Swelling of phospholipid floating bilayers: the effect of chain length

TL;DR

This study investigates how the chain length of saturated di-acyl phosphocholine lipids affects the equilibrium distance and fluctuations of floating bilayers near a substrate, across gel to fluid phase transitions.

Contribution

It provides new insights into the influence of lipid chain length on bilayer interactions and bending rigidity in different phase states.

Findings

Longer chains increase the equilibrium distance between bilayers.

Membrane fluctuations vary with chain length and phase state.

Bending rigidity depends on lipid chain length and temperature.

Abstract

The equilibrium distance between two lipid bilayers stable in bulk water and in proximity of a substrate was investigated. Samples consisted of a homogeneous lipid bilayer, floating near an identical bilayer deposited on the hydrophilic surface of a silicon single crystal. Lipids were saturated di-acyl phosphocholines, with the number of carbon atoms per chain, n, varying from 16 to 20. The average and r.m.s. positions of the floating bilayer were determined by means of neutron specular reflectivity. Samples were prepared at room temperature (i.e. with the lipids in the gel phase) and measurements performed at various temperatures so that the whole region of transition from gel to fluid phase was explored. Data have been interpreted in terms of competition between the interbilayer potential and membrane fluctuations and used to estimate the bending rigidity of the bilayer.