The interpretation of the time-resolved fluorescence anisotropy of diphenylhexatriene-phosphatidylcholine using the compound motion model.

Time-resolved fluorescence anisotropy experiments on lipid membranes can provide estimates of the molecular order and motion on microscopic scales. For the analysis of anisotropy data the so-called compound motion model was recently introduced to overcome problems with conventional models. We show that this novel model gives good fits for the time-resolved anisotropy of the fluorescent probe diphenylhexatriene-phosphatidylcholine (DPHPC) and can be successfully used to interpret experiments with DPHPC embedded in small unilamellar vesicles of the lipids DMPC, POPC, DOPC, DLPC, DERPC, DOPE, POPE, EGGPG and SQDG. The lifetime and order parameters are found to be intermediate between those found for the related DPH and TMA-DPH fluorescent probes, while the rotational diffusion of DPHPC is much slower. These findings can be rationalised in terms of the position of the DPH-fluorophore of DPHPC in the bilayer.