Observation of elementary edge dislocations in phospholipid multilayers and of their annealing as a determination of the permeation coefficient

Abstract

We have observed the elementary edge dislocations in a phospholipid smectic liquid crystal lightly doped with a uniformly distributed, fluorescent, lipid analogue. Scanning the fluorescence intensity of a wedge crystal with 8 μm spatial resolution provided adequate photon statistics to detect changes of one bilayer in fifty. Fresh samples contain a dislocation density of about 1 × 107/cm2 which must anneal away before the bilayer edges in the wedge become clearly distinguishable. Annealing of dimyristoyl phosphatidylcholine (DMPC) requires 2-4 weeks at 35 °C in the Lα phase and does not occur during 3 months at 17 °C in the Pβ' phase. The annealing process requires the transfer of lipid molecules between neighbouring bilayers ; thus the annealing time depends upon the permeation coefficient λ p which appears in the viscoelastic equations for a smectic liquid crystal and provides a convenient determination of λp. We find λp is about 1 × 10-30 cm2/poise at 37 °C and is considerably smaller at 17 °C. Additional defects appear when the sample is cooled through the transition temperature; these anneal away within 2 days if the temperature is raised again within a short time, but require the full 2-4 weeks if the sample is in the Pβ' phase for more than a day

Mechanism of Lipid Nanodrop Spreading in a Case of Asymmetric Wetting

“…Their core is, respectively, filled with polar heads and water molecules, or with the aliphatic chains. Were the two dislocation lines at the same height, the monolayer and the additional bilayer would be disconnected and the only mechanism by which they could exchange material would be permeation, which is expected to be hindered in a humid atmosphere [29][30][31]. In our experiments, molecular exchange between adjacent monolayers is supposed to occur exclusively via the dislocation lines, which directly connect each pair of adjacent leaflets [29].…”

Lung lamellar body amphiphilic topography: A morphological evaluation using the continuum theory of liquid crystals: II. Disclinations, edge dislocations, and irregular defects

“…Climb, on the other hand, requires that the bilayers be broken locally and reformed so that the lipid molecules flip-flop between layers. This requires a significant activation energy and is slow (Chan and Webb, 1981). Although dislocations increase the free energy of an LMB, the kinetics of dislocation annihilation are sufficiently slow to allow a significant defect population to exist in a given aggregate (Chan and Webb, 1981;Zasadzinski, 1985;Zasadzinski et al, 1985).…”

“…Liquid crystal defects, such as edge dislocations and disclinations (see Figs. 1-5), common to thermotropic nematic and smectic-A liquid crystals (Friedel, 1922;deGennes, 1974;Bouligand, 1972;Pershan, 1974;Klkman, 1975Klkman, , 1983; Berreman et al, 1986), and lyotropic in vitro lamellar and nematic phases (Kleman et al, 1977; Chan and Webb, 1981; Benton and Miller, 1983;Schneider et al, 1983;Zasadzinski et al, 1985;Oswald and Allain, 1985; Benton et al, 1986;Zasadzinski, 1986;Zasadzinski and Meyer, 1986) are also found in human and mammalian lung multilamellar bodies. Their configurations correspond closely to those predicted by continuum theory (Ossen, 1933;Frank, 1958;Pershan, 1974;deGennes, 1974;Kleman, 1983).…”

“…Edge dislocations and disclinations have important effects on the physical properties of smectic and lamellar phases. They act as pathways for enhanced diffusion or segregation of water or other molecules within the LMB (Schneider et al, 1983); and they may mediate phase transitions (Helfrich, 1981;Allain, 1987;Allain et al, 1987), promote interbilayer transport (Chan and Webb, 1981), and act as sites for membrane fusion or disruption (Horn, 1984;Siegel, 1984;Zasadzinski, 1986). The morphology of the defect cores, which can be either hydrophobic or hydrophilic, determines what kinds of molecules (polar or nonpolar) encounter enhanced diffusion pathways and the degree of enhancement.…”

“…Large-amplitude undulations are often associated with edge dislocation defects in liposomes and LMB (Schneider et al, 1983;Zasadzinski et al, 1985;Zasadzinski, 1986). Strains are largest in the vicinity of dislocation defects (Pershan, 1974;Chan and Webb, 1981;Klkman, 1983;Zasadzinski et al, 1985); a population of defects might be necessary to catalyze the transition by providing the necessary strains.…”