Josué Mendes Filho

Unveiling the structure and composition of titanium oxide nanotubes through ion exchange chemical reactions and thermal decomposition processes

Neste trabalho reportamos reacoes de troca ionica e decomposicao termica em nanotubos de oxido de titânio, obtidos pelo tratamento hidrotermico de TiO 2 e NaOH. Considerando os resultados obtidos, sugerimos uma nova composicao quimica para os nanotubos: Na 2 Ti 3 O 7 ·nH 2 O. Os resultados tambem indicam que a estrutura da parede dos nanotubos seria isoestrutural as lamelas observadas para o Na 2 Ti 3 O 7 bulk. Dependendo da natureza da lavagem (agua deionizada ou solucao acida) executada no nanotubo apos o tratamento hidrotermico a concentracao de ions Na + pode ser modificada atraves de um processo de troca ionica do Na + por H + . Tais resultados permitem sugerir a seguinte formula quimica geral para os nanotubos obtidos: Na 2-x H x Ti 3 O 7 ·nH 2 O (0≤ x ≤2), sendo x dependente das condicoes de lavagens. In this paper we report the ion exchange reactions and the thermal decomposition of titanium oxide nanotubes, obtained by hydrothermal treatment of TiO 2 and NaOH. Based on these results we propose a new composition for the as-prepared nanotubes as Na 2 Ti 3 O 7 ·nH 2 O. Our results also suggest that nanotube walls have structure similar to those observed in the layer of the bulk Na 2 Ti 3 O 7 . Depending on how the washing process is performed on the nanotubes (water or acid solutions) the Na + content can be modified via the exchange reaction of Na

Electronic and Structural Properties of Oxygen-Doped BN Nanotubes

The structural and electronic properties of oxygen substitutional doping in a (10,0) BN nanotube were obtained using ab initio calculation based on the density functional theory. For the oxygen replacing a boron atom in the tube (OB), the structure is locally deformed. In the case of nitrogen substitution (ON), however, the tube structure remains practically the same with negligible deformation observed around the oxygen atom. The electronic band structure for OB nanotubes is modified by the appearance of three strongly localized states, two of then as gap states. In the case of ON nanotubes the Fermi level is shifted into the conduction band inducing a metallic character to the doped tube. The analysis of the formation energies shows that the ON substitution is more favorable, particularly in the case of a boron-rich environment

Phonons in ferroelectric Bi2WO6: Raman and infrared spectra and lattice dynamics

Bi2WO6 ferroelectric single crystal was investigated by micro-Raman scattering and infrared spectroscopies. Symmetry of modes was established and the mode assignment was proposed.

The encapsulation of β-lapachone in 2-hydroxypropyl-β-cyclodextrin inclusion complex into liposomes: a physicochemical evaluation and molecular modeling approach.

The aim of this study was to encapsulate lapachone (β-lap) or inclusion complex (β-lap:HPβ-CD) in liposomes and to evaluate their physicochemical characteristics. In addition, the investigation of the main aspects of the interaction between β-lap and 2-hydroxypropyl-β-cyclodextrin (HPβ-CD), using both experimental and molecular modeling approaches was discussed. Furthermore, the in vitro drug release kinetics was evaluated. First, a phase solubility study of β-lap in HPβ-CD was performed and the β-lap:HPβ-CD was prepared by the freeze-drying technique. A 302-fold increase of solubility was achieved for β-lap in HPβ-CD solution with a constant of association K(1:1) of 961 M(-1) and a complexation efficiency of β-lap of 0.1538. (1)H NMR, TG, DSC, IR, Raman and SEM indicated a change in the molecular environment of β-lap in the inclusion complex. Molecular modeling confirms these results suggesting that β-lap was included in the cavity of HPβ-CD, with an intermolecular interaction energy of -23.67 kJ mol(-1). β-lap:HPβ-CD and β-lap-loaded liposomes presented encapsulation efficiencies of 93% and 97%, respectively. The kinetic rate constants of 183.95±1.82 μg/h and 216.25±2.34 μg/h were calculated for β-lap and β-lap:HPβ-CD-loaded liposomes, respectively. In conclusion, molecular modeling elucidates the formation of the inclusion complex, stabilized through hydrogen bonds, and the encapsulation of β-lap and β-lap:HPβ-CD into liposomes could provide an alternative means leading eventually to its use in cancer research.

Functionalization of single-wall carbon nanotubes through chloroform adsorption: theory and experiment

The interaction of chloroform (CHCl(3)) with single-wall carbon nanotubes (SWCNT) is investigated using both first principles calculations based on Density Functional Theory and vibrational spectroscopy experiments. CHCl(3) adsorption on pristine, defective, and carboxylated SWCNTs is simulated, thereby gaining a good understanding of the adsorption process of this molecule on SWCNT surfaces. The results predict a physisorption regime in all cases. These calculations point out that SWCNTs are promising materials for extracting trihalomethanes from the environment. Theoretical predictions on the stability of the systems SWCNT-CCl(2) and SWCNT-COCCl(3) are confirmed by experimental TGA data and Fourier Transform Infrared Spectroscopy (FT-IR) experiments. Results from resonance Raman scattering experiments indicate that electrons are transferred from the SWCNTs to the attached groups and these results are in agreement with the predictions made by ab initio calculations.

A single molecule rectifier with strong push-pull coupling

We theoretically investigate the electronic charge transport in a molecular system composed of a donor group (dinitrobenzene) coupled to an acceptor group (dihydrophenazine) via a polyenic chain (unsaturated carbon bridge). Ab initio calculations based on the Hartree-Fock approximations are performed to investigate the distribution of electron states over the molecule in the presence of an external electric field. For small bridge lengths (n=0-3) we find a homogeneous distribution of the frontier molecular orbitals, while for n>3 a strong localization of the lowest unoccupied molecular orbital is found. The localized orbitals in between the donor and acceptor groups act as conduction channels when an external electric field is applied. We also calculate the rectification behavior of this system by evaluating the charge accumulated in the donor and acceptor groups as a function of the external electric field. Finally, we propose a phenomenological model based on nonequilibrium Greens function to rationalize the ab initio findings.

Novel polymorphs of the anti-Trypanosoma cruzi drug benznidazole

Benznidazole (N-benzyl-2-(2-nitro-1H-imidazol-1-yl)acetamide), is a nitro-heterocyclic drug used in the treatment of Chagas disease. Despite the fact that this drug was released more than 30 years ago, little information about its solid state properties is available in the literature. In this study, it was verified that this drug exhibits three polymorphs, which were characterized in situ by X-ray powder diffraction, thermal analysis, hot stage microscopy and infrared spectroscopy. The thermodynamic relationships among these polymorphs were also discussed.

Nanosized Pt-containing Al2O3 as an efficient catalyst to avoid coking and sintering in steam reforming of glycerol

The action of nanosized Pt-containing Al2O3 catalysts to avoid coking and sintering was studied in steam reforming of glycerol. The solids exhibited almost 100% conversion toward syngas produced at a suitable water to glycerol ratio. Depending on the promoter, a drastic drop in hydrogen yield was observed due to coking and sintering effects. Spent catalyst characterizations by Raman, HRTEM, XRD, TG and SEM-EDS as well as textural property techniques showed that coking, rather than sintering, was the main cause that determined the low hydrogen selectivity of nanosized Pt-containing Al2O3 with La2O3 or ZrO2. In contrast, coking did not cover the active sites of Pt-containing Al2O3 with MgO or CeO2. Thus, steam suppressed carbon deposition and improved the nanosized Pt/MgO–Al2O3 catalyst stability in the steam reforming of glycerol.

Molecular flexibility and structural instabilities in crystalline l-methionine.

We have investigated the dynamics in polycrystalline samples of l-methionine related to the structural transition at about 307K by incoherent inelastic and quasielastic neutron scattering, X-ray powder diffraction as well as ab-initio calculations. l-Methionine is a sulfur amino acid which can be considered a derivative of alanine with the alanine R-group CH3 exchanged by CH3S(CH2)2. Using X-ray powder diffraction we have observed at ~190K an anomalous drop of the c-lattice parameter and an abrupt change of the β-monoclinic angle that could be correlated to the anomalies observed in previous specific heat measurements. Distinct changes in the quasielastic region of the neutron spectra are interpreted as being due to the onset and slowing-down of reorientational motions of the CH3-S group, are clearly distinguished above 130K in crystalline l-methionine. Large-amplitude motions observed at low frequencies are also activated above 275K, while other well-defined vibrations are damped. The ensemble of our results suggests that the crystalline structure of l-methionine is dynamically highly disordered above 275K, and such disorder can be linked to the flexibility of the molecular thiol-ether group.

Vibrational and thermal properties of crystalline topiramate

Topiramate, a powerful anticonvulsant drug, was investigated by X-ray diffractometry, FT-Raman, FT-IR, TGA and DTA techniques as well as by DFT calculations. From this study it was possible to tentatively assign most of the normal vibrational modes of the crystal. Thermal analysis from room temperature to 900 oC shows that the material does not present any structural phase transition and that the decomposition occurs in a two-step exothermic process.