Study of energy transfer from 7-amino coumarin donors to the rhodamine 6G acceptor in lecithin vesicles and sodium taurocholate-lecithin mixed aggregates.

The energy transfer using 7-amino coumarin dyes as the donor and rhodamine 590 (Rh6G) as the acceptor was investigated in lecithin vesicles and sodium taurocholate (NaTC)-lecithin mixed aggregates using steady-state and time-resolved fluorescence spectroscopy. All energy transfer parameters were calculated. The coumarin 153-Rh6G pair is the most efficient donor-acceptor pair as reflected by the value of k(ET). With addition of NaTC in lecithin, in the case of the coumarin 153-Rh6G pair, the energy transfer rate or efficiency does not change very much, whereas in the case of the coumarin 151-Rh6G pair, the energy transfer rate decreases 2-fold upon going from lecithin vesicles to NaTC-lecithin mixed aggregates where the molar ratio is 2.5. It is mainly due to the deeper location of coumarin 153 in the lipid bilayer or in mixed aggregates. Rotational relaxation data also support this idea.