How the functional group substitution and solvent effects affect the antioxidant activity of (+)-catechin?

Abstract

Based on the density functional theory method, the antioxidant activity of (+)-Catechin (CAT) and its two derivatives, substituted by the electron-donating group -N(CH3)2 (CAT-DA) and electron-withdrawing group -CF3 (CAT-TF), were explored in gas and solvent phases. The parameters related to three antioxidant mechanisms: hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET), were calculated. Results indicate the antioxidant reaction of these three compounds tends to the HAT mechanism in gas phase with the lowest BDE values of 75.2 kcal/mol, 74.4 kcal/mol and 78.6 kcal/mol for CAT, CAT-DA and CAT-TF, respectively, and prefers to the SPLET mechanism in the studied solvents. Furthermore, the increased solvent polarity can promote the expression of SET-PT mechanism, but inhibit the SPLET mechanism. Strikingly, CAT-DA shows the largest the highest occupied molecular orbital energies (−5.317 eV and − 5.570 eV in gas and ethanol phase) and the lowest vertical ionization potentials (6.817 eV and 5.270 eV in gas and water phase) among the three compounds, suggesting that this compound would exhibit the strongest electron-donating ability. The above results mean that introducing the -N(CH3)2 group into the structure of CAT would effectively improve its antioxidant activity, which provides a theoretical reference for the synthesis of more efficient antioxidants.