Lateral organization of pyrene-labeled lipids in bilayers as determined from the deviation from equilibrium between pyrene monomers and excimers

Abstract

In lipid bilayers, pyrene and pyrene-labeled lipids form excimers in a concentration-dependent manner. The aromatic amine N,N-diethylaniline (DEA), which has a high membrane-to-medium partition coefficient, quenches the monomers only, and therefore it is expected that under conditions in which the monomers are in equilibrium with the excimers due to the mass law, the Stern-Volmer coefficient (K(sv)) for monomers (M), defined as K(M), should be identical to that of the excimer (E), defined as K(E), and K(E)/K(M) = 1.0. This is indeed the case for pyrene and pyrene valerate in egg phosphatidylcholine small unilamellar vesicles. However, for pyrene decanoate and pyrene dodecanoate in these vesicles, and for N-[12-(1- pyrenyl)dodecanoyl]-sphingosylphosphocholine in a matrix of either N-stearoyl sphingosylphosphocholine or 1-palmitoyl-2-oleoyl phosphatidylcholine, K(E)