Phase transition affects energy transfer efficiency in phospholipid vesicles

The fluorescence quenching of 6-propionyl-2-dimethylaminonaphtalene (PRODAN) and 6-dodecanoyl-2-dimethylaminonaphtalene (LAURDAN) by octadecyl rhodamine B (ORB) in a model system of small unilamellar vesicles (SUV) of dipalmitoylphosphatidyl-choline (DPPC) was investigated. Non-linear Stern-Volmer behaviour was observed in both systems in the gel phase (25 °C) and in the fluid phase (50 °C), resulting from association processes and from static quenching. The relative quenching efficiencies of both dyes depend on the phase state of the bilayer and indicate a deeper incorporation of PRODAN and LAURDAN into the membrane in its fluid phase than in its gel phase.