Total publications: 603
553. Fermi resonance coupling in the C-H stretching region of methoxide adsorbed on clean Ru(001): a combined RAIRS and theoretical study
in SURFACE SCIENCE, 2004, ISSN: 0039-6028, Volume: 566,
Article, Indexed in: crossref, scopus, wos
A combined reflection-absorption infrared spectroscopy (RAIRS) and theoretical study on methoxide adsorbed on clean Ru(001) enabled to interpret the C-H stretching region of the spectrum. The Fermi resonance between the fundamental stretching modes and the overtones of the deformations has been analyzed. Density functional cluster model calculations (DFT) showed that methoxide adsorbs preferentially on hcp threefold cavities, and provided the unperturbed vibrational frequencies. Once corrected by the experimentally determined frequencies, they were used to calculate the Fermi resonance coupling constants by a normal mode model, assuming the local symmetry suggested by the experimental results (C-s). The present approach shows that a reliable description of the experimental C-H stretching region of adsorbed methoxide on Ru(001) may be obtained.
554. Fluorobenzene-argon ground-state intermolecular potential energy surface
in JOURNAL OF CHEMICAL PHYSICS, 2004, ISSN: 0021-9606, Volume: 120,
Article, Indexed in: crossref, scopus, wos
The ground-state intermolecular potential energy surface for the fluorobenzene-argon van der Waals complex is evaluated using the coupled-cluster singles and doubles including connected triple excitations model, with the augmented correlation consistent polarized valence double-zeta basis set extended with a set of 3s3p2d1f1g midbond functions. In the surface minima the Ar atom is located above and below the fluorobenzene plane at a distance of 3.562 Angstrom from the fluorobenzene center of mass and at an angle of 6.33degrees with respect to the axis perpendicular to the fluorobenzene plane. The corresponding binding energy is 391.1 cm(-1). Both these results and the eigenvalues obtained from the potential compare well with the experimental data available. (C) 2004 American Institute of Physics.
555. Modeling chemical and biological systems: A successful course for undergraduate students
in JOURNAL OF CHEMICAL EDUCATION, 2004, ISSN: 0021-9584, Volume: 81,
Article, Indexed in: crossref, scopus, wos
This article examine an optional course "Modeling Chemical and Biological System". Rather than following the traditional format of lectures and practical classes, the course is organized into separate practical projects introducing the theory as it is needed. Computer aided software engineering tools are used to animate and visualize the discussions.
556. Natural inhibitors of proteases - pharmacological target for destabilization/stabilization of the protease/inhibitor complex
in FUNDAMENTAL & CLINICAL PHARMACOLOGY, 2004, ISSN: 0767-3981, Volume: 18,
Abstract, Indexed in: wos
557. Phenolic acid derivatives with potential anticancer properties - a structure-activity relationship study. Part 1: Methyl, propyl and octyl esters of caffeic and gallic acids
in BIOORGANIC & MEDICINAL CHEMISTRY, 2004, ISSN: 0968-0896, Volume: 12,
Article, Indexed in: crossref, scopus, wos
The antiproliferative and cytotoxic properties of polyphenolic acid derivatives, structurally related with the natural models caffeic and gallic acids. have been tested in human cervix adenocarcinoma cells (HeLa). Simultaneous structural information was obtained for these Compounds through theoretical ab initio methods. This study was conducted for the following esters: methyl caffeate (MC, 1), propyl caffeate (PC, 2), octyl caffeate (OC, 3), methyl gallate (MG, 4), propyl gallate (PG, 5) and octyl gallate (OG, 6). A significant growth-inhibition effect was assessed for some of these compounds, clearly dependent on their structural characteristics. Marked structure-activity relationships (SARs)-namely the number of hydroxyl ring substituents-were found to rule the biological effect of such systems.
558. Toward the prediction of the activity of antioxidants: Experimental and theoretical study of the gas-phase acidities of flavonoids
in JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY, 2004, ISSN: 1044-0305, Volume: 15,
Article, Indexed in: crossref, scopus, wos
The relative gas-phase acidities were determined for eight flavonoids, applying the kinetic method, by means of electrospray-ion trap mass spectrometry. The experimental acidity order, myricetin > luteolin > quercetin > (+/-)-taxifolin > kaempferol > apigenin > (+)-catechin > (+/-)-naringenin shows good agreement with the order obtained by theoretical calculations at the B3LYP/6-311 + G(2d,2p)//HF/6-31G(d) level. Moreover, these calculations provide the gas-phase acidities of the different OH groups for each flavonoid. The calculated acidity values (Delta(ac)H), corresponding to the most favorable deprotonation, cover a narrow range, 314.8-330.1 kcal/mol, but the experimental method is sensitive enough to differentiate the acidity of the various flavonoids. For all the flavones and the flavanol, catechin, the 4'-hydroxyl group is the most favored deprotonation site whereas for the flavanones studied, taxifolin and naringenin, the most acidic site is the 7-hydroxyl group. On the other hand, the 5-hydroxyl, in flavones and naringenin, and the 3-hydroxyl, in taxifolin and catechin, are always the less acidic positions. The acidity pattern observed for this family of compounds mainly depends on the following structural features: The ortho-catechol group, the 2,3 double bond and the 4-keto group. (C) 2004 American Society for Mass Spectrometry.
559. A direct classical trajectory study of the acetone photodissociation on the triplet surface
in JOURNAL OF CHEMICAL PHYSICS, 2003, ISSN: 0021-9606, Volume: 119,
Article, Indexed in: crossref, scopus, wos
Product energy distributions (PEDs) for the photodissociation of acetone at 266, 248, and 193 nm were evaluated by direct classical trajectory calculations on the lowest triplet potential energy surface. CASSCF(8,7) and MRCI+Q calculations were first performed to obtain a set of high-level ab initio data with which the semiempirical parameters were refined. The trajectories were initiated at the barrier, using two different microcanonical sampling methods. The results obtained for the excess energies corresponding to excitation at 266 and 248 nm are in good agreement with the experimental product energy partitioning, supporting a dissociation event taking place on the T-1 surface after intersystem crossing from the initially exited S-1 state. At 193 nm, the results obtained with the two sampling methods show significant discrepancies. The PEDs calculated with the anharmonic sampling procedure appear to be consistent with the experimental data. (C) 2003 American Institute of Physics.
560. A direct DFT dynamics study of the photodissociation of triplet acetaldehyde
in CHEMICAL PHYSICS LETTERS, 2003, ISSN: 0009-2614, Volume: 375,
Article, Indexed in: crossref, scopus, wos
Photodissociation of acetaldehyde at 308 nm via the radical CH3 + HCO channel has been studied on the triplet state surface by DFT classical trajectory calculations using the B3LYP/6-31G* electronic structure method. A rotational analysis of product HCO predicts a non-Boltzmann distribution and that the energy is partitioned preferentially along the b and c axes rather than axis a. Product HCO is produced with no vibration excitation but the radical CH3 is predicted to be vibrationally excited. These results corroborate the most recent LIF experiment on this reaction. When the product energies are scaled, to take into account a possible underestimation of the B3LYP/6-31G* reverse barrier height. the resulting energies are in excellent agreement with experiment.