Maria Paluch

Electrical properties of free surface of water and aqueous solutions.

The investigations, both experimental and theoretical, concerning the sign and the magnitude of the surface potential drop at the water/air interface and across adsorbed films presented in many papers are surveyed.

Cholesterol and phytosterols effect on sphingomyelin/phosphatidylcholine model membranes—Thermodynamic analysis of the interactions in ternary monolayers

In this work thermodynamic analysis of the interactions between lipids in ternary sphingomyelin/DPPC/sterol Langmuir films were performed to compare the effect of cholesterol, beta-sitosterol and stigmasterol on a model membrane. The condensing effect of the respective sterols and the interactions between molecules in ternary mixtures were analyzed on the basis of the excess area per molecule and the excess free energy of mixing values. The stability of the mixed monolayers was verified with the free energy of mixing values. The conclusions on the ordering effect of sterols were drawn from the analysis of the compression modulus values. It was found that the stoichiometry of the mixed films of the highest thermodynamic stability and of the strongest interactions is the same for all the sterols investigated. The results obtained prove that the mammalian sterol induces the strongest contraction of the area and reveals the strongest stabilizing and ordering effect among the investigated sterol. Stigmasterol was found to condense a model membrane in a weaker extent as compared to beta-sitosterol, however, the differences in ordering properties of both phytosterols are less pronounced. The magnitude of the influence of the investigated sterols on a model membrane was thoroughly discussed from the point of view of the structure of their side chain, which determines the geometry of a sterol molecule.

Electrical properties of some adsorbed films at the water―air interface

Abstract Measurements of surface potential (ΔV) and surface tension (Δσ) of aqueous solutions of acetic acid, chloro-, dichloro-, trichloroacetic acid, and alcohols (methanol, ethanol, 2,2,2-trifluoroethanol) were used for the determination of effective dipole moments (μ) and their separate components. For this purpose, the Helmholtz equation (in the form presented by Demchak and Fort (5)) have been applied. The contributions from the reorientated water molecules ( μ 1 /ϵ 1 ), and from hydrophilic ( μ φ - COOH , μ φ- OH ) and hydrophobic ( μ φ- CH 3 , μ φ- CH 2 Cl , μ φ- CHCl 2 , μ φ- CF 3 ) groups and the local dielectric permittivity in the vicinity of these groups were calculated.

Electrical properties of adsorbed films of some aromatic compounds at the water/air interface

Abstract Surface tension (Δσ) and electric surface potential (ΔV) measurements of aqueous solutions of some aromatic compounds (benzoic, p-toluic and p-fluorobenzoic acid, benzaldehyde, and tolualdehyde) were used to determine effective dipole moments using the Helmholtz equation. Knowing the effective dipole moments the surficial orientations of adsorbed molecules were estimated. Using the latter and applying the formula presented by R. J. Demchak and T. Fort (J. Colloid Interface Sci. 46, 191 (1974) ) the separate components of effective dipole moments connected with reorientation of water molecules ( μ 1 ϵ 1 ), hydrophilic ( μ φ- COOH , μ φ- CHO ) and hydrophobic ( μ φ- CH 3 , μ φ- F ) groups, and local dielectric permittivities in the vicinity of these groups (ϵ2, ϵ3) were calculated.

Effect of para-substituted phenols on the surface potential and on the surface tension at the water/air interface

Abstract Electric surface potentials (by jet method) and surface tension (by maximum bubble pressure method) of aqueous solutions of phenol, p -methyl, p -methoxy, p -bromo, and p -nitrophenol at temperatures of 20, 30, and 40°C were investigated. The adsorption properties of the above-mentioned compounds (free energy of adsorption Δ G °, enthalpy Δ H °, entropy Δ S °, and surface dipole moment μ at the free surface of water are discussed.

Surface properties of some acetic acid derivatives at the water/air interface

Abstract Electric surface potential (Δ V ) and surface tension (Δ σ ) measurements of aqueous solutions of trifluoro-, trichloro-, tribromo-, and trimethylacetic acid were used to determine the surface activity, orientation of molecules, effective dipole moments (connected with water molecules, hydrophilic and hydrophobic groups), and local dielectric permittivity of the surface layer.

Electrical properties of the mixed films of 2,2,2-trifluoroethanol—ethanol at the water/air interface

Abstract The coadsorption of 2,2,2-trifluoroethanol and ethanol at free water surface was investigated. The effective dipole moment of 2,2,2-trifluoroethanol has been determined using the Helmholtz equation. The calculations have been done on the base of surface excess values, got from surface tension measurements and surface potential changes of aqueous solutions of 2,2,2-trifluoroethanol. Knowing the effective dipole moment and composition of mixed film the surface potential was calculated.

Differences in surface behaviour of galactolipoids originating from different kind of wheat tissue cultivated in vitro

The aim of presented researches was to investigate the physicochemical properties of Langmuir monolayer of galactolipids extracted from two different kinds of plastids: immature embryos and inflorescences. Differences between the physicochemical properties of the plastid membranes may help to explain different physiological processes, such as plant regeneration. Surface pressure (pi) vs. molecular area (A) isotherms of the monogalactosyldiacylglycerol (MGDG)/digalactosyldiacylglycerol (DGDG) monolayers of various molar ratios were measured at 15 degrees C. Galactolipids were extracted from two different types of tissue: inflorescences and embryos. Based on the analysis of the pi-A isotherms, the properties of monolayers, such as collapse pressure (pi(coll)), limiting area (A(lim)), compressibility modulus (C(s)(-1)), excess free energy of mixing (DeltaG(EXC)) and free energy of mixing (DeltaG(MIX)), were calculated. The results show that pure MGDG and DGDG and their mixtures form liquid-expanded monolayers, independently on the kind of tissue. Galactolipids originating from inflorescences produce more compressible films at the air/water interface, with larger limiting area per molecule and lower stability against the collapse process. MGDG and DGDG are miscible and form non-ideal mixed monolayers at the air/water interface. Negative values of DeltaG(EXC) were calculated for the mixture of galactolipids originating from inflorescences, with the content of MGDG, x(MGDG)>0.6. In the case of embryos, the negative values of DeltaG(EXC) were found for x(MGDG) approximately 0.5. Therefore, the attractive interactions between MGDG and DGDG exist in the mixtures of these compositions. As it is shown by negative values of DeltaG(MIX), mixed monolayers are more stable compared with unmixed ones.

Electrical properties of the monolayers of p-phenol derivatives

Abstract The effective dipole moments of adsorbed molecules, functional groups, and water contained in the surface layer were determined using the Helmholtz equation. The calculations were done on the basis of surface excess values, obtained from surface tension measurements and surface potential changes of aqueous solutions of p-halogenphenols, p-methylphenol, and aniline.

Properties of insoluble mixed monolayers of lipids at the water/air interface

A study of monolayer mixing behaviour in binary d,l-dipalmitoyl phosphatidylcholine/ 3-monopalmitoyl glycerol mixtures was undertaken. For this purpose, the isotherms of surface pressure versus molecular area were acquired at four different tempera-tures and a surface thermodynamic analysis was applied to these isotherms.