DETECTION AND IMAGING OF OXYGEN-CENTERED FREE-RADICALS WITH LOW-FREQUENCY ELECTRON-PARAMAGNETIC RESONANCE AND SIGNAL-ENHANCING DEUTERIUM-CONTAINING SPIN TRAPS

We have identified and imaged oxygen-centered free radicals with low-frequency electron paramagnetic resonance (EPR) spectroscopy and deuterium-containing spin traps to probe the feasibility of spin trapping deep in large (approximately 10 cm), heterogeneous aqueous/hydrophobic (e.g., biologic) systems. Spectra at 250 MHz from spin trapping superoxide and hydroxyl radicals in aqueous solutions of deuterated analogs of DMPO (5,5-dimethyl-1-pyrroline-1-oxyl) were obtained, and the superoxide measurements were compared with those at X-band. Modification of X-band spectral line positions occurs due to the breakdown of the high-field approximation. Solution of the Breit-Rabi equations governing low-field measurements reproduces most of the observed line position changes. Sensitivity is found to scale with (frequency)N, with N approximately 1.6 largely compensated for by the increase in sample volume. A two-dimensional spectral-spatial image of a phantom filled with heterogeneous concentrations of spin trap and subjected to gamma radiation from Co-60 is presented.