Density functional theory (DFT) calculations were performed to evaluate the antioxidant activity of molecules commonly present in many Mediterranean foods. A series of interesting systems, including tyrosol, hydroxytyrosol, gallic, and caffeic acids, belonging to the family of phenols, resveratrol of the stilbenes family, epicatechin, kaempferol, and cianidin as examples of flavonoids and, at last, a simplified model of R-tocopherol (6-hydroxy-2,2,5,7,8-pentamethylchroman (HPMC)) were studied. Conformational behavior was examined at the B3LYP/6-311++G(3df,2p) level of theory, in the gas phase and in two solvents with different polarity (water and benzene), with the aim to compute the bond dissociation enthalpy (BDE) for the O-H bonds and the adiabatic ionization potentials (IP). BDE and IP for these systems do not follow the same trends in gas and solution phases: the major differences with respect to vacuum are found as when water computations are performed. On the basis of the computed BDE and IP values, the most active systems able to transfer an H-atom seem to be R-tocopherol followed by hydroxytyrosol, gallic acid, caffeic acid, and epicatechin. Instead, kaempferol and resveratrol appear to be the best candidates for an electron-transfer mechanism.

Gold nanoparticles supported on P25 titania (Au/TiO(2)) exhibit photocatalytic activity for UV and visible light (532 nm laser or polychromatic light λ > 400 nm) water splitting. The efficiency and operating mechanism are different depending on whether excitation occurs on the titania semiconductor (gold acting as electron buffer and site for gas generation) or on the surface plasmon band of gold (photoinjection of electrons from gold onto the titania conduction band and less oxidizing electron hole potential of about -1.14 V). For the novel visible light photoactivity of Au/TiO(2), it has been determined that gold loading, particle size and calcination temperature play a role in the photocatalytic activity, the most active material (Φ(H2) = 7.5% and Φ(O2) = 5.0% at 560 nm) being the catalyst containing 0.2 wt % gold with 1.87 nm average particle size and calcined at 200 °C.

When irradiated with visible light (λ > 400 nm) 1 wt % gold-supported ceria nanoparticles generate oxygen from water (10.5 μmol·h(-1)) more efficiently than the standard WO(3) (1.7 μmol·h(-1)) even under UV irradiation (9.5 μmol·h(-1)). This remarkable photocatalytic activity arises from a novel preparation method to reduce the particle size of ceria (5 nm) by means of electrostatic binding of Ce(4+) to alginate gel, subsequent supercritical CO(2) drying, and calcination. The low loading of Au is crucial for the observed high catalytic activity.

In this review, we briefly summarize the reliability of the density functional theory (DFT)-based methods to accurately predict the main antioxidant properties and the reaction mechanisms involved in the free radical-scavenging reactions of chemical compounds present in food. The analyzed properties are the bond dissociation energies, in particular those involving OH bonds, electron transfer enthalpies, adiabatic ionization potentials, and proton affinities. The reaction mechanisms are hydrogen-atom transfer, proton-coupled electron transfer, radical adduct formation, single electron transfer, sequential electron proton transfer, proton-loss electron transfer, and proton-loss hydrogen-atom transfer. Furthermore, the chelating ability of these compounds and its role in decreasing or inhibiting the oxidative stress induced by Fe(III) and Cu(II) are considered. Comparisons between theoretical and experimental data confirm that modern theoretical tools are not only able to explain controversial experimental facts but also to predict chemical behavior.

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The complexes formed by the simplest amino acid, glycine, with different bare and hydrated metal ions (Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+)) were studied in the gas phase and in solvent in order to give better insight into the field of the metal ion-biological ligand interactions. The effects of the size and charge of each cation on the organization of the surrounding water molecules were analyzed. Results in the gas phase showed that the zwitterion of glycine is the form present in the most stable complexes of all ions and that it usually gives rise to an eta(2)O,O coordination type. After the addition of solvation sphere, a resulting octahedral arrangement was found around Ni(2+), Co(2+), and Fe(2+), ions in their high-spin states, whereas the bipyramidal-trigonal (Mn(2+) and Zn(2+)) or square-pyramidal (Cu(2+)) geometries were observed for the other metal species, according to glycine behaves as bi- or monodentate ligand. Despite the fact that the zwitterionic structure is in the ground conformation in solution, its complexes in water are less stable than those obtained from the canonical form. Binding energy values decrease in the order Cu(2+) > Ni(2+) > Zn(2+) approximately Co(2+) > Fe(2+) > Mn(2+) and Cu(2+) > Ni(2+) > Mn(2+) approximately Zn(2+) > Fe(2+) > Co(2+) for M(2+)-Gly and Gly-M(2+) (H(2)O)(n) complexes, respectively. The nature of the metal ion-ligand bonds was examined by using natural bond order and charge decomposition analyses.

The stationary points characterizing the potential energy profiles of the complexation process of the proline unusual α-amino acid with the alkali metal ions M+ (Li+, Na+ and K+) were investigated by density functional theory using the B3LYP hybrid potential and the 6-311++G** basis set. Different types of M+ coordinations on several proline conformers were considered. Results show that Li+, Na+, and K+ cations bind very similarly to the proline. In the M+-proline lowest-energy conformer, the cation appears always coordinated to both the oxygen atoms of the zwitterionic form of the amino acid which presents the up ring pucker. The complexes obtained by the interaction of the alkali ions with both the carbonyl oxygen and nitrogen of the α-amino acid were found, in all cases, at energy values not too far from those of the global minima. Absolute metal ion affinities were computed using various exchange-correlation functionals.