Evaluation of the antioxidant activity of selected flavonoids and their metal complexes

Experimental evidence showed that binding flavonoids to the metal ions can result with significant change of their biological effects (i.e. radical scavenging activity, cytotoxic activity, interactions with double stranded DNA or RNA). The aim of the study is to explore the putative change of the antioxidant activity between selected flavonoids (rutin, naringenin and quercetin) and their metal complex with Ruthenium using different methods (DPPH radical scavenging test, FRAP assay and Briggs-Rauscher oscillating reaction). Quercetin and rutin exhibited very high radical scavenging activity by DPPH method. Ruthenium-quercetin and ruthenium-rutin metal complexes showed weaker radical scavenging activity than pure quercetin and rutin. Ruthenium-naringenin as well as pure naringenin, did not show any activity. Quercetin and rutin showed the antioxidant activity by FRAP assay, while naringen showed no activity. Ruthenium complexes with quercetin and rutin showed weaker antioxidant activity than pure flavonoids. In comparison with pure naringenin, ruthenium complex with naringenin exhibited good antioxidant activity. Selected pure flavonoids showed good antioxidant activity by Briggs-Rauscher method, while the activity of their metal complexes was weaker that those of pure flavonoids. Within this study, other flavonoid-metal complexes will also be investigated (titanium, lantan). Results of this study showed that binding flavonoids to metal ions changes their antioxidant activity. Depending on measurement conditions, this activity of pure flavonoid can be increased or decreased. The detailed mechanism of detected changes merits further investigations.