INTERACTION OF n-DECANE WITH EGG YOLK PHOSPHATIDYLCHOLINE BILAYERS: EXCIMER FLUORESCENCE PROBE AND X-RAY DIFFRACTION STUDY

The influence of n-decane on the lipid bilayer thickness and on the frequency of lateral collisions of the excimer fluorescence probe 1-pyrenedodecanoic acid was studied in unilamellar and multilamellar egg yolk phosphatidylcholine (EYPC) model membrane systems. In multilamellar systems, the n-decane molecules are located predominantly in the bilayer center between apposing monolayers. Up to n-decane:EYPC=1:1 molar ratio studied, this location brings about a significant increase in the bilayer thickness, but the frequency of the excimer fluorescence probe collisions is not influenced. The collision frequency decreases significantly in unilamellar liposomes up to n-decane:EYPC=0.4:1 molar ratio. The bilayer thickness does not change up to this molar ratio, the n-decane molecules are located thus in the bilayer paralell to the lipid acyl chains. At higher molar ratios, n-decane slightly increases the bilayer thickness in unilamellar liposomes without having any effect on the excimer probe collision frequency. This suggests location in the center of bilayer like in the multilamellar systems. The different curvature radii can cause differences in the n-decane location in multiand unilamellar systems. Possible consequences for n-decane biological effects are discussed.