Engelmann Mark D, Bobier Robert T, Hiatt Terrance, Cheng I Francis
Department of Chemistry, University of Idaho, Moscow, Idaho 83844-2343, USA.
Biometals. 2003 Dec;16(4):519-27. doi: 10.1023/a:1023480617038.
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.
常见的金属螯合剂二乙三胺五乙酸（DTPA）和乙二胺四乙酸（EDTA）在生化研究中常被用作生理低分子量铁络合物的模型，或用于常见的生化实验方案。在生化文献中，关于EDTA和DTPA是促氧化剂还是抗氧化剂添加剂存在明显的矛盾。这种明显的矛盾令人困惑，因为在化学体系中，亚铁EDTA和亚铁DTPA是众所周知的芬顿反应试剂。在本研究中，我们研究了EDTA、DTPA和柠檬酸盐的铁络合物的伏安特性，以及配体与金属比例（L:M）对该络合物还原过氧化氢所产生的电催化（EC'）波的影响。在1:1的比例下，络合物的循环伏安波表明存在对应于Fe(II/III)L电对的可逆物种，以及第二个不可逆还原峰。对于EDTA和柠檬酸盐，在较高的L:M比例下，第二个不可逆伏安峰降低。EDTA、DTPA和柠檬酸盐的1:1铁络合物明显诱导了过氧化氢的催化还原。在相对于铁过量100倍以上的过氧化氢存在下，与1:1比例相比，较高的L:M比例大大降低了催化EC'波。在过氧化氢与铁的比例小于50时，L:M比例对EC'电流的影响很小。这些观察结果可能解释了生化文献中明显的差异。如果L:M较低（小于1），添加EDTA或DTPA可能会增强氧化过程，而如果该比例以及过氧化氢的相对量都很高（配体过量），正在进行的氧化过程的速率可能会降低。鉴于这些配体在生化研究中的广泛应用，本研究的影响尤为重要。
