Thermodynamic and spectroscopic features of the behaviour of amphotericin b in aqueous medium

ROMANINI, DIANA; AVALLE, GABRIELA; NERLI, BIBIANA; PICÓ, GUILLERMO

Biophysical Chemistry

Elsevier Science Ltd.

Año: 1999 vol. 77 p. 69 - 77

0301-4622

The interaction between amphotericin B molecules in aqueous medium solution was studied using absorption and circular dichroism approaches. The results showed that at concentrations below 1 mM of amphotericin B, an equilibrium between the monomer and aggregate occured with a constant of approximately 0.6=106 My1. The aggregate formation constant was dependent on the experimental conditions of the medium: its value increased at acidic pH values, while alkaline medium induced the equilibrium displacement to the monomer formation. Either neutral salts or chaotropic agents such as urea prevented the formation of the aggregate. The presence of net electrical charge on the amine and carboxyl groups plays a role in the thermodynamic stability of the aggregate. A hydrophobic effect was also found between the monomer form and the water molecules of neighbours. In the aggregate formation water molecules were released contributing to an increase in the entropic change.