Distance measurements using partial donor-donor energy migration within pairs of fluorescent groups in lipid bilayers

For distance measurements the fluorescence relaxation was explored within pairwise interacting chemically identical, but photophysically different fluorescent groups. The recently developed theory (Kalinin, S. V.; et al. Spectrochim. Acta, Part A 2002, 58, 1087-1097) of partial donor-donor energy migration (PDDEM) was tested on lipid vesicles as a model system, which, for example, enables arrangement of a pH gradient between the inside and outside of the lipid bilayer. Time-correlated single-photon counting and steady-state fluorescence experiments were per-formed on mono- and bis-lipid derivatives of fluorescein solubilized in lipid bilayers. The PDDEM approach was successfully applied in the analyses of the different experiments. The distances extracted between the fluorescein groups of bis-fluorescein derivatives in lipid vesicles composed 1,2-dioleoyl-sn-glycero-3-phosphocholine and 1,2-dimyristoyl-sn-glycero-3-phosphocholine were found to be in reasonable agreement with independent measurements of the bilayer thickness.