Sara B. Honorato

Molecular Structure and Vibrational Spectroscopic Investigation of Secnidazole Using Density Functional Theory

Secnidazole (alpha,2-dimethyl-5-nitro-1H-imidazole-1-ethanol) is an antimicrobical drug, and it is particularly effective in the treatment of amebiasis, giardiasis, trichomoniasis, and bacterial vaginosis. Secnidazole crystallizes as a hemihydrate, which belongs to a monoclinic system having space group P2(1)/c, with a = 12.424 A, b = 12.187 A, c = 6.662 A, and beta = 100.9 degrees. The optimized geometries and total energies of different conformers of the secnidazole molecule have been determined by the method of density functional theory (DFT). For both geometry and total energy, it has been combined with B3LYP functionals having extended basis sets 4-31G, 6-31G, and 6-311++G(d,p) for each of the three stable conformers of secnidazole. Using this optimized structure, we have calculated the infrared and Raman wavenumbers and compared them with the experimental data. The calculated wavenumbers are in an excellent agreement with the experimental values. Based on these results, we have discussed the correlation between the vibrational modes and the crystalline structure of the most stable conformer of secnidazole. A complete assignment is provided for the observed Raman and IR spectra.

Far Infrared Slab Lensing and Subwavelength Imaging in Crystal Quartz

Departamento de F´isica, Universidade Federal do Ceara´, Campus Pici, 60455-900 Fortaleza CE, Brazil(Dated: November 20, 2012)We examine the possibility of using negative refraction stemming from the phonon polaritonresponse in an anisotropic crystal to create a simple slab lens with plane parallel sides, and show thatimaging from such a lens should be possible at room temperature despite the effects of absorptionthat are inevitably present due to phonon damping. In particular, we consider the case of crystalquartz, a system for which experimental measurements consistent with all-angle negative refractionassociated with the phonon polariton response have already been demonstrated. Furthermore, weinvestigate the possibility of subwavelength imaging from such materials, and show that it shouldbe possible for certain configurations.

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.

On the Thermal Stability of the Diethylcarbamazine-Fortified Table Salt Used in the Control of Lymphatic Filariasis

Diethylcarbamazine, administered as a water-soluble citrate salt, has been used for more than 50 years as the first-line drug in the treatment of lymphatic filariasis. Mass drug administration programs have been successful in reducing microfilaremia and providing important collateral deworming benefits. One of these initiatives is based on the addition of diethylcarbamazine citrate to table salt. The fortified salt retaining the efficacy of the drug in reducing microfilaremia, but there is little information about its behavior above room temperature. In this study, the thermal stability of diethylcarbamazine, as a free base and a citrate salt, was investigated by differential scanning calorimetry and thermogravimetry under different conditions. Diethylcarbamazine does not release hazardous degradation substances above its melting point. It was also confirmed that this drug is stable at normal cooking temperatures, even when dry heat cooking methods, such as baking or grilling, are considered. However, if the drug is formulated as a salt, as in the case of the citrate, special attention needs to be given to the degradation substances of the counter ion.

Rankamaite from the Urubu pegmatite, Itinga, Minas Gerais, Brazil: Crystal chemistry and Rietveld refinement

Abstract A new occurrence of rankamaite is here described at the Urubu pegmatite, Itinga municipality, Minas Gerais, Brazil. The mineral forms cream-white botryoidal aggregates of acicular to fibrous crystals, intimately associated with simpsonite, thoreaulite, cassiterite, quartz, elbaite, albite, and muscovite. The average of six chemical analyses obtained by electron microprobe is (range in parentheses, wt%): Na2O 2.08 (1.95-2.13), K2O 2.61 (2.52-2.74), Al2O3 1.96 (1.89-2.00), Fe2O3 0.01 (0.00-0.03), TiO2 0.02 (0.00-0.06), Ta2O5 81.04 (79.12-85.18), Nb2O5 9.49 (8.58-9.86), total 97.21 (95.95-101.50). The chemical formula derived from this analysis is (Na1.55K1.28)Σ2.83(Ta8.45Nb1.64Al0.89 Fe3+0.01Ti0.01)Σ11.00[O25.02(OH)5.98]Σ31.00. Rankamaite is an orthorhombic “tungsten bronze” (OTB), crystallizing in the space group Cmmm. Its unit-cell parameters refined from X‑ray diffraction powder data are: a = 17.224(3), b = 17.687(3), c = 3.9361(7) Å, V = 1199.1(3) Å3, Z = 2. Rietveld refinement of the powder data was undertaken using the structure of LaTa5O14 as a starting model for the rankamaite structure. The structural formula obtained with the Rietveld analyses is: (Na2.21K1.26)Σ3.37(Ta9.12Nb1.30 Al0.59)Σ11.00[O26.29(OH)4.71]Σ31.00. The tantalum atoms are coordinated by six and seven oxygen atoms in the form of distorted TaO6 octahedra and TaO7 pentagonal bipyramids, respectively. Every pentagonal bipyramid shares edges with four octahedra, thus forming Ta5O14 units. The potassium atom is in an 11-fold coordination, whereas one sodium atom is in a 10-fold and the other is in a 12-fold coordination. Raman and infrared spectroscopy were used to investigate the room-temperature spectra of rankamaite.

Negative refraction of far-infrared radiation in quartz

A new design concept for optical devices comes from the mathematical view of space-time in general relativity. The desired optical path is determined by coordinate transformations.

All-Angle Negative Refraction from the Phonon Response in Anisotropic Crystals

We consider how all-angle negative refraction may be induced in anisotropic crystals by making use of the phonon response. We investigate, both theoretically and experimentally, the example of crystal quartz at far infrared wavelengths.