Chemical implications and considerations on techniques used to assess the in vitro antioxidant activity of coordination compounds

Abstract Consumption of fruits, including seeds and peels, provides some natural products that can act as antioxidant molecules and assist in combating oxidative stress. In recent years, the coordination of natural products to different metal centers of both s-p and d-block metals has been applied as a strategy to optimize their antioxidant activity. In addition, much research has been addressing the use of metal complexes containing Schiff bases as ligands to act on antioxidant barrier. Coordination compounds are an alternative to the use of traditional synthetic antioxidants, because metal complexes present advantages such as variety in coordination number, geometry, and oxidation states, which facilitates and favors the redox processes associated with antioxidant action. Antioxidant capacity should be assessed using different interrelated methods. Methodological standardization provides the greatest amount of information possible on the antioxidant behavior of metal complexes. Colorimetric methods are the most used; however, electron paramagnetic resonance (EPR) is an alternative for metallic complexes, since color has no influence on the results. Knowledge about methodologies, including their advantages and limitations, allows a reliable assessment of the antioxidant potential of coordination complexes, and thus enables application in different situations where antioxidant molecules are needed, as in food preservation, dietary supplements, smart composite packaging, among others.