Electrochemical and Solution Structural Characterization of Fe(III) Azotochelin Complexes: Examining the Coordination Behavior of a Tetradentate Siderophore

Abstract

We report an electrochemical setup comprising a boron-doped diamond (BDD) working electrode for the electrochemical study of iron(III) catecholate siderophores. We demonstrate its successful application in the voltammetric investigation of iron(III) azotochelin, an iron complex of a bis(catecholate) siderophore. Cyclic voltammetry results, when complemented by UV−vis and native electrospray ionization-mass spectrometry (ESI-MS) characterization, reveal the formation of a coordinatively unsaturated tetracoordinate 1:1 complex of Fe:azotochelin (M 1 :L 1 ) at neutral pH, contrary to iron(III) tetradentate siderophore complexes of other classes which favor the hexacoordinate environment of an M 2 :L 3 species. A notable effect of pH and buffer composition on the reduction potential of iron(III) azotochelin is demonstrated. Lower pH values and buffers encompassing primary or secondary amines facilitate a positive potential shift of up to +290 mV and +250 mV vs Ag/AgCl 3 M NaCl, respectively. The study was extended to the investigation of the iron(III) complexes of hexadentate siderophores. For tris(catecholate) siderophores, enterobactin and protochelin, the reduction potentials were found to lie beyond the potential window accessible to the BDD electrode; however, we were successful in observing the electrochemical behavior of a tris(hydroxamate) siderophore, ferricrocin.

A Siderophore Mimicking Gelation Component for Capturing and Self-Separation of Fe(III) from an Aqueous Solution of Mixture of Metal Ions

“…Interestingly, though there are several reports where chelating ligands are presented as siderophore mimics, − there are no such reports available where the system picks up iron­(III) selectively from an aqueous solution with a mixture of different metal ions and self-separates from the system. On the other hand, in soft materials, only a few examples are reported as siderophore-mimicking gels in terms of binding Fe­(III) ions − In this work, we have purposefully designed and synthesized a compound N 2 , N 4 , N 6 -(1,3,5-triazine-2,4,6-triyl)­tris­(benzene-1,3,5-tricarbohydrazide) CBTC for mimicking the hydroxamate type siderophore.…”