Reaction of a model siderophore with Ni(II), Co(II) and Zn(II) in aqueous solution: Kinetics and spectroscopy

A spectroscopic study was performed showing that the [Fe(III)(L2−)2]1− (L2− = dopacatecholate) complex reacts with Ni(II), Co(II) and Zn(II) in an aqueous solution containing S2O32- resulting in the soluble [M(L1−)3]1− (L1− = dopasemiquinone; M = Ni(II), Co(II) or Zn(II) complex species. The Raman and IR spectra of the [CTA][M(L1−)3] complexes, CTA = hexadecyltrimethylammonium cation, in the solid state were obtained. The kinetic constants for the metal substitution reactions were determined at four different temperatures, providing values for ΔH≠, ΔS≠ and ΔG≠. The reactions were slow (k = 10−11 M s−1) and endothermic. The system investigated can be considered as a simplified model to explain some aspects of siderophore chemistry.