On the nature of the lipid monolayer phase transition

Abstract

An improved technique to study transferred lipid monolayers by electron microscopy and electron diffraction is presented. In combination with a microfluorescence technique it provides a powerful technique to study the microstructure of monolayers. It is demonstrated that the non-horizontal slope of the isotherms at the fluid-to-crystalline phase transition is due to the coexistence of fluid and crystalline phases up to the second order like transition to the completely condensed crystalline state. An electrostatic model is presented which explains (1) the thermodynamic stability of the fluid-solid coexistence, (2) the non-horizontal slope of the transition region, (3) the existence of a pressure dependent but uniform size of the crystalline platelets at the initial slope of the transition region

Protein/lipid interactions in phospholipid monolayers containing the bacterial antenna protein B800–850

“…The second effect, the removal of the liquid inclusions in the dendrites has been observed after addition of divalent ions and may thus be caused by the same mechanism [26]. These inclusions may be stabilized by electrostatic forces: as the molecu-82 lar density between liquid and solid phase differs, the charge density and thus the electric potential in the two phases differ [27]. …”

Lipid-packing perturbation of model membranes by pH-responsive antimicrobial peptides

“…The Langmuir monolayer, a model system that mimics a single leaflet of the bilayer, has been extensively used to investigate lateral lipid-lipid interactions, as well as the impact of antimicrobial peptide on lipid packing (Fischer et al 1984;Worthman et al 1997;Eeman et al 2006;Neville et al 2006;Bouffioux et al 2007;Dennison et al 2008;Wilke 2014). The main advantage of this system is that the molecular density and lipid composition can be varied without limitation, while the pressure-area isotherms are monitored by simultaneous visualization of the monolayer with microscopy techniques (Lösche et al 1983;Henon and Meunier 1991;Möhwald 1995;Kaganer et al 1999;Lheveder et al 2000).…”

“…The packing and orientation of the hydrophobic tails of the lipid molecules change during the compression, giving rise to phase transitions from a loosely unordered gaslike phase to a liquid phase or to a highly ordered condensed phase, similar to a 2-D vant'Hoff isotherm. Some lipids present both the liquid-expanded (LE) and the liquid-condensed (LC) phases and a plateau of coexistence of these phases (Fischer et al 1984). In the phase coexistence region, solid domains are formed and grow during the compression of the lipid film (Heckl et al 1986;Miller and Mohwald 1987;Vanderlick and Möhwald 1990).…”

Distribution of cooperative unit size of amphiphilic molecules in the phase coexistence region in Langmuir monolayers

“…Arriaga et al discussed the relation between the nonhorizontal plateau and the finite rigidity of a microheterogeneous medium composed of two coexisting phases [7]. The possibility of polar-headgroup interactions [8] and interphase strain effects [9] were also invoked to explain the experimentally observed nonhorizontal isotherms. Besides the above experimental viewpoints, present theoretical treatments of nonhorizontal isotherms are based on discontinuous transitions with the formation of two-dimensional molecular aggregates such as surface micelles [10] or small molecular clusters (or submicroscopic domains) [11].…”