Lipid Bilayers and Membrane Dynamics: Insight into Thickness Fluctuations

Andrea C. Woodka, Paul D. Butler, Lionel Porcar, Bela Farago, and Michihiro Nagao

Phys. Rev. Lett. 109, 058102 – Published 31 July 2012

Abstract

Thickness fluctuations have long been predicted in biological membranes but never directly observed experimentally. Here, we utilize neutron spin echo spectroscopy to experimentally reveal such fluctuations in a pure, fully saturated, phosphocholine lipid bilayer system. These fluctuations appear as an excess in the dynamics of undulation fluctuations. Like the bending rigidity, the thickness fluctuations change dramatically as the lipid transition temperature is crossed, appearing to be completely suppressed below the transition. Above the transition, the relaxation rate is on the order of 100 ns and is independent of temperature. The amplitude of the thickness fluctuations is $3.7 Å \pm 0.7 Å$ , which agrees well with theoretical calculations and molecular dynamics simulations. The dependence of the fluctuations on lipid tail lengths is also investigated and determined to be minimal in the range of 14 to 18 carbon tails.

Received 2 February 2012

DOI:https://doi.org/10.1103/PhysRevLett.109.058102

Authors & Affiliations

Andrea C. Woodka

NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6102, USA

Paul D. Butler

NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6102, USA and Department of Chemical & Biomolecular Engineering, University of Delaware, Newark, Delaware 19716, USA

Lionel Porcar and Bela Farago

Institut Laue Langevin, 6 rue Jules Horowitz, BP 156-38042, Grenoble Cedex 9, France

Michihiro Nagao^*

NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6102, USA and Center for Exploration of Energy and Matter, Indiana University, Bloomington, Indiana 47408, USA