Da. Vandersijs et al., THE INTERPRETATION OF FLUORESCENCE ANISOTROPY DECAYS OF PROBE MOLECULES IN MEMBRANE SYSTEMS, Chemical physics letters, 216(3-6), 1993, pp. 559-565
Previous analyses of the fluorescence anisotropy decays of 1- rimethyl
ammonio)-6-phenyl]-phenyl-1,3,5-hexatriene (TMA-DPH) probe molecules i
n lipid vesicles using the Brownian rotational diffusion model yield o
rientational distribution functions with a significant population of m
olecules with their axes parallel to the bilayer plane. We show that t
his unsatisfactory situation arises from the way the model fits the fa
st decaying components of the fluorescence anisotropy. A plausible and
consistent description of the anisotropy decay is obtained if these c
omponents are ascribed to fast, though restricted, local motions of th
e probe molecules within a slowly rotating ''cage'' in the lipid struc
ture. The ''cage'' may be envisaged as a cavity between the lipid mole
cules, so that its position and orientation changes with the internal
motions of the hydrocarbon chains. While this approach utilizes five a
djustable parameters in the least-squares fits, it has the merit of yi
elding unimodal distribution functions with the TMA-DPH molecules pref
erentially oriented along the normal to the local bilayer surface.