Effect of the phospholipid head group in antibiotic-phospholipid association at water-air interface

We studied the interactions of tetracycline antibiotics, TCs, with phospholipid monolayers with the two-fold aim of elucidating the mechanism of action of TCs and to provide a first step for the realization of bio-mimetic sensor for such drugs by means of the Langmuir-Blodgett technique. Preliminary surface tension studies demonstrated that surface activity of tetracycline is moderate and dependent on the pH of the subphase. We selected three phospholipids having hydrophobic chains of the same length but differing in the polar head structures, i.e. dipalmitoylphosphatidylcholine, dipalmitoylphosphatidylethanolamine, and dipalmitoylphosphatidic acid. Surface pressure- and surface potential- area isotherms were employed to investigate the behavior of the phospholipid monolayers at the water-air interface when tetracycline was added to the aqueous subphase. Analysis of the results indicated that the electrostatic interaction is the driving force for migration of tetracycline towards the interface where localized adsorption to the head groups occurs. Nevertheless, such interactions appear to be insufficient to promote penetration of tetracycline through the hydrophobic layer.