X-band continuous-wave (cw) EPR was carried out at room temperature on a Bruker ELEXSYS II EPR spectrometer at 9.8 GHz with 100 kHz modulation frequency, 2 G modulation amplitude, 2 mW power, and 20 dB attenuation. Aliquots of 150 μl samples were contained in WG-812 quartz flat cell (Wilmad) and the in situ irradiation during EPR experiments was provided by a ~8 watt UVA system placed in front of the optical window of the resonator. Each spectrum was acquired as a mean of 10 accumulated scans. The C-PC concentration for all EPR experiments were kept the same at 1 mg/ml. Spectral simulations were performed by EasySpin16 (link) integrated into MATLAB using the “esfit” least-squares function and were used to assist with signal assignments and g-value determination.
For spin trapping experiments, the trapping agents, 2,2,6,6-tetramethylpiperidine (TEMP) or 5,5-dimethyl-1- pyrroline N-oxide (DMPO), were freshly prepared in DMSO at 10-fold concentration and mixed with C-PC samples at pH 3.0–9.0 before the measurements to a final concentration of 1.0 × 10−2 M. For quenching experiments, 8 mM sodium azide (NaN3) were added to the same C-PC samples prior to the addition of 1.0 × 10−2 M DMPO and the EPR measurements.
For spin trapping experiments, the trapping agents, 2,2,6,6-tetramethylpiperidine (TEMP) or 5,5-dimethyl-1- pyrroline N-oxide (DMPO), were freshly prepared in DMSO at 10-fold concentration and mixed with C-PC samples at pH 3.0–9.0 before the measurements to a final concentration of 1.0 × 10−2 M. For quenching experiments, 8 mM sodium azide (NaN3) were added to the same C-PC samples prior to the addition of 1.0 × 10−2 M DMPO and the EPR measurements.