Transporte eletrônico e propriedades termodinâmicas de nanobiomoléculas

We use a tight-binding formulation to investigate the transmissivity and the currentvoltage (I_V) characteristics of sequences of double-strand DNA molecules. In order to reveal the relevance of the underlying correlations in the nucleotides distribution, we compare theresults for the genomic DNA sequence with those of arti_cial sequences (the long-range correlated Fibonacci and RudinShapiro one) and a random sequence, which is a kind of prototype of a short-range correlated system. The random sequence is presented here with the same _rst neighbors pair correlations of the human DNA sequence. We found that the long-range character of the correlations is important to the transmissivity spectra, although the I_V curves seem to be mostly inuenced by the short-range correlations. We also analyze in this work the electronic and thermal properties along an _-helix sequence obtained from an _3 peptide which has the uni-dimensional sequence (Leu-Glu-Thr- Leu-Ala-Lys-Ala)3. An ab initio quantum chemical calculation procedure is used to obtain the highest occupied molecular orbital (HOMO) as well as their charge transfer integrals, when the _-helix sequence forms two di_erent variants with (the so-called 5Q variant) and without (the 7Q variant) _brous assemblies that can be observed by transmission electron microscopy. The di_erence between the two structures is that the 5Q (7Q) structure have Ala ! Gln substitution at the 5th (7th) position, respectively. We estimate theoretically the density of states as well as the electronic transmission spectra for the peptides using a tight-binding Hamiltonian model together with the Dyson's equation. Besides, we solve the time dependent Schrodinger equation to compute the spread of an initially localized wave-packet. We also compute the localization length in the _nite _-helix segment and the quantum especi_c heat. Keeping in mind that _brous protein can be associated with diseases, the important di_erences observed in the present vi electronic transport studies encourage us to suggest this method as a molecular diagnostic tool

A few-body treatment of low energy atomic collisions involving exotic particles

Faddeev-type equations are applied to three-charged particle systems. The rather satisfactory results are obtained for low energy e(+)H elastic scattering and muonic transfer reactions. The cross sections for antihydrogen formation from antiproton-positronium collisions are calculated using a six state model (Ps[1s2s2p], (H) over bar[1s2s2p]).

Understanding the origin of photoluminescence in disordered Ca0.60Sr0.40WO4: An experimental and first-principles study

Visible photoluminescence (PL) was observed for the first time at room temperature in structurally disordered calcium strontium tungstate powder, Ca0.60Sr0.40WO4 (CSW), obtained by the polymeric precursor method. The PL behavior of CSW powders has been analyzed as a function of the disorder rate, based on experimental and theoretical studies. Quantum mechanical theory based on density functional theory at the B3LYP level has been employed to study the electronic structure of two periodic models representing both crystalline and disordered powders. Their electronic structures have been analyzed in terms of density of states, band dispersion and charge densities. The calculations indicate a break in symmetry when passing from crystalline to disordered models, creating localized electronic levels above the valence band. Moreover, a negative charge transfer process takes place from the [WO3] cluster to the [WO4] cluster. The polarization induced by the break in symmetry and the existence of localized levels favors the creation of trapped holes and electrons, originating the PL phenomenon. (c) 2007 Elsevier B.V. All rights reserved.

Surface Passivation of Nanoporous TiO2 via Atomic Layer Deposition of ZrO2 for Solid-State Dye-Sensitized Solar Cell Applications

We report here the utilization of atomid layer deposition to passivate surface map states in mosoporous TiO2 nanoparticles for solid state dye sensitized solar cells based on 9,9'-spirobifluorene (spiro-OMeTAD). By depositing ZrO2 films with angstrom-level precision, coating the mesoporous TiO2 produces over a two-fold enhancement in short-circuit current density, as compared to a control device. Impedance spectroscopy measurements provide evidence that the ZrO2 coating reduces recombination lossed at the TiO2/spiro-OMeTAD interface and passivates localized surface states. Low-frequency negative capacitances, frequently observed in nanocomposite solar cells, have been associated with the surface-state mediated charge transfer from TiO2 to the spiro-OMeTAD.

Platinum-coated nanostructured oxides for active catalytic electrodes

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Electrochemical and spectroscopic characterization of screen-printed gold-based electrodes modified with self-assembled monolayers and Tc85 protein

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Optimization of incubation time of protein Tc85 in the construction of biosensor: Is the EIS a good tool?

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Electrochemical capacitance spectroscopy and capacitive relaxation of the changeover process in iron hexacyanoferrate molecular compound

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Eletrodo de pasta de carbono em minicavidade de contato sólido

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Spectrophotometric determination of diclofenac in pharmaceutical preparations assisted by microwave oven

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Electrochemical stability of SnO2-based coated Ti electrodes

The electrochemical behavior of SnO2-SbOx, based electrodes, with and without the addition of RuO2, was studied by cyclic voltammetry, service life measurements and electrochemical impedance spectroscopy in 0.5 M H2SO4 the physical characteristics of these materials were investigated using SEM, EDX and XRD. The resulting cyclic voltammograms obtained using SnO2-SbOx, and SnO2-SbOx-RuO2(x), x = 30, 5, 1 and 0.4 % showed that the OER overpotential decreased with the addition of RuO2. In the repetitive triangular potential voltammetry applied to the SnO2 electrode without and with RuO2 (1%), a higher anodic current is observed during the first potential scan; it is explained in terms of the oxidation of the Ti substrate. The addition of 1% RuO2 increased the service life from 8 to 20 hours at 10 mAcm(-2), while at 50 mAcm(-2) this increase was from 1 to 8 hours. AC Impedance diagrams obtained for the Ti/SnO2-SbOx and Ti/SnO2-SbOx-RuO2 electrodes at the rest potential and at a potential in the OER region can be explained by a single equivalent circuit containing two elements in series. The results showed that the charge transfer resistance and the resistance of the oxide film are lower in the oxide film containing RuO2. Surface analysis of Ti/SnO2-SbOx, revealed that it is relatively porous and formed by clusters of small particles. The Ti/SnO2-SbOx-RuO2 (1%) film is more compact, though. XRD analysis showed that a Sn1-xTixO2 oxide is formed on the Ti/SnO2-SbOx with 1% and without RuO2 electrodes.

Theoretical study of MgO(001) surfaces: Pure, doped with Fe, Ca, and Al, and with and without adsorbed water

Ab initio calculations of large cluster models have been performed in order to study water adsorption at the five-fold coordinated adsorption site on pure Mg(001) and MgO(001) surfaces doped with Fe, Ca, and Al. The geometric parameters of the adsorbed water molecule have been optimized preparatory to analysis of binding energies, charge transfer, preferential sites of interaction, and bonding distances. We have used Mulliken population analysis methods in order to analyze charge distributions and the direction of charge transfer. We have also investigated energy gaps, HOMO energies, and SCF orbital energies as well as the acid-base properties of our cluster model. Numerical results are compared, where possible, with experiment and interpreted in the framework of various analytical models. (C) 2001 John Wiley & Sons, Inc.

Room-temperature photoluminescence in structurally disordered SrWO4

Intense and broad visible photoluminescent (PL) band in structurally disordered SrWO4 compounds was observed at room temperature. The polycrystalline scheelite strontium tungstate (SrWO4) samples prepared by the polymeric precursor method at different temperatures of annealing were structurally characterized by x-ray diffraction and Fourier transform Raman spectroscopy measurements. Quantum-mechanical calculations showed that the local disorder in the cluster of the network modifiers Sr has a very important role in the charge transfer. The experimental and theoretical results are in good agreement, indicating that the generation of the intense visible PL band can be related to short-range order-disorder degree in the scheelite structure. (c) 2006 American Institute of Physics.

Dissociation and electrooxidation of primaquine diphosphate as an approach to the study of anti-chagas prodrugs mechanism of action

This paper describes the voltammetric behavior of primaquine as a previous support to the further understanding of the delivery and action mechanisms of its respective synthesized prodrugs. There are few papers describing the drug behavior and most of the time no correlation between oxidation process and pH is done. Our results showed that primaquine oxidation is a one-step reaction involving two electrons with the charge transfer process being strongly pH-dependent in acid medium and pH-independent in a weak basic medium, with the neutral form being easily oxidized.This leads to the conclusion that quinoline nitrogen ring neutralization is a determinant step to the formation of the oxidized primaquine form. The existence of a relationship between the primaquine dissociation equilibrium and its electrooxidation process is shown.This work points the importance of voltammetric methodology as a tool for further studies on quantitative relationship studies between chemical structure and biological activity (QSAR) for electroactive drugs. (C) 2000 Elsevier B.V. S.A. All rights reserved.

Electrochemical studies with a Cu-5wt.%Ni alloy in 0.5 M H2SO4

The electrochemical behavior of the annealed Cu-5wt.%Ni alloy in 0.5 M H2SO4 was studied by means of open-circuit potential (E-OCP) measurements, cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and quasi-stationary linear potential sweep. The hydrodynamics of the system was also studied. This material is constituted by a single a, phase. The anodic behavior of a Cu-Ni alloy in H2SO4 consists fundamentally on the electrodissolution of Cu, its main component, and the formation of a sulfur-containing passive layer. The presence of Ni decreases the rate of Cu oxidation, mostly at high positive potentials. The impedance spectra, obtained for the unrotating electrode, can be interpreted in terms of a simple charge-transfer reaction across a surface layer. When the electrode is rotated, the occurrence of an inductive loop evidenced the existence of an adsorbed layer. All the resistance estimated from the proposed equivalent circuits diminished with the electrode rotation rate, emphasizing the influence of ion transport in the overall electrode process. The system presented two anodic Tafel slopes: 40 mV dec(-1) for E < 255 mV and 67 mV dec(-1) for E > 275 mV. A Tafel slope of 40 mV dec(-1) evidences that copper dissolution can be interpreted in terms of the mechanism proposed by Mattsson and Bockris. The second Tafel suggests that at potentials more positive than 275 mV, copper dissolves according to a mechanism that considers the disproportionation of adsorbed Cu(1) species. (C) 2003 Elsevier Ltd. All rights reserved.