Fluorescent probes in model membranes I: anthroyl fatty acid derivatives in monolayers and liposomes of dipalmitoylphosphatidylcholine.

A study of three fluorescent anthroyl probes has been carried out using pure and mixed monomolecular films with dipalmitoylphosphatidylcholine. In addition, fluorescence depolarization and differential scanning calorimetry data were obtained from dipalmitoylphosphatidylcholine vesicles with incorporated anthroyl probes. The three probes used were 2-(9-anthroyl)palmitic acid. 12-(9-anthroyl)stearic acid, and 16-(9-anthroyl)palmitic acid. The latter probe was synthesized for these studies. In monolayers the probes shifted the onset of the liquid-condensed/liquid-expanded monolayer phase transition with the extent of the shift decreasing in the order: 2-(9-anthroyl)palmitic acid greater than 12-(9-anthroyl)stearic acid greater than 16-(9-anthroyl)stearic acid. A corresponding decrease in the gel-liquid crystalline bilayer transition temperature (Tc) showed the same order of perturbation in both the fluorescence depolarization and differential scanning calorimetry data. Locating the anthroyl entity in the center of the bilayer would appear to provide a minimum perturbation.