Several aspects related to the antioxidant activity of ellagic acid were investigated using the density functional theory. It was found that this compound is unusually versatile for protecting against the toxic effects caused by oxidative stress. Ellagic acid, in aqueous solution at physiological pH, is able of deactivating a wide variety of free radicals, which is a desirable capability since in biological systems, these species are diverse. Under such conditions, the ellagic acid anion is proposed as the key species for its protective effects. It is predicted to be efficiently and continuously regenerated after scavenging two free radicals per cycle. This is an advantageous and unusual behavior that contributes to increase its antioxidant activity at low concentrations. In addition, the ellagic acid metabolites are also capable of efficiently scavenging a wide variety of free radicals. Accordingly, it is proposed that the ellagic acid efficiency for that purpose is not reduced after being metabolized. On the contrary, it provides continuous protection against oxidative stress through a free radical scavenging cascade. This is an uncommon and beneficial behavior, which makes ellagic acid particularly valuable to that purpose. After deprotonation, ellagic acid is also capable of chelating copper, in a concentration dependent way, decreasing the free radical production. In summary, ellagic acid is proposed to be an efficient multiple-function protector against oxidative stress.

The relative free radical scavenging activity of beta-carotene, lycopene, and torulene toward OOH radicals has been studied using density functional theory. Hydrogen atom transfer (HAT) and radical adduct formation (RAF) mechanisms have been considered. All the possible reaction sites have been included in the modeling, and detailed branching ratios are reported for the first time. The reactions of hydrocarbon carotenoids (Car) with peroxyl radicals, in both polar and nonpolar environments, are predicted to proceed via RAF mechanism, with contributions higher than 98% to the overall OOH + Car reactions. Lycopene and torulene were found to be more reactive than beta-carotene. In nonpolar environments the reactivity of the studied carotenoids toward peroxyl radical follows the trend LYC > TOR > BC, whereas in aqueous solutions it is TOR > LYC > BC. OOH adducts are predicted to be formed mainly at the terminal sites of the conjugated polyene chains. The main addition sites were found to be C5 for beta-carotene and lycopene and C30 for torulene. The general agreement between the calculated magnitudes and the available experimental data supports the predictions from this work.

The OOH radical scavenging activity of canolol (CNL) has been studied in aqueous and lipid solutions, using the density functional theory. CNL is predicted to react about 3.6 times faster in aqueous solution than in lipid media. The overall rate coefficients are predicted to be 2.5 × 10(6) and 6.8 × 10(5) M(-1) s(-1), respectively. The OOH radical scavenger activity of canolol is predicted to be similar to that of carotenes, higher than that of allicin, and much higher than that of melatonin. Branching ratios for the different channels of reaction are reported for the first time. It was found that the reactivity of canolol toward OOH radicals takes place almost exclusively by H atom transfer from the phenolic moiety in canolol, regardless of the polarity of the environment. Taking into account that the reactivity of peroxyl radicals is significantly lower than that of other reactive oxygen species, canolol is proposed to be a very good antioxidant.

The OOH radical scavenging activity of sinapinic acid (HSA) has been studied in aqueous and lipid solutions, using the Density Functional Theory. HSA is predicted to react about 32.6 times faster in aqueous solution than in lipid media. The overall rate coefficients are predicted to be 5.39 × 10(5) and 1.66 × 10(4) M(-1) s(-1), respectively. Branching ratios for the different channels of reaction are also reported for the first time, as well as the UV-Vis spectra of the main products of reaction. It was found that the reactivity of sinapinic acid towards OOH radicals takes place almost exclusively by H atom transfer from its phenolic moiety. However it was found to react via SET, at diffusion-limit controlled rate constants, with ˙OH, ˙OCCl(3) and ˙OOCCl(3) radicals. It was found that the polarity of the environment and the deprotonation of HSA in aqueous solution, both increase the reactivity of this compound towards peroxyl radicals.