ESR Spatiotemporal Measurement Using the Rapid Field Scan L-Band ESR-CT System for Determination of Rate Constants of Nitroxide Radical Reduction

The rate constants of nitroxide reduction by ascorbate ion were determined from a time-series measurement of ESR images, that is, ESR spatiotemporal images, which were measured with a rapid field scan L-band ESR-CT system. Two test tubes containing the phosphate buffer solutions of 3-carbamoyl-2,2,5,5-tetramethylpyrrolidin-l-yloxy (C-PROXYL) and ascorbate ion with different concentrations were placed together in the loop-gap resonator and a time-series measurement of 2-dimensional ESR images were obtained. The first-order rate constants for each reduction were determined from the time course of the total gray scale at each test tube region. These rate constants agreed with those measured individually from L-band or X-band ESR spectra.