Properties and the locations of a set of fluorescent probes sensitive to the fluidity gradient of the lipid bilayer.

The synthesis and properties of a set of four fluorescent probes (n-(9-anthroyloxy) fatty acids, n = 2, 6, 9, 12) sensitive to the fluidity gradient of the lipid bilayer are described. Fluorescent quenching experiments show that the probes locate at a graded series of depths in the bilayer. A fifth probe, methyl-9-anthroate, locates near the bilayer centre. As an example of their application, the probes are used to study the phase transitions of dipalmitoyl phosphatidyl-choline. Changes in the rotational relaxation times of the probes across the transitions are more pronounced at the centre of the bilayer than at the surface.