Several ligands specific for the chelation of ferrous ions, such as ferrozine, bipyridine and phenanthroline, are readily available and commonly used in analytical chemistry and in many iron-protein studies. Among these iron ligands, ferrozine is more frequently used because of its higher water solubility and molar absorptivity. Here, we use UV-vis spectrophotometry and three common chromogenic reagents, ferrozine, bipyridine and phenanthroline to detect and quantify the concentration of ferrous ions in aqueous solutions, owing to the unique absorption spectra, specific molar absorptivity, and characteristic colors of these Fe2+-chelator complexes. Our results show that the kinetics of the formation of the {Fe(II)-(ferrozine)3} and {Fe(II)-(bipyridine)3} complexes, but not the{Fe(II)-(phenanthroline)3} complex depend on the concentration of the chelator. Contrary to literature reports, the molar absorptivity values of these complexes under excess chelator concentrations were (30,000 ± 2,500 M-1cm-1) for ferrozine at 562 nm, (11,660 ± 350 M-1cm-1) for bipyridine at 522 nm, and (12,550 ± 260 M-1cm-1) for phenanthroline at 510 nm. Our results have important implications in the quantification of iron in biological systems and reveal optimal experimental conditions that must be employed for the accurate measurements of ferrous ions in aqueous solutions.

Complexation of ferrous ions by ferrozine, bipyridine and phenanthroline

ACS Spring Meeting 2021

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