Adiabatic Molar Compressibilities Research Articles

Volumetric, compressibility, surface tension and viscometric studies of CTAB in aqueous solutions of polymers (PEG and PVP) at different temperatures

In the present manuscript, we intend to examine the effect of neutral polymers (polyethylene glycol and polyvinyl pyrrolidone) and their blends on the post-micellization of the cationic surfactant, CTAB using conventional techniques such as density, speed of sound, surface tension and viscosity. From the parent data of density and speed of sound, we evaluated the volumetric parameters, namely apparent molar volume volumes (ϕv) and adiabatic molar compressibility (ϕk) along with various acoustical parameters of importance. The volumetric properties reveal different kinds of interactions that are present in the ternary system especially at lower and higher surfactant concentration without taking into consideration the post-micellar effect. Surface tension further strengthens the effect of these polymers in terms of electrostatic and hydrophobic interactions which show that surface tension decreases as the PEG content increases in the polymer mixture as compared to PVP. This may be due to the presence of residual positive charge on the PVP molecule which makes it less interactive towards the cationic surfactant. Viscosity result are further analysed in terms of relative viscosity (ηr) and viscous relaxation time (τ). All these parameters form the basis of the discussion of the effect of these neutral polymers on the physical properties of CTAB. The effect of temperature has also been discussed.

Solution Thermodynamics of highly fluorinated gemini bispyridinium surfactants for biomedical applications

Highly fluorinated gemini surfactants are relevant in pharmaceutical field, owing their ability to deliver genes to the respiratory or to the biliar epithelium, where hydrogenated interfering surfactants are present. We report for the first time the thermodynamic properties of the solutions of 1,1′-Bis(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl)-2,2 n-methylenebispyridinium dichloride (n=4, 8, 12). The gene delivery ability of the dichlorides and the structure of the DNA nanoparticles are strictly related to their solution enthalpic properties, resulting in a very sensitive probe of the behaviour of the molecule in solution. Dilution enthalpies, density and sound velocities vs. molality for dichlorides and dimethanesulfonates with different spacer length, n, were measured. The evaluation of apparent and partial molar enthalpies as a function of concentration of the dimethanesulfonate suggests that the effect of the counterion is additive and the values obtained for the hydrogenated surfactants can be transferred to the fluorinated ones, allowing the prediction of enthalpic properties in solution. No evidence of the structure change in solution is found in the trends of volumetric properties vs. m. and the group contribution of the CH2 for both the dichlorides and the dimethanesulfonates results additive as well as the effect of the counterion. The adiabatic molar compressibilities seem to be independent from the counterion and show in micellar region a plateau value much greater than in the case of the more traditional hydrogenated gemini surfactants, indicating a less compact structure of the micelles, probably due to the repulsion between hydrogenated and fluorinated moieties of the molecules.

Acoustic and Volumetric Properties of Diluted Solutions of Water in Ionic Liquids

Herein, we report the densities and speeds of sound in binary mixtures of three hydrophobic and one hydrophilic ionic liquids: 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, [C4mim][NTf2], 1-butyl-1-methylpyrrolidinium bis[(trifluoromethyl)sulfonyl]imide, [C4mpyr][NTf2], 1-propyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, [C3mim][NTf2] and 1-ethyl-3-methylimidazolium thiocyanate, [C2mim][SCN], with water at 298.15 K and 0.1 MPa. The concentration range of water, which encompassed relatively small values well below the saturation point, is often regarded as an impurity for hydrophobic ionic liquids. On the basis of experimental results the molar volume, adiabatic molar compressibility, partial molar volume and apparent molar volume, as well as, partial molar and apparent molar isentropic compressibility properties were then calculated. Interesting results are obtained using the solutions based on the hydrophilic [C2mim][SCN], since these mixtures are characterized by relatively low density and high values of speed of sound. Furthermore, the partial molar volumes and partial molar adiabatic compressibilities of water in solution with [C2mim][SCN] are the lowest among the investigated in mixtures with ionic liquids. However, in the case of the hydrophobic ionic liquid solutions, only small differences are observed for molar adiabatic compressibilities with the change of the cation structure, i.e. for water + [C4mim][NTf2] or + [C4mpyr][NTf2]. A more pronounced difference has been observed for the partial molar compressibility of water in solutions with these two ionic liquids.

Second-Order Derivatives of the Gibbs Energy for Liquid Mixtures of Alcohol + Heptane at Pressures up to 100 MPa

Second-order thermodynamic derivative properties, such as isobaric thermal molar expansions, isothermal and adiabatic molar compressibilities, and isochoric molar heat capacities of (ethanol, decan-1-ol, 2-methyl-2-butanol) + heptane mixtures at pressures up to 100 MPa and in the temperature range from 293.15 K to 318.15 K were derived from experimental speed-of-sound u(T, p), density ρ(T, p = 0.1 MPa), and isobaric heat-capacity Cp(T, p = 0.1 MPa) data using appropriate thermodynamic relations. Excess values for the given properties were calculated according to the criterion of thermodynamic ideality of a mixture (Douheret et al., Chem. Phys. Chem. 2, 148 (2001)), i.e., assuming that the chemical potential of component i in the ideal liquid mixture is equal to the chemical potential of component i in the mixture of perfect gases. The deviations from ideality for the mixtures under test have been explained in terms of the self-association of alcohols in solution which produces a strong departure from random mixing, the change in the non-specific interactions during mixing, and the packing effects.

Adiabatic compressibilities of some synthesized derivatives of dihydropyrimidines in N,N-dimethylformamide and dimethyl sulfoxide at 298.15 K

Sound velocities of solutions of some derivatives of dihydropyrimidines (DHPMs) in N,N-dimethylforamide (DMF) and dimethyl sulfoxide (DMSO) were measured at 298.15 K over a wide range of concentration. Adiabatic compressibilities, apparent adiabatic molar compressibilities and apparent adiabatic molar volumes were also evaluated. Results of sound velocity measurements provide useful information about ion-ion and ion-solvent interactions and are of significant help in understanding the behavior of electrolytes in solutions.

Adiabatic Compressibilities of Divalent Transition-Metal Perchlorates and Chlorides in N,N-Dimethylacetamide and Dimethylsulfoxide

Sound velocities of solutions of manganese(II), cobalt(II), nickel(II), copper(II), and zinc(II) perchlorates and chlorides in N,N-dimethylacetamide (DMA) and dimethylsulfoxide (DMSO) were measured at 298.15 K. Adiabatic compressibility coefficients of the solutions were determined, and apparent adiabatic molar compressibilities of the salts at infinite dilution were evaluated and discussed.

Biologically active bisquaternary ammonium chlorides: physico?chemical properties of long chain amphiphiles and their evaluation as non-viral vectors for gene delivery

The biological properties of bisquaternary ammonium salts, which are derivatives of N,N-bisdimethyl-1,2-ethanediamine (bis-C(n)BEC), of general formula /C(n)H(2n+1)OOCCH2(CH3)2N(+)CH2CH2N(+)(CH3)2CH2COOC(n)H(2n+1)/2Cl-, were investigated (n=10, 12, 14). The interaction with model membrane was studied by differential scanning calorimetry experiments, and the apparent adiabatic molar compressibility of their solution as a function of concentration was obtained by sound velocity measurements. Their biological activities were assayed by Electrophoresis Mobility Shift, MTT proliferation, and transient transfection. All the investigated compounds interact with the DNA and are able to transfect DNA, when they are co-formulated with DOPE, with an efficiency significantly greater than that of a standard commercial transfection reagent. Bis-C(14)BEC is the only molecule able to deliver DNA inside the cells without a helper lipid, as shown by EGFP expression, albeit with a low efficiency in comparison with a standard commercial transfection reagent. This may be due to a slightly different interaction of bis-C14BEC from bis-C10BEC and bis-C12BEC with phospholipid bilayers. Bis-C10BEC and bis-C12BEC show a slight fluidizing effect, while bis-C14BEC increases stability of both the gel and the rippled gel phases.

First Evaluation of the Thermodynamic Properties for Spheres to Elongated Micelles Transition of Some Propanediyl-α,ω-bis(dimethylalkylammonium bromide) Surfactants in Aqueous Solution

The apparent and partial molar enthalpies, apparent molar volumes, and adiabatic compressibilities at 298 K of the aqueous solutions of the cationic gemini surfactants propanediyl-alpha,omega-bis(octyldimethylammonium bromide) (8-3-8) and propanediyl-alpha,omega-bis(dodecyldimethylammonium bromide) (12-3-12) have been measured as a function of concentration. The trends of the partial molar enthalpies versus concentration are the first well documented thermodynamic evidence of sphere to rod transition in the micellar phase, involving a detectable quantity of heat, and allow the determination of the change in enthalpy associated with this transition. The changes in enthalpies upon micellization and for the sphere to elongated micelles transition, DeltaH(s)(-->)(r), have been obtained from the experimental data by using a pseudo-phase transition approach: -1.5 kJ mol(-1) for 8-3-8 and -3.9 kJ mol(-1) for 12-3-12. No evidence of the above transition is found in the trends of volumetric properties versus m. The apparent adiabatic molar compressibilities for the compounds under investigation are also reported here for the first time: a negative group contribution for the methylene group is evaluated, when the surfactants are present in solution as a single molecule, reflecting its solvation structure. In the micellar phase, the -CH(2)- group contribution becomes positive. A value of 1.17 x 10(-3) cm(3) bar(-1) mol(-1) for the change in adiabatic molar compressibility upon micellization is obtained. The lower values of the methylene group contributions to the volumetric properties for the monomers support the hypothesis of partial association of the chains before the cmc.