Langmuir films of pure antibiotic ionophores and of mixtures with phospholipid at different temperatures

New results are presented concerning insertion of two antibiotic ionophores Lasalocid and Monensin as sodium salts (LAS-Na, MON-Na) in biomimetic memb ranes. Langmuir films of Dipalmitoylphosphatidylcholine (DPPC) have been us ed as model systems. Evolution of the compression isotherms has been invest igated below the gel - liquid crystal phase transition, between the ambiant , and temperatures approching physiological conditions, not only for the pu re antibiotics but also for the antibiotic - lipid mixtures, the molecular ratio rho antibiotic/lipid equal to 0.1. In the mixed films with LAS-Na, th e antibiotic molecule is well maintained by the film also when raising the temperature, whereas MON-Na is expelled above the low pressure region. The results are discussed and compared with effects produced in model systems o f bilayers submitted to similar temperature variations.