Journal of Solution Chemistry (v.39, #10)

Densities, viscosities, and refractive indices of three amino acids (glycine, L-alanine, and L-valine) in aqueous solutions of an ionic liquid, 1-propyl-3-methylimidazolium bromide, have been measured at 298.15 K. These data have been used to calculate apparent molar volumes (V φ ), viscosity B-coefficients, and molar refractions of these mixtures. The standard partial molar volumes ( $V_{phi}^{0}$ ) and standard partial molar volumes of transfer ( $Delta_{mathrm{tr}}V_{phi}^{0}$ ) have been determined for these amino acid solutions from these density data. The resulting values of $V_{phi}^{0}$ and $Delta_{mathrm{tr}}V_{phi}^{0}$ for transfer of amino acids from water to aqueous ionic liquid solutions have been interpreted in terms of solute + solvent interactions. These data also indicate that hydrophobic interactions predominate in L-alanine and L-valine solutions. Linear correlations were found for both $V_{phi}^{0}$ and the viscosity B-coefficient with the number of carbon atoms in the alkyl chain of the amino acids, and have been used to estimate the contribution of the charged end groups ( $mathrm{NH}_{3}^{+}$ , COO), the CH2 group, and other alkyl chains of the amino acids. The viscosity and molar refractivity results have been used to confirm the conclusions obtained from volumetric properties.
Keywords: Amino acids; Ionic liquid; Apparent molar volume; Viscosity

Densities and Viscosities of Tris(acetylacetonato)cobalt(III) Complex Solutions in Various Solvents by Haruko Ikeuchi; Mitsuhiro Kanakubo; Shin Okuno; Rika Sato; Koichi Fujita; Manatsu Hamada; Nobuhiro Shoda; Kenta Fukui; Koji Okada; Hikaru Kanazawa; Akira Iimori; Daisaku Miyake; Takeshi Takeda; Gen P. Satô (1428-1453).
The densities and the viscosities of tris(acetylacetonato)cobalt(III) solutions in acetonitrile, dichloromethane, chloroform, tetrachloromethane, benzene, toluene, ethylbenzene, and p-xylene were measured in the dilute concentration regions at several temperatures ranging from 278 to 313 K under ambient pressure. The partial molar volumes of the solvents and solute were calculated. They are independent of concentration and increase slightly as the temperature increases. The viscosity A- and B-coefficients of the Jones-Dole equation were obtained. The A-coefficients were found to be zero within experimental error. The B-coefficients are positive and decrease as the temperature increases. Thermodynamic quantities of activation for viscous flow were calculated on the basis of Eyring’s viscosity equation. From the quantities obtained in this study, along with some information from the literature, it is suggested that structure-making interactions occur between the segments of the complex and the solvent molecules. These interactions include electrostatic interactions between the local charge on the complex and the dipole moment of the solvent in solutions of acetonitrile and dichloromethane, interlocking packing interactions along C 3-axis of the complex with solvent in solutions of chloroform and tetrachloromethane, and π-electron interactions between the chelate ring of the complex and the solvent in solutions of benzene, toluene, ethylbenzene, and p-xylene.
Keywords: Density; Viscosity; Viscosity B-coefficient; Eyring’s viscosity equation; Partial molar volumes; Thermodynamic quantities of activation for viscous flow; Tris(acetylacetonato)cobalt solutions; Organic solvents

The apparent molar volumes V 2,φ , apparent molar isentropic compressibilities K S,2,φ , and enthalpies of dilution of aqueous glycine, alanine, α-amino butyric acid, valine, and leucine have been determined in aqueous 1.0 and 2.0 mol⋅dm−3 sorbitol solutions at 298.15 K. These data have been used to calculate the infinite dilution standard partial molar volumes $V_{2,m}^{0}$ , partial molar isentropic compressibilities $K_{S,2,m}^{0}$ , and enthalpies of dilution Δdil H 0 of the amino acids in aqueous sorbitol, along with the standard partial molar quantities of transfer of the amino acids from water to aqueous sorbitol. The linear correlation of $V_{2,m}^{0}$ for this homologous series of amino acids has been utilized to calculate the contribution to $V_{2}^{0}$ of the charged end groups ( $mathrm{NH}_{3}^{+}$ , COO), the CH2 group, and other alkyl chains of the amino acids. The results for the standard partial molar volumes of transfer, compressibilites and enthalpies of dilution from water to aqueous sorbitol solutions have been correlated and interpreted in terms of ion–polar, ion–hydrophobic, and hydrophobic–hydrophobic group interactions. A comparison of these thermodynamic properties of transfer suggest that an enhancement of the hydrophilic/polar group interactions is operating in ternary systems of amino acid, sorbitol, and water.
Keywords: Partial molar volume; Partial molar isentropic compressibility; Enthalpy of dilution; α-Amino acids; Hydration number; Sorbitol

The partial molar volume at infinite dilution of aqueous solutions of 3-aminopropanoic acid, 4-aminobutanoic acid, 5-aminopentanoic acid and 6-aminohexanoic acid were determined at T=(293.15,298.15,303.15 and 308.15 K) from density measurements. The thermodynamic behavior of the aqueous α,ω-amino acid solutions is compared with that reported for α-amino acids in water. The interaction volume is calculated and the influence of charged and uncharged groups of the amino acids is discussed in terms of solute–solvent interactions.
Keywords: α,ω-Amino acids; Partial molar volume; Group contribution; Solute–solvent interactions; Interaction volume

Speciation of the Vanadium(III) Complexes with 1,10-Phenanthroline, 2,2′-Bipyridine, and 8-Hydroxyquinoline by Leydi Erika Sarmiento; Mildred Rodríguez; Lorenzo Echevarria; Vito Lubes (1484-1491).
The complex species formed between vanadium(III) and 1,10-phenanthroline (phen), 2,2′-bipyridine (bipy), and 8-hydroxyquinoline (8hq) were studied in aqueous solution by means of electromotive forces measurements, emf(H), at 25 °C with 3.0 mol⋅dm−3 KCl as the ionic medium. The potentiometric data were analyzed using the least-squares computational program LETAGROP, taking into account the hydrolytic vanadium(III) species formed in solution. Analysis of the vanadium(III)–phen system data shows the formation of [VHL]4+, [V(OH)L]2+, [V2OL2]4+ and [V2OL4]4+ complexes. In the vanadium(III)–bipy system the [VHL]4+, [V(OH)L]2+, [V2OL2]4+ and [V2OL4]4+ complexes were observed, and in the vanadium(III)–8hq system the complexes [V(OH)L]+, [V(OH)2L], [VL2]+ and [VL3] were detected.
Keywords: Vanadium(III) complexes; 1,10-Phenanthroline; 2,2′-Bipyridine; 8-Hydroxyquinoline; Potentiometric studies; Speciation

Excess Molar Volumes of Ternary Mixtures of a Cyclic Ether with Aromatic Hydrocarbons at 308.15 K by Rajesh K. Siwach; Dimple Sharma; Sunil K. Jangra; V. K. Sharma (1492-1500).
Excess molar volumes, $V_{ijk}^{E}$ , are reported for ternary mixtures of tetrahydropyran (i)+benzene (j)+toluene or o- or p-xylenes (k) and tetrahydropyran (i)+toluene (j)+o- or p-xylenes (k) as a function of composition at 308.15 K. These $V_{ijk}^{E}$ values have been fitted to the Redlich–Kister equation to predict ternary adjustable parameters and standard deviations. The measured $V_{ijk}^{E}$ data have been analyzed in terms of Graph theory (which involves the topology of the constituents of mixtures). It has been observed that $V_{ijk}^{E}$ values predicted by Graph theory compare well with their corresponding experimental values.
Keywords: Tetrahydropyran; Aromatic hydrocarbons; Excess molar volumes; Connectivity parameter of third degree; Specific interactions

To understand the thermodynamic characteristics of cationic surfactants in binary mixtures, the aggregation behavior of hexadecyltrimethylammonium chloride (CTAC) has been investigated in ethylene glycol (EG) + water solvent mixtures at different temperatures and EG to water ratios. The critical micelle concentration (CMC) and degree of counter ion bonding (β) were calculated from electrical conductivity measurements. An equilibrium model for micelle formation was applied to obtain the thermodynamic parameters for micellization, including the standard Gibbs energies of micellization ( $Delta G_{mathrm{mic}}^{mathrm{o}})$ , standard enthalpies of micelle formation ( $Delta H_{mathrm{mic}}^{mathrm{o}})$ and standard entropies of micellization ( $Delta S_{mathrm{mic}}^{mathrm{o}})$ . Our results show that $Delta G_{mathrm{mic}}^{mathrm{o}}$ is always negative and slightly dependent on temperature. The process of micellization is entropy driven in pure water, whereas in EG + water mixtures the micellization is enthalpy driven.
Keywords: Thermodynamic properties; Critical micelle concentration; CTAC; EG

Solvatochromic Probes Absorbance Behavior in Mixtures of 2-Hydroxy Ethylammonium Formate with Methanol, Ethylene Glycol and Glycerol by Hadi Salari; Ali Reza Harifi-Mood; Mohammad Reza Elahifard; Mohammad Reza Gholami (1509-1519).
Solute-solvent and solvent-solvent interactions were investigated for binary mixtures of an ionic liquid (IL) 2-hydroxy ethylammonium formate as with methanol, ethylene glycol and glycerol. The physicochemical properties of the solvent mixtures at 25 °C, over the whole range of mole fractions, were determined using solvatochromic probes. High normal polarity ( $E_{T}^{N}$ ) in the alcohol-rich region confirms solute-solvent interactions in this medium. Dipolarity/polarizability (π ) show a different trend to $E_{T}^{N}$ with a positive deviation from ideal behavior in IL-glycerol mixtures. However, these deviations for other solvent mixtures are insignificant. Contrary to what is observed for $E_{T}^{N}$ and π , hydrogen-bond donor (HBD) acidity and hydrogen-bond acceptor (HBA) basicity demonstrate similar trends. The applicability of the combined nearly-ideal binary solvent/Redlich-Kister (CNIBS/R-K) equation for the correlation of various parameters provides a simple computational model to correlate and/or predict various solvatochromic parameters for many binary solvent systems.
Keywords: Ionic liquids; Solvatochromic properties; 2-Hydroxy ethylammonium formate; Solute-solvent and solvent-solvent interactions

Fluorescence Quenching of Tris(2,2′-bipyridine)Ruthenium(II) Dichloride by Certain Organic Dyes by M. Asha Jhonsi; A. Kathiravan; G. Paramaguru; C. Manivannan; R. Renganathan (1520-1530).
Fluorescence quenching of [Ru(bpy)3]2+ by a series of organic dyes has been investigated by using the steady state fluorescence technique in aqueous medium. The dyes used are anthraquinone dyes: uniblue, acid blue 129, alizarin, alizarin red S and the azo dyes: congo red, sunset yellow, methyl orange, tartrazine, acid orange 63, methyl red and erichrome black T. The quenching of [Ru(bpy)3]2+ was found to obey the Stern-Volmer equation and the corresponding Stern-Volmer plots were linear indicating dynamic quenching. The quenching rate constants (k q) were calculated from the fluorescence data. The mechanism of quenching was discussed on the basis of the quenching rate constants as well as the reduction potential of dyes. The electron transfer mechanism has been proved by the calculation of Gibbs energy changes (ΔG et) by applying the Rehm-Weller equation.
Keywords: Fluorescence quenching; Electron transfer; Dyes

The densities of binary mixtures of ethylammonium nitrate (EAN) ionic liquid (IL) and γ-butyrolactone (BL) have been measured over the entire range of concentrations at 293.15, 298.15, 303.15, 308.15, 313.15 and 318.15 K and under ambient pressure. Experimental densities were used to calculate excess molar volumes

Raman Spectra of Tungsten-Bearing Solutions by Alexander F. Redkin; Galina V. Bondarenko (1549-1561).
Raman spectroscopy at 25 °C was performed to analyze speciation in quenched solutions after experiments on sodium tungstates and sodium tungstate bronze dissolution at t=500 °C, p=1000 bar. The experiments were conducted under different oxidation-reduction conditions in sodium chloride solution media. The spectra of the quenched solutions were different from those of the reference solutions of 0.02 mol⋅kg−1 W(VI) (H2O) in the pH range 2.3–7.2. Thermodynamic models were established and the fields of predominance of different isopolytungstate species at 25–50 °C were determined. The experimental results of tungstate dissolution demonstrates that reduced tungstate solutions may contain a significant amount of tungsten species with valence states lower than W(VI).
Keywords: Raman spectroscopy; Tungsten; Sodium tungstate; Sodium tungstate bronze; Speciation; Isopolytungstate species; Thermodynamic calculations

Formation equilibria of cobalt(II) complexes of 2-(aminomethyl)-benzimidazole (AMBI) and the ternary complexes Co(AMBI)L (L = aliphatic or aromatic dicarboxylic acids) were investigated in aqueous solutions at 25 °C and 0.1 mol⋅dm−3 ionic strength. Stoichiometry and stability constants are reported for the complexes formed. The speciation of the complexes was resolved. Values of

pK a Determinations for Montelukast Sodium and Levodropropizine by Ibrahim Narin; Salih Sarioglan; Beril Anilanmert; Hayati Sari (1582-1588).
The pK a constants and relative abundances of unionized and ionized forms of Montelukast sodium {the sodium salt of 2-[1-[[(1R)-1-[3-[2-(7-chloroquinolin-2-yl)ethenyl] phenyl]-3-[2-(2-hydroxypropan-2-yl)phenyl]propyl]sulfanylmethyl]cyclopropyl]acetic acid} and Levodropropizine {(2S)-3-(4-phenylpiperazin-1-yl)propane-1,2-diol} were determined potentiometrically from measurements at various pHs. These determinations were in order to relate their pK a values with their bioavailability and to provide chemical data to be used in their analysis.
Keywords: Potentiometric titration; Drug research; Acidity; Protonation; Dissociation constant; Ionization