Electron Paramagnetic Resonance and Ultraviolet/Visible study of Compounds I and II in hte Horseradish Peroxidase-H2O2-silk fiber reaction system

The enzymatic oxidation of silk with H2O2 in the presence of Horseradish Peroxidase (HRP) has been investigated. Two intermediate complexes have been observed during this reaction. Both of them can be attributed to Fe4+ ions axially bonded to an oxygen atom and to a porphyrin radical (P•). In the most unstable of them, indicated as Compound II, the chemical bond between [FeIV=O]2+ and P• was weaker than in the other, indicated as Compound I. The former Compound disappeared within one hour of reaction, at difference with the latter, traces of which were observed even after three weeks with dried samples. However, the chemical bond between [FeIV=O]2+ and P• in Compound I weakened during the sample ageing. All these phenomena have been enlightened by Electron Paramagnetic Resonance (EPR) and spectrophotometric Ultra Violet and Visible (UV/Vis) measurements.