RESUMO

Mefloquine (MQ) is an antimalarial medication prescribed to treat or malaria prevention.. When taken by children, vomiting usually occurs, and new doses of medication frequently need to be taken. So, developing pediatric medicines using taste-masked antimalarial drug complexes is mandatory for the success of mefloquine administration. The hypothesis that binding mefloquine to an ion-exchange resin (R) could circumvent the drug's bitter taste problem was proposed, and solid-state 13C cross-polarization magic angle spinning (CPMAS) NMR was able to follow MQ-R mixtures through chemical shift and relaxation measurements. The nature of MQ-R complex formation could then be determined. Impedimetric electronic tongue equipment also verified the resinate taste-masking efficiency in vitro. Variations in chemical shifts and structure dynamics measured by proton relaxation properties (e.g., T1ρH) were used as probes to follow the extension of mixing and specific interactions that would be present in MQ-R. A significant decrease in T1ρH values was observed for MQ carbons in MQ-R complexes, compared to the ones in MQ (from 100-200 ms in MQ to 20-50 ms in an MQ-R complex). The results evidenced that the cationic resin interacts strongly with mefloquine molecules in the formulation of a 1:1 ratio complex. Thus, 13C CPMAS NMR allowed the confirmation of the presence of a binding between mefloquine and polacrilin in the MQ-R formulation studied.

RESUMO

We investigated each of the successive transformations of this material using ab initio calculations based on DFT. Possible structures produced from three reaction steps of the thermal treatment were simulated. Thermodynamic analysis was performed to assess the energy stability of each reaction. The dehydration of the interlamellar region confirmed the selective loss of water molecules, with axial H2O being responsible for the first part of the mass loss experimentally observed in TG-DTA while the loss of equatorial H2O molecules is observed above 150 °C. The reactions of the proposed intermediates after dehydration indicated that the formation of a zeolite Si14O28 is thermodynamically unfavorable in relation to zeolite sodium silicate. Kinetic effects and new heat treatment protocols should be studied to improve the understanding of these materials. The final steps indicated that after the condensation of the layers, sodium silicate was formed together with quartz.

RESUMO

In this work, a two-dimensional coordination polymer was synthesized and the structure was determined by single-crystal X-ray diffraction. The crystal structure belongs to the space group Pna21 and was characterized by Raman and FT-infrared spectroscopy, powder X-ray diffraction and Brunauer-Emmett-Teller surface area analysis. Catalyst activities were evaluated through the synthesis of glycerol carbonate from glycerol and urea using a batch reactor. After the optimization of both reaction and reaction conditions, the activity results showed that the coordination polymer used as a heterogeneous catalyst has good values of conversions and selectivity for the manufacturing of glycerol carbonate in a fine-chemical process. The analysis of powder X-ray diffraction and spectroscopy for the coordination polymer employed, before and after the reaction, shows that some changes have taken place in the crystal structure during the process, in spite of a recovery at the end of the reaction. The advantages and limitations of the coordination polymer were discussed and compared with those of the previous heterogeneous catalysts in the literature.

RESUMO

The intercalated layered materials are commonly built from structures complex enough to have large unit cells and, because of this, calculations of their electronic structures are very demanding in terms of memory, processing and time. Also, the versatility of these compounds enables the synthesis of a large number of derived materials difficult to characterize. Only in the last two decades, a combination of theoretical methodologies and advances in processing made density-functional theory (DFT) calculations quite interesting as an investigation tool for this family of materials. Since the intercalated layered or lamellar compounds correspond to a large group of important classes of materials and their experimental data were, and are still being, generated, only a small part of the data comes from electronic structure simulations. In this review, we have listed some relevant types of intercalated lamellar materials, the useful methodologies implemented in the standard suit of codes for DFT calculations and examples of the many applications of the calculations to the understanding of physical and chemical properties, to the planning of novel materials with desirable properties, and even to assist the structural characterization, by simulating complex results from nuclear magnetic resonance, vibrational spectroscopy and powder X-ray diffraction. In addition to the properties simulated directly as observables, other quantities such as density of states, partial charges and electronic density difference, provide relevant information about the materials and their behavior under diverse physical and chemical conditions. The combination of the geometric, electronic and vibrational structures also leads to the simulations of thermodynamic potentials, entropy and phase diagrams in the solid state. This significant ensemble of research tools makes DFT calculations very compelling and useful to gain new insights into innovation developments for intercalated lamellar materials.

RESUMO

The experiments of carvedilol form II, form III, and hydrate by (13)C and (15)N cross-polarization magic-angle spinning (CP MAS) are reported. The GIPAW (gauge-including projector-augmented wave) method from DFT (density functional theory) calculations was used to simulate (13)C and (15)N chemical shifts. A very good agreement was found for the comparison between the global results of experimental and calculated nuclear magnetic resonance (NMR) chemical shifts for carvedilol polymorphs. This work aims a comprehensive understanding of carvedilol crystalline forms employing solution and solid-state NMR as well as DFT calculations.

Assuntos

Carbazóis/química , Espectroscopia de Ressonância Magnética/métodos , Modelos Químicos , Propanolaminas/química , Isótopos de Carbono/química , Carvedilol , Cristalização , Cristalografia por Raios X , Estrutura Molecular , Isótopos de Nitrogênio/química

RESUMO

This ab initio study was performed to better understand the correlation between intercalated water molecules and layered double hydroxides (LDH), as well as the changes that occur by the dehydration process of Zn-Al hydrotalcite-like compounds containing Cl⁻ and CO3²â» counterions. We have verified that the strong interaction among intercalated water molecules, cointercalated anions, and OH groups from hydroxyl layers is reflected in the thermal stability of these compounds. The Zn(2/3)Al(1/3)(OH)2Cl(1/3)·2/3H2O hydrotalcite loses all the intercalated water molecules around 125 °C, while the Zn(2/3)Al(1/3)(OH)2(CO3)(1/6)·4/6H2O compound dehydrates at about 175 °C. These values are in good agreement with experimental data. The interlayer interactions were discussed on the basis of electron density difference analyses. Our calculation shows that the electron density in the interlayer region decreases during the dehydration process, inducing the migration of the Cl⁻ anion and the displacement of the hydroxyl layer from adjacent layers. Changes in these compound structures occur to recover part of the hydrogen bonds broken due to the removal of water molecules. It was observed that the chloride ion had initially a lower Löwdin charge (Cl(-0.43)), which has increased its absolute value (Cl(-0.58)) after the water molecules removal, while the charges on carbonate ions remain invariant, leading to the conclusion that the Cl⁻ anion can be more influenced by the amount of water molecules in the interlayer space than the CO3²â» anion in hydrotalcite-like compounds.

RESUMO

The reaction of HF molecules with brucite, Mg(OH)(2), leading to the formation of Mg(OH)(2-x)F(x), was theoretically studied by ab initio density functional theory (DFT) with periodic boundary conditions. We proposed as mechanism for this reaction four elementary steps: adsorption of the HF molecule, OH(-) liberation from brucite as a water molecule, desorption of the newly formed H(2)O, and rearrangement of the F(-) anion into a hydroxyl position. For the Mg(OH)(2-x)F(x) formation, with x = 1/9, the final product, outcome from an initially adsorbed HF molecule, we computed the Helmholtz free energy variation DeltaF = -23 kcal/mol. The calculated frequency for the most intense infrared band, a Mg-F stretching mode, was 342 cm(-1). Two transition states, corresponding to the hydroxyl reacting with a proton forming a water molecule and migration of a fluoride anion into a hydroxyl vacancy, were computed. The calculated reaction barriers indicate that the reaction between Mg(OH)(2) layers and HF molecules is slow and irreversible.

RESUMO

The present work describes the crystal structure, vibrational spectra, and theoretical calculations of ammonium salts of 3,5-bis-(dicyanomethylene)cyclopentane-1,2,4-trionate, (NH(4))(2)(C(11)N(4)O(3)) [(NH(4))(2)CV], also known as ammonium croconate violet. This compound crystallizes in triclinic P1 and contains two water molecules per unit formula. The crystal packing is stabilized by hydrogen bonds involving water molecules and ammonium cations, giving rise to a 3D polymeric arrangement. In this structure, a pi-stacking interaction is not observed, as the smaller centroid-centroid distance is 4.35 A. Ab initio electronic structure calculations under periodic boundary conditions were performed to predict vibrational and electronic properties. The vibrational analysis was used to assist the assignments of the Raman and infrared bands. The solid structure was optimized and characterized as a minimum in the potential-energy surface. The stabilizing intermolecular hydrogen bonds in the crystal structure were characterized by difference charge-density analysis. The analysis of the density of states of (NH(4))(2)CV gives an energy gap of 1.4 eV with a significant contribution of carbon and nitrogen 2p states for valence and conduction bands.

RESUMO

The electronic g-tensor and hyperfine coupling constants were calculated for cyanide coordination complexes [M(CN)4]3- (M = Ni, Pd, Fe, Ru, Os) in KCl or NaCl host lattices through an embedded calculation approach using the Density Functional Theory and compared with previous experiments. For all tested complexes, the B3LYP functional is in good agreement with the experiments for the hyperfine coupling constants. For the electronic g-tensor calculations, performed using the coupled perturbed SCF theory, some discrepancies were found, and the best agreements with the experimental values were achieved by the B3LYP functional.