An iron-based molecular redox switch as a model for iron release from enterobactin via the salicylate binding mode

The iron release mechanism from protonated ferric enterobactin [Fe-III(ente robactinH(3))] via the salicylate binding mode was probed. For this purpose , a tripodal dodecadentate Ligand incorporating three salicylamide (OO) and three bipyridine (NN) binding sites was synthesized as well as iron comple xes thereof. It was shown that a ferric ion coordinates selectively to the hard salicylamides and a ferrous ion binds to the softer bipyridines. Upon reduction or oxidation, the iron translocates reversibly and intramolecular ly from one site to the other, thus displaying switchlike properties. Both states were characterized by cyclic voltammetry and visible and Mossbauer s pectroscopy. The Mossbauer spectrum for the ferric complex is fully consist ent with that obtained by Pecoraro et al. upon lowering the pH of [Fe-III(e nterobactin)](3-) solutions (Pecoraro, V. L., et al. J. Am. Chern. Sec. 198 3, 105, 4617), thus supporting the alternative iron release mechanism from enterobactin via the salicylate binding mode.