Steric repulsion between phosphatidylcholine bilayers

Abstract

The change in pressure needed to bring egg phosphatidylcholine bilayers into contact from their equilibrium separation in excess water has been determined as a function of both distance between the bilayers and water content. A distinct upward break in the pressure-distance relation appears at an interbilayer separation of about 5 A, whereas no such deviation is present in the pressure-water content relation. Thus, this break is not a property of the dehydration process per se, but instead is attributed to steric repulsion between the mobile lipid head groups that extend 2-3 A into the fluid space between bilayers. That is, electron density profiles of these bilayers indicate that the observed break in the pressure-spacing relation occurs at a bilayer separation where extended head groups from apposing bilayers come into steric hindrance. The pressure-spacing data are used to separate steric pressure from the repulsive hydration pressure, as well as to quantitate the range and magnitude of the steric interaction. An appreciable fraction of the measured steric energy can be ascribed to a decrease in configurational entropy due to restricted head-group motion as adjacent bilayers come together.

Adsorption of Membrane-Associated Proteins to Lipid Bilayers Studied with an Atomic Force Microscope: Myelin Basic Protein and Cytochrome c

“…From X-ray scattering experiments, the thickness of a fully hydrated pure EPC bilayer was determined to be 6.3 nm and a headgroup-headgroup distance of 4 nm has been reported. 47 This is consistent with the punch-through distances we have observed (Table 2). Because images of bilayers were flat, and identical characteristic force curves ( Figure 1d) were found at any random position of the sample, we conclude that the mica was homogeneously covered by a lipid bilayer.…”

Fluid phase structure of EPC and DMPC bilayers

“…For each lipid we present the results for the fully hydrated sample (P = 0) and for one of the less hydrated samples. The hydrocarbon thickness per monolayer is (McIntosh et al, 1987;Nagle and Wiener, 1988) is , where we choose D H = 9 Å, consistent with neutron diffraction results (Buldt et al, 1979), to estimate the PC headgroup thickness. Fig.…”

Gelation of liposome interior A novel method for drug encapsulation

“…For X-ray diffraction experiments, empty and leaded llposomes were pelleted (230,000 × g, 10 h) and sealed in thin walled glass capillary tubes. Specimens were mounted in a point collimation X-ray camera and diffraction patterns were recorded on Kodak DF-F-5 Xray film in a flat plate film cassette as described previously [12,13]. Liposome pellets could be redisporsed with no change in particle size, as measured by dynamic light scattering (Coulter N 4SD) or loss of drug encapsulation.…”