LOCAL POLARITY AT THE POLAR HEAD LEVEL OF LIPID VESICLES USING DANSYLFLUORESCENT-PROBES

The effect of different parameters on the interfacial polarity of phos pholipid vesicles was studied using two polarity-sensitive fluorescent probes, dansyldihexadecylamine (DA) and dansylphosphatidylethanolamin e (DPE), The analysis was based on the Stokes shift and steady-state f luorescence anisotropy changes with different parameters. The influenc e of surface curvature, lipid composition, and surface charge density was analyzed in small and large unilamellar vesicles and in multilamel lar vesicles at different temperatures and in different lipid phase st ates, The membranes showed significant polarity, packing constraints, and hydration degree changes at the polar head level when different va riables were imposed. The comparative analysis of the probe response d emonstrates that each dansyl derivative yields different information a bout membrane changes. DA appears to be more sensitive to packing cons traints and hydration, probably due to its molecular structure and loc ation at the interface level. DPE seems to sense polarity values avera ged in the region where its polar head can pivot, and is, as expected, susceptible to electrostatic interactions. (C) 1998 Academic Press.