Lisbeth Ter-Minassian-Saraga

Characterization of kmno4/h2so4-oxidized polyethylene surfaces by means of ESCA and45ca2+ adsorption

Abstract The chemical constitution of KMnO4/H2SO4-oxidized (sulfated) polyethylene (PE) surfaces has been explored by means of ESCA utilizing chemical shifts, peak intensity data, and chemical tagging reactions. In addition, the adsorption of Ca2+ ions on sulfated PE was quantified by radiotracer measurements. Comparisons have been made with KClO3/H2SO4 and K2Cr2O7/H2SO4 as oxidizing agents and through replacing polyethylene by polystyrene. According to the present study the main chemical groups on a Download : Download full-size image . In the oxidation grooves, dissociable −COOH groups are also present in appreciable amounts. By annealing, a smoother and more homogeneous sulfated surface is produced, the composition of which strongly depends upon the state of the ionic groups at the heat treatment.

Ionized monolayers as models for polyelectrolytes

Abstract The selective adsorption of trace PoIV complex ions by ionized monolayers of cationic soaps adsorbed at a 1 M HC1 solution/air interface was studied. The monolayers behave like two-dimensional ion-exchangers. An original device was set up to measure their surface potentials using two 241Am ionizing electrodes. The adsorption-distribution coefficient of the trace anions increased with the total surface potential of the ionized monolayer. It appears that a singly charged complex anion is adsorbed, PoC16H−, which penetrates behind the plane of the positively charged head-groups.

Wetting of polyethylene by water, methylene iodide and methylene iodide-decalin mixtures

Abstract The wettability of oxidized polyethylene films was studied with pure liquids (water and methylene iodide) and practically nonpolar mixtures of Decalin and methylene iodide. A linear variation was found of the wettability of these films with the chemical composition of their surfaces (determined by adsorption of radioactive 45 Ca ions). A value of γ s d for the polyethylene was found with the nonpolar mixtures of methylene iodide and Decalin and the values of the solid-liquid polar interactions ( I sl P ) for oxidized polyethylene were deduced. Dipole-dipole and induced dipole-dipole interactions between the pure liquids and the oxidized and unoxidized polyethylene were calculated for two possible orientations of the hydrocarbon chains to the surface and compared with the experimental results. Generally a poor agreement was obtained, mainly due to the difficulty in estimating the correct values for the distances between molecules or groups. However, a better agreement was obtained assuming that the chains were perpendicular to the surface.

Cooperativity of an acid phospholipid reaction with basic hydrophobic polyelectrolytes or with the apoprotein proteolipid from myelin: I. Surface pressure, surface potential, and recombination studies with monolayers☆

Abstract For two types of mixed monolayers the surface pressure and surface potential have been measured as a function of their composition. They were formed by spreading of an acidic phospholipid and either a basic polysoap or a basic hydrophobic protein from myelin. The reaction was followed by using a radioactive counterion as an indicator. It was found that with the polysoap, highly charged by dissociation, the reaction with the acidic lipid was cooperative, contrary to the case of the protein which was not highly charged. For both, however, screening of the electrostatic repulsion between the ionized groups of the polyions by the lipid charge appears as a “condensation” of the polyions and of the lipid. Models are suggested to interpret this condensation and the mutual structuration of the polyions and of the lipid molecules. They are extended to biological membrane structures in the absence or in the presence of applied force or electrical fields.

Lyophilization and rehydration of liposomes

Abstract Many studies have been undertaken with the aim of proving the potentiality of liposomes and vesicles as drug carriers. However, the results obtained have not yet been developed industrially. One of the reasons for this is the lack of a satisfactory liposome and vesicle preservation method. This study deals with the behaviour of liposomes during lyophilization processes, either in the presence or in the absence of sodium ioxitalamate and maltose. The bilayers are constiluted either by dipalmitoylphosphatidylcholine (DPPC) alone or as a mixture with cholesterol (7/2). The liposome are characterized by their size, their microscopic structure and by release of the active agent. To complete the pharmaceutical study, differential scanning calorimetry (DSC) has been used to analyse the evolution of liposome hydration.

Subtransition and hydration studies of fully hydrated DPPc gel-phase

Abstract The amounts of structural and hydration water of the fully hydrated (DPPC) dipalmitoylphosphatidylcholine sub-gel phase have been studied using the approach of Ter-Minassian-Saraga, L., and Madelmont, G. (J. Colloid Interface Sci. 85, 375–388 (1982)). These amounts are not significantly different from those of the Lβ′ phase. Also, the molar enthalpy L of melting of the frozen structural water is the same for both gel phases. The interesting result which emerges from our experiments is the enhancement of the resolution of the peak (in the heating thermogram) corresponding to the frozen structural water melting. The explanation provided for this enhancement is that long annealing durations of the gel phase, inside which the water is liquid, favors the phase separation between the excess bulk water and the sub-gel phase and the crystallization of DPPC chains inside the larger liposomes thus formed.

Polymer interface analysis by ESR spectra of Mn(II)

Abstract Carbonyl groups were formed on the surface of low-density polyethylene by chemical oxidation. The treated surfaces were studied by scanning electron microscopy, ATR, IR spectroscopy, and 45Ca2+ adsorption. Paramagnetic probe ions Mn(II) were adsorbed and the ESR spectra obtained for various surface compositions and thermal treatments of polyethylene. The results obtained show that ESR spectroscopy may become a promising, nondestructive method of analysis of solid polymer interfaces.

Cooperativity of an acid phospholipid reaction with basic hydrophobic polyelectrolytes or with the apoprotein proteolipid from myelin. Part II: Collapse and respreading of the mixed films

Abstract Cycles of compression-expansion of mixed monolayers formed by spreading mixtures of an acidic phospholipid, Na phosphatidylinositolmonophosphate, extracted from wheat, and the polysoap poly(2-methyl-5-vinyl-hexylpyridinium bromide) have been performed. The phospholipid is a ligand for the polysoap monomers. The films collapse and respread reversibly when the films contain an excess of the phospholipid. When the films contain an excess of the polysoap or only the pure polysoap, polysoap molecules desorb or are ejected into the aqueous substrate when the film surface pressure exceeds a first collapse pressure. A second collapse pressure is attained at higher surface pressures when the excess polysoap has desorbed. Therefore, in contrast to the mixed films with an excess of phospholipid, the collapsed and irreversibly desorbed pure polysoap cannot respread. The relevance of these experiments to the behavior of biological membranes and of the monolayers at the surface of the liquid lining of lung alveoli is considered.

Isaxonine base is a strong perturber of phospholipid bilayer order and fluidity—A differential scanning calorimetry and spin labeling study

The effects of the neurotropic drug isaxonine on fully hydrated dipalmitoyl-phosphatidyl-choline (DPPC) bilayers has been studied in the temperature range 0 degree-60 degrees, using differential scanning calorimetry and electron spin resonance spectroscopy, with two stearic acid spin labels. At low concentration (1% mol/mol), isaxonine is trapped in the polar interface and enhances the phospholipid multibilayers organization in the gel state. In contrast, at high concentration (30% mol/mol), the drug disorganizes the phospholipidic structures and may induce domain formation by phase separation. The strong interactions of isaxonine at the lipid-water interface change the ionization state of the stearic acid spin labels which become totally ionized. Then isaxonine acts as a modifier of the surface pH of the bilayer. The strong membrane effects of isaxonine may explain in part its pharmacological properties in vivo.

Behaviour of a lyotropic-smectic liquid crystal between mica surfaces a study of the fully hydrated egg-lecithin

Abstract The behaviour of three egg-lecithin (EL)—water (W) mixtures, 60% (w/w):I, 50% (w/w):II and 30% (w/w):III, squeezed out or sucked in between two mica surfaces was investigated using an apparatus designed by J.N. Israelachvili. Mixture I is a lyotropic-smectic liquid crystal (LSLC), in contrast to II and III in which the LSLC is in equilibrium with a separated phase of excess water. The force F applied to the micasheet holders, the “separation” D between the mica surfaces and the average refractive index were measured for 1 A stepwise-thinning process was mainly observed on compressing mixtures I and II from separation 30 The contact area of the flattened-mica sheets increased with the force F at separation Dmin. Assuming that an effective elastic parameter can be defined for our composite system (mica sheet + glue), we interpret the F—contact-area dependence using the theory of Johnson et al. and deduce values of average normal pressures or stresses of the order of 10 mN m−2 on the flat mica—mica contact. At such pressures the values of λ and the repeat distance of the LSLC formed by EL + W and measured by X-ray diffraction are similar. The refractive index n of I is independent of separation for Dmin