Diffusion in two dimensions: Comparison between diffusional fluorescence quenching in phospholipid vesicles and in isotropic solution

The formalism developed in a previous paper is applied to the study of diffusion in an isotropic medium and in phospholipid vesicles as models for spherical and cylindrical diffusion theory, respectively. Pyrene was chosen as a fluorescence probe and diffusion was studied by observing quenching of monomer fluorescence by excimer formation at high pyrene concentration. The process of diffusion-dependent fluorescence quenching was better described by a theory which takes into account the finite time required to establish a diffusion gradient than by a time-independent theory. Furthermore, better fit to the data was obtained when the appropriate diffusion model (spherical or cylindrical) was used. The diffusion coefficient for pyrene in dimyristoyl lecithin at 30 °C was 3×10−8 cm2/sec. Proton magnetic resonance was used to determine the location of pyrene in the lipid.