A study of the stability of amphotericin B monolayers

Abstract

Amphotericin B (AmB) is a polyene antibiotic used as an antimycotic agent that forms relatively stable monolayers at low surface pressures (π) at the air/water interface. At increased π values, however, the monolayer structure undergoes a rearrangement, which is manifest as a constant surface pressure plateau in the corresponding π-A curve. Beyond such a plateau, when the monolayer is in a liquid condensed state, the area occupied by the molecules in the film is so small that this suggests the antibiotic is to some extent dissolved in the subphase. In order to confirm this hypothesis, the behaviour of AmB spread on various subphases was examined under variable conditions regarding the number of AmB molecules deposited, the rate at which the surface film was compressed and the temperature and ionic strength of the subphase. Relaxation experiments involving measurements of the rate of molecular area decrease at a constant surface pressure were also carried out. Based on the results, AmB desorption is diffusion controlled at low surface pressures and arises from its dissolution in two consecutive steps at surface pressures beyond those of plateau in the π -A curves, where AmB molecules are assumed to lie normal to the subphase surface.