Fluorescence decay kinetics of pyrene in membrane vesicles.

The fluorescence decay kinetics of pyrene incorporated into artificial and natural membrane vesicles has been studied by pulse fluorimetry. The emission of monomeric pyrene and its excimer embedded in sonicated liposomes prepared from dipalmitoylphosphatidylcholine and a mixture of this phospholipid and dipalmitoylphosphatidylserine follows a multiple exponential decay law at temperatures both below and above their thermal transitions (10--48 degrees C). When pyrene is incorporated into fragmented skeletal sarcoplasmic reticulum vesicles, the emission decay exhibits similar multiple exponential character. The decay of the monomer in the phospholipid vesicles can be adequately described by three exponential terms. The experimental decays observed with both types of vesicles deviate significantly from a previously proposed model in which departure of the decay of pyrene monomer from monoexponentiality is qualitatively related to a time dependence in the diffuslipid vesicles can be adequately described by three exponential terms. The experimental decays observed with both types of vesicles deviate significantly from a previously proposed model in which departure of the decay of pyrene monomer from monoexponentiality is qualitatively related to a time dependence in the diffuslipid vesicles can be adequately described by three exponential terms. The experimental decays observed with both types of vesicles deviate significantly from a previously proposed model in which departure of the decay of pyrene monomer from monoexponentiality is qualitatively related to a time dependence in the diffusion-controlled formation of excimers from ground state and excited monomers. It is suggested that the observed decays are compatible with a reaction scheme involving excited state interaction.