Phase Transitions in a Single Supported Phospholipid Bilayer: Real-Time Determination by Neutron Reflectometry.

Yuri Gerelli

doi:10.1103/physrevlett.122.248101

Abstract

Time- and temperature-resolved neutron reflectometry allowed us to perform the real-time characterization of the structural changes taking place across phase transitions in solid supported-lipid bilayers (SLBs). We identified the presence of an isothermal phase transition, characterized by a symmetrical rearrangement of lipid molecules in both bilayer leaflets, followed by the main thermotropic phase transition, and characterized by an independent melting of the two leaflets. We demonstrated that the presence of a substrate increases the enthalpy of melting by the same amount for both SLB leaflets with respect to the values reported for freestanding bilayers. These results are highly relevant for the further understanding of cooperative structural dynamics in SLBs and for the investigation of thermally activated processes such as the transmembrane lipid translocation (flip flop).

Highlights

Lipid bilayers are thin films made of two layers of lipid molecules
Phase transitions in lipid bilayers have been widely studied in solution aggregates, such as vesicles [6,7,8,9], or in solid-supported stacks of hundreds of bilayers in controlled humidity environments [10]
The main common result is a substantial broadening of the gel-to-fluid phase transition (PT) with respect to that observed in freestanding bilayers in solution

Summary

Introduction

Lipid bilayers are thin films made of two layers of lipid molecules. Solid-supported lipid bilayers (SLBs) are widely used tools in biological and technological studies for the investigation of interactions and molecular processes involved in cell function [1,2], disease [3], and for sensing applications [4,5]. The main common result is a substantial broadening of the gel-to-fluid phase transition (PT) with respect to that observed in freestanding bilayers in solution. The initial and final structure of the bilayers was characterized using the contrast variation method [30] at 25 and 60 °C in the gel and fluid phases, respectively.

Results

Conclusion