Relaxation rates for spirocyclohexyl nitroxyl radicals are suitable for interspin distance measurements at temperatures up to about 125 K

Between 65 and 175 K, nitroxyl radicals with spirocyclohexyl groups at the 2- and 6-positions of the piperidine ring exhibit spin echo dephasing rates that are slower than for nitroxyl radicals with 2,5-gem-dimethyl or 2,6-gem-dimethyl substituents that are currently used as spin labels, and are slow enough to permit DEER measurements at temperatures up to about 125 K for spin labels with analogous ring structures.