Location and nature of the surface membrane binding site of ciprofloxacin:A fluorescence study

In this work, the interaction between the antibiotic ciprofloxacin (CPX) an d liposomes formed with zwitterionic and acidic phospholipids was studied u sing fluorescence methods. Binding of 1-anilino-8naphthalene sulfonate to t he liposome surface was dependent on the presence of CPX and the lipid comp osition. The data were fitted to a Freundlich-like isotherm. The binding co nstant (K), maximum concentration bound to liposomes (C-m), and cooperativi ty (b) were obtained. K values, in the presence and absence of CPX, were us ed to calculate the variation in the surface potential (Delta Psi) of the l iposomes. Fluorescence quenching and anisotropy measurements suggest that t he drug interacts with the headgroups of the phospholipids and does not pen etrate deeper in the bilayer. No significant changes were observed in the c ooperativity of the phospholipid transition. Hydrogen bonding with dip almi toylphosphatidyl-ethanolamine and electrostatic interactions with dipalmito ylphosphatidylglycerol and zwitterionic phospholipids such as dipalmitoylph osphatidylcholine appear to be involved in the interaction occurring in nat ural membranes.