Determining the Dependence of Interfacial Tension on Molecular Area for Phospholipid Monolayers Formed at Silicone Oil-Water and Tricaprylin-Water Interfaces by Vesicle Fusion
Year: 2021
Journal: Langmuir, Volume 37, JUN 22, page 7527–7535
Authors: Kataoka-Hamai, Chiho; Kawakami, Kohsaku
Phospholipid monolayers formed at oil-water interfaces have been used to explore biological interface properties. Thus, monolayer systems need to be quantitatively understood. Previously, we investigated the formation of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) monolayers at silicone oil-water interfaces to determine the dependence of interfacial tension, gamma, on the area per lipid, a, compared to that of the closely packed monolayers, a(cp). This study aims to develop a method to obtain the gamma-a relationship from the gamma-a/a(cp), data by investigating POPC monolayers at the silicone oil-water and tricaprylin-water interfaces. Pendant drop tensiometry was used to obtain the dependence of gamma on a/a(cp). Furthermore, by calculating the surface pressure, Pi, from gamma and multiplying a/a(cp), with an estimated a(cp), value, the dependence of Pi on a was obtained. When a value approximately equal to the a of POPC bilayers was assigned to a(cp), the resultant Pi-a profile partially or approximately completely overlapped with the Pi-a isotherms obtained for the monolayers at the air-water interface using a Langmuir trough. The overlap for the silicone oil-water interface occurred at a <= 77 angstrom(2), while that for the tricaprylin-water interface occurred in approximately the entire a region. The results indicate that the H of the condensed monolayers is little affected by bulk oil. Thus, the gamma-a relationship for the oil-water interface can be determined by comparing the compression isotherm with the one obtained for the air-water interface.
