Lucildes Pita Mercuri

Thermal behavior and decomposition kinetics of rifampicin polymorphs under isothermal and non-isothermal conditions

The thermal behavior of two polymorphic forms of rifampicin was studied by DSC and TG/DTG. The thermoanalytical results clearly showed the differences between the two crystalline forms. Polymorph I was the most thermally stable form, the DSC curve showed no fusion for this species and the thermal decomposition process occurred around 245 oC. The DSC curve of polymorph II showed two consecutive events, an endothermic event (Tpeak = 193.9 oC) and one exothermic event (Tpeak = 209.4 oC), due to a melting process followed by recrystallization, which was attributed to the conversion of form II to form I. Isothermal and non-isothermal thermogravimetric methods were used to determine the kinetic parameters of the thermal decomposition process. For non-isothermal experiments, the activation energy (Ea) was derived from the plot of Log β vs 1/T, yielding values for polymorph form I and II of 154 and 123 kJ mol-1, respectively. In the isothermal experiments, the Ea was obtained from the plot of lnt vs 1/T at a constant conversion level. The mean values found for form I and form II were 137 and 144 kJ mol-1, respectively.

Stability evaluation of tocopheryl acetate and ascorbyl tetraisopalmitate in isolation and incorporated in cosmetic formulations using thermal analysis

In view of the increase in the number of cosmetic preparations containing antioxidant vitamins, chiefly, due to their action in preventing the process of skin aging, there is a need to develop pre-formulation studies and to validate analytical methods in order to obtain high quality products. Thus, the objective of this research was to evaluate and compare the thermal behavior of tocopheryl acetate and ascorbyl tetraisopalmitate as raw materials, and incorporated into a base cream. Thermogravimetry (TG / DTG) and differential scanning calorimetry (DSC) were used for this purpose. Both vitamins were found to be stable up to 250oC. The base cream (placebo) and the sample (base cream containing the vitamins) presented different weight loss. Thermal analysis has shown itself to be an excellent tool for the characterization of these vitamins and can be used in routine analysis for quality control of this type of cosmetic formulation.

Microwave synthesis of FDU-1 silica with incorporated humic acid and its application for adsorption of Cd2+ from aqueous solutions

This work describes microwave synthesis of FDU-1 materials with and without humic acid. FDU-1 is cage-like ordered mesoporous silica with a face-centered cubic structure. The FDU-1 samples were prepared using poly(ethylene oxide)-poly-(butylene oxide)-poly(ethylene oxide) triblock copolymer (EO39BO47EO39) as template and tetraethyl orthosilicate (TEOS) as silica source. The samples with incorporated humic acid were synthesized by using different concentrations of humic acid, i.e., 1.0, 1.5 and 2 mmoles. The resulting materials were characterized by thermogravimetry, elemental analysis, nitrogen adsorption, and small angle X-ray diffraction. The samples with incorporated humic acid were tested for removal of Cd2+ from aqueous solutions at pH=6. It is shown that the incorporation of humic acid into FDU-1 afforded materials with high adsorption capacity for cadmium ions. These materials seem to be promising adsorbents for removal of cadmium and related heavy metal ions from aqueous solutions.

Photoluminescence and thermoanalytical studies of complexes based on 5-Cl-8-hydroxyquinoline and calix[4]arene ligands.

A innovative 5-Cl-8-oxyquinolinepropoxycalix[4]arene ligand (2) have been prepared, exhibiting, at room temperature, blue fluorescent light emission and resulting in shift band to green fluorescent light (fluorescence mode) in the presence of coordinated Eu(III) and Tb(III) ions. Terbium complex presented phosphorescence emission as noted by typical bands at 490 nm, 545 nm and 585 nm. TG/DTG data exhibited typical thermal behavior for these compounds, however DSC curves showed the melting temperature near 300 °C for the samples, demonstrating an unusual thermal stability when quinoline derivatives are attached to calix[4]arene matrix. This fact strongly suggests an effective approach to preparing the photoluminescent compound associating high chemical and thermal stability.

Encapsulation study of citalopram and risperidone into nanostructured silica SBA-15 for in vitro release evaluation

Ordered mesoporous silica, SBA-15, presents non-toxic nature; high pore volume and high surface area; thermal, hydrothermal and mechanical stabilities. These features may enable its use as a carrier for commonly prescribed drugs in psychiatric practice: citalopram (CIT) and risperidone (RIS). Thermogravimetry/derivative thermogravimetry (TG/DTG) and ultraviolet and visible absorption spectrophotometry (UV–Vis) were used to determine drug quantity into/onto ECIT (CIT encapsulated into SBA-15), ERIS (RIS encapsulated into SBA-15), MCIT (mixture of CIT with SBA-15) and MRIS (mixture of RIS with SBA-15). All materials were characterized through: TG/DTG, differential scanning calorimetry, elemental analysis, Fourier transform infrared absorption spectrophotometry and nitrogen adsorption–desorption. A general solvent-based method for loading these psychoactive drugs into non-functionalized SBA-15 showed to retard their liberation in simulated gastric and intestinal media when compared to physical mixtures performance. It is expected that the functionalization of this nanostructured silica may increasingly extend the dissolution of CIT and RIS after encapsulation process, leading to application in controlled release systems.