Figure A1.
Quenching of the transient bi-radical by nitric oxide. Electron paramagnetic resonance spectrum obtained upon irradiation of a 5 × 10−4-M solution of estrone in acetonitrile under UV-B. A solution of estrone (0.5 mM) dissolved in acetonitrile was degassed with nitrogen in order to avoid in situ formation of nitric dioxide. The solution was then saturated with a mixture containing 5% nitric oxide in nitrogen, and was allowed to flow through a conventional Electron paramagnetic resonance spectroscopy (EPR) flat cell (Suprasil) at a rate of 1 mL/min. The solution saturated with nitric oxide was continuously irradiated in the EPR cavity by the means of a Xenon illuminator (model LUZ-XE, Luzchem). The EPR spectra were recorded at room temperature on a FA-100 JEOL EPR spectrometer. The experimental setting was as followed: microwave power 1 mW, modulation width 0.1 mT, sweep time 1 min, time constant 0.03 s.