Electron spin T2 of a nitroxyl radical at 250 MHz measured by rapid-scan EPR

Rapid-scan electron paramagnetic resonance (EPR) was used to measure the room temperature spin-spin relaxation time T-2 for the per-deuterated nitroxyl radical, 4-oxo-2,2,6,6-tetramethyl-piperidin-1-oxyl-d(16) in water at 250 MHz. Signals were recorded on a locally constructed system using either sinusoidal or triangular magnetic field scans. Values of T-2 were obtained by simulation of the rapid-scan response and were systematically shorter for the high-field line (m, = - 1) than for the m, = 0 or + 1 lines. For m, = + 1, the value of T-2 increased from 0.41 +/- 0.03 mu s at 0.5 mM to 0.53 +/- 0.03 mu s at 0.1 or 0.2 mM. For m, = - 1, T2 increased from 0.35 0.03 mu s at 0.5 mM to 0.42 +/- 0.03 mu s at 0.1 or 0.2 mM. These values put lower bounds on the values of T, for this nitroxyl at 250 MHz.