3PT148 Localization of Liquid-Ordered/Liquid-Crystalline Phase Separation at a Lipid Bilayer Suspended over Microwells(The 50th Annual Meeting of the Biophysical Society of Japan)

Dipalmitoylphosphatidylcholine (DPPC) was hydrated in 0.2–60 mM solution of CaCl2in heavy water and thoroughly homogenized by freezing-thawing process. Small-angle neutron scattering (SANS) shows formation of unilamellar vesicles in the range 1–60 mM of CaCl2. From the Kratky–Porod plot ln [I(Q)Q2] vs.Q2of SANS intensityI(Q)in the range of scattering vectorsQcorresponding to the interval 0.001 Å−2≤Q2≤0.006 Å−2, the vesicle bilayer radius of gyrationRgand the bilayer thickness parameterdgwere obtained. The structure of the bilayer displays different behavior for the gel phase and the liquid-crystalline phase: In the gel phase (at 20°C), the values ofdgindicate nonlinear changes in the lipid bilayer thickness, with a maximum at ~5 mM CaCl2. In the liquid-crystalline phase (at 60°C), the parameter of the lipid bilayer thicknessdg=43.2±0.3 Å is constant within the concentration range 1≤cCa≤40 mM. Vesicles prepared at 60 mM CaCl2show within experimental error, the same values ofdgas pure DPPC unilamellar vesicles prepared by extrusion using polycarbonate filter with pores of diameter 500 Å.

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Liquid-Liquid Crystalline Phase Separation in Biological Filamentous Colloids: Nucleation, Growth and Order-Order Transitions of Cholesteric Tactoids

Soft Matter ◽

10.1039/d1sm00466b ◽

2021 ◽

Author(s):

Paride Azzari ◽

Massimo Bagnani ◽

Raffaele Mezzenga

Keyword(s):

Phase Separation ◽

Crystalline Phase ◽

Liquid Crystalline ◽

Liquid Crystalline Phase ◽

Technological Processes ◽

Nucleation Growth

The process of Liquid-Liquid Crystalline Phase Separation (LLCPS) in filamentous colloids is at the very core of multiple biological, physical and technological processes of broad significance. However, the complete theoretical...

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Interaction of surfactants with vesicle membrane of dipalmitoylphosphatidylcholine. Effect on gel-to-liquid-crystalline phase transition of lipid bilayer

Chemistry and Physics of Lipids ◽

10.1016/0009-3084(86)90085-x ◽

1986 ◽

Vol 42 (4) ◽

pp. 261-270 ◽

Cited By ~ 45

Author(s):

Tohru Inoue ◽

Kenji Miyakawa ◽

Ryosuke Shimozawa

Keyword(s):

Phase Transition ◽

Lipid Bilayer ◽

Crystalline Phase ◽

Liquid Crystalline ◽

Liquid Crystalline Phase ◽

Vesicle Membrane ◽

Crystalline Phase Transition

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Mechanism of liposome destabilization by polycationic amino acids

Bioscience Reports ◽

10.1007/bf01207455 ◽

1995 ◽

Vol 15 (3) ◽

pp. 151-160 ◽

Cited By ~ 15

Author(s):

Richard M. Epand ◽

Wendy Lim

Keyword(s):

Phase Transition ◽

Amino Acids ◽

Phase Separation ◽

Physical Properties ◽

Crystalline Phase ◽

Emission Intensity ◽

Liquid Crystalline ◽

Liquid Crystalline Phase ◽

Lateral Phase Separation ◽

Presence And Absence

Polycationic amino acids induce the leakage and fusion of liposomes containing anionic lipids. We have investigated the nature and extent of the changes in membrane physical properties caused by these polypeptides which could result in the observed membrane destabilization. We found that in the range of pH 5 to pH 7 both poly-l-histidine and poly-l-lysine were ineffective in shifting the bilayer to hexagonal phase transition temperature of dielaidoylphosphatidylethanolamine, either in the presence of absence of 1-palmitoyl-2-oleoylphosphatidylserine. We also studied the gel to liquid crystalline phase transition properties of 1:1 mixtures of phosphatidylserine and phosphatidylethanolamine, both in dimyristoyl forms as well as the 1-palmitoyl-2-oleoyl forms, as a function of pH and in the presence and absence of polycationic amino acids. We observed that these two lipids were largely miscible at all pH values and in the presence and absence of the polypeptides. However, there was some increased tendency for phase separation at higher pH and in the absence of polypeptide. Thus neither changes in curvature strain nor lateral phase separation induced by the polycationic amino acids could account for their marked ability to induce leakage and fusion. Phosphatidylethanolamine labelled with pyrene on one of the acyl chains gives rise to fluorescent emission from both monomer and excimer forms. The ratio of emission intensity from these two forms is indicative of lateral phase separation and the degree of lateral mobility of this probe. In equimolar mixtures of the 1-palmitoyl-2-oleoyl forms of phosphatidylserine and phosphatidylethanolamine in the liquid crystalline phase at 30 °C we find little effect of pH on the ratio of excimer to monomer emission intensity. However poly-l-lysine markedly lowers the fraction of excimer emission from these liposomes through the pH range from 5 to 7. Poly-l-histidine lowers the excimer to monomer emission ratio at pH 5 but not at pH 7. This is opposite to what one would expect for lateral phase separation and is interpreted at being the consequence of the polypeptide lowering the rate of lateral diffusion of the lipids. This effect of poly-l-histidine is observed over a range of temperatures from 0 to 40°C in both gel and liquid crystalline phases. There is no evidence from the behaviour of the pyrene fluorescent probe for lipid interdigitation. We conclude that the promotion of leakage and fusion in anionic liposomes by polycationic amino acids is not a result of large changes in the physical properties or arrangements of the lipids but rather to a surface binding of the polyamino acids.

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