Application of Badger's rule to heme and non-heme iron-oxygen bonds: An examination of ferryl protonation states

The applicability of Badger's rule to heme and non-heme iron-oxygen bonds is examined to gain insights into the protonation state of enzymatic ferryl species. The long Fe-O bonds reported in the crystal structures of the ferryl forms of myoglobin, cytochrome c peroxidase and catalase deviate substantially from the values predicted by Badger's rule, while the short Fe-O bonds obtained from X-ray absorption measurements are in good agreement with Badger's rule.