Navegando por Autor "Freire, V. N."
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Artigo Charge transport in fibrous/not fibrous -helical and variant peptides(American Institute of Physics, 2011-01-31) Bezerril, Leonardo Mafra; Fulco, Umberto Laino; Oliveira, Jonas Ivan Nobre; Corso, Gilberto; Albuquerque, Eudenilson Lins de; Freire, V. N.; Caetano, W. S.Although differing only by the Ala→Gln substitution at the fifth or seventh position of the 3-peptide amino acid sequence Leu-Glu-Thr-Leu-Ala-Lys-Ala3, the 5Q3 variant forms fibrous assemblies more attenuated than those of the 3-peptide, while the 7Q3 variant does not form fibrils. A tight-binding transport modeling was performed to obtain their current-voltage patterns, with hopping energies of the dipeptides calculated within the density functional theory framework. Beyond the semiconductor character, we obtain that the current pattern can be used to distinguish them, suggesting that it can be useful for the development of devices as diagnostics tools for amyloidosislike diseasesArtigo Electronic specific heat of an a3-helical polypeptide and its biochemical variants(Elsevier, 2012-07-23) Bezerril, Leonardo Mafra; Mendes, G. A.; Albuquerque, Eudenilson Lins de; Fulco, Umberto Laico; Caetano, E. W. S.; Freire, V. N.We perform a theoretical study of the temperature dependent electronic specific heat at constant volume CV ðTÞ for a fibrous a3-helical polypeptide, which has the amino acid sequence (Leu-Glu-Thr-Leu-Ala-Lys- Ala)3, considering only its primary structure. We focus also on two different variants of the a3-helical polypeptide, namely those with (5Qa3 variant, mutation Ala5Gln) and without (7Qa3 variant, mutation Ala7Gln) fibrous assemblies. The energy spectra are calculated using a two-dimensional Schrödinger equation within a tight-binding approximation in which the isolated amino acid vertical ionization energy and the hopping terms are found using density functional theory computationsArtigo Evidence of magnetic polaronic states in La_{0.70}Sr_{0.30}Mn_{1-x}Fe_{x}O_{3} manganites(American Physical Society, 2003-02-19) Araújo, José Humberto de; Souza Filho, A. G.; Faria, J. L. B.; Guedes, I.; Sasaki, José Marcos; Freire, P. T. C.; Mendes Filho, J.; Xavier Jr, M. M.; Cabral, Francisco de Assis Olímpio; Costa, J. A. P. da; Freire, V. N.We have performed x-ray, electrical resistivity, and Raman scattering measurements in La0.70Sr0.30Mn12xFexO3 manganites, with x varying from 0 to 0.40. The appearance of new peaks in the Raman spectra as the Fe content increases is attributed to either otherwise forbidden Raman modes that become active due to symmetry breaking effect or to the phonon density of states features, which arise due to a disorder-induced phenomenon. The softening of some phonon modes suggests the evidence of magnetic polaronic states in the insulating paramagnetic phase of these manganites. Our observations are discussed in connection with the x-ray diffraction and electrical resistivity data.Artigo A quantum chemistry investigation of a potential inhibitory drug against the dengue virus(Royal Society of Chemistry, 2016) Ourique, G. S.; Vianna, Jéssica de Fátima; Lima Neto, José Xavier de; Oliveira, J. I. N.; Mauriz, Paulo Wilson; Vasconcelos, Manoel Silva de; Caetano, E. W. S.; Freire, V. N.; Albuquerque, Eudenilson Lins de; Fulco, Umberto LaicoWe present an in silico study of the interaction energy between NS2B–NS3, a serine protease of the dengue virus (DENV), and the inhibitor benzoyl-norleucine-Lys-Arg-Arg-aldehyde (Bz-nKRR-H), a crucial step in the design and development of dengue's antiviral drugs, using quantum chemistry calculations based on the density functional theory (DFT) at the generalized gradient approximation (GGA). The interaction energies between the inhibitor Bz-nKRR-H and each amino acid belonging to the binding site was calculated through the molecular fragmentation with conjugate caps (MFCC) approach employing a dispersion corrected exchange-correlation functional. Besides the interaction energy, we also calculated the distances, types of molecular interactions, and the atomic groups involved in the process. Our results show that the interaction energy of the system reached convergence at 15.0 Å, with the central residues identified in this interaction radius, as well as their attraction/repulsion energies, all of them being important inputs to improve the effectiveness of antiviral drugs to avoid the dissemination of the dengue virusArtigo Structural, electronic and optical properties of ilmenite and perovskite CdSnO3 from DFT calculations(IOP Publishing, 2010-10-12) Sesion Junior, Paulo Dantas; Henriques, J. M.; Barboza, C. A.; Albuquerque, E. L.; Freire, V. N.; Caetano, E. W. S.CdSnO3 ilmenite and perovskite crystals were investigated using both the local density and generalized gradient approximations, LDA and GGA, respectively, of the density functional theory (DFT). The electronic band structures, densities of states, dielectric functions, optical absorption and reflectivity spectra related to electronic transitions were obtained, as well as the infrared absorption spectra after computing the vibrational modes of the crystals at q = 0. Dielectric optical permittivities and polarizabilities at ω = 0 and ∞ were also calculated. The results show that GGA-optimized geometries are more accurate than LDA ones, and the Kohn–Sham band structures obtained for the CdSnO3 polymorphs confirm that ilmenite has an indirect band gap, while perovskite has a direct band gap, both being semiconductors. Effective masses for both crystals are obtained for the first time, being highly isotropic for electrons and anisotropic for holes. The optical properties reveal a very small degree of anisotropy of both crystals with respect to different polarization planes of incident light. The phonon calculation at q = 0 for perovskite CdSnO3 does not show any imaginary frequencies, in contrast to a previous report suggesting the existence of a more stable crystal of perovskite CdSnO3 with ferroelectric properties