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Abstract

The common metal chelation agents, DTPA and EDTA are often used as models for physiological low-molecular weight iron complexes in biochemical studies, or for common biochemical protocols. In the biochemical literature there are apparent conflicts as to whether EDTA and DTPA are pro-oxidant or antioxidant additives. This apparent conflict is puzzling since in chemical systems FeIIEDTA and FeIIDTPA are well known Fenton reaction reagents. In this investigation we examined the voltammetric characteristics of the iron complexes of EDTA, DTPA, and citrate and the effect of the ligand:metal ratio (L:M) on the electrocatalytic (EC') waves that result from reduction of H2O2 by this complex. At a ratio of 1:1, the cyclic voltammetric waves of the complexes indicate the presence of a reversible species corresponding to the Fe(II/III)L couple, along with a second irreversible reduction peak. The second irreversible voltammetric peak decreases at higher L:M ratios for EDTA and citrate. The 1:1 iron complexes of EDTA, DTPA, and citrate clearly induce the catalytic reduction of H2O2. In the presence of a greater than 100 fold excess of H2O2 relative to iron, higher L:M ratios greatly reduced the catalytic EC' wave compared to the 1:1 ratios. At H2O2:Fe ratios less than 50, the L:M ratio has very little effect of the EC' current. These observations may explain the apparent discrepancies in the biochemical literature. Addition of EDTA or DTPA may enhance oxidative processes if the L:M is low (less than unity), whereas rates of on-going oxidative processes may decrease if that ratio, along with the relative amount of H2O2, are both high (excess ligand). The impact of this study is of particular importance given the widespread use of these ligands in biochemical studies.

Metals, Toxicity and Oxidative Stress

“…For example ligands like nitrilotriacetate (NTA) and ATP are known to bind Fe and cause oxidation of lipids and DNA damage [38]. The hexadentate ligand, ethylenediaminetetraacetic acid (EDTA), can also induce Fenton-chemistry mediated radical damage [39]. It was observed that autoxidation of Fe(II) is enhanced by EDTA and also by NTA, but inhibited by o-phenanthroline and deferoxamine.…”

Optimization of a DNA Nicking Assay to Evaluate Oenocarpus bataua and Camellia sinensis Antioxidant Capacity

“…Moreover, the presence of organic solvent inhibits Fenton’s reaction and prevents DNA strand breaks. Therefore, questions still remain as to the actual effect of iron and ethylenediaminetetraacetic acid (EDTA) in DNA degradation, indeed Engelmann et al have clearly shown that iron, EDTA and H 2 O 2 ratio modify the Fenton reaction output [19]. The objective of this study was to establish the optimal conditions for the plasmid nick assay related to concentration of Fenton reagents and incubation time for various solvents used for the extraction of polyphenolics.…”

Redox potentials of Ti(IV) and Fe(III) complexes provide insights into titanium biodistribution mechanisms

“…Citrate as an α-hydroxy carboxylic acid is included in our plot, but for reasons described below is not used in the linear least squares analysis. The interactions of these common metal chelators with Fe(III) are well understood and the reduction potentials of many of the corresponding complexes are available in the literature [32][33][34][35][36]. However, few electrochemical data are available for the corresponding Ti(IV) complexes [37][38][39][40].…”