Heterogeneous Rotational Diffusion in Lipid Monolayers

The rotational correlation time of the lipid probe NBD-PC is measured using fluorescence anisotropy for two lipid species. We measure the rotational diffusion in a monolayer of DPPC which displays a phase transition at room temperature from the liquid-expanded to the liquidcondensed phase. The constant rotational diffusion of the probe throughout the phase transition reflects the measurement of dynamics in only the liquid-expanded phase. We contrast the dynamic changes during this phase coexistence to the continuous density increase observed in DMPC at room temperature. We observe a non-exponential decay of the probe diffusion consistent with heterogeneity of the orientational dynamics.