George Ricardo Santana Andrade

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.

The effect of mechanical grinding on the formation, crystalline changes and dissolution behaviour of the inclusion complex of telmisartan and β-cyclodextrins

Telmisartan (TEL) was entrapped into β-cyclodextrin aiming the improvement of its biopharmaceutical properties of low solubility. A solid state grinding process was used to prepare the molecular inclusion complex (MIC) for up to 30min. The inclusion ratio of drug and β-cyclodextrin was established as 1:2 and 1:3 (mol/mol) by phase solubility study and Job Plot. DSC, XRPD and FTIR confirmed the molecular interactions between TEL and β-cyclodextrin. Computer molecular modeling supports the presence of hydrogen bonds between guest and host and demonstrated the most probable complexes configuration. MIC_1:2_30 and MIC_1:3_30 enhanced the dissolution rate of the drug achieving a delivery rate comparable with the reference medicine available in the market (81% and 87% in 5min, for MIC_1:3_30 and Micardis(®), respectively). These formulations showed rapid and effective antihypertensive effect against angiotensin II in rats up to 180min, with statistically significant results against placebo and control in the first 30min after administration.

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.

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.

Development and characterization of microencapsules containing spray dried powder obtained from Brazilian brown, green and red propolis

The aim of this study was to obtain dried powders from the brown, green and red varieties of the Brazilian propolis by spray drying, using gum arabic and maltodextrin as encapsulating materials. Propolis microparticles were evaluated for particle size, X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), moisture, water activity, solubility, hygroscopicity, encapsulation efficiency, total phenolic content, flavonoids and antioxidant activity (DPPH, ABTS+, FRAP, ORAC). Bioactive compounds were determined by UPHLC-QqQ-MS/MS. The results showed that the microparticles presented spherical forms, smooth surfaces, amorphous characteristics, low water activity, moisture and hygroscopicity, high solubility, good encapsulation efficiency, good antioxidant activity, although a reduction in total phenolics and flavonoids from the non-encapsulated propolis. The most important compounds in propolis powders were artepillin C, kaempferide, p-coumaric acid, luteolin, chlorogenic acid, kaempferol and caffeic acid. Spray-drying of propolis is a viable option to increase its use in food and pharmaceutical applications.

Computer simulation and spectroscopic study of inclusion complexes of cyclodextrins with luminescent porphyrins

Here we report a computational study of the structure, thermodynamic and spectroscopic properties of 1:1 and 2:1 inclusion complexes of luminescent porphyrins in ?-cyclodextrin. Semiempirical PM6 (Parametric Method 6) calculation allowed the optimization of the structure of the complexes, showing that the inclusion in the CD cavity changes significantly the porphyrin ring planarity for the 2:1 complexes. Thermodynamic calculations evidenced that the inclusion complex formation is slightly endothermic and that it is a non-spontaneous process in the absence of water molecules. Finally the calculated spectra were found to be in very good agreement to previously reported experimental ones.

Ordered micro-mesoporous carbon from palm oil cooking waste via nanocasting in HZSM-5/SBA-15 composite: Preparation and adsorption studies

This work reports the preparation of HZSM-5/SBA-15 micro-mesoporous materials with composite structure by mechanosynthesis and their use as templates to micro-mesoporous carbons, with palm oil cooking waste as carbon source. HZSM-5/SBA-15 composites were prepared in different mass proportions (25:75, 50:50 and 75:25) by a mechanosynthetic strategy. The palm oil waste was infiltrated into the template pores by a two-step procedure involving grinding followed by stirring the suspension in an oil solution and carbonization under inert atmosphere. SEM images showed the efficiency of mechanosynthesis for all mass proportions, while textural properties were strongly influenced by the presence of SBA-15. A comparison of 50% HZSM-5/SBA-15 mixture with pristine SBA-15 and uncalcined SBA-15 as carbon templates evidenced that the 50% HZSM-5/SBA-15 mixture lead to the carbon with the highest surface area and pore volume. The resulting carbon material was studied as adsorbent to different dye molecules, including molecules with different charges and sizes. Results revealed that the carbon has a significantly higher affinity for cationic dyes, that the mesopore structure favors high diffusion rates and that the surface groups have a very high affinity for cationic dye molecules.