates

Abstract: Molecular dynamics simulations have been performed on oligo(ethylene oxide)s of various molecular weights doped with the lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI) in order to explore the mechanism of Li+ transport in materials covering the range from liquid electrolytes to prototypes for high molecular weight poly(ethylene oxide)-based polymer electrolytes. Good agreement between MD simulations and experiments is observed for the conductivity of electrolytes as a function of molecular weight. Unlike Li+ transport in liquid ethylene carbonate (EC) that comes from approximately equal contributions of vehicular Li+ motion (motion together with solvent) and Li+ diffusion by solvent exchange, Li+ transport in oligoethers was found to occur predominantly by vehicular motion. The slow solvent exchange of Li+ in oligo(ethylene oxide)s highlights why high molecular weight amorphous polymer electrolytes with oligo(ethylene oxide)s solvating groups suffer from poor Li+ transport. Ion complexation and correlation of cation and anion motion is examined for oligoethers and compared with that in EC.

Lactonization and protonation of gluconic acid : A thermodynamic and kinetic study by potentiometry, NMR and ESI-MS

Abstract: In acidic aqueous solutions, gluconate protonation is coupled with lactonization of gluconic acid. With the decrease of pC{sub H}, two lactones ({delta}/{gamma}) are sequentially formed. The {delta}-lactone forms more readily than the {gamma}-lactone. In 0.1 M gluconate solutions, if pC{sub H} is above 2.5, only the {delta}-lactone is generated. When pC{sub H} is decreased below 2.0, the formation of the {gamma}-lactone is observable although the {delta}-lactone predominates. At I = 0.1 M NaClO{sub 4} and room temperature, the deprotonation constant of the carboxylic group, using the NMR technique, was determined to be log K{sub a} = 3.30 {+-} 0.02; the {delta}-lactonization constant, by the batch potentiometric titrations, was obtained to be log K{sub L} = - (0.54 {+-} 0.04). Using ESI-MS, the rate constants of the {delta}-lactonization and the hydrolysis at pC{sub H} {approx} 5.0 were estimated to be k{sub 1} = 3.2 x 10{sup -5} s{sup -1} and k{sup -1} = 1.1 x 10{sup -4} s{sup -1}, respectively.

Densities and Volumetric Properties of Binary Mixtures of Formamide with 1-Butanol, 2-Butanol, 1,3-Butanediol and 1,4-Butanediol at Temperatures between 293.15 and 318.15 K

Abstract: The densities of binary mixtures of formamide (FA) with 1-butanol, 2-butanol, 1,3-butanediol, and 1,4-butanediol, including those of the pure liquids, over the entire composition range were measured at temperatures (293.15, 298.15, 303.15, 308.15, 313.15 and 318.15) K and atmospheric pressure. From the experimental data, the excess molar volume, VmE, partial molar volumes, \(\smash{\overline V _{m,1}^\circ }\) and \(\smash{\overline V _{m,2}^\circ }\), at infinite dilution, and excess partial molar volumes, \(\smash{\overline V _{m,1}^{\circ {\rm E}}}\) and \(\smash{\overline V _{m,2}^{\circ {\rm E}}}\), at infinite dilution were calculated. The variation of these parameters with composition and temperature of the mixtures are discussed in terms of molecular interactions in these mixtures. The partial molar expansivities, \(\smash{\overline E _1^\circ}\) and \(\smash{\overline E _2^\circ}\), at infinite dilution and excess partial molar expansivities, \(\smash{\overline E _1^{\circ {\rm E}}}\) and \(\smash{\overline E _2^{\circ {\rm E}}}\), at infinite dilution were also calculated. The VmE values were found to be positive for all the mixtures at each temperature studied, except for FA + 1-butanol which exhibits a sigmoid trend wherein VmE values change sign from positive to negative as the concentration of FA in the mixture is increased. The VmE values for these mixtures follow the order: 1-butanol < 2-butanol < 1,3-butanediol < 1,4-butanediol. It is observed that the VmE values depend upon the number and position of hydroxyl groups in these alkanol molecules.

Interactions of Some Amino Acids with Aqueous N,N-Dimethylacetamide Solutions at 298.15 and 308.15 K: A Volumetric Approach

Abstract: The apparent molar volumes, Vφ, of glycine, L-alanine and L-serine were obtained in aqueous 0 to ∼4 mol⋅kg−1 N,N-dimethylacetamide (DMA) solutions from density measurements at 298.15 and 308.15 K. The standard partial molar volume, Vφo, and standard partial molar volumes of transfer, ΔtrVφo, were determined for these amino acids. It has been shown that hydrophilic-hydrophilic interactions between charged groups of the amino acids and the —CON= group of DMA are predominant in the case of glycine and L-serine, but for L-alanine the interactions between its side group (—CH3) and DMA are predominant. An increase in temperature increases the standard partial molar volumes but decreases the transfer volumes of the amino acids. The results have been interpreted in terms of cosphere overlap model.

Water Activity and Osmotic Coefficients in Solutions of Glycine, Glutamic Acid, Histidine and their Salts at 298.15 K and 310.15 K

Abstract: From vapor pressure osmometry data, the activity of water, osmotic coefficients and mean ionic activity coefficients of glycine (m=0.006−3.2 mol⋅kg−1), L-histidine (m=0.005−0.23 mol⋅kg−1), L-histidine monohydrochloride (m=0.008−0.63 mol⋅kg−1), glutamic acid (m=0.004−0.05 mol⋅kg−1), sodium L-glutamate (m=0.007−0.6 mol⋅kg−1), and calcium L-glutamate (m=0.008−0.6 mol⋅kg−1) have been obtained in aqueous solutions at 298.15 and 310.15 K. The Pitzer equations and the mean spherical approximation (MSA) are used for theoretical modeling. The results are supplied as reference thermodynamic material for the characterization of more complex molecules such as proteins.

Volumetric Investigations on Interactions of Acidic/Basic Amino Acids with Sodium Acetate, Sodium Propionate and Sodium Butyrate in Aqueous Solutions

Abstract: The apparent molar volumes, Vφ, of L-aspartic acid, L-glutamic acid, L-lysine monohydrate and L-arginine in water and in aqueous (0.1, 0.25, 0.5 and 1.0) mol⋅kg−1 sodium acetate and sodium propionate, and (0.1, 0.25 and 0.5) mol⋅kg−1 sodium butyrate solutions have been determined at 288.15, 298.15, 308.15 and 318.15 K from density measurements. The partial molar volumes at infinite dilution, V2o, obtained from Vφ data, have been used to calculate hydration numbers and partial molar expansibilities of amino acids in water and in the presence of the studied cosolutes at different temperatures. These parameters have been discussed in terms of various interactions between the acidic/basic amino acids and organic salts in these solutions. The effect of the hydrophobic chain length of the carboxylate ions has also been discussed.

Enthalpy of Solvation Correlations for Gaseous Solutes Dissolved in Toluene and Carbon Tetrachloride Based on the Abraham Model

Abstract: Data have been assembled from the published literature on the enthalpies of solvation for more than 100 compounds in toluene and carbon tetrachloride. It is shown that an Abraham solvation equation with five descriptors can be used to correlate the experimental solvation enthalpies to within standard deviations of 2.19 and 2.070 kJ⋅mol−1 for toluene and carbon tetrachloride, respectively. The derived correlations provide very accurate mathematical descriptions of the measured enthalpy of solvation data at 298 K that in the case of carbon tetrachloride span a range of 105 kJ⋅mol−1. Division of the experimental values into a training set and a test set shows that there is no bias in the predictions, and that the predictive capability of the correlations is better than 2.5 kJ⋅mol−1.

A thermodynamic study on the binding of calcium ion with myelin basic protein

Abstract: The interaction of myelin basic protein (MBP) from the bovine central nervous system with divalent calcium ion was studied by isothermal titration calorimetry at 27 °C in aqueous solution. The extended solvation model was used to reproduce the enthalpies of Ca2+-MBP interaction over the whole range of Ca2+ concentrations. The solvation parameters recovered from the solvation model were attributed to the structural change of MBP due to the metal ion interaction. It was found that there is a set of two identical and non-interacting binding sites for Ca2+ ions. The association equilibrium constant is 0.021 μmol⋅dm−3. The molar enthalpy of binding is ΔH=−15.10 kJ⋅mol−1.

Liquid Densities and Excess Molar Volumes for Binary Systems (Ionic Liquids + Methanol or Water) at 298.15, 303.15 and 313.15 K, and at Atmospheric Pressure

Abstract: Binary excess molar volumes, VmE, have been evaluated from density measurements, using a vibrating tube densimeter over the entire composition range for binary liquid mixtures of ionic liquids 1-ethyl-3-methyl-imidazolium diethyleneglycol monomethylethersulphate [EMIM]+[CH3(OCH2CH2)2OSO3]− or 1-butyl-3-methyl-imidazolium diethyleneglycol monomethylethersulphate [BMIM]+[CH3(OCH2CH2)2OSO3]− or 1-methyl-3-octyl-imidazolium diethyleneglycol monomethylethersulphate [MOIM]+[CH3(OCH2CH2)2OSO3]−+methanol and [EMIM]+[CH3(OCH2CH2)2OSO3]−+water at 29815, 30315 and 31315 K The VmE values were found to be negative for all systems studied The VmE results are explained in terms of intermolecular interactions and packing effects The experimental data were fitted by the Redlich-Kister polynomial

Chromium(III) Hydroxide Solubility in the Aqueous K+-H+-OH--CO2- HCO3-- CO32--H2O System: A Thermodynamic Model

Abstract: Chromium(III)-carbonate reactions are expected to be important in managing high-level radioactive wastes. Extensive studies on the solubility of amorphous Cr(III) hydroxide solid in a wide range of pH (3–13) at two different fixed partial pressures of CO2(g) (0.003 or 0.03 atm.), and as functions of K2CO3 concentrations (0.01 to 5.8 mol⋅kg−1) in the presence of 0.01 mol⋅dm−3 KOH and KHCO3 concentrations (0.001 to 0.826 mol⋅kg−1) at room temperature (22±2 °C) were carried out to obtain reliable thermodynamic data for important Cr(III)-carbonate reactions. A combination of techniques (XRD, XANES, EXAFS, UV-Vis-NIR spectroscopy, thermodynamic analyses of solubility data, and quantum mechanical calculations) was used to characterize the solid and aqueous species. The Pitzer ion-interaction approach was used to interpret the solubility data. Only two aqueous species [Cr(OH)(CO3) 2 2− and Cr(OH)4CO 3 3− ] are required to explain Cr(III)-carbonate reactions in a wide range of pH, CO2(g) partial pressures, and bicarbonate and carbonate concentrations. Calculations based on density functional theory support the existence of these species. The log 10 K° values of reactions involving these species [{Cr(OH)3(am) + 2CO2(g)⇌Cr(OH)(CO3) 2 2− +2H+} and {Cr(OH)3(am) + OH−+CO 3 2− ⇌Cr(OH)4CO 3 3− }] were found to be −(19.07±0.41) and −(4.19±0.19), respectively. No other data on any Cr(III)-carbonato complexes are available for comparisons.

Re-evaluation of the Activity Coefficients of Aqueous Hydrochloric Acid Solutions up to a Molality of 16.0 mol·kg −1 Using the Hückel and Pitzer Equations at Temperatures from 0 to 50 °C

Abstract: The simple three-parameter Pitzer and extended Huckel equations were used for calculation of activity coefficients of aqueous hydrochloric acid at various temperatures from 0 to 50 °C up to a molality of 5.0 mol·kg−1. A more complex Huckel equation was also used at these temperatures up to a HCl molality of 16 mol·kg−1. The literature data measured by Harned and Ehlers J. Am. Chem. Soc. 54, 1350–1357 (1932) and 55, 2179–2193 (1933) and by Akerlof and Teare [J. Am. Chem. Soc. 59, 1855–1868 (1937)] on galvanic cells without a liquid junction were used in the parameter estimations for these equations. The latter data consist of sets of measurements in the temperature range 0 to 50 °C at intervals of 10 °C, and data at these temperatures were used in all of these estimations. It was observed that the estimated parameters follow very simple equations with respect to temperature. They are either constant or depend linearly on the temperature. The values for the activity coefficient parameters calculated by using these simple equations are recommended here. The suggested new parameter values were tested with all reliable cell potential and vapor pressure data available in literature for concentrated HCl solutions. New Harned cell data at 5, 15, 25, 35, and 45 °C up to a molality of 6.5 mol·kg−1 are reported and were also used in the tests. The activity coefficients obtained from the new equations were compared to those calculated by using the Pitzer equations of Holmes et al. [J. Chem. Thermodyn. 19, 863–890 (1987)] and of Saluja et al. [Can. J. Chem. 64, 1328–1335 (1986)] at various temperatures, and by using the extended Huckel equation of Hamer and Wu [J. Phys. Chem. Ref. Data 1, 1047–1099 (1972)] at 25 °C.

Phase Behavior of Aqueous Na–K–Mg–Ca–Cl–NO3 Mixtures: Isopiestic Measurements and Thermodynamic Modeling

Abstract: A comprehensive model has been established for calculating thermodynamic properties of multicomponent aqueous systems containing the Na+, K+, Mg2+, Ca2+, Cl− and NO 3 − ions. The thermodynamic framework is based on a previously developed model for mixed-solvent electrolyte solutions. The framework has been designed to reproduce the properties of salt solutions at temperatures ranging from the freezing point to 300 °C and concentrations ranging from infinite dilution to the fused salt limit. The model has been parameterized using a combination of an extensive literature database and new isopiestic measurements for thirteen salt mixtures at 140 °C. The measurements have been performed using Oak Ridge National Laboratory’s (ORNL) previously designed gravimetric isopiestic apparatus, which can also detect solid phase precipitation. In addition to various Na–K–Mg–Ca–Cl–NO3 systems, results are reported for LiCl solutions. Water activities are reported for mixtures with a fixed ratio of salts as a function of the total apparent salt mole fraction. The isopiestic measurements reported here simultaneously reflect two fundamental properties of the system, i.e., the activity of water as a function of solution concentration and the occurrence of solid–liquid transitions. The thermodynamic model accurately reproduces the new isopiestic data as well as literature data for binary, ternary and higher-order subsystems. Because of its high accuracy in calculating vapor–liquid and solid–liquid equilibria, the model is suitable for studying deliquescence behavior of multicomponent salt systems.

The Oxidation of Iron(II) with Oxygen in NaCl Brines

Abstract: The oxidation of nanomolar levels of iron(II) with oxygen has been studied in NaCl solutions as a function of temperature (0 to 50 °C), ionic strength (0.7 to 5.6 mol⋅kg−1), pH (6 to 8) and concentration of added NaHCO3 (0 to 10 mmol⋅kg−1). The results have been fitted to the overall rate equation: $$\mathrm{d}\mbox{[Fe(II)]}/\mathrm{d}t=-k_{\mathrm{app}}\mbox{[Fe(II)]}[\mbox{O}_{2}]$$ The values of kapp have been examined in terms of the Fe(II) complexes with OH− and CO32−. The overall rate constants are given by: $$k_{\mathrm{app}}=\alpha_{\mathrm{Fe}2+}k_{\mathrm{Fe}}+\alpha_{\mathrm{Fe(OH)}+}k_{\mathrm{Fe(OH)}+}+\alpha_{\mathrm{Fe(OH)}2}k_{\mathrm{Fe(OH)}2}+\alpha_{\mathrm{Fe(CO3)}2}k_{\mathrm{Fe(CO3)}2}$$ where αi is the molar fraction and ki is the rate constant of species i. The individual rate constants for the species of Fe(II) interacting with OH− and CO32− have been fitted by equations of the form: $$\begin{array}{l}\ln k_{\mathrm{Fe}2+}=21.0+0.4I^{0.5}-5562/T\\[6pt]\ln k_{\mathrm{FeOH}}=17.1+1.5I^{0.5}-2608/T\\[6pt]\ln k_{\mathrm{Fe(OH)}2}=-6.3-0.6I^{0.5}+6211/T\\[6pt]\ln k_{\mathrm{Fe(CO3)}2}=31.4+5.6I^{0.5}-6698/T\end{array}$$ These individual rate constants can be used to estimate the rates of oxidation of Fe(II) over a large range of temperatures (0 to 50 °C) in NaCl brines (I=0 to 6 mol⋅kg−1) with different levels of OH− and CO32−.

Thermodynamic Modeling of Aqueous Aluminum Chemistry and Solid-Liquid Equilibria to High Solution Concentration and Temperature. I. The Acidic H-Al-Na-K-Cl-H2O System from 0 to 100 °C

Abstract: In this paper, we describe the development of a thermodynamic model that calculates solute/solvent activities and solid-liquid equilibria in the acidic aluminum system, H-Al3+-Na-K-Cl-H2O, to high molality from 0 ° to ≈100 °C. The model incorporates the concentration-dependent, specific interaction equations for aqueous solutions of Pitzer (Activity Coefficients in Electrolyte Solutions, 2nd edn., pp. 75–153, CRC Press, Boca Raton, 1991). Parameterization of this model adds Al3+ specific interactions in the binary Al-Cl-H2O and ternary Al-H-Cl-H2O, Al-Na-Cl-H2O and Al-K-Cl-H2O systems as well as the standard chemical potentials of AlCl3⋅6H2O(s) and Al(OH)3(s) (gibbsite) in the 0 ° to 100 °C range to our variable temperature (0–250 °C) model of acid-base reactions in the H-Na-K-OH-Cl-HSO4-SO4-H2O system (Christov and Moller in Geochim. Cosmochim. Acta 68:1309, 2004). In constructing our aluminum model, we used Emf, osmotic, equilibrium constant and solubility data. New Emf measurements using the cell Pt|H2(g, 101.325 kPa)|HCl(m 1), AlCl3(m 2)|AgCl(s)|Ag|Pt at temperatures ranging from 0 to 45 °C and at total ionic strength ranging from 0.1 to 3 mol⋅kg−1 are presented. Gibbsite and boehmite, AlOOH(s), solubility data are used in testing the model. Limitations of the model due to data insufficiencies are discussed.

Kinetics and Mechanism of the Reactions Between Triphenylphosphine, Dialkyl Acetylenedicarboxilates and a NH-Acid, Pyrazole, by UV Spectrophotometry

Abstract: Kinetic studies were made of the reactions between triphenylphosphine and dialkyl acetylenedicarboxylates in the presence of a NH-acid such as pyrazole. To determine the kinetic parameters of the reactions, the reaction progress was monitored by UV spectrophotometry. The second-order fits were automatically drawn and the values of the second-order rate constant (k 2) were automatically calculated using standard equations. In the temperature range studied, the dependence of ln k 2 on the reciprocal temperature was consistent with the Arrhenius equation. Furthermore, useful information was obtained from studies of the effect of solvent, structure of the reactants (different alkyl groups within the dialkyl acetylenedicarboxylates), and also the concentration of reactants on the rate of reaction. The mechanism was confirmed to involve a steady-state condition with the first step of the reaction being the rate-determining step.

Investigation of the Electrochemical Reduction of Benzophenone in Aprotic Solvents Using the Method of Cyclic Voltammetry

Abstract: The reduction of benzophenone (Bzph) in 3-pentanone (PEN), acetone (ACE), N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF), tetrahydrofuran (THF), acetonitrile (ACN) and dimethyl sulfoxide (DMSO) with n-tetrabutylammonium hexafluorophosphate (TBAPF6) as background electrolyte was studied using the technique of cyclic voltammetry at the temperature of 263.15 K. The half-wave potentials (E 1/2) were extracted. The reduction of Bzph occurs in two successive one-electron steps to produce first the free radical anion Bzph− and then the dianion Bzph2−. The results indicated that the radical anion Bzph− is reoxidized to Bzph in all investigated solvent media whereas the dianion Bzph2− is reoxidized to Bzph− only in THF. The heterogeneous electron-transfer rate constants (k s ) were evaluated by employing the electrochemical rate equation proposed by Nicholson. The rate of electron transfer for the Bzph/Bzph− couple was found to be relatively slow in all investigated solvent media. Consequently, the electron-transfer processes can be recognized as quasi-reversible. The diffusion coefficients (D) of Bzph in the investigated solvent media have been calculated using the modified Randles-Sevcik equation. The effect of the physical and chemical properties of the solvent medium on the electrochemical behavior of Bzph has been examined.

Inclusion Complexation of Loratadine with Natural and Modified Cyclodextrins: Phase Solubility and Thermodynamic Studies

Abstract: The extent and mode of solubility enhancement exerted by the cyclodextrins (α-, β-, γ-, and HP-β-CDs) on loratadine (Lort) have been experimentally measured under controlled conditions in buffered aqueous solutions. Rigorous nonlinear regression analysis of the phase solubility diagrams obtained in 0.1 mol⋅L−1 phosphate buffer at pH=7.0 and 25 °C revealed the following: neutral Lort (pKa=4.6) tends to form soluble 1:1 and 1:2 Lort/CD complexes with all four of the examined CDs, where complex stability follows the decreasing order β-CD>HP-β-CD>γ-CD>α-CD. The hydrophobic character of Lort constitutes about 66% of the driving force for complex formation whereas specific interactions contribute 11.2 kJ⋅mol−1 towards the stability of the complexes. Thermodynamic studies showed that Lort/CD complex formation was favored by large enthalpic contributions but was impeded by negative entropic changes. Dissolution studies indicate that the dissolution rate of Lort from the freeze-dried Lort/β-CD complex is significantly higher than that of the corresponding physical mixture. Both DSC studies and molecular mechanical modeling of Lort/β-CD interactions were carried out to explore the possible formation of inclusion complexes.

D2O — H2O Solvent Isotope Effects on the Apparent Molar Volumes of Tetramethyl-bis-urea (Mebicarum) Solutions

Abstract: Densities of solutions of tetramethyl-bis-urea (TMbU) or “Mebicarum” in H2O and D2O, with solute mole fraction concentrations (x2) ranging up to 3.2 × 10−3, have been measured at 288.15, 298.15, 308.15 and 318.15 K using a precision vibrating-tube densimeter. The limiting apparent molar volumes, Vφ,2∞, and expansibilities, Ep, φ, 2∞, of the solute have been calculated. The isotope effect δ Vφ,2∞(H2O → D2O;T) is negative, monotonously decreases in magnitude with temperature and reverses sign at T ≈ 318 K. Water (H2O, D2O) and TMbU molecules in infinitely- and highly-dilute aqueous solutions form H(D)-bonded hydration complexes with a high packing density. The hydration of TMbU should be treated as a superposition of two mechanisms, hydrophobic and hydrophilic, with the latter one predominating.

Fatty Acid Methyl Esters as Biosolvents of Epoxy Resins: A Physicochemical Study

Abstract: The C8 to C18 fatty acid methyl esters (FAME) have been compared as solvents for two epoxy resin pre-polymers, bisphenol A diglycidyl ether (DGEBA) and triglycidyl p-aminophenol ether (TGPA). It was found that the solubilization limits vary according to the ester and that methyl caprylate is the best solvent of both resins. To explain these solubility performances, physical and chemical properties of FAME were studied, such as the Hansen parameters, viscosity, binary diffusion coefficient and vaporization enthalpy. Determination of the physicochemical parameters of FAME was carried out by laboratory experimentations and by calculation from bibliographic data. The Hansen parameters of FAME and epoxy resins pre-polymers were theoretically and experimentally determined. The FAME chain length showed a long dependence on the binary diffusion parameters and kinematic viscosity, which are mass and momentum transport properties. Moreover, the vaporization enthalpy of these compounds was directly correlated with the solubilization limits.

Ammonia catalyzed hydrolysis-condensation kinetics of tetraethoxysilane/dimethyldiethoxysilane mixtures studied by 29Si NMR and SAXS

Abstract: In-situ 29Si liquid-state nuclear magnetic resonance (NMR) was used to investigate the ammonia catalyzed hydrolysis and condensation of the mixed systems of tetraethoxysilane (TEOS) and dimethyldiethoxysilane (DDS) dissolved in methanol. With ammonia catalysis, the hydrolysis reaction orders for TEOS and DDS in the mixed systems remained first order, which is similar to that observed for their corresponding single silane component precursor systems. The hydrolysis rate constant for TEOS in the mixed systems was larger than that of TEOS in the single silane component precursor systems. Meanwhile, the hydrolysis rate constants of DDS in the mixed precursor systems were smaller than those of DDS in the single silane component precursor systems. The hydrolysis and condensation kinetics showed more compatible hydrolysis-condensation relative rates between TEOS and DDS, which remarkably affected the final microstructure of the resulting silica particles. Small angle X-ray scattering (SAXS) experiments showed a typical double fractal structure in the particulate networks.

Volumetric Properties of Aqueous Binary Mixtures of 1-Butanol, Butanediols, 1,2,4-Butanetriol and Butanetetrol at 298.15 K

Abstract: Excess molar volumes, VmE, and partial molar volumes, ↕2, have been determined for dilute aqueous solutions of 1-butanol, 1,2-butanediol, 2,3-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2,4-butanetriol and 1,2,3,4-butanetetrol (erythritol) at 298.15 K, as a function of composition from density measurements. The limiting partial molar volumes, ↕2∞, of alcohols in aqueous solution are evaluated through extrapolation. Interactions of the different solutes with water are discussed in terms of the relationship among polar and non-polar groups on water structure and the effect of the position of hydroxyl groups in the molecule.

On the Determination of Partial Molar Volumes, Partial Molar Refractions, Mean Electronic Polarizabilities and Effective Molecular Radii from Dilute Multi-component Data alone using Response Surface Models

Abstract: A quaternary system consisting of three solutes, namely ethanol, diethylene glycol (DEG) and triethylene glycol (TEG) in benzene at 298.15 K and 1.0125 × 105 Pa was studied. An experimental design in the range of concentration 0.006 < xsolute−i < 0.023 was explored, optimizing the metric distance among the solutes to avoid clustering. On-line simultaneous experimental measurements using a densitometer and a refractometer were utilized to measure bulk solution density and bulk refractive index, respectively. Response surface models describing the total molar volume and total molar refraction were employed to determine the partial molar volumes and the partial molar refractions of each solute from the dilute multi-component data alone. Neither densities nor refractive indices of any of the pure components were used and no binary information was required for the analysis. Definitions for the mean electronic polarizability and the effective molecular radius of a solute based on the partial molar refraction were introduced. Subsequently, the mean electronic polarizabilities and the effective molecular radii for each solute in multi-component solutions, as well as the solvent were determined. The results obtained for the partial molar volumes, partial molar refractions, electronic polarizabilities and the effective molecular radii were in good agreement with those obtained from independent binary experiments as well as those from literature binary data.

Interference of Copper(II) ions with Non-covalent Interactions in Uridine or Uridine 5′-Monophosphate Systems with Adenosine, Cytidine, Thymidine and their Monophosphates in Aqueous Solution

Abstract: Coordination reactions of copper(II) ions and their effect on non-covalent interactions in uridine (Urd) or uridine 5′-monophosphate (UMP) systems with nucleosides (Ado, Cyd, Thd) and nucleotides (AMP and CMP) in aqueous solutions have been studied. At high pH the effective coordination centers are deprotonated N(3) atoms from Urd and Thd, whereas at low pH, the N(3) atoms of pyrimidine nucleosides are blocked for coordination and the metallation sites are endocyclic nitrogen atoms from Ado, Cyd, AMP and CMP. Moreover, at low pH, the main reaction center in nucleotide solutions is the phosphate group. The NMR study has proven the occurrence of non-covalent ion-dipole interactions and stacking interactions in the systems considered. Introduction of a copper ion in the majority of systems causes the disappearance of weak interactions between ligands. The structures of the complexes in solution have been inferred from the equilibrium study: an analysis of the pH range of their occurrence with respect to the pH range of deprotonation of particular groups in the compounds studied, using Vis, EPR and 13C as well as 31P NMR spectral analysis.

Spectroscopic Investigations on the Interaction of Crystal Violet with Nonionic Micelles of Brij and Igepal Surfactants in Aqueous Media

Abstract: The behavior of the triphenylmethane dye crystal violet in aqueous solutions containing polyoxyethylene nonionic surfactants was investigated using absorption and fluorescence spectroscopic techniques. The interactions of the dye were examined in micellar media in order to prevent dye aggregation and to ensure maximum dye and surfactant interaction. The relative fluorescence enhancements and the binding constants of the dye to the surfactant micelles were determined. The micropolarities of the micellar environment sensed by the pyrene probe were estimated from the I 1/I 3 intensity ratios of the fluorescence spectra of pyrene. The fluorescence quenching of pyrene by hexadecylpyridinium chloride was investigated in aqueous surfactant mixtures at a fixed concentration of surfactant in order to determine the aggregation numbers. Attempts were made to correlate the binding constants obtained in this investigation to various micellar parameters.

The Influence of Ionic Strength on Yttrium and Rare Earth Element Complexation by Fluoride Ions in NaClO4, NaNO3 and NaCl Solutions at 25 °C

Abstract: Stability constants of the form F β 1(M)=[MF2+][M3+]−1[F−]−1 (where [MF2+] represents the concentration of a yttrium or a rare earth element (YREE) complex, [M3+] is the free YREE ion concentration, and [F−] is the free fluoride ion concentration) were determined by direct potentiometry in NaNO3 and NaCl solutions. The patterns of log10 F β 1(M) in NaNO3 and NaCl solutions very closely resemble stability constant patterns obtained previously in NaClO4. For a given YREE, stability constants obtained in NaClO4 were similar to, but consistently larger than F β 1(M) values obtained in NaNO3 which, in turn, were larger than formation constants obtained in NaCl. Stability constants for formation of nitrate and chloride complexes ( $_{\mathrm{NO}_{3}}\beta_{1}(\mathrm{M})=[\mathrm{MNO}_{3}^{2+}][\mathrm{M}^{3+}]^{-1}[\mathrm{NO}_{3}^{-}]^{-1}$ and Cl β 1(M)=[MCl2+][M3+]−1[Cl−]−1) derived from F β 1(M) data exhibited ionic strength dependencies generally similar to those of F β 1(M). However, in contrast to the somewhat complex pattern obtained for F β 1(M) across the fifteen member YREE series, no patterns were observed for nitrate and chloride complexation constants: neither $_{\mathrm{NO}_{3}}\beta_{1}(\mathrm{M})$ nor Cl β 1(M) showed discernable variations across the suite of YREEs. Nitrate and chloride formation constants at 25 °C and zero ionic strength were estimated as log10 $_{\mathrm{NO}_{3}}\beta_{1}^{\mathrm{o}}(\mathrm{M})=0.65\pm 0.06$ and log10 Cl β 1 o (M)=0.71±0.05. Although these constants are identical within experimental uncertainty, the distinct ionic strength dependencies of $_{\mathrm{NO}_{3}}\beta_{1}(\mathrm{M})$ and Cl β 1(M) produced larger differences in the two stability constants with increasing ionic strength whereby Cl β 1(M) was uniformly larger than $_{\mathrm{NO}_{3}}\beta_{1}(\mathrm{M})$ .