ABSTRACT
We have determined the positional correlation functions in aligned stacks of fully hydrated phospholipid bilayers from the thermal diffuse scattering measured by nonspecular x-ray reflectivity. While fair agreement can be obtained between experiment and linear smectic theory at length scales above 120 A, significant deviations occur at small r, which are tentatively attributed to collective protrusion modes.
Subject(s)
Lipid Bilayers/chemistry , Models, Chemical , Phospholipids/chemistry , Biomimetic Materials/chemistry , Hot Temperature , Scattering, Radiation , X-RaysABSTRACT
We present a temperature dependent x-ray reflectivity study of highly oriented, fully hydrated multilamellar phospholipid membranes. Both the specular and diffuse (nonspecular) x-ray reflectivity were measured for dimyristoyl-sn-glycero-phosphocholine (DMPC) and oleoyl-palmitoyl-sn-glycero-phosphocholine (POPC) on silicon substrates in excess water. In this configuration the repeat distance as well as the fluctuation spectra can be determined as a function of temperature. Both model systems studied exhibit a discontinuous unbinding transition from a substrate bound, multilamellar state to a state of freely dispersed bilayers in water. In the unbound phase a single membrane remains on the substrate.
Subject(s)
Lipid Bilayers/chemistry , Lipid Bilayers/metabolism , Phospholipids/chemistry , Phospholipids/metabolism , Dimyristoylphosphatidylcholine/chemistry , Dimyristoylphosphatidylcholine/metabolism , Phosphatidylcholines/chemistry , Phosphatidylcholines/metabolism , Scattering, Radiation , Silicon , Temperature , Thermodynamics , Water/metabolism , X-RaysABSTRACT
We present a quantitative study of specular and diffuse (non-specular) x-ray and neutron reflectivity from highly aligned phospholipid membranes deposited on solid substrates. The height-height correlation function could be obtained from the diffuse scattering without further model assumptions. The results differ significantly from the linear theory of smectic elasticity. We argue that the diffuse scattering is dominated by static liquid-crystalline defects, rather than thermal fluctuations.
Subject(s)
1,2-Dipalmitoylphosphatidylcholine/chemistry , Membrane Lipids/chemistry , Diffusion , Lipid Bilayers/chemistry , Membrane Fluidity , Neutrons , Scattering, Radiation , X-Ray DiffractionABSTRACT
The fusion of lipid membranes at the air-water interface has been detected with the use of x-ray reflection as a high-resolution, surface-sensitive technique. The rate of this fusion for dimyristoylphosphatidylcholine (DMPC) bilayers is the highest at 29 degrees C, which coincides with the chain-melting phase-transition temperature for the top membrane layers. After 6 hours of incubation a stack of at least ten surface-ordered membrane bilayers in equilibrium with the bulk vesicle suspension is formed. Such fusion is thus surface-catalyzed but not restricted to the first surface layer. The process involves partial membrane dehydration near the solution surface which decreases toward the bulk.
