The microelement Calcium enhances the reactivity of Rutin towards singlet oxygen

Abstract

Flavonoids deactivate efficiently singlet oxygen and could be valuable antioxidants in systems under oxidative stress, in particular if a flavonoid rich diet was previously consumed. Furthermore, in the presence of metal ions, the flavonoid reactivity towards singlet oxygen is enhanced. In this work we report the results of singlet oxygen quenching by the complex form edfrom the interaction between the glycoside rutin and Ca+2, the most abundant macroelement in the humanbody. The results obtained, indicates that the glycoside Rutin forms a stable association complex with Ca+2 ions in both, MeOH and water as solvents with stability constants equal to 5.5 M-1 and 10.3 M-1. The complex reacts with moderate to high rates with singlet oxygen with total rate constants (kT = kr + kq) of (5.82 ± 0.47) x 105 M-1 s-1 and (509.7 ± 40.8) x 105 M-1s-1 and chemical reaction constants of (1.10 ± 0.08) x 105 M-1 s-1 and (8.99 ± 0.91) x 105 M-1 s-1 in methanol and water, respectively. The high value of the physical quenching rate constant in water, suggest that the association complex Rutin – Ca+2 could be a more efficient antioxidant in biological media than the glycoside. Furthermore, the ratio kr/kT for the complex equal to 0.022 indicates that the physical quenching of 1O2 predominates largely over the chemical reaction, then, the quenching effect of Rutin - Ca+2 complex take place practically without antioxidant loss, a very wanted characteristic of molecules with capabilities to protect biological systems under oxidative stress conditions.