Structure and Thermotropic phase Behavior of Fluorinated Phospholipid Bilayers: A combined Attenuated Total Reflection FTIR Spectroscopy and Imaging Ellipsometry Study

Abstract

Lipid bilayers consisting of lipids with terminally perfluoroalkylated chains have remarkable properties. They exhibit increased stability and phase-separated nanoscale patterns in mixtures with nonfluorinated lipids. In order to understand the bilayer properties that are responsible for this behavior, we have analyzed the structure of solid-supported bilayers composed of 1,2-dipalmitoylsn-glycero-3-phosphocholine (DPPC) and of a DPPC analogue with 6 terminal perfluorinated methylene units (F6-DPPC). Polarized attenuated total reflection Fourier-transform infrared spectroscopy indicates that for F6-DPPC, the tilt of the lipid acyl chains to the bilayer normal is increased to 39° as compared to 21° for native DPPC, for both lipids in the gel phase. This substantial increase of the tilt angle is responsible for a decrease of the bilayer thickness from 5.4 nm for DPPC to 4.5 nm for F6-DPPC, as revealed by temperature-controlled imaging ellipsometry on microstructured lipid bilayers and solution atomic force microscopy. During the main phase transition from the gel to the fluid phase, both the relative bilayer thickness change and the relative area change are substantially smaller for F6-DPPC than for DPPC. In light of these structural and thermotropic data, we propose a model in which the higher acyl-chain tilt angle in F6-DPPC is the result of a conformational rearrangement to minimize unfavorable fluorocarbon-hydrocarbon interactions in the center of the bilayer due to chain staggering.

The influence of salinity on surfactant miscibility in mixed dipalmitoylphosphatidylcholine – perfluorooctadecanoic acid monolayer films

“…Comparing these results to the molecular length of DPPC (2.8 nm [36] and others) suggests that with a pure water subphase, DPPC deposits nearly normal to the mica surface but takes on an angle of $60°f rom vertical upon deposition from a saline subphase. The precise explanation for the difference in tilt angle of the surfactants with salinity is presently unclear (C18F also adopts a significant tilt angle with respect to the solid substrate, as reported below), though DPPC adopting a significant tilt angle to the substrate normal is consistent with reports for a number of phospholipid systems, including those described by Schuy et al [37] for DPPC and partially fluorinated DPPC, as well as those by Katsaras [38] for DPPC multilayers. Images of pure C18F films are shown in Fig.…”

Pressure cell for investigations of solid–liquid interfaces by neutron reflectivity

“…Protocols have been developed to self-assemble and immobilize single lipid bilayers and multibilayers as well as proteins at solid-liquid interfaces for further study under physiological conditions by neutron reflectivity 2 and in situ surface sensitive infrared spectroscopy. 3 These systems are of particular interest as they are archetypes of any cell membrane. Many biomolecules can be coupled to those membranes or polymer brushes grafted to solid supports.…”

SEIRA Spectroscopy on a Membrane Receptor Monolayer Using Lipoprotein Particles as Carriers

“…Orientation of the NABB particles in the monolayer relative to the surface Using the linear dichroism of the CH stretch bands of a lipid bilayer, the orientation of lipids in the lipoprotein particles and, hence, the orientation of the particles themselves, relative to the surface, can be determined. Polarized ATR-FTIR spectroscopy of oriented dry multilamellar films of POPC vesicles was used to produce component spectra A xy and A z for polarization in the xy-plane of the bilayer and along the z axis perpendicular to it, respectively, as described previously (42) (Fig. 3 A, inset).…”