TIME-DOMAIN SIMULATIONS OF THE INFLUENCE OF EXCHANGE ON CW-ESR LINESHAPES AND ELECTRON-SPIN ECHO EXPERIMENTS

The dynamics of lipid molecules in reconstituted membrane systems can be investigated using pulsed electron spin resonance (ESR) experiments monitoring the decay of the Hahn spin echo of nitroxide probes. Of pa rticular importance is the determination of the exchange rates of the lipids between the immobilized layer around the protein molecules and the bulk lipid bilayer. Here we show that this exchange process can be incorporated in a straightforward way into numerical simulations of b oth electron spin echo (ESE) experiments and continuous wave electron spin resonance (CW-ESR) spectra. To this end we exploit trajectories o f the stochastic orientations of the probe molecules. The simulations indicate that experimental Hahn echo signals will be observed from a l ipid-protein system if the residence time of a nitroxide label in the boundary layer is longer than 200 ns. (C) 1998 Elsevier Science B.V. A ll rights reserved.