Analysis of the ESR spectra of the cholestane spin label in oriented multibilayers of lecithin and cholesterol in the gel state

Abstract

The ESR spectra of the cholestane spin label in macroscopically oriented multibilayers of dipalmitoyllecithin and cholesterol have been studied in the temperature region from −17 to 40°C, below the liquid crystalline transition temperature of these systems. A qualitative analysis of the angular dependence of the powderlike ESR spectra is given, showing that in the pure lecithin system the molecules are tilted, whereas in multibilayers with 10 mole % cholesterol or more, no tilt of the molecules is found. The ESR spectra were computer simulated, using a simple exponential distribution function for the orientation of the spin label molecules in the bilayer, in terms of a static tilt angle and spread angle. In addition the components of the g-factor and hyperfine tensors of the cholestane spin label have been determined. A comparison has been made of the components of the g-factor and hyperfine tensors obtained from the computer simulation and components reported in the literature, which have been obtained with spin labels in single-crystal hosts.