DFT study of the effect of solvent on the H-atom transfer involved in the scavenging of the free radicals ●HO2 and ●O2 − by caffeic acid phenethyl ester and some of its derivatives

Abstract

H-atom transfer from caffeic acid phenethyl ester (CAPE), MBC (3-methyl-2-butenyl caffeate), BC (benzoic caffeate), P3HC (phenethyl-3-hydroxycinnamate), and P4HC (phenethyl-4-hydroxycinnamate) to the selected free radicals (·)HO2 and (·)O2(-) was studied. Such a transfer can proceed in three different ways: concerted proton-coupled electron transfer (CPCET), electron transfer followed by proton transfer (ET-PT), and proton transfer followed by electron transfer (PT-ET). The latter pathway is sometimes competitive with SPLET (sequential proton loss electron transfer) in polar media. Analyzing the thermodynamic descriptors of the reactions of CAPE and its derivatives with co-reactive species-in particular, the free energies of reactions, the activation barrier to the CPCET mechanism, and their rate constants-appears to be the most realistic method of investigating the H-atom transfers of interest. These analyses were performed via DFT calculations, which agree well with the data acquired from experimental studies (IC50) and from CBS calculations. The CPCM solvation model was used throughout the work, while the SMD model-employed as a reference-was used only for CAPE. The main conclusion drawn from the analysis was that SPLET is the mechanism that governs the reaction of phenolic acids with (·)HO2, while PT-ET governs the reaction of phenols with (·)O2(-). In kinetic investigations of the CPCET process, the rate constant decreases as the solvent polarity increases, so the reaction velocity slows down.

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

“…The B3LYP hybrid functional was used throughout the computations; the use of this functional is because of the previous work [25,26] done on the three molecular systems where the B3LYP where used. This functional consists of the Becke's three parameters exact exchange functional (B3) [43] combined with the non-local gradient corrected correlation functional (due to Lee-Yang-Parr (LYP)) [44].…”

“…These compounds were studied experimentally on the DNA damage by Sestili et al [24] where they showed that all these three compounds are able to chelate Fe 2+ . We did in our previous work [25,26] the theoretical study of their antioxidant activity. Therefrom, we found that MBC was the good antioxidant but not more than quercetin, the one of the best antioxidant known.…”

“…To look deeply the antioxidant action of chelates, the superoxide radical O 2 ÅÀ and its hydrated form HO 2 Å were used in this work to test these chelates. They were required because of their abundance in the human organism [26].…”

Protective Effects of Dihydromyricetin against •OH-Induced Mesenchymal Stem Cells Damage and Mechanistic Chemistry

“…Atom transfer can be further classified into several subtypes: hydrogen atom transfer (HAT), concerted proton-coupled electron transfer (CPCET), electron transfer followed by proton transfer (ET-PT), proton transfer followed by electron transfer (PT-ET), and sequential proton loss electron transfer (SPLET) among others [35]. As a stable free radical, DPPH‚ can be reduced by phytophenols to DPPH-H (Equation (3)) [36].…”

“…Molecules 2016, 21, 604 6 of 13 sequential proton loss electron transfer (SPLET) among others [35]. As a stable free radical, DPPH• can be reduced by phytophenols to DPPH-H (Equation (3)) [36].…”