Stoichiometric characteristics and resonance Raman spectra of azidosemimethemerythrin

With extra precautions to remove dissolved oxygen, reduction of aquomethemerythrin with dithionite occurs with a stoichiometry very close to 1.0. The aquosemimethemerythrin so produced combines with N3- ion almost on a 1:1 basis per monomer. Resonance Raman spectra of azidosemimethemerythrin differ from those of azidomethemerythrin in the position of the Fe-N stretching frequency and in the absence of a feature corresponding to a mu-oxo bridge, but in both complexes the internal azide stretch occurs at the same frequency and the substitution of isotopically unsymmetrical 15N14N-2 leads to a splitting of the Fe-N band. These observations provide some insight into the structural features of the binuclear functional site.