Effect of subtransition in 1,2-dipalmitoylphosphatidylcholine model membrane on the spin probe motion

The effect of subgel----gel phase transition (subtransition) on conventional electron spin resonance spectra of cholestane, fatty acid and alkylammonium-type spin probes has been studied in aqueous 1,2-dipalmitoyl-sn-phosphatidylcholine dispersions. The cooperative onset of the cholestane spin probe rotation about its long axis, with an effective correlation time of 2-3 ns, has been detected at a temperature coinciding with the calorimetric substransition, indicating onset of the host lipid rotational motion. The lipid rotation results in dissolution of the spin probe clusters in the host lipid. In the gel phase, the lateral distribution of impurity molecules is more isotropic than in the subgel phase.