Fig. 7. Spontaneous conversion of the superoxo (PFe^III–O₂^–/Cu^ICD₂) complex in 0.05 M phosphate buffer at pH 7.0 and 25 °C. The spectrum was recorded at 15 s intervals. The inset shows the logarithmic first-order rate constants (k_obs) for the conversion as a function of the pH of the solution.