Paramagnetic fluorescence quenching in a model membrane: a consideration of lifetime and temperature

To expand our understanding of paramagnetic quenching in membranes, the rel ationship between fluorophore excited-state lifetime (tau), temperature, an d the collisional quenching was studied. Specifically, the ability of tempo to quench the steady-state and time-resolved emission from five lipophilic fluorophores (diphenylhexatriene, perylene, phenanthrene, pyrene, and trip henylene) partitioned into egg phosphatidylcholine (EggPC) liposomes was ex amined. Also, the temperature dependence of spin-labeled androstane to quen ch the emission (steady-state and time-resolved) from perylene in EggPC lip osomes was determined. Unexpectedly, in EggPC liposomes, the apparent quenc hing efficiency decreased with increasing tau until the effect leveled off above similar to 20 ns. Moreover, in EggPC liposomes, dynamic quenching dec reased with increasing temperature. The results suggest that in membranes, paramagnetic quenching is more complex than generally recognized. (C) 1999 Elsevier Science B.V. All rights reserved.