THE TRANSVERSE LOCATION OF FLUOROPHORES IN LIPID BILAYERS AND MICELLES AS DETERMINED BY FLUORESCENCE QUENCHING TECHNIQUES

Abstract— A fluorescence quenching technique has been used to determine the absolute partition coefficients of a set of n -doxyl stearates which partition between the aqueous and lipid phases of a phospholipid dispersion, and it is shown that the values of the coefficients vary in a systematic way depending on the position of the doxyl group on the acyl chain of the fatty acid. The n -doxyl stearates quench the fluorescence of n -(9-anthroyloxy) fatty acids in lipid bilayers, and consideration of the absolute partition coefficients of the quencher and of the microviscosity of the bilayer is necessary to extract information about the proximity of the fluorophore and quencher. In addition, quenching of the fluorescent fatty acids with a quencher which is small relative to the width of the lipid bilayer allows determination of both the absolute and local partition coefficients, the latter referring to a subvolume of the bilayer within which quenching occurs. The relationship between absolute and local partition coefficients is defined for micelles and bilayers and a method for determining the relative transverse positions of the anthroyloxy rings in these structures is described.