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.