Biomembrane phase transitions

Abstract

The rich thermotropic behavior of lipid bilayers is addressed using phenomenological theory informed by many experiments. The most recent experiment not yet addressed by theory has shown that the tilt modulus in DMPC lipid bilayers decreases dramatically as the temperature is lowered toward the main transition temperature TM . It is shown that this behavior can be understood by introducing a simple free energy functional for tilt that couples to the area per molecule. This is combined with a chain melting free energy functional in which the area is the primary order parameter that is the driver of the main transition. Satisfactory agreement with experiment is achieved with values of the model parameters determined by experiments, but the transition is directly into the gel phase. The theory is then extended to include the enigmatic ripple phase by making contact with the most recent experimentally determined ripple structure.

Audio to microwave frequency dielectric study of the pretransition region in DPL-water systems

“…The thermotropic phase transitions in lipid bilayers are actively studied [ 11 because these systems are important relative to bio-membrane systems [2,3]. The molecular structure and the temperature dependence of the phospholipid-water mixtures have been investigated by X-ray diffraction [4,5] and by calorimetric measurements [6].…”

Heat capacity measurements of two-dimensional self-assembled hexadecanethiol monolayers on polycrystalline gold

“…On the microscopic level H m2D will be associated with the population and energetics of the generation of gauche defects over the broad temperature range (formation energy of a gauche defect is about 2 kJ/ mol-defect for a free alkane). 34 Another explanation 29 is that melting process of SAMs should also be compared to the gel-to-liquid crystalline transition.…”

Amphiphilic Molecules and Liquid Crystals

“…The recent physical studies on lipids have been briefly reviewed by Nagle and Scott in Physics Today [8]. A slightly older review, from a somewhat different point of view is the article by Dennis Chapman [9].…”