R. Seoane

Study of penetration of amphotericin B into cholesterol or ergosterol containing dipalmitoyl phosphatidylcholine Langmuir monolayers

Abstract The interactions of amphotericin B (AmB) with sterols and phospholipids have been studied by adsorption of AmB from aqueous solutions into Langmuir monolayers from dipalmitoyl phosphatidylcholine (DPPC), ergosterol, cholesterol and their mixtures. The results show that AmB exhibits stronger interaction with cholesterol than ergosterol in one-component monolayers. However, for DPPC–sterol monolayers, the effectiveness of AmB penetration depends on the proportion of both film components in the mixed film as well as on the strength of interaction between DPPC and particular sterol.

Study of the interaction of cholesterol with potentially hypocholesterolemic substances in a monolayer form

Abstract The behaviour of mixed monolayers of cholesterol (chol) and stigmastanil phosporylcholine (SPC) at the air–water interface was studied and compared with that of the cholesterol–arachidonic acid (Ara) system in order to examine the molecular interactions between the film components. The structural characteristics of the mixed films was determined from the π – A isotherms recorded on an automated Langmuir-type film balance. The studies confirm that the mixed films are homogeneous and their components exhibit negative deviations from ideality as the result of mutual interactions at the interface. The magnitude of these interactions depends on the surface pressure region, temperature, as well as the system composition. Values of the thermodynamic parameters such as Δ G exc , Δ S exc and Δ H exc provide evidence for the presence of interactions, which are stronger in the chol–SPC system than in the chol–Ara mixed films.

A study of the behaviour of mixed monolayers of amphotericin B and dipalmitoyl phosphatidic acid based on hysteresis experiments

Amphotericin B (AmB) monolayers consist of three distinct regions: a liquid expanded phase at low surface pressures, a liquid condensed phase at high surface pressures and a transitional phase that gives a plateau at 10 mN/m in the π -A curves. The presence of such a plateau is ascribed to a change in the orientation of AmB molecules from a horizontal to a vertical position relative to the air/water interface. Dipalmitoyl phosphatidic acid (DPPA) gives a condensed mono-layer, the π-A curves for which exhibit a slope change at 25 mN/m that has been ascribed to an orientational change in the nonpolar chains from a tilted to a vertical position relative to the interface. An equimolar mixture of AmB and DPPA exhibits a surface behaviour in-between those of the pure components, which includes a phase transition at 20 mN/m that suggests the existence of interactions between the components; such interactions result in deviations from the ideal behaviour reflected in plots of the mean molecular area against the mole fractions of the components. On spreading separately on the interface, the two components are initially immiscible, but become miscible gradually with time. Hysteresis experiments reveal that AmB is desorbed into the subphase by effect of its solubility, being decreased by DPPA; this is attributed to interactions between the polar heads of the two components causing AmB molecules to be retained on the surface and giving rise to positive deviations from the ideal behaviour as a result.