Spin exchange of nitroxyl radicals in H2O and D2O.

By means of continuous wave electron spin resonance (cw ESR) in the X and L bands, the spin exchange of series of different concentrations of the spin probes 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL), and 4-(trimethylamino)-2,2,6,6-tetramethylpiperidine-1-oxyl iodide (CAT-1) in H(2)O and D(2)O have been examined. The rate constants k(e) of the spin exchange have been determined by complete spectra simulations, as well as directly from hyperfine line broadenings and concentration depending line shifts. The obtained results showed a good agreement.