Image:Nitroxide Clore Iwahara 2009.jpg

This are example nitroxide spin labels used for biomolecular NMR. Image is taken from Clore_Iwahara_2009, chemical reviews. (Clore, G. M., and Iwahara, J. (2009) Theory, practice, and applications of paramagnetic relaxation enhancement for the characterization of transient low-population states of biological macromolecules and their complexes, Chem Rev 109, 4108-4139)