ON THE THERMODYNAMICS OF ANTIOXIDANT ACTION OF NATURALLY OCCURRING HYDROXYDERIVATIVES OF CIS-CINNAMIC ACID

Antioxidant activity represents one of the important features of phenolic acids, such as hydroxyderivatives of cinnamic acid. However, in the case of cis-cinnamic acid derivatives, corresponding thermochemistry data can be still considered scarce. This work is focused on the two most relevant mechanisms of primary antioxidant action in gas-phase, non-polar benzene and in aqueous solution. Reaction enthalpies describing thermodynamics of Hydrogen Atom Transfer (HAT) and Sequential Proton-Loss – Electron Transfer (SPLET) mechanisms were theoretically investigated using (SMD) M06-2X/6-311++G(d,p) method for cis-ortho-coumaric, cis-meta-coumaric, cis-para-coumaric, cis-ferulic, cis-sinapic and cis-caffeic acid and their carboxylate anions. The effect of carboxyl COOH group deprotonation on the thermodynamics of studied mechanisms was assessed for the three environments.