ESR lineshapes and kinetic behavior of nitroxide spin probes in micellar solutions

The ESR spectrum of the nitroxide radical 2,2,6,6-tetramethylpiperidine-N-oxide (TEMPO) has been investigated in aqueous solutions of the following surfactants:n-octylammonium bromide, sodiumn-octylsulfonate,n-decylammonium bromide,n-docecyltrimethylammonium bromide, and sodiumn-dodecylsulfate. The spectra were recorded at 25° C as function of surfactant concentration in the ranges 0–0.5m for the C₁₀ and C₁₂ compounds and 0–1.0m for the others. Analysis of the spectra using computer simulation methods yields the hyperfine coupling constanta _H and the widthW _H of the partially resolved lines in the proton hyperfine structure. Changes in these variables with surfactant concentration are interpreted from medium effects on the magnetic properties of the radical, kinetics of radical-micelle interactions, and rotational dynamics of the nitroxide probe in these solutions.