Iara F. Gimenez

Sulfadiazine/hydroxypropyl-β-cyclodextrin host–guest system: Characterization, phase-solubility and molecular modeling

In this work we prepared and characterized an inclusion complex of the dihydropteroate synthase inhibitor sulfadiazine (SDZ) in 2-hydroxypropyl-beta-cyclodextrin (HPBCD). From the phase-solubility diagram we observed an increase in the water solubility of the drug, calculating a binding constant of 1879M(-1). The inclusion mode involves a NH(2)-in orientation of the drug in the HPBCD cavity, according to the 2D NMR (ROESY) data and confirmed by molecular modeling using the semiempirical PM6 and RM1 methods.

One-step preparation of CdS nanocrystals supported on thiolated silica-gel matrix and evaluation of photocatalytic performance

Here we report the use of a thiol-functionalized silica-gel to prepare supported CdS nanocrystals by a facile one-step procedure. Upon changing the relative proportion of the matrix we obtained nanocrystals with different average sizes and size distributions, as evidenced by spectroscopic measurements as well as TEM images. Photoluminescence spectra also indicated that the main effect of the matrix is related to the size control since the spectral profiles were found to be strongly dependent on the excitation wavelength. The performance of the material in the photocatalytic degradation of two commercial dyes (methylene blue and rhodamine 6G) has been tested under sunlight radiation, showing promising results. Almost complete decolorization has been observed after 80 min of exposure, with no adsorption on the silica surface.

Characterization, phase solubility and molecular modeling of α-cyclodextrin/pyrimethamine inclusion complex

An inclusion complex between the dihydrofolate reductase inhibitor pyrimethamine (PYR) and alpha-cyclodextrin (alpha-CD) was prepared and characterized. From the phase-solubility diagram, a linear increase of PYR solubility was verified as a function of alpha-CD concentration, suggesting the formation of a soluble complex. A 1:1 host-guest stoichiometry can be proposed according to the Jobs plot, obtained from the difference of PYR fluorescence intensity in the presence and absence of alpha-CD. Differential scanning calorimetry (DSC) measurements provided additional evidences of complexation such as the absence of the endothermic peak assigned to the melting of the drug. The inclusion mode characterized by two-dimensional (1)H NMR spectroscopy (ROESY) involves penetration of the p-chlorophenyl ring into the alpha-CD cavity, in agreement to the orientation optimized by molecular modeling methods.

Ecomateriais: desenvolvimento e aplicação de materiais porosos funcionais para proteção ambiental

Fundamental aspects of the conception and applications of ecomaterials, in particular porous materials in the perspective of green chemistry are discussed in this paper. General recommendations for description and classification of porous materials are reviewed briefly. By way of illustration, some case studies of materials design and applications in pollution detection and remediation are described. It is shown here how different materials developed by our groups, such as porous glasses, ecomaterials from biomass and anionic clays were programmed to perform specific functions. A discussion of the present and future of ecomaterials in green chemistry is presented along with important key goals.

Physicochemical study and characterization of the trimethoprim/2-hydroxypropyl-γ-cyclodextrin inclusion complex.

Here we report the preparation of a trimethoprim/2-hydroxypropyl-γ-cyclodextrin inclusion complex along with a physicochemical study, structural characterization, and molecular modeling of the complex. As main results, we observed from phase-solubility studies at two temperatures (20 °C and 35 °C) that the association constants decrease with increasing temperature. Values for K(1:1) constant were of the same magnitude order of those found for the parent γ-CD. The inclusion orientation as evidenced by ROESY measurements involves the inclusion of the 3,4,5-trimethoxybenzyl ring in the CD cavity from the larger rim. This is in agreement with semiempirical molecular modeling calculation.

Conductive carbon―clay nanocomposites from petroleum oily sludge

Oily sludge samples formed in water-oil separation tanks from a petroleum industry were collected, characterized and heat-treated at different temperatures, in order to yield carbon-clay composites. EDX microanalysis, XRD and FTIR data revealed that before carbonization the oily sludge was formed mainly by a mixture of quartz, montmorillonite, calcite, barite and oil residues. After carbonization, mineral phases present were mainly quartz, anorthite and gehlenite, in addition to graphitic and disordered carbon domains, according to XRD, Raman and TEM measurements. A preliminary evaluation of the electrical conductivity performed by Impedance Spectroscopy revealed that the composites formed are conductive, exhibiting conductivity values typical of semiconductors, in contrast to the precursor material.

Ternary cyclodextrin polyurethanes containing phosphate groups: Synthesis and complexation of ciprofloxacin

Synthesis of ternary polyurethanes (PUs) from hexamethylenediisocyanate, β-cyclodextrin and β-glycerophosphate (acid and calcium salt) was studies varying synthesis parameters such as monomer proportion, heating method (reflux and microwave), and catalyst amount. Favorable conditions were provided by microwave irradiation and use of β-glycerophosphoric acid although the results suggest that it is possible to obtain ternary PUs with the calcium salt. FTIR data indicated the existence of secondary urea linkages. After characterization of ternary PUs by FTIR spectroscopy, XRD and thermal analysis, as well as evidences that the cyclodextrin cavities remained active toward inclusion of guest molecules, the possibility of inclusion of the antibiotic ciprofloxacin was evaluated. Absence of ciprofloxacin melting peak in DSC curves indicated that it is molecularly dispersed within the polymer, possibly included in the cyclodextrin. In vitro release experiments suggested additional non-inclusion interactions, showing also that the use of dialysis membranes may mask the actual release profile.

Structural and theoretical-experimental physicochemical study of trimethoprim/randomly methylated-β-cyclodextrin binary system.

Here we report the structural characterization, physicochemical study and molecular modeling of the inclusion complex of trimethoprim in randomly methylated beta-cyclodextrin. The phase-solubility diagram obtained at pH 7.0 exhibited a linear behavior for the RAMEB concentrations studied suggesting a 1:1 stoichiometry and absence of aggregation in solution. From stoichiometric determination by the continuous variation method we confirmed a 1:1 stoichiometry. To make a detailed characterization of the inclusion mode, spectroscopic measurements by infrared and 1D and 2D (1)H NMR spectroscopy provided evidence that the inclusion mode is characterized by inclusion of the trimethoxyphenyl ring in the cavity; interactions with methyl groups located in the border of the cavity were also detected. The structure proposed was also confirmed by semiempirical molecular modeling.

Preparation of Aun quantum clusters with catalytic activity in β-cyclodextrin polyurethane nanosponges.

Here we report the use of β-cyclodextrin polyurethane nanosponges cross-linked with 1,6-hexamethylene diisocyanate as a template for the preparation of Aun quantum clusters, by the core-etching of glutathione-capped Au nanoparticles. The study of temporal evolution of the core-etching process using different Au concentrations indicated that formation of Aun clusters embedded in the nanosponge is favored by the use of lower Au concentrations, since it began at shorter times and lead to higher cluster loading. An estimation of the number of Au atoms based on the maximum photoluminescence wavelength suggested that, depending on the Au concentration and the core etching time, clusters with 11-15 atoms were formed. After excluding the possibility of an inclusion complex formation, evaluation of the catalytic activity of nanosponge-loaded Aun clusters toward the reduction of 4-nitrophenol has shown that the reaction is catalyzed by the Aun clusters with no induction time, following the Langmuir-Hinshelwood kinetic model.

Hollow carbon nanostructures obtained from hydrothermal carbonization of lignocellulosic biomass

Here we describe a new method for obtaining carbon nanocages at relatively low temperatures using a low-cost lignocellulosic waste material as carbon precursor. Coconut coir dust has been submitted to hydrothermal carbonization in the presence of clays minerals such as sepiolite, attapulgite, and montmorillonite followed by a demineralization step. Just after hydrothermal treatment, the samples prepared in the absence of the clays presented a sponge-like morphology as typically described for hard-plant tissues submitted to this treatment while the samples heated in the presence of clays were fundamentally heterogeneous. After chemical etching with hydrofluoric acid, the sample free from clays exhibited irregular round-shaped particles with poorly defined cavities. For samples containing clays, on the other hand, the chemical etching lead to well-defined carbon nanocages as long as the particles were successfully etched such as attapulgite and montmorillonite. For sepiolite, however, the presence of residual inorganic particles was observed along with irregularly shaped hollow nanostructures. Finally, Raman measurements revealed the typical features of amorphous carbons.