Metal-anion interactions, transferrins

This result is interesting but perhaps not very satisfying, since it puts an upper limit on the metal-anion distance without unequivocally revealing whether the anion is directly coordinated to the metal ion. To get at this question, we attached a nitroxyl spin-labeled anion to transferrin to determine whether its electron paramagnetic resonance signal was broadened by interaction with specifically bound Fe(III) (49). The mechanism of such broadening would be similar to that in the NMR experiments, but now there is an electron-electron interaction rather than an electron-nuclear interaction as before. 

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