Total publications: 603
545. Electrochemical study of ion transfer of acetylcholine across the interface of water and a lipid-modified 1,2-dichloroethane
in JOURNAL OF PHYSICAL CHEMISTRY B, 2005, ISSN: 1520-6106, Volume: 109,
Article, Indexed in: crossref, scopus, wos
The ion transfer of acetylcholine (AcH+) ions across the unmodified and phospholipid-modified water 1,2-dichloroethane (DCE) interface has been studied by means of square-wave and cyclic voltammetry, as well as by electrochemical impedance spectroscopy. After being transferred in the organic phase, the AcH+ ions undergo chemical reactions with the phospholipids. The overall behavior of the experimental system studied in the presence of phospholipids has been compared with the theoretical results of an ECrev reaction. The kinetic parameters of the chemical interactions between AcH+ and the phospholipids have been determined from the voltammetric and impedance measurements. Additional characterization of those interactions has been made by using the surface tension measurements.
546. Energy partitioning in association processes
in INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 2005, ISSN: 0020-7608, Volume: 104,
Article, Indexed in: crossref, scopus, wos
in this work, the partition method introduced by Melo and Ramos has been extended to enable the decomposition of the stabilization energies associated with molecular association processes into physical meaningful components (conformational rearrangement, nonbonding, bonding, and polarization plus charge transfer). This partition scheme, within a semiempirical formalism, enables a complete separability of the above-mentioned components. The molecular system has also been partitioned into perturbed and bulk regions, defined as flexible variable-size entities. This procedure enables one to evaluate the range of the perturbation originated by an association process. Several association processes (covalent and noncovalent) have been studied using this methodology. The results obtained enable us to conclude that the current decomposition scheme can be used for understanding the cohesive phenomena. (c) 2005 Wiley Periodicals, Inc.
547. Enzymatic formation of ions and their detection at a three-phase electrode
in JOURNAL OF SOLID STATE ELECTROCHEMISTRY, 2005, ISSN: 1432-8488, Volume: 9,
Article, Indexed in: crossref, scopus, wos
An electrochemical method for the detection of enzymatically created anions is described that uses a thin-film electrode with decamethylferrocene as an electroactive redox probe. The enzymatic oxidation of glucose with enzyme glucose oxidase produces gluconic acid as a final product. The oxidation of decamethylferrocene dissolved in the thin-nitrobenzene film, that is spread on the working graphite electrode and submerged in the aqueous solution containing glucose and glucose oxidase, is followed by the up-take of gluconate anions from the aqueous phase to nitrobenzene. The peak currents of the square-wave voltammetric responses of that system are a linear function of the glucose concentration in the milimolar range from 0.1 mmol/L to 0.7 mmol/L (R-2 = 0.994).
548. Experimental and DFT study of the aza-Diels-Alder reaction between cyclopentadiene and protonated benzylimine derivated from glyoxylates
in TETRAHEDRON, 2005, ISSN: 0040-4020, Volume: 61,
Article, Indexed in: crossref, scopus, wos
The Diels-Alder reaction of protonated N-benzyl imine of methyl glyoxylate with cyclopentadiene in different solvents gave mixtures of exolendo adducts. The exolendo selectivity of the reaction was elucidated by NMR experiments. Theoretical calculations by means of density functional theory (DFT) at the B3LYP/6-31G(d) level have also been performed to elucidate the molecular mechanism of this reaction. The DFT results suggest a highly asynchronous concerted mechanism, which in turn can explain the preferred exo stereoselectivity of the reaction. Inclusion of solvent effects enhances the exo selectivity, and this effect increases with the polarity of the solvent, in good agreement with the experimental findings.
549. Molecular dynamics simulations of angiotensin II in aqueous and dimethyl sulfoxide environments
in JOURNAL OF PHYSICAL CHEMISTRY B, 2005, ISSN: 1520-6106, Volume: 109,
Article, Indexed in: crossref, scopus, wos
Angiotensin II (Ang II) is an octapeptidic hormone, which plays an important role in the mechanisms of blood pressure control. In this work, extensive molecular dynamics (MD) simulations have been carried out on this peptide, both in aqueous and in dimethyl sulfoxide (DMSO) environments. Experimentally proposed models for the structure of angiotensin II in both environments are not consensual and the results obtained have provided some further insight about the structural properties of this hormone. In these simulations, the N-terminus of Ang II in the aqueous environment has been associated with a considerable larger flexibility than the correspondent C-terminus, but this was not found in the case of the DMSO environment. This is consistent with the assumption that the biological activity of Ang II is associated with its C-terminal residues embedded in a hydrophobic environment of its AT1 receptor. Other features detected in DMSO environment were an H(His6 imidazole)-O(Phe8 carboxylate) hydrogen bond and a salt-bridge structure involving the AspI and Arg2 side chains. An additional important conformational feature is the spatial proximity between Tyr4 and His6 in both water and DMSO environments. This molecular feature may trigger the interest for the synthetic chemists to apply rational design for the synthesis of novel ATI antagonists.
550. p-difluorobenzene-argon ground state intermolecular potential energy surface
in JOURNAL OF PHYSICAL CHEMISTRY A, 2005, ISSN: 1089-5639, Volume: 109,
Article, Indexed in: crossref, scopus, wos
The ground state intermolecular potential energy surface for the p-difluorobenzene-Ar van der Waals complex is evaluated using the coupled cluster singles and doubles including connected triple excitations [CCSD(T)] model and the augmented correlation consistent polarized valence double-zeta basis set extended with a set of 3s3p2d1f1g midbond functions. The surface minima are characterized by the Ar atom located above and below the difluorobenzene center of mass at a distance of 3.5290 angstrom. The corresponding binding energy is -398.856 cm(-1). The surface is used in the evaluation of the intermolecular level structure of the complex. The results clearly improve previously available data and show the importance of using a good correlation method and basis set when dealing with van der Waals complexes.
551. Special issue: A collection of papers presented at the 30th international congress of theoretical chemists of Latin Expression, Porto, Portugal, 8-12 September 2004 - Foreword
in JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 2005, ISSN: 0166-1280, Volume: 729,
Editorial Material, Indexed in: crossref, scopus, wos
552. Accurate intermolecular ground state potential of the Ne-HCl van der Waals complex
in JOURNAL OF CHEMICAL PHYSICS, 2004, ISSN: 0021-9606, Volume: 121,
Article, Indexed in: crossref, scopus, wos
From an accurate ground state intermolecular potential energy surface we evaluate the rovibrational spectrum of the Ne-HCl van der Waals complex. The intermolecular potential is obtained by fitting a considerable number of interaction energies obtained at the coupled cluster singles and doubles including connected triple excitations level and with the augmented correlation consistent polarized valence quintuple zeta basis set extended with a set of 3s3p2d1f1g midbond functions. This basis set is selected after a systematic basis set study carried out at geometries close to those of the three main surface stationary points. The surface is characterized by two linear minima, i.e. Ne-ClH and Ne-HCl, with distances from the Ne atom to the HCl center of mass of 3.398 and 3.833 Angstrom, respectively; and binding energies of -65.10 and -66.85 cm(-1), respectively. These results agree well with the experimental data available in contrast to previous theoretical results. The rovibrational spectra calculated for the different isotopic species are also compared to the experiments. (C) 2004 American Institute of Physics.