Figure 1. ESR spectra of eugenol radical at pH 6.9–12.7. Eugenol, 100 mM: (a) 50% dimethylsulfoxide with NaHCO₃/NaCO₃; (b) 50% dimethylsulfoxide with potassium hydroxide (KOH); (c-f) 50% dimethylsulfoxide with calcium hydroxide [Ca(OH)₂]; * = eugenol radical; arrow = amplified eugenol radical. Assay for the radical intensity of eugenol with or without potassium hydroxide or calcium hydroxide has been described in the text.