Location and orientation of DODCI in lipid bilayer membranes: effects of lipid chain length and unsaturation

The location and orientation of a linear dye molecule, DODCI, in lipid bilayer membrane were determined by the effect of viscosity and refractive index of the aqueous medium on the fluorescence properties of the dye bound to the membrane. The membrane-bound dye is solubilized in two sites, one near the surface (short fluorescence lifetime) and another in the interior of the membrane (long lifetime). The ratio of the dye in the two locations and the orientation of the dye (parallel or perpendicular to the membrane) are sensitive to the lipid chain length and unsaturation in the alkyl chain. The fraction of the dye in the interior region is higher for short alkyl chains (C12 > C14 >C16 much greater than C18 approximate to C20) and in unsaturated lipids (C14:1 > C14:0, C16:1 > C16:0). These experimental results are consistent with the general principle that the penetration of an amphiphilic organic molecule Into the interior region of the membrane is more when the structure of the bilayer is more fluid-like. (C) 1999 Elsevier Science B.V. All rights reserved.