Étude théorique de l’activité antioxydante de l’acide cinnamique et ses dérivés

Abstract

The present work reports a computational study of the antioxidant activity of cinnamic acid (ACin) and its derivatives such as caffeic (ACaf), ferulic (AFer), o-coumaric (Ao-coum), p-coumaric (Ap-coum) and sinapic (ASin) acids. On the basis of a series of thermodynamic parameters calculated at the M06-2X/6-311++G(d,p) level of theoretical, we have developed a comparative study concerning their free radical scavenging activity in the gas phase and polar solutions (water and methanol). This discussion allowed us to elucidate both the most favorable mechanism from the thermodynamic point of view, allowing to describe the antioxidant activity of these molecules and to give the order of antioxidant activity of the systems studied according to the medium. For this purpose, it appears that caffeic acid and sinapic acid have a higher antioxidant activity respectively in gaseous and solvent medium (water and methanol) according to the HAT (Hydrogen Atom Transfer) pathway, which was the thermodynamically favorable mechanism. However, calculations related to the harmonic oscillator model of aromaticity (HOMA) suggest that radicals resulting from the abstraction of H stabilize more as the central benzene cycle loses structural aromaticity. Furthermore, the global reactivity indices vary in the three (03) environments and seem to be good indicators of the global reactivity of these molecules towards radicals.