INFLUENCE OF VESICLE CURVATURE ON FLUORESCENCE RELAXATION KINETICS OFFLUOROPHORES

The effect of membrane curvature on the fluorescence decay of 2-p-tolu idinyl-naphthalene-6-sulfonic acid (TNS), 2-(9-anthroyloxy) stearic ac id (2-AS) and 12-(9-anthroyloxy)-stearic acid (12-AS) was investigated for egg lecithin vesicles of average diameter d(m) = 22 nm and 250 nm . The biexponential fluorescence decay of TNS at the red edge of the e mission spectrum was analysed according to the model of Gonzalo and Mo ntoro [1]. Over the entire temperature range (1-40 degrees C) the smal l TNS labelled vesicles showed significantly shorter solvent relaxatio n times tau(r) than their larger counterparts (e.g. 1.3 ns compared wi th 2.1 ns at 5 degrees C), indicating a higher mobility of the hydrate d headgroups in the highly curved, small vesicles. The fluorescence de cay of both AS derivatives is also biexponential. While the shorter de cay times (1-3 ns) are practically identical for small and targe vesic les, the longer decay times (5-14 ns) are identical only for 12-AS but not for 2-AS. This indicates that the microenvironment is similar in small and large vesicles deep in the membrane in spite of the differen ces in curvature.