Lanthanide(III) complexes are more active inhibitors of the Fenton reaction than pure ligands

Abstract

Objectives: This study is an extension to our finding of direct anti-oxidant activities of lanthanide(III) complexes with the heterocyclic compound, 5-aminoorotic acid (AOA). In this experiment, we used AOA and coumarin-3-carboxylic acid as the two heterocyclic compounds with anti-oxidant potential, to produce the complexes with different lanthanides.

Methods: Lanthanide(III) complexes were tested on the iron-driven Fenton reaction. The product of this reaction, the hydroxyl radical, was detected by HPLC.

Results: All complexes as well as their ligands had positive or neutral effect on the Fenton reaction but their behavior was different. Both pure ligands in low concentration ratio to iron were inefficient in contrast to some of their complexes. Complexes of neodymium, samarium, gadolinium, and partly of cerium blocked the Fenton reaction at very low ratios (in relation to iron) but the effect disappeared at higher ratios. In contrast, lanthanum complexes appeared to be the most promising. Both blocked the Fenton reaction in a dose-dependent manner.

Conclusion: Lanthanide(III) complexes were proven to block the iron-driven production of the hydroxyl radical. Second, the lanthanide(III) element appears to be crucial for the anti-oxidant effect. Overall, lanthanum complexes may be promising direct anti-oxidants for future testing.

Keywords:

• Anti-oxidant
• 5-Aminoorotic acid
• Coumarin-3-carboxylic acid
• Iron
• Lanthanide(III)

Acknowledgements

We would like to thank Dr Alexander Oulton for English correction.

Disclaimer statements

Contributors J.M.: experiments, P.M. and L.S.: study design and coordination, I.K.: synthesis of tested compounds, P.M. and I.K.: preparation of the manuscript.

Funding The work was supported by the grant of The Czech Science Foundation (project No. P303/12/G163). I.K. acknowledges the financial support from the University Grant Commission (project No. 32/ 2014).

Conflicts of interest None.

Ethics approval This work does not include animals and it is not a clinical study.