Enthalpies Of Dilution Research Articles

Enthalpies of transfer of ubiquinone-0 from water to aqueous surfactant solutions at various temperatures

Mixing and dilution enthalpies of aqueous solutions of 2,3-dimethoxy-5-methyl-1,4-benzoquinone (UQ0) and of N,N-dimethyl-dodecylamine-N-oxide (DDAO) were measured and used to calculate the enthalpies of transfer δH(W →W +S) of UQ0 from water to DDAO aqueous solutions at 20‡, 25‡, 30‡, and 35‡C. From the dependence of δH(W →W +S) on surfactant concentration, the distribution constant between aqueous and micellar phases and the standard transfer enthalpy of UQ0 from water to DDAO micelles were evaluated along with the standard transfer free energy and entropy. The approach used required knowledge of the CMC and micellization enthalpy at each temperature. Thus, the thermodynamics of micellization of DDAO was studied by means of dilution enthalpy measurements at the several temperatures.

Interactions between poly(vinylpyrrolidone) and ionic surfactants at various solid/water interfaces: a calorimetric investigation

The interaction of a neutral hydrophilic polymer poly(vinylpyrrolidone) (PVP) with sodium dodecylsulfate (SDS) and cetyltrimethylammonium bromide (CTAB) was studied at various solid/liquid interfaces and different surfactant coverages using an essentially calorimetric method of investigation. It was observed that the differential enthalpy of dilution of PVP in the presence of the bare particles of alumina, titanium dioxide and silica is endothermic in the two first cases and exothermic in the presence of silica. An extremum of enthalpy of dilution was observed at the same polymer concentration in the presence of the three types of mineral oxide particles. The interaction between coadsorbed PVP and SDS was found to be endothermic on alumina at all surfactant coverages, whereas it was exothermic between PVP and SDS micelles in bulk aqueous solutions. This observation suggests that PVP adsorption on alumina occurs through interactions between adsorbed PVP moieties and SDS monomers and does not involved adsorbed surfactant aggregates. CTAB adsorbed strongly on silica and on titanium dioxide above their respective isoelectric points. However, the PVP enthalpy change upon addition of the polymer to the CTAB-coated mineral oxides was small, confirming the absence of strong interactions between cationic surfactants and neutral hydrosoluble polymers at solid/liquid interfaces. These results indicate that if the interaction between a surfactant and a polymer is small in the bulk aqueous solution, it will be only marginally changed by forcing both types of solute species to interact at a solid/liquid interface.

Comparison of the cosurfactant character of 1-butanol and phenol in sodium dodecylsulfate aqueous solutions from relative enthalpies of dilution at 298.15 K

Heats of dilution of 1-butanol and phenol in aqueous micellar solutions of sodium dodecylsulfate (SDS) have been measured at 298.15 K with a dynamic-flow Picker microcalorimeter and used for determining the relative apparent molar enthalpies of dilution ( L ø,3 ) of solutes. The variation of L ø,3 for both solutes, at low concentrations, as a function of the surfactant concentration provides evidence of a postmicellar transition occurring at 0.2 mol kg −1 in SDS solutions. In each micellar domain, at concentrations below and above 0.2 mol kg −1, the limiting apparent molar enthalpies of dilution of the solute (extrapolated to 1 m=0 from the linear dependence of the inverse of surfactant concentration predicted by the pseudophase model), reflect various trends. For 1-butanol, both values are close to one another, whereas for phenol, where the sign of the linear slopes also changes, the limiting values are noticeably different. The latter indicates that a modification of the counterion binding, accompanying the postmicellar transition, occurred. For concentrated solute mixtures at fixed surfactant composition, an analysis of the variation of the abnormal, relative apparent molar enthalpies of dilution of 1-butanol with its unique concentration, shows that 1-butanol is strongly trapped in alcohol aggregates stabilized by the surfactant and, consequently, acts as a good cosurfactant capable of forming microemulsions. Alternatively, although phenol hydrophobicity is similar to that of 1-butanol, owing to its acid character, it is mostly solubilized in the aqueous layer of micelles and does not penetrate deeply towards the micellar interior and, hence, could not be considered as a very efficient cosurfactant.

Hydrophilic groups determine preferential configurations in aqueous solutions. A calorimetric study of monocarboxylic acids and monoalkylamines at 298.15 K

Abstract Enthalpies of dilution of binary aqueous solutions containing monocarboxylic acids and monoalkylamines have been determined by microcalorimetry at 298.15 K. Pairwise self-interaction coefficients of the virial expansion of the excess enthalpies were evaluated and compared with those obtained for alkan-1-ols. The values of the coefficients are positive and increase differently with increasing number of carbon atoms on the alkyl chain, depending on the nature of the functional groups. For all series, starting with the terms containing five methylene groups, the coefficients tend to attain a constant value. Attempting to explain this behaviour, the attention was focused on the nature of the hydration of the alkyl chain.

Characterization of Ligand Binding of a Soluble Human Insulin-like Growth Factor I Receptor Variant Suggests a Ligand-induced Conformational Change

Details of the signal transduction mechanisms of the tyrosine kinase family of growth factor receptors remain elusive. In this work, we describe an extensive study of kinetic and thermodynamic aspects of growth factor binding to a soluble extracellular human insulin-like growth factor-I receptor (sIGF-IR) variant. The extracellular receptor domains were produced fused to an IgG-binding protein domain (Z) in transfected human 293 cells as a correctly processed secreted alpha-beta'-Z dimer. The receptor was purified using IgG affinity chromatography, rendering a pure and homogenous protein in yields from 1 to 5 mg/liter of conditioned cell media. Biosensor technology (BIAcore) was applied to measure the insulin-like growth factor-I (IGF-I), des(1-3)IGF-I, insulin-like growth factor-II, and insulin ligand binding rate constants to the immobilized IGF-IR-Z. The association equilibrium constant, Ka, for the IGF-I interaction is determined to 2.8 x 10(8) M-1 (25 degrees C). Microcalorimetric titrations on IGF-I/IGF-IR-Z were performed at three different temperatures (15, 25, and 37 degrees C) and in two different buffer systems at 25 degrees C. From these measurements, equilibrium constants for the 1:1 (IGF-I:(alpha-beta'-Z)2) receptor complex in solution are deduced to 0.96 x 10(8) M-1 (25 degrees C). The determined heat capacity change for the process is large and negative, -0.51 kcal (K mol)-1. Further, the entropy change (DeltaS) at 25 degrees C is large and negative. Far- and near-UV circular dichroism measurements display significant changes over the entire wavelength range upon binding of IGF-I to IGF-IR-Z. These data are all consistent with a significant change in structure of the system upon IGF-I binding.

Adsorption Enthalpy and Adsorption Isotherm of Tetradecylpyridinium Bromide on Na-Montmorillonite

The adsorption enthalpy and the adsorption isotherm of tetradecylpyridinium bromide (TPB) onto a Na–montmorillonite suspension and the dilution enthalpy of the TPB solution have been determined at 298.15 K. The dilution process is endothermic and the adsorption process is exothermic. For ion exchange adsorption, the interaction between TP+and the montmorillonite is much stronger than that between Na+and the montmorillonite because the cumulative adsorption enthalpy increases dramatically with adsorption amount. For molecular adsorption, however, the interaction between TPB and the clay is much weaker.

Demixing of Mixed Micelles. Thermodynamics of Sodium Perfluorooctanoate−Sodium Dodecanoate Mixtures in Water

Conductivity, density, heat capacity, enthalpy of dilution, and osmotic coefficient measurements of water−sodium perfluorooctanoate (NaPFO)−sodium dodecanoate systems were carried out as functions of the surfactants' total molality (mt) at different mole fractions (XNaPFO). From conductivity data, the critical micelle concentration (cmc) and the degree of ionization (β) of the micelles were derived. The cmc's of the micelles are higher than those of the pure surfactants while β depends linearly on XNaPFO. At a given mole fraction, the apparent molar volume (VΦ) and heat capacity (CΦ) of the mixture increases and decreases monotonically with mt, respectively. From data in the premicellar region, the standard (infinite dilution) partial molar properties (Yo) of the mixtures were calculated for both volume and heat capacity. Yo depends linearly on XNaPFO according to the ideal behavior. From data in the postmicellar region, the excess properties (Yexc) for the mixed micelles formation from pure micelles were calculated. The values of the excess volumes and heat capacities are positive and negative, respectively, in the whole range of composition. The excess free energy (Gexc) is negative while both enthalpy and entropy are positive. On the basis of the pseudophase transition model and experimental evidences, the Gexc vs composition profile was derived. This profile indicates the presence of a critical point for 0.4 ≤ XNaPFO ≤ 0.6. According to this approach, Gexc was calculated for some mixtures. It turned out that sodium dodecanoate and sodium dodecyl sulfate micelles are miscible in the whole range of composition while ammonium perfluorononanoate (NH4PFN) and ammonium dodecyl sulfate micelles are partially miscible, and the coexistence of the two mixed micelles pseudophases occurs in the range 0.43 ≤ XNH4PFN ≤ 0.75. In the case of the sodium decyl sulfate−sodium perfluorooctanoate system, only a critical point is present.

Enthalpy of interaction of some amides with ammonium methanoate in water at 25°C Interactions between ionic groups and peptide and hydrophobic groups

J. Fernández, . Nieves García-Lisbona, T. H. Lilley and H. Linsdell, J. Chem. Soc., Faraday Trans., 1997, 93, 407 DOI: 10.1039/A605740C

Enthalpies of dilution of aqueous solution of LiCl, KCl, and CsCl at 300, 325, and 350°C

Enthalpies of dilution of aqueous solution of LiCl, KCl, and CsCl at 300, 325, and 350°C

Classification of calorimetric titration plots for alkyltrimethylammonium and alkylpyridinium cationic surfactants in aqueous solutions

Calorimetric titration plots for deaggregation of micelles formed by alkylpyridinium and alkyltrimethylammonium surfactants are classified into three types, A, B and C, depending on the shape of the plot of the enthalpy of dilution as a function of surfactant concentration. For Type A plots the recorded heat of injection q changes sharply between two parts of the titration curve over which the recorded heats are effectively independent of the composition of the solution in the sample cell. For Type B plots, the change is less sharp and both parts of the plot show dependences of heat q on solution composition, a pattern accounted for in terms of solute–solute interactions. Type C plots are complicated, in that no sharp change in q is recorded, the complexity of the plots being accounted for in terms of micelle–monomer equilibria over a range of surfactant concentrations and related enthalpies of deaggregation.

Enthalpies of Dilution of Aqueous Solutions of LiCl, KCl, and CsCl at 300, 325, and 350°C

Dilution enthalpies, measured using isothermal flow calorimetry, are reported for aqueous solutions of LiCl, KCl, and CsCl at 300°C and 11.0 MPa, 325°C and 14.8 MPa, and 350°C and 17.6 MPa. The concentration range of the chloride solutions was 0.5 to 0.02 m. Parameters for the Pitzer excess Gibbs ion-interaction equation were determined from the fits of the experimental heat data. Equilibrium constants, enthalpy changes, entropy changes, and heat capacity changes for ion association of the chloride salts were estimated from the heat data. For all systems, the enthalpy and entropy changes were positive and had accelerating increases with temperature. The resulting equilibrium constants show significant, but smaller, increases with temperature.

Excess free energy, enthalpy and entropy of surfactant-surfactant mixed micelle formation

Enthalpies of dilution and osmotic coefficients of sodium decylsulfate (NaDeS)-dodecyldimethylamine oxide (DDAO) mixtures in water were determined at 298 and 310 K, respectively. From the enthalpies of dilution, the apparent and then the partial molar relative enthalpies of the surfactant mixtures were calculated. From the osmotic coefficients, calculated at 298 K, the non-ideal free energies were derived. The latter were combined with the partial molar relative enthalpies to obtain the non-ideal entropies. From the apparent molar properties, using a previously reported approach, the excess thermodynamic properties for the surfactant-surfactant mixed micelle formation in water were evaluated as functions of the mixture composition at some total micellized concentration. In the whole range of the mixture composition, the excess free energy is negative, indicating that the mixed micelle formation is favoured with respect to that of pure micelles. This process is governed by the enthalpy and/or the entropy, depending on the mixture composition. The effect of the alkyl chain length was also studied by comparing the present results to those of the sodium dodecylsulfate-DDAO mixture.

Thermodynamic studies on N,N,N-octyloctyldimethyl ammonium chloride in water-urea mixtures

The densities, heat capacities and enthalpies of dilution at 298 K and the osmotic coefficients at 310 K were measured for N,N,N-octyloctyldimethylammonium chloride (OOAC) in aqueous urea solution as a function of urea ( m u) and surfactant ( m s) concentrations in order to determine, in comparison with the lower homologue N,N,N-pentyloctyldimethylammonium chloride, OPAC, the influence of the hydrophobic tail on the properties of a double-chain surfactant in the presence of an additive like urea. From specific conductivity data, the critical micelle concentration (cmc) and the degree of the counterion dissociation (β) have been calculated. From the thermodynamic data, the molar apparent volumes, V φ , heat capacities, C φ , and apparent molar relative enthalpies, L φ , were derived as a function of m u and m s at 298 K.

Thermodynamic studies on water-β-cyclodextrin-surfactant ternary systems

Conductance measurements are reported for double chain surfactants like N,N,N-octylpentyldimethylammonium (OPAC) and N,N,N-octyloctyldimethylammonium chlorides (OOAC) in water-β-cyclodextrin solution. From the specific conductivity data, the apparent critical micelle concentration (cmc ∗) and the degree of counterion dissociation (β) were obtained at a fixed β-CD concentration ( m βCD = 0.01190 mol kg −1, besides from the cmc ∗ value and that in water (cmc) the stoichiometry of the surfactant-β-CD complex was calculated. Densities, heat capacities, enthalpies of dilution at 298 K and osmotic coefficients at 310 K were measured for the same systems; the apparent molar volumes, V λ , and heat capacities, C λ , of two surfactants in β-CD solution, calculated as functions of surfactant concentrations m s, have made possible to obtain the properties of transfer of the surfactant from water to β-CD-water solutions.

Effect of the Counterion on Thermodynamic Properties of Aqueous Micellar Solutions of 1-(3,3,4,4,5,5,6,6,6-Nonafluorohexyl) Pyridinium Halides: II. Apparent and Partial Molar Enthalpies and Osmotic Coefficients at 313 K

We report a thermodynamic study of the aqueous solutions of 1-(3,3,4,4,5,5,6,6,6-nonafluorohexyl) pyridinium chloride, bromide, and iodide andN-octyl pyridinium iodide. Dilution enthalpies and osmotic coefficients of the aqueous solutions of these cationic surfactants have been measured at 313 K as a function of the concentration. The experimental data are expressed in terms of apparent and partial molar quantities. The changes in thermodynamic properties upon micellization have been obtained from the experimental data by using a pseudo phase transition approach. The cmc at 313 K have been evaluated from the plot of the milliosmolality, the measured quantity, vs molality. From the comparison with the trends of the enthalpies at 298 K of the same set of compounds, the effect of temperature on the energetics of their solutions can be derived. The trends of thermodynamic properties vs molality and the micellization parameters confirm that the effect of the counterions, however strong and inversely proportional to the radius of the hydrated counterion, seems to be reduced with respect to the hydrogenated analogs. The curves of the apparent and partial molar enthalpies vsmfor the bromide and the iodide are lowered, with respect to the curve of the chloride, by an amount comparable to that at 298 K. This observation suggests that the changes in the absolute trends of the curves and in the micellization enthalpies are due to the modification of the more mobile hydrophobic hydration shell of the perfluoroalkyl chain, whereas the hydration sphere of the counterions is practically unaffected. The heat capacity data and the comparison with the behaviour of hydrogenated analogs is in agreement with the above observation. The trends of the free energies confirm that the degree of counterion binding, β, and the aggregation number,n, increase with the increasing of the radius of the hydrated counterion.

Thermodynamic Study of Aqueous Micellar Solutions of Biologically Active Bisquaternary Ammonium Chlorides

Thermodynamic properties of aqueous solution of bisquaternary ammonium salts, which are derivatives ofN,N-bisdimethyl-1,2-ethanediamine (bis-Cn-BEC), of general formula/CnH2n+1OOCCH2(CH3)2N[formula]CH2CH2N[formula](CH3)2CH2COOCn-H2n+1/2Cl−(bis-Cn-BEC, where the subscriptnstands for the number of carbon atoms of the alkyl chain bound to the carboxyl group) are here reported and compared with those of the corresponding monomers. Dilution enthalpies have been measured by means of a flow type microcalorimeter at 313 K, and densities have been measured by means of a vibrating tube densimeter at 298 K. Apparent and partial molar quantities have been obtained from the experimental data and expressed as a function of molalities, assuming the infinite dilution as standard state. The changes in enthalpy and in volume upon micellization have been evaluated by assuming the pseudo-phase transition model. From the calculated enthalpy changes at 313 K and that previously reported at 298 K, the changes in heat capacity for micellization has been evaluated. The data suggest the hypothesis that the alkyl chain in the dimers are already partially associated in solution. Moreover, the trends of the cmc as a function of the chain length for monomers and dimers suggest that the association of the chains probably leaves out the first three methylene groups of the alkyl chains bound to the carboxylic groups. The packing parameter,P, gives 0.37 for bis-C10-BEC, and the formation of rod-like micelles is therefore suggested.

Enthalpy of dilution of aqueous CaCl 2 solutions at 308.15 K

The enthalpy of dilution of water-CaCl 2 solutions was measured at 308.15 K and up to a molality of 7.050 using a TRONAC 450-458 isoperibol calorimeter. The experimental data were corelated using the ion interaction model of Pitzer.

Osmotic coefficients and enthalpies of dilution of aqueous sodium n-alkane-1-sulphonates at the temperatures (298.15, 313.15, 328.15, and 343.15) K

Osmotic coefficients of aqueous solutions of sodium n-octane-1-sulphonate, sodium n-decane-1-sulphonate, sodium n-dodecane-1-sulphonate, and sodium n-tetradecane-1-sulphonate at the temperature T= 328.15 K and at molalities ranging from (0.01 to 0.30) mol·kg -1were estimated from vapour pressure osmometer measurements. Integral enthalpies of dilution for aqueous solutions of the same surfactants from T= 298.15 K to T= 343.15 K and at final molalities ranging from about (0.1 to 3.0)· m( cmc) were also measured, where m( cmc) denotes the critical micelle molality. Data for each surfactant were treated using a mass-action model that includes cation-anion interaction terms in the activity coefficient expressions for one anionic micellar species and the monomeric surfactant species. Ion-ion interaction parameters were estimated from the osmotic coefficients, and the temperature coefficients of these parameters were estimated from the enthalpies of dilution. Treatment of the enthalpies of dilution with the model also led to estimated values of Δ r H m ofor the formation reaction of micelles and to the corresponding values m= m( cmc). A simultaneous fit of all the enthalpies for each surfactant yielded numerical values of a small number of parameters for simple equations that describe the rather complex behaviour of aqueous surfactant solutions in terms of an equilibrium constant and activity coefficient equations and their temperature derivatives.

Molar excess enthalpies of n‐monohaloalkanes + n‐monohaloalkanes mixtures. Estimation of DISQUAC interchange energy parameters

AbstractMolar excess enthalpies, H, at 298.15 K and atmospheric pressure were determined for six binary liquid mixtures [x{iodethane or 1‐iodobutane or bromoethane or 1‐bromobutane or 1‐chloropropane or 1‐chloropentane} + (1 ‐ x) 1‐fluoropentane]. These experimental results along with the data available in the literature on molar excess Gibbs energies, G, activity coefficients at infinite dilution, In γ, and molar excess enthalpies, H, for n‐monohaloalkane + n‐monohaloalkane mixtures, are examined on the basis of the DISQUAC group‐contribution model. The interchange energies of the contacts between two different halogen atoms are entirely dispersive and were determined in this work. The model reproduces reasonably well most of the experimental data. For a given n‐monohaloalkane, mixed with the other n‐monohaloalkanes, it can be seen that the values of the dispersive interchange energies coefficients of the Gibbs energy, C, and enthalpy, C, the contact between the two different halogen atoms, X and Y, and the experimental equimolar values of the excess thermodynamic properties G(x1 = 0.5), and H(x1 = 0.5), have the same trend as the gas‐phase electric dipole moment, p, of the molecule X‐Y. The same trend is also observed for the difference in the electric polarizability, Δα, between the halogen atoms X and Y.

Thermodynamic properties of dilution of chondroitin 4-sulfate having tetraalkylammonium counterions

The dilution enthalpies,ΔdilH, of tetraalkylammonium chondroitin 4-sulfate (R4NChSA) and polyacrylate (R4NPAA) having methyl (Me), ethyl (Et), propyl (Pr) and butyl (Bu) as alkyl groups (R) were measured to elucidate the effects of hydrophobic counterions. TheΔdilH of R4NChS-A and R4NPAA were negative (exothermic) and decreased as the carbon number of tetraalkylammonium cation (R4N+) increased. These results were found to possess the same effects onΔdilH as these of bromides. The non-electrostatic terms of dilution enthalpiesΔdilHn of R4NChS and R4NPAA were evaluated by using the electrostatic terms ofΔdilH obtained from Manning's theory. TheΔdilHn of R4NChS-A and R4NPAA decreased, i.e., their exothermic tendencies increased as the carbon number of R4N+ increased, and the rate of decrease of the R4NPAA was more than that of the R4NChS-A. These results are discussed in relation to the increase of the hydrated water structure around R4N+ on dilution.