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Abstract: Ionic liquids have potentials as green materials in a variety of fields. It is the case that in their application in industry, ionic liquids are often used together with molecular solutes/solvents. In this paper, systematical measurements of viscosities and conductivities for the binary and quasi-binary mixtures of ionic liquids with molecular solutes were performed over the whole concentration range. The variation tendency of viscosities/conductivities with composition of the mixtures was explained through the disruption of molecular solutes to ionic association or aggregation of the ionic liquids. A exponential equation with empirical parameter A suggested initially by Seddon et al. was used to describe the dependence of viscosities on the mole fraction of molecular solutes, and the physical meaning of A was analyzed based on a theoretical equation deduced from rate process theory. At the same time, another exponential equation with parameter C was proposed to correlate the experimental date of the product of conductivity and viscosity, and satisfactory results were obtained over the entire range of concentration. The main factors affecting the parameter C were discussed. It is expected that the new data and correlation equations reported in this work will be useful for the application of ionic liquids in chemical industry. [Copyright &y& Elsevier]

The thermodynamics and phase behavior of mixtures of cationic gemini surfactant decanediyl-α,ω-bis(dodecyldimethylammonium bromide) (12-10-12) and sodium dodecylsulfate (SDS) were studied in the dilute SDS-rich region. The enthalpy of interaction between both surfactant monomers before the critical micelle concentration for the mixture (cmc mix ) was determined by isothermal titration calorimetry (ITC). After the cmc mix , ITC results exhibited a first process associated with a large endothermic enthalpy change followed by a second one with a very small exothermic enthalpy change. In the same regions, the conductivity curves show an increase in slope after the break, followed by a plateau region, respectively for the two processes. The combined results from the various methodologies used lead us to propose that the first process reflects the formation of non-spherical micelles and the second one the vesicle formation. The area per catanionic complex was obtained through surface pressure measurements, leading to an apparent packing parameter ⩾1. The observed behavior may be rationalized on the basis of the hypothesis that both surfactants distribute asymmetrically in the vesicle bilayers and unevenly in the non-spherical micelle. In order to get structural information Cryo-TEM experiments were performed, which provided images that support this interpretation. From all the information gathered a phase diagram was mapped, including three one-phase regions of spherical micelles, non-spherical micelles and vesicles. [ABSTRACT FROM AUTHOR]

In the present work, seven 1-allyl-3-methylimizodalium carboxylate ionic liquids (ILs), including 1-allyl-3-methylimizodalium formate [Amim][HCOO], acetate [Amim][CH 3 COO], propionate [Amim][CH 3 CH 2 COO], butyrate [Amim][CH 3 (CH 2 ) 2 COO], glycollate [Amim][HOCH 2 COO], lactate [Amim][CH 3 CHOHCOO]) and benzoate [Amim][C 6 H 5 COO], have been synthesized and characterized. Density ( ρ ) and conductivity ( σ ) have been determined experimentally for these ILs at 298.15 K and atmospheric pressure. Then molar volume ( V m ), standard entropy ( S °), lattice energy ( U POT ) and molar conductivity ( Λ ) of the ILs have been derived from the density and conductivity data. Ionicity of the ILs has been estimated using the Walden plot. Meanwhile, how anionic structure of the ILs affects the volumetric and conductivity properties of 1-allyl-3-methylimidazolium carboxylate ILs has been discussed from the analysis of structure–property relationship. [ABSTRACT FROM AUTHOR]

Abstract: Densities, conductivity, fluorescence and UV–vis absorption spectroscopy of glycyl dipeptide+ionic liquid (1-dodecyl-3-methylimidazolium bromide ([C12mim]Br))+water mixtures have been measured at different temperatures. From density data, the standard partial molar volume , standard partial molar volume of transfer for three glycyl dipeptides from water to aqueous [C12mim]Br solutions (Δt V o), partial molar expansibility and Hepler's constant have been calculated. Through the electrical conductivity measurements, the critical micellar concentration (c cmc) and a series of thermodynamic parameters of micellization of [C12mim]Br in aqueous glycyl dipeptide solutions are evaluated. Effects of temperature and hydrocarbon chain length of the glycyl dipeptides on the volumetric properties of dipeptides and critical micelle concentration (c cmc) of [C12mim]Br were examined. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interactions of [C12mim]Br with glycyl dipeptides, and the aggregation behavior of [C12mim]Br. From the results of UV–vis absorption spectra, the binding constant between dipeptide and [C12mim]Br above the c cmc was determined. [Copyright &y& Elsevier]

Abstract: The interactions of glycyl dipeptides (glyglycine, glycyl-l-valine and glycyl-l-leucine) with sodium perfluorooctanoate (SPFO) in aqueous solutions have been investigated by means of density, conductivity, fluorescence spectroscopy, and UV–vis spectroscopy. The standard partial molar volume (), standard partial molar volume of transfer for dipeptide from water to aqueous SPFO solutions (Δt V o), partial molar expansibility () and Hepler’s constant have been calculated from density data. Electrical conductivity was used to estimate the critical micellar concentration (ccmc) and the thermodynamic parameters of micellization of SPFO in aqueous glycyl dipeptide solutions. Effects of temperature and hydrocarbon chain length of the glycyl dipeptides on the volumetric properties of dipeptides and critical micelle concentration (ccmc) of SPFO were examined. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interactions of SPFO with glycyl dipeptides, and the aggregation behaviour of SPFO. From the results of UV-vis absorption spectra, the binding constant between dipeptide and SPFO above the ccmc was determined. [Copyright &y& Elsevier]

Abstract: Micellization and related thermodynamic parameters of a conventional anionic surfactant sodium dodecyl sulfonate (C12SO3Na) in various compositions of water–dipeptide mixed media have been studied by means of conductivity and fluorescence spectroscopy at five temperatures ranging between 298.15K and 318.15K. The electrical conductivity data have been utilized to calculate the values of critical micelle concentration (c cmc) and the counterion binding constant (β) of C12SO3Na. From c cmc values, it is observed that the micellization tendency of the surfactant increases in the presence of dipeptides. Thermodynamic parameters (ΔG m o, ΔH m o and ΔS m o) of micellization of C12SO3Na in aqueous dipeptide solutions have been obtained by applying the mass action model and an enthalpy–entropy compensation effect was observed. The effect of dipeptides on the micellar properties of C12SO3Na depends upon their nature and concentration, as well as the temperature. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interaction of C12SO3Na with dipeptides, and the aggregation behavior of C12SO3Na. The results have been interpreted in terms of solute–solvent interactions and structural changes in the mixed solutions. The interaction difference of C12H25SO3Na/C12H25SO4Na with dipeptides was also studied and it was found that C12H25SO3Na were seen to interact more weakly than their sulfate analogues. [Copyright &y& Elsevier]

Abstract: The interactions of glycyl dipeptides (glycylglycine, glycyl-l-valine and glycyl-l-leucine) with sodium caprylate (NaC8) in aqueous solution have been investigated by a combination of density, conductivity and fluorescence methods. Apparent molar volumes (V 2, ϕ ), standard partial molar volumes (), and standard partial molar volumes of transfer from water to aqueous NaC8 solutions (Δ t V o) are evaluated using density data. The limiting molar conductivity of sodium caprylate (Λ o) and its anion contribution , as well as the Stokes’ radii of caprylate anion in aqueous glycyl dipeptide solutions have been calculated using conductivity data. Pyrene fluorescence spectra were used to estimate the critical micellar concentration (c cmc) of NaC8 in aqueous dipeptide solutions. The analysis shows that the interactions of sodium caprylate with charged and polar groups of glycyl dipeptides are dominating over the sodium caprylate-non-polar group interactions over the entire concentration range of sodium caprylate. From the volumetric data, it is suggested that the glycyl dipeptides are solubilized in the palisade layer of sodium caprylate micelles. The decrease in Λ o values of sodium caprylate with an increase in dipeptide concentration is attributed to the interaction of sodium caprylate with the dipeptides and increasing viscosity of solvent. The addition of dipeptide in water decreases the c cmc of NaC8. The interactions of glycyl dipeptides with sodium caprylate increase with the increase in the size of side chain of carboxylate anions and of glycyl dipeptides. [Copyright &y& Elsevier]

Abstract: Densities, conductivities, and fluorescence spectra of {sodium dodecyl sulfate (SDS)+glutamine dipeptide+water} mixtures were measured as a function of temperature. The density data have been utilized to calculate apparent molar volumes, standard partial molar volumes (), standard partial molar volumes of transfer from water to aqueous SDS solutions (Δt V o), the hydration number, partial molar expansibility (), and Hepler’s constant of glutamine dipeptides. The critical micellar concentration (c cmc) and the degree of counterion dissociation of SDS micelles obtained from electrical conductivity data have been estimated at various concentrations of glutamine dipeptide. Thermodynamic parameters of micellization of SDS in aqueous dipeptide solutions have been determined from c cmc values and an enthalpy–entropy compensation effect was observed for the ternary systems. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interaction of SDS with glutamine dipeptide, and the aggregation behavior of SDS. The results have been interpreted in terms of solute–solvent interactions and structural changes in the mixed solutions. [Copyright &y& Elsevier]

Abstract: The effect of glycyl dipeptides (glycylglycine, glycyl-L-valine, and glycyl-L-leucine) on the micellar properties of gemini surfactant pentamethylene-1,5-bis(dodecyldimethylammonium bromide) (12-5-12) has been investigated by means of conductivity and fluorescence spectroscopy. The results obtained from conductivity show that the effect of glycyl dipeptides depends upon their nature and concentration, as well as the temperature. The values of critical micelle concentration (cmc) of 12-5-12 have been estimated in water+glycyl dipeptide media at various concentrations of dipeptide in the 293.15–318.15K temperature range at 5K intervals. From cmc values, it is observed that the micellization tendency of the surfactant increases in the presence of glycyl dipeptides. Thermodynamic parameters (ΔG m o , ΔH m o , and ΔS m o ) of micellization of 12-5-12 in aqueous glycyl dipeptide solutions have been obtained by applying the mass action model and an enthalpy–entropy compensation effect was observed. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interaction of 12-5-12 with glycyl dipeptides, and the aggregation behavior of 12-5-12. [Copyright &y& Elsevier]

Abstract: The apparent molar volume (V 2,ϕ ) of glutamine dipeptides (glycyl-l-glutamine and l-alanyl-l-glutamine) and the molar conductivity (Λ) of sodium caproate (NaC6) have been determined from density and conductance measurements, respectively. The values of V 2,ϕ were utilized to deduce the standard partial molar volumes , standard partial molar volumes of transfer for glutamine dipeptides from water to aqueous sodium caproate solutions (Δt V o), hydration number (n H) and volumetric interaction coefficients. An increase in transfer volumes and a decrease in hydration numbers of the glutamine dipeptides with increasing sodium caproate concentration have been explained due to stronger interactions of sodium caproate with the charged center and polar groups of the glutamine dipeptides compared to the sodium caproate-nonpolar group of dipeptide interactions. From the molar conductivity of sodium caproate, the limiting molar conductivity of sodium caproate (Λ 0) and Walden products (Λ 0 η 0) were calculated. The decrease in Λ 0 and Walden products with increase in glutamine dipeptide concentration is attributed to the interactions of sodium caproate with glutamine dipeptides and the friction resistance of the solvent medium. Both the hydration number for glutamine dipeptides and Walden products values in peptide–sodium carboxylate–water systems are in the order: sodium acetate>sodium butyrate>sodium caproate. This can be ascribed to the fact that the interactions of dipeptides with sodium carboxylate increase with the increase in the size of side chain of carboxylate anions. [Copyright &y& Elsevier]

Abstract: Densities and conductivity data for the sodium carboxylate (sodium acetate and sodium butyrate)–dipeptides {(glycyl-l-glutamine and l-alanyl-l-glutamine)+water} systems were determined at T =298.15K. The apparent molar volumes of the peptides and the molar conductivity (Λ) of sodium acetate and sodium butyrate have been calculated. These data have been utilized to deduce the standard partial molar volumes (), standard partial molar volumes of transfer for dipeptide from water to aqueous sodium carboxylate solutions (Δt V °), volumetric interaction coefficient, the limiting molar conductivity (Λ °), and Walden product (Λ ° η). Both and Δt V ° for the dipeptides increase with increasing concentration of sodium carboxylate. The interpretation is that this result arises from the dominant interactions of the sodium carboxylate with the charged group and polar groups of peptides. The decrease in Λ ° of sodium carboxylate with increasing dipeptide concentration and nonconstant Walden product are attributed to the interactions of sodium carboxylate with peptide and friction resistance of the solvent medium. [Copyright &y& Elsevier]

Abstract: Viscosities and densities of d-glucose–water mixtures were measured, and conductivities in the NiSO4–d-glucose–water system were also measured at 278.15–308.15K in 5K intervals. Based on the Lee–Wheaton conductivity equation, values of limiting molar conductivities Λ 0 and association constants K A were obtained. Changes in the standard thermodynamic functions, Gibbs energy enthalpy and entropy for a process of ion-pair formation were calculated at different temperatures. The results show that (1) at given temperatures, the Λ 0 values for 1/2NiSO4 decrease with increasing concentrations of d-glucose; (2) at fixed concentrations of d-glucose, the Λ 0 values for 1/2NiSO4 increase with increasing temperature; and (3) the process of association of NiSO4 is controlled by the change in entropy . [Copyright &y& Elsevier]

Abstract: Activity coefficients, Gibbs energy interaction parameters (g ES), salting constants (k S), limiting molar conductivities (Λ 0), and Walden products (Λ 0 η) for the calcium nitrate−monosaccharide (d-glucose and d-galactose)–water systems were determined from electrical potential and conductance measurements. Results show that both the g ES and Λ 0 η values for saccharide−calcium nitrate–water systems are in the order: d-glucose> d-galactose. This can be ascribed to the fact that the interactions of Ca2+ with d-galactose are stronger than those of the ions with d-glucose. d-Glucose is salted-out whereas d-galactose is salted-in by calcium nitrate in water, which results from the difference in stereo-structures of the saccharide molecules (axial hydroxyl, a-OH-4 and equatorial hydroxyl, e-OH-4). [Copyright &y& Elsevier]