Long-Range Smectic Coupling of Phase Separated Domains in Ternary Mixture Lipid Multilayers

Abstract

Lipid multilayers serve as suitable and convenient bio-mimetic systems and are broadly used for studies of lipid membrane structure and function. It is known that many mixed lipid systems undergo phase separation as a function of temperature. Here we report that, in multilayers, the lateral phase separation in the bilayers is accompanied by long-range columnar order of the two phases along the normal to the bilayers arising from the coupling of two-dimensional intra-layer phase separation and inter-layer smectic ordering. Quantitative analysis of real-time dynamical experiments of confocal florescence microscopy reveal an interplay between intra-layer domain growth and inter-layer coupling, while X-ray reflectivity studies establish that the phase-separated domains are correlated normal to the lamellae over hundreds of bilayers. Through reconstruction of relative electron density profiles, XRR data also offer insight into differences in the domain structure on nm length scales. The microscopic understanding of two coexisting and domain-aligned multilamellar phases advanced by our experiments shed new light on the role of water in organizing membrane phases in stacked bilayers - a phenomenon of possible relevance to the mechanism of inter-layer lipid-lipid interactions in biological membranes.View Large Image | View Hi-Res Image | Download PowerPoint Slide