Biomedical subjects

Pedro Salvador

Publications and source records attributed to Pedro Salvador.

8 recordsLinked to original sources

PubMed2007

On the quality of the hardness kernel and the Fukui function to evaluate the global hardness.

An approximated hardness kernel, which includes the second derivative with respect to the density of the kinetic energy, the electron-electron coulomb repulsion, and the exchange density functionals, has been tested for the calculation of the global hardness. The results obtained for a series of 40 cations and neutral systems and 16 anions represent in most cases an improvement of the results obtained using the HOMO-LUMO gap approach and indicate the viability of this approach to evaluate global hardness. In addition, the relevance of the Fukui function approximation and the role of the three components of the hardness kernel in the evaluation of the global hardness have been analyzed.

Anions↗

PubMed2006

Photoelectrochemical behavior of nanostructured WO3 thin-film electrodes: The oxidation of formic acid.

Nanostructured tungsten trioxide thin-film electrodes are prepared on conducting glass substrates by either potentiostatic electrodeposition from aqueous solutions of peroxotungstic acid or direct deposition of WO3 slurries. Once treated thermally in air at 450 degrees C, the electrodes are found to be composed of monoclinic WO3 grains with a particle size around 30-40 nm. The photoelectrochemical behavior of these electrodes in 1 M HClO4 apparently reveals a low degree of electron-hole recombination. Upon addition of formic acid, the electrode showed the current multiplication phenomenon together with a shift of the photocurrent onset potential toward less positive values. Photoelectrochemical experiments devised on the basis of a kinetic model reported recently [I. Mora-Seró, T. Lana-Villarreal, J. Bisquert, A. Pitarch, R. Gómez, P. Salvador, J. Phys. Chem. B 2005, 109, 3371] showed that an interfacial mechanism of inelastic, direct hole transfer takes place in the photooxidation of formic acid. This behavior is attributed to the tendency of formic acid molecules to be specifically adsorbed on the WO3 nanoparticles, as evidenced by attenuated total reflection infrared spectroscopy.

Electrochemistry↗

PubMed2006

Aromaticity measures from fuzzy-atom bond orders (FBO). The aromatic fluctuation (FLU) and the para-delocalization (PDI) indexes.

In the past few years, there has been a growing interest for aromaticity measures based on electron density descriptors, the para-delocalization (PDI) and the aromatic fluctuation (FLU) indexes being two recent examples. These aromaticity indexes have been applied successfully to describe the aromaticity of carbon skeleton molecules. Although the results obtained are encouraging, because they follow the trends of other existing aromaticity measures, their calculation is rather expensive because they are based on electron delocalization indexes (DI) that involve cumbersome atomic integrations. However, cheaper electron-sharing indexes (ESIs), which in principle could play the same role as the DI in such aromaticity calculations, can be found in the literature. In this letter we show that PDI and FLU can be calculated using fuzzy-atom bond order (FBO) measures instead of DIs with an important saving of computing time. In addition, a basis-set-dependence study is performed to assess the reliability of these measures. FLU and PDI based on FBO are shown to be both good aromaticity indexes and almost basis-set-independent measures. This result opens up a wide range of possibilities for PDI and FLU to also be calculated on large organic systems. As an example, the DI and FBO-based FLU and PDI indexes have also been calculated and compared for the C60 molecule.

Journal Article↗

PubMed2005

Comparison of the AIM delocalization index and the Mayer and fuzzy atom bond orders.

In this paper the behavior of three well-known electron-sharing indexes, namely, the AIM delocalization index and the Mayer and fuzzy atom bond orders are studied at the Hartree-Fock level. A large number of five-membered ring molecules, containing several types of bonding, constitute the training set chosen for such purpose. A detailed analysis of the results obtained shows that the three indexes studied exhibit strong correlations, especially for homonuclear bonds. The correlation is somewhat poorer but still significant for polar bonds. In this case, the bond orders obtained with the Mayer and fuzzy atom approaches are normally closer to the formally predicted bond orders than those given by the AIM delocalization indexes, which are usually smaller than those expected from chemical intuition. In some particular cases, the use of diffuse functions in the calculation of Mayer bond orders leads to unrealistic results. In particular, noticeable trends are found for C-C bonds, encouraging the substitution of the delocalization index by the cheaper fuzzy atom or even the Mayer bond orders in the calculation of aromaticity indexes based on the delocalization index such as the para-delocalization index and the aromatic fluctuation index.

Journal Article↗

PubMed2005

Density functional energy decomposition into one- and two-atom contributions.

The present work provides a generalization of Mayer's energy decomposition for the density-functional theory (DFT) case. It is shown that one- and two-atom Hartree-Fock energy components in Mayer's approach can be represented as an action of a one-atom potential V(A) on a one-atom density rho(A) or rho(B). To treat the exchange-correlation term in the DFT energy expression in a similar way, the exchange-correlation energy density per electron is expanded into a linear combination of basis functions. Calculations carried out for a number of density functionals demonstrate that the DFT and Hartree-Fock two-atom energies agree to a reasonable extent with each other. The two-atom energies for strong covalent bonds are within the range of typical bond dissociation energies and are therefore a convenient computational tool for assessment of individual bond strength in polyatomic molecules. For nonspecific nonbonding interactions, the two-atom energies are low. They can be either repulsive or slightly attractive, but the DFT results more frequently yield small attractive values compared to the Hartree-Fock case. The hydrogen bond in the water dimer is calculated to be between the strong covalent and nonbonding interactions on the energy scale.

Journal Article↗

PubMed2005

Photoelectrochemical behavior of nanostructured TiO(2) thin-film electrodes in contact with aqueous electrolytes containing dissolved pollutants: a model for distinguishing between direct and indirect interfacial hole transfer from photocurrent measurements.

A model for describing the photoelectrochemical behavior of nanostructured TiO(2) thin-film electrodes in contact with aqueous electrolytes containing dissolved pollutant species is presented. The model correlates the steady-state photocurrent, the illumination intensity, and the specific photooxidation mechanism for dissolved pollutant species in competition with water molecules. For physical events, the model considers the existence of hole trapping at surface states and the specific hole-transfer mechanisms taking place at the semiconductor-electrolyte interface (direct, via photogenerated valence-band free holes or indirect, via photogenerated surface-bound OH radicals or both). The model has been applied to the study of the photooxidation of aqueous solutions of formic acid and methanol. In agreement with previous results concerning massive polycrystalline electrodes, methanol is found to be photooxidized via indirect hole transfer, whereas formic acid is photooxidized mainly with the participation of valence-band free holes.

Journal Article↗

PubMed2004

Calculation of trans-hydrogen-bond 13C-15N three-bond and other scalar J-couplings in cooperative peptide models. A density functional theory study.

We report B3LYP DFT calculations on peptide models that consider the effects of cooperative interactions with proximate H-bonds and local geometry at the H-bonding site upon trans-H-bond (13)C-(15)N three-bond scalar J-couplings. The calculations predict that cooperative interactions with other H-bonds within a H-bonding chain can significantly increase the magnitude of these couplings. Such increases are due to a combination of the presence of the neighboring H-bonds and the slight increase in C=O distances expected for peptide H-bonds near the centers of H-bonding chains. The energies of H-bonds inferred from H-bonding distances, alone, could be significantly in error if the effects of neighboring H-bonds are ignored.

Carbon Isotopes↗

PubMed2003

Anthropogenic and natural influence on the PM(10) and PM(2.5) aerosol in Madrid (Spain). Analysis of high concentration episodes.

Non-mineral carbon is the main component of PM10 and PM2.5 at an urban roadside site in Madrid accounting for more than 50% of the total bulk mass in winter pollution episodes. In these cases a 70-80% of the particle mass is anthropogenic. Particles of crustal/mineral origin contribute significantly to the observed PM10 concentrations, especially in spring and summer. They have also been found in the PM2.5 fraction although secondary particles are the next most important contributor in this size. Long-range transport particle episodes of Saharan dust significantly contribute to exceedence of the new daily limiting PM10 value in the urban network and at nearby rural background stations. This type of long-range transport event also influences PM2.5 concentrations. The crustal contribution can account for up to 67 and 53% of the PM10 and PM2.5 bulk mass in such cases.

Aerosols↗