Localisation of BODIPY-labelled phosphatidylcholines in lipid bilayers

Abstract

A series of sn-2 acyl-labelled phosphatidyl-cholines (PC), bearing 4,4-difluoro-1-3-5-7-tetra-methyl-4-bora-3a,4a-diaza-s-indacene-8-yl (Me₄-BODIPY) at the end of the C_n-acyl chains were solubilised in unilamellar vesicles and studied with respect to the order and location of the Me₄-BODIPY (denoted: B) group. The obtained results are based on time-resolved electronic energy transfer from donors (2-(9-anthroyloxy)-stearic acid) localised in the lipid–water interface to acceptors BnPC (n = 3, 5, 7, 9, 11, 13, 15), as well as the energy migration among the Me₄-BODIPY groups of BnPC:s. The donor–acceptor and the donor–donor experiments strongly suggest that the Me₄-BODIPY group in BnPC tends to loop back close to the lipid–water interface. The Me₄-BODIPY groups, residing in the two bilayer leaflets, are located at approximately the same depth, and transversally separated by ca. 27 Å for all n-values. Close to the interface, the optimal transversal distribution widens somewhat with increasing length of the sn-2 acyl chain. The obtained order parameter profile of the BnPC:s is also compatible with such a location.