SPECTRAL PROPERTIES OF 3,3'-DIETHYLOXADICARBOCYANINE INCLUDED IN PHOSPHOLIPID LIPOSOMES

Absorption and fluorescence data of 3,3'-diethyloxadicarbocyanine iodi de (DODCI) bound with phospholipid liposomes with different polar head groups were analyzed. The lipid-bound dye was found to be a mixture o f monomers and non-fluorescent H-aggregates (including dimers). Also, the amounts of each form were dependent on the lipid species and on th e lipid/dye molar ratio. Highly efficient aggregation was ob served in the presence of negatively charged liposomes composed of phosphatidyl serine and phosphatidylinositol-4,5-diphosphate. The aggregation was f ollowed by strong fluorescence quenching of the monomeric form present in the system, which was interpreted as a result of non-radiative exc itation energy transfer from the dye monomers to the aggregates. Doubl e exponential decay functions were found for the emission of the lipid -bound dye. (C) 1997 Elsevier Science S.A.