Nino Russo

Antioxidant activity of trans-resveratrol toward hydroxyl and hydroperoxyl radicals: a quantum chemical and computational kinetics study.

In this work, we have carried out a systematic study of the antioxidant activity of trans-resveratrol toward hydroxyl ((•)OH) and hydroperoxyl ((•)OOH) radicals in aqueous simulated media using density functional quantum chemistry and computational kinetics methods. All possible mechanisms have been considered: hydrogen atom transfer (HAT), proton-coupled electron transfer (PCET), sequential electron proton transfer (SEPT), and radical adduct formation (RAF). Rate constants have been calculated using conventional transition state theory in conjunction with the Collins-Kimball theory. Branching ratios for the different paths contributing to the overall reaction, at 298 K, are reported. For the global reactivity of trans-resveratrol toward (•)OH radicals, in water at physiological pH, the main mechanism of reaction is proposed to be the sequential electron proton transfer (SEPT). However, we show that trans-resveratrol always reacts with (•)OH radicals at a rate that is diffusion-controlled, independent of the reaction pathway. This explains why trans-resveratrol is an excellent but very unselective (•)OH radical scavenger that provides antioxidant protection to the cell. Reaction between trans-resveratrol and the hydroperoxyl radical occurs only by phenolic hydrogen abstraction. The total rate coefficient is predicted to be 1.42 × 10(5) M(-1) s(-1), which is much smaller than the ones for reactions of trans-resveratrol with (•)OH radicals, but still important. Since the (•)OOH half-life time is several orders larger than the one of the (•)OH radical, it should contribute significantly to trans-resveratrol oxidation in aqueous biological media. Thus, trans-resveratrol may act as an efficient (•)OOH, and also presumably (•)OOR, radical scavenger.

Metal-ligand interactions : from atoms, to clusters, to surfaces

Ligands on clusters - adsorbates on surfaces the chemistry of transition metal clusters surface science studies of molecular adsorbates on solid surfaces - a series of case studies concepts in heterogeneous catalysis electronic structure theory for transition metal systems - a survey selectivity in catalysis by metals and alloys metal-CO interactions - well-defined surfaces and supported particles linear semibridging carbonyls 5 the structure and bonding of the chromium cyclopentadienyl dicarbonyl dimer carbon dioxide organometallic chemistry - theoretical developments quantum chemical models of chemisorption on metal surfaces catalytic reactions of transition metal clusters and surfaces from ab initio theory reactivity and electronic structure of organometallic radicals density functional theory - principles and applications to metal-ligand interactions density functional model calculations for homogeneous and heterogenous catalysis a general energy decomposition scheme for the study of metal-ligand interactions in complexes clusters and solids physiochemical characterization of novel polymeric copper complexes with long-chain aliphatic diamines.

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.

Theoretical determination of electron affinity and ionization potential of DNA and RNA bases

The ionization potentials and electron affinities of thymine, cytosine, adenine, guanine, and uracil were determined at density functional level using different exchange‐correlation functionals and basis sets. Results showed that the computed ionization potentials are very close to the experimental counterparts. The sign of adiabatic electron affinities of adenine, thymine, and uracil is unaffected by the used level of theory while that for guanine and cytosine depends on both the used potential and basis set. Vertical electron affinities are always negative in agreement with the experimental indications.

Pyranoanthocyanins: A Theoretical Investigation on Their Antioxidant Activity

The antioxidant radical scavenging capacity of pyranoanthocyanins present in aged wine and coming from the chemical transformation undergone by anthocyanins was theoretically explored by DFT/B3LYP methods. The two main working mechanisms (H atom donation and single-electron transfer) were investigated, and the O-H bond dissociation energy (BDE) and ionization potential (IP) parameters were computed in the gas phase and in water and benzene solutions. Results indicated that systems possessing the catechol functionality as well as the o-dimethoxy motif are good candidates to donate a H atom to the free radicals, inactivating them. Compounds with a higher degree of electron delocalization may work within the single-electron transfer mechanism. Results provided molecular insight into factors that influence the radical scavenging potential of anthocyanins and then the beneficial health effects of these wine pigments.

The Second-Generation Anticancer Drug Nedaplatin: A Theoretical Investigation on the Hydrolysis Mechanism

The hydrolysis reaction processes of the second-generation platinum derivative Nedaplatin have been studied using density functional theory (DFT) combined with the conductor-like dielectric continuum model (CPCM) approach, in order to obtain detailed data on its mechanism of action. The first and the second hydrolysis of Nedaplatin, corresponding to the ring opening followed by the loss of the ligand, respectively, have been explored in neutral and acid conditions. The influence of an extra water molecule which could assist the degradation processes has also been considered including in our models an explicit water molecule other than the reactive one. The computed potential energy surfaces show that the rate limiting step in neutral conditions is the first hydrolysis process and, consequently, the double hydrated complex is suggested to be the species reacting with the DNA purine bases, while in acid conditions the trend is different, with the second hydrolysis process being the rate limiting step. The results obtained in this work allow us to make a comparison with the trends previously found for the other platinum anticancer drugs currently used in the medical protocols.

Solvation effects on reaction profiles by the polarizable continuum model coupled with the Gaussian density functional method

An efficient version of the polarizable continuum model for solvation has been implemented in the Gaussian density‐functional‐based code called deMon. Solvation free energies of representative compounds have been calculated as a preliminary test. The hydration effects on the reaction profile of the Cl−+CH3Cl→ClCH3+Cl− reaction and the thermodynamics of the Menschutkin reaction have also been investigated. Finally, the conformational behavior of the 1,2‐diazene cis–trans isomerization process in water was examined. Comparisons between the results obtained and the available experimental data and previous theoretical computations have been made. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 290–299, 1998

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.

Geometries, singlet‐triplet separations, dipole moments, ionization potentials, and vibrational frequencies in methylene (CH2) and halocarbenes (CHF, CF2, CCl2, CBr2, and CI2)

The geometrical structure, harmonic vibrational frequencies, ionization potentials, and singlet‐triplet gaps of simple substituted halocarbenes (CHF, CF2, CCl2, CBr2, and CI2) have been investigated by using the linear combination of Gaussian‐type‐orbital local‐spin‐density method. Optimized geometries, as well as vibrational frequencies, are in good agreement with available experimental data. The obtained values of singlet‐triplet splittings (ΔEST) computed taking into account the nonlocal corrections are very close to experimental and previous theoretical investigations employing extended configuration interaction contributions. Many of the calculated properties obtained here have not yet been determined both experimentally and theoretically.

LANL2DZ basis sets recontracted in the framework of density functional theory

In this paper we report recontracted LANL2DZ basis sets for first-row transition metals. The valence-electron shell basis functions were recontracted using the PWP86 generalized gradient approximation functional and the hybrid B3LYP one. Starting from the original LANL2DZ basis sets a cyclic method was used in order to optimize variationally the contraction coefficients, while the contraction scheme was held fixed at the original one of the LANL2DZ basis functions. The performance of the recontracted basis sets was analyzed by direct comparison between calculated and experimental excitation and ionization energies. Results reported here compared with those obtained using the original basis sets show clearly an improvement in the reproduction of the corresponding experimental gaps.