Energetic and Structural Properties of Two Phenolic Antioxidants: Tyrosol and Hydroxytyrosol

Abstract

Theoretical and experimental studies on the energetic, structural and some other relevant physicochemical properties of the antioxidant tyrosol (1), hydroxytyrosol (1OH) molecules and the corresponding radicals 1 rad• and 1O rad • are reported in this work. The experimental values of the gas-phase enthalpy of formation, Δ f H m 0 (g), in kJ•mol −1 , of 1 (−302.4 ± 3.4) and 1OH (−486.3 ± 4.1) have been determined. Quantum chemical calculations, at DFT (M05-2X) and composite ab initio G3 and G4 levels of theory, provided results that served to (i) confirm the excellent consistency of the experimental measurements performed, (ii) establish that the stabilizing effect of H-bond of hydroxyethyl chain and aromatic ring (OH•••π interaction) is smaller in radicals than in parent molecules, (iii) deducecombining experimental data in isodesmic reactionsΔ f H m 0 (g) of radicals 1 rad • (−152.3 ± 4.4 kJ• mol −1 ) and 1O rad • (−370.6 ± 3.8 kJ•mol −1 ), (iv) estimate a reliable O−H bond dissociation enthalpy, BDE of 1 (368.1 ± 5.6 kJ•mol −1 ) and of 1OH (333.7 ± 5.6 kJ• mol −1 ), and (v) corroborateusing "BDE criteria"than 1OH is a more effective antioxidant than 1.

Tyrosol as a Neuroprotector: Strong Effects of a “Weak” Antioxidant

“…The low antiradical/antioxidant activity of Tyr compared with the closely related hydroxyTyr compound is due to the following circumstances: the presence of 1 hydroxyl radical phenol ring did not allow efficient scavenging of radicals; effective Tyr concentrations are in the range of µM concentrations and significantly exceed the effective concentration of hydroxyTyr; Tyr accumulates intracellularly more slowly and probably reaches effective concentrations that have protective effects later [ 34 , 48 , 88 , 89 ].…”

Antiradical Properties of N-Oxide Surfactants—Two in One

“…In the hydrogen atom transfer, the X−H bond dissociation enthalpy (BDE) should be considered a crucial parameter [ 32 , 39 , 40 , 43 ], as the more weakly bonded H atoms would be more active in the scavenging reaction given in equation 2. BDE was calculated at 298 K as the enthalpy difference for the reaction [ 40 , 41 , 43 , 45 ]: surf − H → surf • + • H …”

Experimental and Computational Studies on the Gas-Phase Acidity of 5,5-Dialkyl Barbituric Acids

“…The quantum chemical calculations were carried out using the Gaussian 09 package . The geometry optimization and thermochemistry data calculations for the neutral 5,5-alkylbarbituric acids, as well as their corresponding deprotonated ions (see the Supporting Information), were obtained by using the Gaussian-n methods (Gn) at G3 and G4 high levels of theory. , These theories have been described in detail in the literature and are well-known to provide very consistent results for a wide range of molecular systems. , …”