Figure 5. Degradation of Mn porphyrins with H₂O₂.

Spectral changes were measured within first 30 minutes for Mn porphyrins MnTBAP³⁻ (A) and MnTE-2-PyP⁵⁺ (B)). Time-dependent reduction in the absorbance at the Soret band for each MnP is shown in inset. (C) Time-dependent degradation of MnTE-2-PyP⁵⁺ with H₂O₂. The degradation of MnTE-2-PyP⁵⁺ was terminated with the addition of catalase. Subsequent addition of GSH did not cause any change in the absorbance indicating irreversible degradation of MnP to non-porphyrin species over the course of ~200 s of reaction. The drop in absorbance is due to a sample dilution. Experiments were carried out at (25±1)°C in 0.05 M tris buffer, pH 7.8 and 0.1 mM EDTA with 10 µM MnP and 0.5 mM H₂O₂. (D) The H₂O₂-driven degradation of several MnPs whose structures impose different steric and electronic effects upon H₂O₂ approach.