Jes fr 30 free radical monitor

The ESR experiments were carried out on a JES-FR 30 Free Radical Monitor (JEOL Ltd., Tokyo, Japan). Operating conditions of the ESR spectrometer were: power, 4 mW; modulation width, 0.1 mT; time constant, 0.3 s. Magnetic fields were calculated by the splitting of MnO (ΔH_3–4 = 8.69 mT).

An HPLC used in the HPLC-ESR consisted of a model 7125 injector (Reodyne, Cotati, CA), a model L-7100 pump (Hitachi Ltd., Ibaraki, Japan). A semi-preparative column (300 mm long × 10 mm i.d.) packed with TSKgel ODS-120T (TOSOH Co., Tokyo, Japan) was used. Flow rate was 2.0 ml/min throughout the HPLC-ESR experiments. For the HPLC-ESR, two solvents were used: solvent A, 50 mM acetic acid; solvent B, 50 mM acetic acid/acetonitrile (20/80, v/v). A following combination of isocratic and linear gradient was used: 0–40 min, 100% A to 20% A (linear gradient); 40–60 min, 80% B (isocratic). The eluent was introduced into a model JES-FR30 Free Radical Monitor (JEOL Ltd.). The ESR spectrometer was connected to the HPLC with a Teflon tube, which passed through the center of the ESR cavity. The operating conditions of the ESR spectrometer were: power, 4 mW; modulation width, 0.2 mT; time constant, 1 s. The magnetic field was fixed at the third peak in the double-triplet ESR spectrum (α^N = 1.58 mT and α^Hβ = 0.26 mT) of the 4-POBN radical adducts (Fig. 1).