Proton NMR study of iron(II)-bleomycin: Assignment of resonances by saturation transfer experiments

The assignment of the paramagnetically shifted resonances of the Fe(II)-bleomycin complex in D₂O has been accomplished using the transfer of saturation method. A number of additional resonances arising from labile N$\text{H}$ protons which are shifted by the metal ion are observed in the ¹H spectrum of the complex in H₂O. The temperature dependence of the chemical shifts is consistent with the formation of an isolated 1:1 complex, but does not obey either the Curie Law or the Curie-Weiss Law. The magnitude of the shifts suggests that the valeric acid hydroxyl (or carbonyl) group, the α-amino group, the imidazole N^π, the carbamoyl oxygen, the pyrimidine N₁ and/or the secondary amino group may be coordinated to the iron(II).