Antioxidative Potency and UV–Vis spectra features of the compounds resulting from the chelation of Fe2+ by Caffeic Acid Phenethyl Ester and two of its derivatives
Abstract Chelation of the solvated iron (II) cation (Fe(H2O)62+ and Fe(CH3OH)62+) by Caffeic Acid Phenethyl Ester (CAPE), 3-Methyl-2-Butenyl Caffeate (MBC) and Benzoic Caffeate (BC) has been investigated through the ONIOM(B3LYP/6-31G(d,p):UFF) calculation and 6-31+G(d) set for Fe2+. The chelates (Fe(CAPE)2+, Fe(MBC)2+ and Fe(BC)2+) were treated by the density functional theory (DFT) calculation and the four ligands (H2O or CH3OH) around the iron were treated by UFF calculation. Time dependent (TD-DFT) calculations were used to reproduce the electronic UV–Vis spectra of chelates. In the thermodynamic point of view, the results indicated that the chelation of Fe2+ by the three molecules was spontaneous and that MBC got the best capacity to chelate Fe2+. The complexes are more antioxidant than the free molecules (CAPE, MBC and BC). The CH3OH molecules appear as the good ligands to enhance the antioxidant efficiency of chelates. Elsewhere the homolytic H-atom transfer (HAT) mechanism was the likely HO2 radical scavenging process compared to the sequential ones. Therefrom the chelates without ligands were the best antioxidant. Considering the ligands, the chelates of CH3OH were the best antioxidant, mostly Fe(MBC)(CH3OH)42+. However the scavenging of the ionic radical O2 − foresaw that the proton transfer followed by electron transfer (PT–ET) mechanism was the preferred process. This kept the antioxidant potency analyses of HAT mechanism. Moreover, the chelates absorbed the red and the infrared radiations confirming the quality of the antioxidative potency of chelates.