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An Iron-Based Molecular Redox Switch as a Model for Iron Release from Enterobactin via the Salicylate Binding Mode
Journal
Inorganic Chemistry
Volume
38
Number
22
Pages / Article-Number
5007-5017
Keywords
Isomers (linkage; of iron(II) vs. iron(III) to salicylamide bipyridine tripodal ligands); Formation constant; Reduction potential (of iron salicylamide bipyridine tripodal complexes); Coordination (of iron(II) vs. iron(III) to salicylamide bipyridine tripodal ligands); Protonation (of salicylamide bipyridine tripodal ligands); Molecular structure (optimized; of iron salicylamide bipyridine tripodal ligand complexes); enterobactin iron release model mol redox switch; iron salicylamide bipyridine
Abstract
The iron release mechanism from protonated ferric enterobactin [FeIII(enterobactinH3)] 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 complexes 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 intramolecularly from one site to the other, thus displaying switchlike properties. Both states were characterized by cyclic voltammetry and visible and Mössbauer spectroscopy. The Mössbauer spectrum for the ferric complex is fully consistent with that obtained by Pecoraro et al. upon lowering the pH of [FeIII(enterobactin)]3- solutions (Pecoraro, V. L., et al. J. Am. Chem. Soc. 1983, 105, 4617), thus supporting the alternative iron release mechanism from enterobactin via the salicylate binding mode.
