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. 2013 Jan 1;3(1):7-13.
doi: 10.4236/ojic.2013.31002.

Synthesis, characterization, and stability of iron (III) complex ions possessing phenanthroline-based ligands

Shawnt Tosonian #  1 , Charles J Ruiz #  1 , Andrew Rios  1 , Elma Frias  1 , Jack F Eichler  1
Affiliations

Synthesis, characterization, and stability of iron (III) complex ions possessing phenanthroline-based ligands

Shawnt Tosonian et al. Open J Inorg Chem. .

Abstract

It has previously been demonstrated that phenanthroline-based ligands used to make gold metallotherapuetics have the ability to exhibit cytotoxicity when not coordinated to the metal center. In an effort to help assess the mechanism by which these ligands may cause tumor cell death, iron binding and removal experiments have been considered. The close linkage between cell proliferation and intracellular iron concentrations suggest that iron deprivation strategies may be a mechanism involved in inhibiting tumor cell growth. With the creation of iron (III) phen complexes, the iron binding abilities of three polypyridal ligands [1,10-phenanthroline (phen), 2,9-dimethyl-1, 10-phenanthroline (methylphen), and 2,9-di-sec-butyl-1, 10-phenanthroline ( sec-butylphen)] can be tested via a competition reaction with a known iron chelator. Therefore, iron (III) complexes possessing all three ligands were synthesized. Initial mass spectrometric and infrared absorption data indicate that iron (III) tetrachloride complex ions with protonated phen ligands (RphenH+) were formed: [phenH][FeCl4], [methylphenH][FeCl4], [ sec-butylphenH][FeCl4]. UV-Vis spectroscopy was used to monitor the stability of the complex ions, and it was found that the sec-butylpheniron complex was more stable than the phen and methylphen analogues. This was based on the observation that free ligand was observed immediately upon the addition of EDTA to the [phenH][FeCl4] and [methylphenH] [FeCl4] complex ions.

Keywords: Complex Ions; Iron (III); Phenanthroline; Polypyridyl Ligands.

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Figures

Figure 1
Figure 1
Representative LIFDI mass spectrometry data for the [Rphen H][FeCl4] complex ions. The spectrum shown is for the [sec-butylphenH][FeCl4] complex ion (compound 3). The molecular ion at m/z = 418 corresponds to the complex ion after the loss of two Cl− ligands; the fragment peak at m/z = 293 corresponds to the protonated sec-butylphen ligand.
Figure 2
Figure 2
Uv-Vis absorbance spectra for the [RphenH] [FeCl4] complex ions and free Rphen ligands. (a) Rphen and [phenH] [FeCl4] (1); (b) methylphen and [methylphenH] [FeCl4] (2); (c) sec-butylphen and [(sec-butylphenH)] [FeCl4] (3).
Figure 3
Figure 3
EDTA stability monitored by UV-Vis absorbance. Spectra are shown at 5-minute intervals after the addition of EDTA in a 20:1 molar ratio. (a) [phenH][FeCl4] (1); (b) [methylphenH][FeCl4] (2); (c) [(sec-butylphenH)][FeCl4] (3).
Scheme 1
Scheme 1
Synthesis of compounds 1-3. R = H (1), −CH3 (2), and −CH(CH3)CH2CH3 (3).
See this image and copyright information in PMC

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