Abstract
Monolayers of phosphatidylcholine (PC), tetradecanol (TD), hexadecanol (HD), octadecanol (OD) and eicosanol (E) and their binary mixtures were investigated at the air/water interface. The surface tension values of pure and mixed monolayers were used to calculate π–A isotherms. The surface tension measurements were carried out at 22 °C using a Teflon trough and a Nima 9000 tensiometer. The interactions between phosphatidylcholine and fatty alcohols (tetradecanol, hexadecanol, octadecanol, eicosanol) result in significant deviations from the additivity rule. An equilibrium theory to describe the behavior of monolayer components at the air/water interface was developed in order to obtain the stability constants, Gibbs free energy values and areas occupied by one molecules of PC–TD, PC–HD, PC–OD and PC–E complexes. We considered the equilibrium between the individual components and the complex and established that phosphatidylcholine and fatty alcohols formed highly stable 1:1 complexes.
Highlights
Many studies have been conducted on the mixed monolayer behavior at the air/water interface
An equilibrium theory to describe the behavior of monolayer components at the air/water interface was developed in order to obtain the stability constants, Gibbs free energy values and areas occupied by one molecules of PC–TD, PC–HD, PC–OD and PC–E complexes
In this paper we present evidence for the formation of 1:1 phosphatidylcholine-fatty alcohol complexes at the air/ water interface
Summary
Many studies have been conducted on the mixed monolayer behavior at the air/water interface. Investigating the surface properties of mixed monolayers is very important since it allows one to obtain information on the molecular interactions between the monolayer components. An insoluble monolayer at the air/water interface is usually considered as a two-dimensional solution, and the surface properties of mixed monolayers are generally studied based on the measurement of the surface pressure–area per molecule (p–A) isotherms of the monolayers (Capuzzi et al 1997; Bordi et al 1999; Chou and Chang 2000; Petelska et al 2011, 2012, 2013). Fatty alcohols are known to self-assemble at the air/water interface to form monolayers with rich phase behavior. While single-component alcohol monolayers have been well studied, mixtures have not. The behavior of mixtures of PC with long chain fatty alcohols or amines is very similar to that of fatty acid–phospholipids mixture, with evidence for 1:1 complex formation (Boggs et al 1986)
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