USE OF ETA-(9-ANTHROYLOXY) FATTY-ACIDS TO DETERMINE FLUIDITY AND POLARITY GRADIENTS IN PHOSPHOLIPID-BILAYERS

A set of n-(9-anthroyloxy) fatty acid probes (n = 2, 6, 9, 12) have been used to examine gradients in fluorescence polarization, lifetime (TF), relative quantum yield (φrel) and positions of emission maxima (γmax) through bilayers composed of synthetic phospholipids. The fluorophores of these probes report the environment at a graded series of depths from the surface to the centre of the bilayer structure. 1. 1. Polarizations decrease as the fluorophore is moved deeper into the bilayer indicating greater rotational motion of the fluorophore in the hydrocarbon core of the bilayer. 2. 2. The different responses of the probe diphenylhexatriene and the anthroyloxy fatty acids to the action of cholesterol on lipid bilayers are discussed in terms of the orientation of these probes in the bilayer and the types of anisotropic rotational motions which result in depolarization of fluorescence. 3. 3. Stearic acid derivatives which have the fluorophore in the 6-, 9- and 12 positions along the acyl chain have a similar response to solvent polarity as measured by values of λmax and φrel in a variety of organic solvents. 4. 4. The position of the emission maximum has little dependence on solvent viscosity, but viscosity does change the degree of vibrational structure seen in the emission spectrum. The vibrational structure itself may be used as an indication of the 'meiroviscosity' gradient in the transverse plane of the bilayer. © 1979.