The Cu2+, Mn2+, and Fe3+ complexes of a 14 membered macrocycle were synthesized and their antioxidant capacities were evaluated against ABTS and DPPH radicals, with the objective of collecting insights into the biomimetic role of the central metal ions. The macrocycle, abbreviated as H2L14, is a derivative of EDTA cyclized with 1,4-diamine, and the moderately flexible macrocyclic frame permits the formation of [ML14·H2O] chelates with octahedral coordination geometries common among the metal ions. The metal complexes were characterized by electrospray-ionization mass spectrometry, Fourier transform infrared spectroscopy, and Raman and X-ray photoelectron spectroscopic methods, as well as thermogravimetric analysis; the octahedral coordination geometries with water coordination were optimized by DFT calculations. The antioxidant assays showed that [FeL14·H2O]+ was able to scavenge synthetic radicals with moderate capacity, whereas the other metal chelates did not show significant activity. The Raman spectrum of DPPH in solution suggests that interaction was operative between the Fe3+ chelate and the radical so as to cause scavenging capability. The nature of the central metal ions is a controlling factor for antioxidant capacity, as every metal chelate carries the same coordination geometry.
Bibliographical noteFunding Information:
Funding: This research was funded by National Council for Science and Technology, CONACYT, grant number RTQS 294810, INFR-2014-01-225455, and CB-I0017-236216.
Acknowledgments: Y.S. thanks CONACYT (Program Fronteras de la Ciencia 563) for the postdoctoral fellowship at CIAD, A.C. We thank Roberto Mora-Monroy, Diego Hernández, and Roberto Carrillo of the University of Sonora, for their technical assistance in the XPS, TGA, and Raman analyses, respectively.
© 2019 by the authors.
- Coordination chemistry
- Theoretical calculation
- Transition metal complexes