EPR LINESHAPES AND DYNAMICS OF TEMPOL SOLUBILIZED IN THE AQUEOUS MICROPHASE OF LECITHIN CYCLOHEXANE/WATER REVERSE MICELLES/

EPR spectral lineshapes of the spin probe TEMPOL hydroxy-2,2,6,6-tetra methyl-1-piperidinyl-1-oxyl), dissolved in the aqueous microphase of e gg-yolk lecithin/cyclohexane/water reverse micelles, have been studied as a function of the water/lecithin molar ratio, R. Although the spec tral profiles reveal in general that the spin probe undergoes a 'fast' reorientational motion in the aqueous phase, the actual lineshapes ar e found to be non-lorentzian. It is shown that, for an accurate linesh ape analysis, the motion-dependent Lorentzian linewidths have to be co nvoluted with an appropriate motion-invariant Gaussian broadening fact or representing unresolved isotropic superhyperfine interactions. Fast reorientational correlation times (tau), assessed from our iterative lineshape fitting procedure, span the range from 6.0 x 10(-10) to 3.0 x 10(-10) s as the R-value is increased.