Lateral Diffusion and Molecular Interaction in a Bilayer Membrane Consisting of Partially Fluorinated Phospholipids

Abstract

Fluorinated lipids and surfactants are attractive biomimetic materials for the extraction and reorganization of membrane proteins because of the biological inertness of fluorocarbons. We investigated the fundamental physical properties of a partially fluorinated phospholipid (F4-DMPC), such as phase transition, area thermal expansion, and lateral lipid diffusion, to evaluate the intermolecular interaction of F4-DMPC in the hydrophobic region quantitatively on the basis of free-volume theory. Fluorescence microscope observation of the supported lipid bilayer (SLB) of F4-DMPC showed that the phase transition between the liquid crystalline and gel phases occurred at 5 °C and that the area thermal expansion coefficient was independent of the temperature near the phase transition temperature. We performed a single particle tracking of the F4-DMPC-SLB on a SiO/Si substrate, to measure the diffusion coefficient and its temperature dependence. The apparent activation energy (E') of lateral lipid diffusion, which is an indicator of intermolecular interaction, was 39.1 kJ/mol for F4-DMPC, and 48.2 kJ/mol for a nonfluorinated 1,2-dioleoyl-sn-glycero-3-phosphocholine as a control. The difference of 9 kJ/mol in E' was significant compared with the difference due to the acyl chain species among nonfluorinated phosphatidylcholine and also that caused by the addition of cholesterol and alcohol in the bilayer membranes. We quantitatively evaluated the attenuation of intermolecular interaction, which results from the competition between the dipole-induced packing effect and steric effect at the fluorocarbon segment in F4-DMPC.

Morphology and Physical Properties of Hydrophilic-Polymer-Modified Lipids in Supported Lipid Bilayers

“…D of the PEG-SLB at C PEG = 0−5% is ∼2 μm 2 /s, which is similar to that of the DOPC-SLB without the PEG-lipid. 44,47,51 PEG-DSPE is considered to be existing in both leaflets of the SLB as in the previous study of POPC-SLB containing PEG-DOPS. 25 Decoupling between the upper and lower leaflets was not observed in FRAP 62 or AFM 63 observations.…”

Fractal analysis of lateral movement in biomembranes

“…The application of the fractal model to describe lateral movement in biomembranes, described in this paper, also gives the proper value of the diffusion coefficient, but the DOPE speed calculated as λ / τ = 257 μm/s is several orders of magnitude lower than the thermal speed. This is thought to be caused by intermolecular interactions in biomembranes (Forstner et al 2008 ; Bag et al 2014 ; Okamoto et al 2016 ) which alter both the walking molecule velocity (Selle et al 2004 ; Hall and Hoshino 2010 ) and the duration of one random walk step (Pace and Chan 1982 ; Ayton and Voth 2004 ).…”

“…A sharp transition from free diffusion to slowed diffusion was observed at a potential depth of about 6 k B T , and then the diffusion coefficient decayed exponentially to a value five orders of magnitude lower at 20 k B T (Forstner et al 2008 ). This value corresponds to an upper Arrhenius activation energy measured for lateral lipid diffusion, 50 kJ/mol, which is an indicator of intermolecular interaction (Bag et al 2014 ; Okamoto et al 2016 ).…”

(Cryo)Transmission Electron Microscopy of Phospholipid Model Membranes Interacting with Amphiphilic and Polyphilic Molecules

“…By replacing one or several hydrogen atoms in the tail region with fluorine atoms, the self-assembly properties of these fluorinated lipids change considerably. Since the early 1980s, the synthesis and self-assembly of fluorinated lipids have been of continuous interest, especially because of the increased stability of the vesicles thus formed [49,50,51] that became suitable for drug-delivery applications [52]. The shape of the vesicles was visualized by negative stain, freeze–fracture, and cryoTEM [52,53,54,55].…”