Polarographic determination of loratadine in pharmaceutical preparations

Loratadine, a potent antihistamine drug, is not directly electroreducible at a dropping mercury electrode; however, by means of a nitration procedure it is possible to obtain a nitro-loratadine derivative which has been identified as 4-(8-chloro-7-nitro-5,6-dihydro-11 H-benzo-[5,6]-cyclohepta-[l,2-b]-pyridin-l l-ylidene)-1-piperidine carboxylic acid ethyl ester. The electrochemical reduction of this derivative at different pHs and concentrations using polarography and cyclic voltammetry was studied. The derivative exhibits a differential pulse polarographic peak due to the reduction of the nitro group. This peak was used in order to develop an analytical procedure for determining loratadine in pharmaceutical dosage forms.

The recovery study shows adequate accuracy and precision for the developed assay and the excipients do not interfere in the determination.     

Effect of pH on the stability of hexokinase and glucose 6-phosphate dehydrogenase

Hexokinase (HK) and glucose 6-phosphate dehydrogenase (G6PDH) are important enzymes used in biochemical studies and in analytical methods. The stability of the enzymes can be affected by several variables, pH being one of them. The effect of pH on the stability of HK and G6PDH was evaluated in this work. Baker’s yeast cells were suspended in 50 mM Tris-HCl buffer (pH 7.5) containing 5.0 mM MgCl2, and submitted to disruption by agitation with glass beads and in the presence of protease inhibitors. The cell-free extract was obtained by centrifugation (2880g; 10 min), followed by dilution into the buffers: 0.1 M acetate-acetic acid (pH: 4.0, 4.5, 5.0, or 5.5), 0.1 M phosphate buffer (pH: 6.0, 6.5, or 7.0), and 0.1 M Tris-HCl buffer (pH: 7.5, 8.0, 8.5, 9.0 or 9.5). The residual activity of HK and G6PDH, expressed as μmol of NADPH formed per min, were measured through a period of buffer-enzyme contact from 0 to 51 h at 4°C. It was observed that up to 4 h both enzymes were stable in all buffers used. However, after 51 h HK was stable at pH 6.0 and 7.5, whereas G6PDH was stable at pH 7.0, 9.5, and between 4.5 and 5.5.     

Focused microwave irradiation-assisted synthesis of N-cyclohexyl-1,2,4-oxadiazole derivatives with antitumor activity

A facile synthesis of 3,5-disubstituted 1,2,4-oxadiazole derivatives under focused microwave irradiation (FMWI) is reported. Arylamidoximes 1a–i and dicyclohexylcarbodiimide (DCC) were carried out in DMF under FMWI to obtain 1,2,4-oxadiazoles 2a–i in 61–81% yields. All compounds exhibited antiproliferative activities in vitro against three human cancer cell lines HCT-116, PC-3, and SNB-19.     

Screening of variables in xylananese recovery using BDBAC reversed micelles

Xylanase recovery by reversed micelles using cationic surfactants (N-benzyl-N-dodecyl-N-bis(2-hydroxyethhyl)ammonium chloride) BDBAC was evaluated under different experimental conditions. A full factorial design with center point was employed to verify the in fluence of different factors on the recovery. A mathematical model was found to represent the xylanese yield (Y) as a function of BDBAC and hexanol: Y=4.32+5.1B+2.64D+0.83B²+1.46D², where B=BDBAC and D=hexanol. The highest xylanase recovery (27%), indicated by the model was attained at pH=8.1, BDBAC=0.38 M and hexanol=8.6%. Under these conditions, and to test the model, a new xylanase extraction was performed in laboratory, giving 29.4% recovery yield, this value was similar to that predicted by the model.     

Production of Biodiesel via Enzymatic Ethanolysis of the Sunflower and Soybean Oils: Modeling

Biodiesel has become attractive due to its environmental benefits compared with conventional diesel. Although the enzymatic synthesis of biodiesel requires low thermal energy, low conversions of enzymatic transesterification with ethanol (ethanolysis) of oils to produce biodiesel are reported as a result of deactivation of the enzyme depending on the reaction conditions. The synthesis of biodiesel via enzymatic ethanolysis of sunflower and soybean oils was investigated. Kinetic parameters for the overall reactions were fitted to experimental data available in the literature with the Ping Pong Bi-Bi mechanism including the inhibition effect of the ethanol on the activity of lipase Novozyme® 435. The model was applied to a batch reactor and the experimental conversions were successfully reproduced. The modeling of a semibatch reactor with continuous addition of ethanol was also performed and the results showed a reduction of roughly 3 h in the reaction time in comparison with the batch-wise operation.     

Downstream processing of inulinase

Candida kefyr DSM 70106 was cultivated in a medium containing inulin as a carbon source. About 92% of the inulinase was recovered directly from the medium. Different concentration (C_f) and enrichment (E_f) factors were obtained, using the following methods: Cross-flow filtration (microfiltration and cell diafiltration were carried out using a rotary filter; enzyme ultrafiltration and diafiltration were performed using a cassette module): C_f = 7.5 and E_f = 2.2; liquid-liquid extraction ofN-Benzyl-N-Dodecyl-N-bis[2-hydroxyethyl] ammonium chloride (BDBAC) reversed micelles: C_f = 2.5 and E_f = 2.7; and expanded-bed adsorption: C_f = 2.8 and E_f = 4.3.     

Pyrolysis of polypropylene: I. Identification of compounds and degradation reactions

Pyrolysis of two polypropylene samples (degrees of isotacticity 0.50 and 0.85) has been carried out by flash pyrolysis and distillation pyrolysis. The analytical coupling of flash pyrolysis, gas chromatography and mass spectrometry allowed the analysis of the degradation products and their evolution with temperature between 500 and 900°C to be followed under different experimental conditions.The mechanism of polypropylene degradation is compared with the radical mechanism of polystyrene degradation.The depolymerization reaction leading to the production of monomer (25%) is not the most important degradation reaction. The transfer reactions predominate and generate the following products: 2,4-dimethyl-1-heptene (27–32%), pentane (ca. 8%), 2,4,6,8-tetramethyl-1-hendecene (7–18%) and 2,4,6-trimethyl-1-nonene (4–10%).