RESONANCE ENERGY-TRANSFER IN A MODEL SYSTEM OF MEMBRANES - APPLICATION TO GEL AND LIQUID-CRYSTALLINE PHASES

Resonance energy transfer between octadecyl rhodamine B (donor) and 1, 1',3,3,3',3'-hexamethylindotricarbocyanine (acceptor) was studied in a model system of membranes (large unilamellar vesicles of dipalmitoylp hosphatidylcholine), using both steady-state and time-resolved techniq ues, In the fluid phase (temperature=50 degrees C) the decay law and t he steady-state theoretical curve for energy transfer in two dimension s are verified. In the gel phase (temperature=25 degrees C) an apparen t reduction of dimensionality is observed, which is explained on the b asis of probe segregation to the defect lines (grain boundaries). An e stimation of the domain size from the model recovered linear probe con centrations is approximately 1750-2000 lipid molecules. In both phases , the existence of a fractal geometry was ruled out.