Search

Some parameters related to the bidimensional interactions between ceramide (CER) and diolcoylphosphatidylcholine (DOPC) molecules, alone and in mixtures of different weight fractions, were deduced from the study of spreading monolayers at the air-water interface. Spreading isotherms were recorded using both 0.1 M NaCl (pH 5.6) and a phosphate buffer solution (pH 7) as subphases in the 15–30°C temperature range. The bidimensional phases of the two components were obtained and their bidimensional miscibility was deduced as a consequence of positive deviations of the surface areas from the additivity relationship and by applying the phase rule at the collapse pressure. Excess surface Gibbs energies, enthalpies and entropies of mixing were also computed. The results obtained showed that the two components were miscible under the experimental conditions at all temperatures investigated, using both the Na + -ion-containing subphase and the buffered one.

The spreading isotherms of DODAC at the water—air interface were determined as a function of temperature. We verified that a study of the spreading film is the starting point for a better understanding of the most suitable conditions to obtain more complex aggregates, such as Langmuir-Blodgett (LB) films or vesicles. When the DODAC monolayer was in a liquid-condensed phase, this resulted in the optimum conditions for obtaining LB multilayers. In contrast, when the monolayer was in a liquid-expanded phase, multi- and unilamellar vesicles were obtained after sonication. Vesicles were also obtained when the system was below the gel-liquid crystal transition temperature ( T c =37°C), but a greater fraction of multilamellar vesicles were formed, as indicated by turbidimetric data.