Ana Paula Garcia Ferreira

Molecular fluorescence in silica particles doped with quercetin-Al3+ complexes

Silica particles doped with quercetin-Al3+ complex were prepared by hydrolysis and condensation of tetraethylorthosilicate (TEOS) using acid and basic catalysis. The acid catalysis resulted in particles with diameter about 200 nm. Basic catalysis with TEOS was performed over a quercetin doped alumina-sol used as a core precursor, and fluorescent finger-shaped SiO2 particles were obtained. The quercetin-alumina-SiO2 fluorescence decays are biexponential, and this character is ascribed to two types of quercetin-Al3+ complexes entrapped in the core of the system.

Thermal behavior and decomposition of oxytetracycline hydrochloride

Abstract The thermal behavior of oxytetracycline hydrochloride (OTC) antibiotic was evaluated using TG–DTA, TG–FTIR and DSC. Information was obtained regarding thermal stability and decomposition steps. From TG–FTIR, it was possible to identify some of the products of its thermal decomposition as chloridric acid, water, isocyanic acid, dimethylamine, methane, carbonic gas and ammonia, and carbon dioxide from the decomposition of the isocyanic acid. According to DSC data, melting occurred concomitantly with decomposition. The TG/DTG, DTA and DSC curves, together with the FTIR spectra of the volatile decomposition products, were used to propose a mechanism for oxytetracycline decomposition.

Thermoanalytical studies of carbamazepine: hydration/dehydration, thermal decomposition, and solid phase transitions

Carbamazepine (CBZ), a widely used anticonvulsant drug, can crystallize and exhibits four polymorphic forms and one dihydrate. Anhydrous CBZ can spontaneously absorb water and convert to the hydrate form whose different crystallinity leads to lower biological activity. The present study was concerned to the possibility of recovering the hydrated form by heating. The thermal behavior of spontaneously hydrated carbamazepine was investigated by TG/DTG-DTA and DSC in dynamic atmospheres of air and nitrogen, which revealed that the spontaneous hydration of this pharmaceutical resulted in a Form III hydrate with 1.5 water molecules. After dehydration, this anhydrous Form III converted to Form I, which melted and decomposed in a single event, releasing isocyanic acid, as shown by evolved gas analysis using TG-FTIR. Differential scanning calorimetry analyses revealed that Form III melted and crystallized as Form I, and that subsequent cooling cycles only generated Form I by crystallization. Solid state decomposition kinetic studies showed that there was no change in the substance after the elimination of water by heating to 120 °C. Activation energies of 98 ± 2 and 93 ± 2 kJ mol-1 were found for the hydrated and dried samples, respectively, and similar profiles of activation energy as a function of conversion factor were observed for these samples.

Synthesis, Characterization and Biological Activities of Biopolymeric Schiff Bases Prepared with Chitosan and Salicylaldehydes and Their Pd(II) and Pt(II) Complexes

In an attempt to enhance chitosan biological activities, biopolymeric Schiff bases of chitosan and different salicylaldehydes and their palladium(II) and platinum(II) complexes were synthesized and tested. The chemical structures of these derivatives were characterized using 1H-NMR, FTIR spectroscopy and XPRD. Thermal analysis was done through TGA/DTG-DTA. Electronic absorption spectra and surface morphologies were analyzed by SEM-EDAX. Chitosan and its derivatives were evaluated for their in vitro antimicrobial activity against two common bacterial and fungal plant pathogens Pseudomonas syringae pv. tomato and Fusarium graminearum, respectively, and for their antitumor activity against a human breast cancer cell line (MCF-7). It was found that, compared to the nonmodified chitosan, chitosan modified with Schiff bases and their complexes was highly toxic against the MCF-7 cell line and had antibacterial effects against P. syringea. However, the modified chitosan derivatives had less pronounced antifungal effects against F. graminearum compared to the nonmodified chitosan, suggesting different modes of action.