Tiziana Marino

Influence of Excitation Wavelength (UV or Visible Light) on the Photocatalytic Activity of Titania Containing Gold Nanoparticles for the Generation of Hydrogen or Oxygen from Water

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.

Efficient Visible-Light Photocatalytic Water Splitting by Minute Amounts of Gold Supported on Nanoparticulate CeO2 Obtained by a Biopolymer Templating Method

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.

Gas-phase metal ion (Li+, Na+, Cu+) affinities of glycine and alanine

The gas-phase metal affinities of glycine and alanine for Li+, Na+ and Cu+ ions have been determined theoretically employing the hybrid B3LYP exchange-correlation functional and using extended basis sets. All computations indicate that the metal ion affinity (MIA) decreases on going from Cu+ to Li+ and Na+ for both the considered amino acids. The absolute MIA values are close to the experimental counterparts with the exception of lithium for which a deviation of about 7 kcal/mol at the B3LYP level is obtained. The optimized structures indicate that Li+, Na+ and Cu+ prefer a bidentate coordination, bonding with both nitrogen and oxygen atoms of amino acids.

Towards non-toxic solvents for membrane preparation: a review

Solvents are used in every chemical process and affect its overall safety, environmental, and economic impact. Membrane processes have attracted increasing interest as sustainable alternatives to traditional technologies, being characterized by reduced energy consumption and use of chemicals. However, the most important membrane preparation techniques are often based on the use of toxic solvents, which reduces the benefit to the environment. Due to the influence of solvent properties such as viscosity, dielectric constant, polarity, and boiling point on the final features and the indispensable prerequisite of dissolving the selected polymer (at room or high temperature, depending on the technique), one of the most difficult but most interesting challenges for membrane scientists is replacing these solvents, such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methyl-2-pyrrolidone (NMP), and tetrahydrofuran (THF), with safer alternatives. In this review, the most relevant steps towards the use of non-toxic solvents in membrane preparation are reported, focusing particular attention on the non-solvent induced and temperature induced phase separation (NIPS and TIPS) techniques. Supercritical CO2 (ScCO2) and ionic liquids (ILs) are promising examples of benign solvents, and their use in membrane preparation will also be described. The total replacement of toxic diluents with greener alternatives still remains at the beginning stages. However, in several cases, membranes prepared using less/non-toxic solvents achieved performance comparable to those produced with classical toxic solvents. This review offers valid support for membrane scientists who wish to reduce the environmental impact of solvent use and increase membrane processes sustainability.

Food Antioxidants: Chemical Insights at the Molecular Level

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.

Radical Scavenging Ability of Gallic Acid toward OH and OOH Radicals. Reaction Mechanism and Rate Constants from the Density Functional Theory

Gallic acid is a ubiquitous compound, widely distributed in the vegetal kingdom and frequently found in the human diet. In the present work, its primary antioxidant activity has been investigated using the density functional theory (DFT), and the quantum mechanics-based test for overall free radical scavenging activity (QM-ORSA) protocol. It was found that gallic acid is a better antioxidant than the reference compound, Trolox, regardless of the polarity of the environment. In addition, gallic acid is predicted to be among the best peroxyl radical scavengers identified so far in nonpolar (lipid) media. This compound is capable of scavenging hydroxyl radicals at diffusion-limited rates, and hydroperoxyl radicals with rate constants in the order of 10(5) M(-1) s(-1). The deprotonation of gallic acid, in aqueous solution, is predicted to increase the protective action of this compound against oxidative stress. Gallic acid was also identified as a versatile scavenger, capable of rapidly deactivating a wide variety of reactive oxygen species (ROS) and reactive nitrogen species (RNS) via electron transfer at physiological pH.

Peptide hydrolysis by the binuclear zinc enzyme aminopeptidase from Aeromonas proteolytica: a density functional theory study.

Aminopeptidase from Aeromonas proteolytica (AAP) is a binuclear zinc enzyme that catalyzes the cleavage of the N-terminal amino acid residue of peptides and proteins. In this study, we used density functional methods to investigate the reaction mechanism of this enzyme. A model of the active site was constructed on the basis of the X-ray crystal structure of the native enzyme, and a model dipeptide was used as a substrate. It was concluded that the hydroxide is capable of performing a nucleophilic attack at the peptide carbonyl from its bridging position without the need to first become terminal. The two zinc ions are shown to have quite different roles. Zn2 binds the amino group of the substrate, thereby orienting it toward the nucleophile, while Zn1 stabilizes the alkoxide ion of the tetrahedral intermediate, thereby lowering the barrier for the nucleophilic attack. The rate-limiting step is suggested to be the protonation of the nitrogen of the former peptide bond, which eventually leads to the cleavage of the C-N bond.

Human Insulin-Degrading Enzyme Working Mechanism

The possible mechanism by which the insulin-degrading enzyme (IDE) zinc-binding protease carries out its catalytic function toward two peptides of different length, simulating a portion of B chain of insulin, was investigated on an enzymatic model consisting of 130 /159 atoms, using the density functional theory method and the hybrid exchange-correlation functional B3LYP in gas phase and in the protein environment. Based on the geometry and relative stabilities of minima and transition states on the potential energy profiles, we determined that proteolysis reaction is exothermic and proceeds quickly as the barrier in the rate-limiting step falls widely within the range of values expected for an enzymatic catalysis, both in vacuum and in protein medium.

The role of glutathione in cadmium ion detoxification: Coordination modes and binding properties – A density functional study

In this investigation the reduced form of glutathione molecule (GSH) was considered as a model in the coordination chemistry of Cd(2+) and group thiol-containing peptides. Three different forms of GSH, corresponding to the prevalent ones in gas-phase and in aqueous solution, were taken into account in the metallation process. The obtained complexes were characterized at the density functional B3LYP level with the purpose to give better insight in the chelation mechanism of GSH with heavy metal ions in living organisms. Solvent effects, whether with explicit water molecules or with polarizable continuum model (PCM), were considered on the most stable cadmium-complexes obtained by every GSH charged species examined.

A proposal for mitochondrial processing peptidase catalytic mechanism.

The reaction mechanism of the Mitochondrial Processing Peptidase enzyme (MPP) was investigated by using hybrid density functional theory. This enzyme removes the NH(2)-terminal targeting signals of nuclear-encoded mitochondrial protein precursors in the mitochondrial matrix. The catalytic process was studied using a model for the active site consisting of 161 atoms locating all the stationary points on the potential energy curve and determining the main energetic, structural, and electronic features that drive the catalysis. Despite the differences between the B3LYP and MPWB1K descriptions, it is possible hypothesize that the rate-limiting step of the reaction is most likely the nucleophilic attack of zinc-bound hydroxide to a carbonyl carbon of the substrate. The results allowed assignment of the proper roles to some active site residues in this mechanism.