DPPC monolayers at the oil/water interface

MOTTOLA, MILAGRO; PERILLO, MARÍA ANGÉLICA

Santiago del Estero

Congreso; XLIV Reunión Anual de la Sociedad Argentina de Biofísica; 2015

Sociedad Argentina de Biofísica

Lipidic microemulsions are systems commonly used to encapsulate, maintain, and release molecules of pharmacological interest. In order to gain insight about interfaces within microemulsions at the molecular level1, by using a Langmuir interfacial trough we have characterized, at different temperature (T), monomolecular layers of DPPC at oil/water interface (O/W) with different viscosity of the upper phase: Vaseline 80 SSU and (1:1) Vaseline 80SSU:n-heptane. For the film preparation, two different techniques were assayed to make adsorbed (AM) or spread monolayers (SM)2. The AM were formed by adsorption of the phospholipid to the interface when the solution was spread over the upper phase. Since the spreading distance from the Wilhelmy plate affected the molecules? diffusion in the O/W, at least 30 min were required for the evaporation of the solvent and the initial surface pressure (πi) stabilization. In contrast, to form SM, the DPPC solution was spread over an air/water interface (A/W), and then the oil was poured over it to obtain the O/W. Similar results were obtained with both techniques but the second method was easiest to perform. The apparent mean molecular areas (MMAapp) of DPPC measured at the O/W were higher than those exhibited at the A/W at the same lateral pressure. Moreover, the bidimensional phase transition of DPPC at the O/W occurred at higher π values than those observed at the A/W at the same T. Furthermore, the shape of the condensed domains, observed by epifluorescence microscopy (EFM), differed slightly according to experimental T and upper phase composition. Our results indicate that alkane molecules from the upper phase insert between the hydrocarbon chains of the phospholipid, and are not squeezed out even at the highest compressions achieved before the collapse point. References: [1] Thoma M, et al. Colloids Surf., A. 95:193-200, 1995. [2] Solovyev A, et al. Energy & Fuels 20:1572-1578, 2006. Acknowledgements: FONCyT, CONICET, SeCyT-UNC.