Polarization modulation infrared reflection-absorption spectroscopy studies of the influence of perfluorinated compounds on the properties of a model biological membrane.

A combination of the Langmuir-Blodgett and Langmuir-Schaefer techniques has been used to build a 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) bilayer at a Au(111) electrode surface with hydrogen-substituted acyl chains in the top leaflet (solution side) and deuterium-substituted acyl chains in the bottom leaflet (gold side). Polarization modulation infrared reflection-absorption spectroscopy was used to determine changes in the conformation and orientation of the acyl chains of DMPC caused by the incorporation of two selected perfluorinated compounds, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), into the top leaflet of the bilayer. The incorporation of perfluorinated compounds into the DMPC bilayer caused a broadening of the methylene peaks and a shift in the methylene band positions toward higher frequencies. In addition, the tilt angle of the acyl chains decreased in comparison to the tilt angle of a pure DMPC bilayer. The reported tilt angles were smaller upon insertion of PFOS ( approximately 24 degrees ) than in the presence of PFOA ( approximately 30 degrees ). Overall, the results show that the incorporation of the perfluorinated acids has an effect on the bilayer similar to that of cholesterol by increasing the membrane fluidity and thickness due to a decrease in the tilt angle of the acyl chains.