Figure 1.

Mössbauer spectra of freeze-quenched samples from the reaction of reduced ToMOH:2ToMOD mixtures with O₂. The samples were frozen before mixing (A) and 0.14 s (B), 2 s (C), and 32 s (D) after mixing. The spectra (vertical bars) are collected at 4.2 K in a 50 mT field applied parallel to the γ-ray beam. The red and orange lines are simulated spectra of the diiron(III) intermediate and diiron(III) product, respectively. The spectrum of the diiron(III) intermediate (red) was modeled with a single quadrupole doublet with δ = 0.55 mm/s, ΔE_Q = 0.67 mm/s and line width = 0.27 mm/s. The spectrum of the diiron(III) product (orange) was simulated as a superposition of two equal intensity quadrupole doublets with parameters δ = 0.52 mm/s, ΔE_Q = 0.73 mm/s and line width = 0.32 for doublet 1 and δ = 0.52 mm/s, ΔE_Q = 0.97 mm/s and line width = 0.28 mm/s for doublet 2. They are plotted at the following absorption intensities: red, 44%, 41% and 13% in B, C, and D; orange, 41% in D. Unreacted diiron(II) protein accounts for ~ 56% of total Fe absorption at maximal accumulation of the intermediate (B). These parameters and intensities are the results of a global analysis of the entire set of the Mössbauer spectra including those that are not depicted here.