Local polarity at the polar head level of lipid vesicles using dansyl fluorescent probes

The effect of different parameters on the interfacial polarity of phospholipid vesicles was studied using two polarity-sensitive fluorescent probes, dansyldihexadecylamine (DA) and dansylphosphatidylethanolamine (DPE), The analysis was based on the Stokes shift and steady-state fluorescence anisotropy changes with different parameters. The influence of surface curvature, lipid composition, and surface charge density was analyzed in small and large unilamellar vesicles and in multilamellar vesicles at different temperatures and in different lipid phase states, The membranes showed significant polarity, packing constraints, and hydration degree changes at the polar head level when different variables were imposed. The comparative analysis of the probe response demonstrates that each dansyl derivative yields different information about membrane changes. DA appears to be more sensitive to packing constraints and hydration, probably due to its molecular structure and location at the interface level. DPE seems to sense polarity values averaged in the region where its polar head can pivot, and is, as expected, susceptible to electrostatic interactions. (C) 1998 Academic Press.