Figure 4. Spectroscopic characterization of the pH 8 intermediate shows that it is likely a breakdown product of Compound I.

(A) High frequency resonance Raman spectroscopy confirms the presence of a ferryl intermediate in the reaction of PAA and DaCld at pH 8. Final concentrations of DaCld and peracetic acid following mixing were 58 μM and 480 mM, respectively (~8 eq PAA). Spectra were measured prior to mixing and via fifteen second acquisitions subsequently. Data were acquired at ambient temperature with 406.7 nm excitation and 12 mW power at the sample. Spectra initiated at 0, 15, 30, 60, and 120 s after mixing are plotted. (B) X-band EPR spectra of DaCld/PAA reaction mixtures measured at 77 K indicate an uncoupled [Fe^IV=O] + (AA•) species. Top: DaCld was reacted with 5 eq PAA acid (50.8 μM DaCld final concentration) at 22 °C. The sample was freeze-quenched into a liquid N₂/isopentane slush after a 50 ms reaction time. Instrument parameters were: 200 G sweep width, 0.5 G modulation amplitude, 2.0 mW power, 100 kHz modulation frequency, and 77 K. Bottom: DaCld (22 μM, final concentration) was reacted with 9 equivalents of PAA at 22 °C. Samples were subsequently frozen in an acetone/liquid nitrogen bath at 14 s and 60 s (less intense signal). Instrument parameters were: 200 G sweep width, 4 G modulation amplitude, 2.0 mW power, 100 kHz modulation frequency, and 77 K.