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.