Chlorin e6-liposome interaction. Investigation by the methods of fluorescence spectroscopy and inductive resonance energy transfer

On the basis of spectral fluorescence and polarization measurements and results obtained on the luminescence quenching of the membrane fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH) by incorporated chlorin e 6 (chl e 6) molecules, it is shown that the interaction of the water-soluble pigment with smaller unilamellar lipid vesicles occurs by a mechanism of partition between the aqueous and lipid phases (partition coefficient K p = 6.7 × 1O 3) and provides rigid fixing of chl e 6 monomers at the boundary between the polar and non-polar parts of the lipid membrane. In terms of inductive resonance electronic excitation energy transfer between DPH and chl e 6 ( R o = 36.2 Å), we have analysed data on DPH fluorescence quenching under different conditions of chl e 6 localization in the lipid bilayer and have concluded that the incorporation of the pigment molecules into the vesicles from the aqueous phase occurs mainly into the external monolayer.