Evaluation of thermal stability of enalapril maleate tablets using thermogravimetry and differential scanning calorimetry

Differential scanning calorimetry (DSC) and thermogravimetry (TG) were used in order to evaluate the thermal stability of an enalapril maleate formulation packaged in two types of packaging, polyvinyl chloride/aluminum blister and aluminum strip. Enalapril and the excipients employed in the formulation were also evaluated by TG and DSC. Tablets were analyzed before and after storage in an acclimatized room at 40 °C and relative humidity of 75 % for 90 days. The DSC and TG results were compared with the results of dosage of enalapril and related compounds obtained by high-performance liquid chromatography. These results indicate an occurrence of chemical interaction between enalapril maleate and the excipients during its storage. After storage, it was observed that the enalapril content reduced and the predominant degradation product was diketopiperazine for both types of packaging. The predominance of diketopiperazine could be related to the absence of sodium bicarbonate in the tablets, alkalinizing agent employed in the thermal stabilization of the drug.     

Thermo-programmed reduction study of Pt/WO<Subscript>x</Subscript>–ZrO<Subscript>2</Subscript> materials by thermogravimetry

The thermo-programmed reduction study of Pt/WO_x–ZrO₂ materials prepared with different tungsten loading were performed by thermogravimetry. The samples were synthesized by impregnation method and calcined at 600, 700 and 800°C. The characterizations of both un-calcined and calcined materials were carried out using different techniques: thermal analysis (TG and DTA), X-ray diffraction (XRD) and thermo-programmed reduction (TPR). TG and DTA analysis of un-calcined were used to determination of calcination temperatures of the samples. XRD diffractograms were useful to help us in the determination of phase presents. TPR profiles showed between three and four events at different temperatures attributed to platinum reduction and the different stages of tungsten specie reduction.     

Lanthanide nitrate complexes with 2-azacyclononanone

Thermal behavior of rare earth nitrate complexes with 2-azacyclononanone (AZA) with Ln(NO₃)₃·3(AZA) composition (where Ln=Gd, Er and Ho) was analyzed in kinetic point of view. Kinetic parameters were calculated from thermogravimetric data. All obtained results were similar. The first decomposition step was representative to the loss of ligand and the residue was essentially Ln₂O₃. Furthermore, a reaction path was proposed for the thermal decomposition of the Ln(NO₃)₃·3(AZA).     

Effects of Adsorbed Polyaniline on Redox Process on MoO3 Surface

The effects exhibited by adsorbed conducting polyaniline on the redox process on a molybdenum oxide surface were studied. Thermogravimetric results indicate a 4% polyaniline deposition. Cyclic voltammograms of the adsorbed polymer on MoO3 show that polyaniline exerts remarkable effects on the molybdenum blue oxidation-reduction process, with oxidation and reduction potentials of 0.33 and 0.18 V, respectively. This effect strongly enhances the electrode response, and can be used as an important tool in qualitative and/or quantitative determinations of molybdenum in solution as well as in any substrate. Copyright 1999 Academic Press.     

Optimization of Extraction Conditions and Characterization of Volatile Organic Compounds of Eugenia klotzschiana O. Berg Fruit Pulp

Eugenia klotzschiana O. Berg is a native species to the Cerrado biome with significant nutritional value. However, its volatile organic compounds (VOCs) chemical profile is not reported in the scientific literature. VOCs are low molecular weight chemical compounds capable of conferring aroma to fruit, constituting quality markers, and participating in the maintenance and preservation of fruit species. This work studied and determined the best conditions for extraction and analysis of VOCs from the pulp of Eugenia klotzschiana O. Berg fruit and identified and characterized its aroma. Headspace solid-phase microextraction (HS-SPME) was employed using different fiber sorbents: DVB/CAR/PDMS, PDMS/DVB, and PA. Gas chromatography and mass spectrometry (GC-MS) were employed to separate, detect, and identify VOCs. Variables of time and temperature of extraction and sample weight distinctly influenced the extraction of volatiles for each fiber. PDMS/DVB was the most efficient, followed by PA and CAR/PDMS/DVB. Thirty-eight compounds that comprise the aroma were identified among sesquiterpenes (56.4%) and monoterpenes (30.8%), such as α-fenchene, guaiol, globulol, α-muurolene, γ-himachalene, α-pinene, γ-elemene, and patchoulene.     

Effect of pretreatment on pyrolysis products of Pennisetum purpureum Schum. by Py-GC/MS

Journal of Thermal Analysis and Calorimetry - Elephant grass (Pennisetum purpureum Schum.) is one such resource with a great amount of carbohydrate and lignin polymers that together represent high...     

Photochromism of 7-(N,N-diethylamino)-4'-hydroxyflavylium in a water-ionic liquid biphasic system

Photochromism of trans-4-(N,N-diethylamino)-2,4'-dihydroxychalcone, with formation of the photoproduct 7-(N,N-diethylamino)-4'-hydroxyflavylium, is promoted in the ionic liquid phase of a water/[bmim][PF6] biphasic system.     

Spectrometric and theoretical investigation of the structures of Cu and Pb/DTPA complexes

Spectrometric and theoretical tools have been employed in this study in order to elucidate the structures of DTPA (diethylenetriaminepentaacetic acid) complexed to copper and lead. Mass spectrometry allowed determining the 1:1 stoichiometry of metal:ligand, while infrared spectroscopy demonstrated that both N and O are sites for complexation. ¹³C NMR analysis showed the existence of free and complexed carboxyl groups, due to a straight singlet at 180.7 ppm (free carboxylic ¹³C) and to a broad signal at 179.3 ppm (complexed carboxylic ¹³C, ² J _Pb…O=C). A distorted NMR signal were observed for the Cu–DTPA carboxyl group, due to the Cu²⁺ paramagnetism. Based on the spectrometric evidences for the metal–DTPA structures, DFT optimizations were carried out and an octahedral-like arrangement for the Cu complex and a “shell-like” arrangement for the Pb complex, both hexa-coordinated, were then proposed for the structures of the titled compounds.

Lanthanum chromites partially substituted by calcium,strontium and barium synthesized by urea combustion

Because of their electrical, magnetic and catalytic properties rare earth and transition metal mixed oxides are important compounds. Lanthanum chromites have been extensively used as solid oxide fuel cell (SOFC) interconnect materials. In this work, lanthanum chromites partially substituted by alkaline earth metals were synthesized by the urea combustion process. TG and DSC techniques were used to evaluate the presence of the organic material in the powder after reaction on the hot plate. The powders were calcinated at 900°C and characterized by XRD and SEM. The results show that the particles have nanometric dimensions and the perovskite structure was formed.