Are thymol, rosefuran, terpinolene and umbelliferone good scavengers of peroxyl radicals?

DFT-based computational calculations have been used to investigate the hydroperoxyl radical scavenging activity of four essential oil constituents namely thymol (Thy), rosefuran (Ros), terpinolene (Ter), and umbelliferone (Umb). Different reaction mechanisms including formal hydrogen transfer (FHT), radical adduct formation (RAF), sequential proton loss electron transfer (SPLET), and sequential electron transfer proton transfer (SETPT) have been examined in the gas phase and physiological environments. It was found that the HOO center dot radical scavenging activity of these compounds is strongly influenced by the environment, which becomes more important in water than pentyl ethanoate. According to the overall reaction rate constants, the phenolic compounds Thy and Umb are predicted to exhibit excellent activity in aqueous solution. Umb with an overall rate constant of 1.44 x 10(8) M-1 s(-1) at physiological pH is among the best HOO center dot radical scavengers in water with activity comparable to that of caffeic acid, higher than those of ascorbic acid, guaiacol and eugenol, and much higher than that of Trolox.

Automated summary

DFT-based computational calculations have shown that thymol and umbelliferone exhibit excellent HOO· radical scavenging activity in aqueous solution. These two compounds have outstanding activity in physiological environments, comparable to that of caffeic acid.