Chapter 15. Introduction to Electron Paramagnetic Resonance (EPR) of Nitroxides

The unpaired electron on a nitroxide makes electron paramagnetic resonance (EPR) the method of choice to characterize the radicals and environment. Anisotropic g-values and anisotropic nitrogen nuclear hyperfine couplings cause EPR spectra of nitroxides to sensitively report their environment and their motion in continuous-wave spectra. Electron spin relaxation times of nitroxide radicals are in a range that is useful for pulsed EPR spectroscopy, with applications to collisions between paramagnetic species, thereby facilitating oximetry, and for measuring distances between two nitroxides or between nitroxides and another paramagnetic species. Nitroxides can be designed with EPR properties optimized for specific applications.