DPPC monolayers at the oil/water interface

MOTTOLA M; PERILLO MA

Santiago del Estero

Congreso; XLIV Reunión Anual de la Sociedad Argentina de Biofísica (SAB); 2015

Sociedad Argentina de Biofísica

Lipidicmicroemulsions are systems commonly used to encapsulate, maintain, and releasemolecules of pharmacological interest. In order to gain insights aboutinterfaces within microemulsions at the molecular level1, by using aLangmuir interfacial trough, we have characterized, at three differenttemperatures (T), monomolecular layers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine(DPPC) at oil/water interfaces (O/W) where the upper phases differed inviscosity: Vaseline 80 SSU/water and Vaseline 80 SSU:n-heptane(1:1)/water. Forthe film preparation, two different techniques were assayed in order to makeadsorbed (AM) or spread monolayers (SM)2. The AM were formed byadsorption of the phospholipid to the interface when the solution was spreadover the upper phase. Since the spreading distance from the Wilhelmy plateaffected the molecules? diffusion in the O/W interface, at least 30 min wererequired for the evaporation of the solvent and the initial surface pressure (πi)stabilization. In contrast, to form SM, the DPPC solution was spread over anair/water (A/W) interface to form a monolayer and then the oil was poured overit to obtain the O/W interface. While the second method was the most frequentlyused and easiest to perform, similar results were obtained with bothtechniques. The apparent mean molecular areas (MMAapp) of DPPC measuredat the O/W interface were higher than those exhibited at the A/W interface at thesame lateral pressure. Moreover, the bidimensional phase transition of DPPC atthe O/W interface occurred at higher π values than those observed with the monolayerat the A/W interface at the same T. Furthermore, thecondensed domains´ shapes revealed by an epifluorescence microscopy (EFM) analysisdiffer slightly according to the experimental T and upper phase compositionassayed. Our results indicate that alkane molecules from the upper phase insertbetween the hydrocarbon chains of the phospholipid and are not squeezed outeven at the highest compressions achieved before the collapse point.