Unusual spin-state transitions in the reduction of ferrylmyoglobin at low temperature

Ferrylmyoglobin is reduced in γ-irradiated aqueous ethylene glycol solutions at 77 K to form a novel ferric low-spin type compound. The transition of the low-temperature product to the final high-spin ferrimyoglobin at higher temperature involves several intermediate species appearing in a sequence as temperature increases. With manifestation of the transient low-spin forms and probably the mid-spin $\text{S}\text{=}\text{3}\text{2}$ state, the process of ferrylmyoglobin reduction is found to display the spin-state transitions scarcely observed in ferric heme reactions.