Microwave‐assisted solvent‐free synthesis of novel benzoxazines: A faster and environmentally friendly route to the development of bio‐based thermosetting resins

Microwave‐assisted organic synthesis (MAOS) is a well‐established technique that has been used in the enhancement of chemical reactions. Here, the versatility of MAOS is explored describing an environmentally friendly one‐pot route to novel bio‐based benzoxazines under solvent‐free conditions. The lignin derivative, guaiacol, along with paraformaldehyde and different conjugated and nonconjugated amines are successfully fused into guaiacol‐derived 3,4‐dihydro‐2H‐1,3‐benzoxazines. The reactions conducted under microwave irradiation are completed much faster than those under traditional heating, reducing the reaction time from hours to only 6 min, with good yields. The chemical structures of novel benzoxazines are confirmed by ¹H and ¹³C NMR spectroscopy, FTIR, and HR‐MS. The thermal behavior of the resins are evaluated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), showing that these polymers have good thermal stability and wide processing‐window, with onset temperature of polymerization above 230 °C. These results indicate dramatic improvement over the traditional methodologies for the production of this class of resins, which are usually obtained by time‐consuming procedures and in the presence of toxic solvents. Therefore, MAOS can be considered a green and efficient strategy for the synthesis of eco‐friendly benzoxazines. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3534–3544     

LC Evaluation of Intestinal Transport of Praziquantel

Praziquantel (PZQ) is a highly lipophilic drug with low aqueous solubility. Despite this, it is well absorbed from the gastrointestinal tract. In this study, a simple LC method was developed and validated, in order to monitor the concentration of PZQ in TC-199 buffer in vitro, in the rat everted gut sac absorption model. PZQ was analyzed by a reversed-phase LC method with an isocratic mobile phase containing acetonitrile and water in the proportions 45:55. The flow-rate was 1 mL min⁻¹ and PZQ was determined by measuring absorbance at 215 nm, at 25 °C. The method was found to be specific, as none of the components of TC-199 or intestinal sac artefacts interfered with the drug peak. Recovery was within acceptable statistical limits. The limit of detection was 0.54 μg mL⁻¹ and the limit of quantitation was 1.63 μg mL⁻¹. The calibration curve was found to be linear in the concentration range of 10–90 μg mL⁻¹ PZQ. The proposed method was found to be rapid and selective and hence can be applied in the monitoring of the absorption of PZQ in in vitro everted gut sac absorption studies.

     

The Catalytic Mechanism of Protein Phosphatase 5 Established by DFT Calculations

In order to elucidate the catalytic mechanism of the Mn–Mn containing serine/threonine protein phosphatase 5 (PP5), we present a density functional theory study with a cluster model approach. According to our results, the reaction occurs through an in‐line concerted transition state with an energy of 15.8 kcal mol^?1, and no intermediates are formed. The important role played by His304 and Asp274 as stabilizers of the leaving group has been shown, whereas the role played by the metal ions seems to be mostly electrostatic. The indispensable requirement of having a neutral active center has been demonstrated by testing different protonation states of the cluster model. We have shown also the importance of describing properly the electronic configuration of the Mn–Mn binuclear centers.     

Thermal behavior of ara?a oil (Psidium cattleianum Sabine)

The ara?á is a well-known fruit, which belongs to the Myrtaceae family, Psidium cattleianum Sabine species, frequently found in the southern region of Brazil. The extraction of ara?a oil was carried out from seeds, and the fatty acid profile of this oil indicates the predominant presence of linoleic acid (81.38%). Thermogravimetry, derivative thermogravimetry, and differential scanning calorimetry (DSC) were used to characterize this oil. In addition, this oil was evaluated by DSC from 25 to ?60?°C, where the crystallization behavior was verified. Details concerning thermal decomposition as well as data of kinetic parameters of these stages have been described here. The kinetic behavior of the thermal decomposition was evaluated from several heating rates with mass samples of 5 and 20?mg in open crucibles under nitrogen and synthetic air atmospheres.     

Determination of RSD921 in human plasma by high-performance liquid chromatography-tandem mass spectrometry using tri-deuterated RSD921 as internal standard: application to a phase I clinical trial.

A fast, sensitive and specific method is presented for the quantification of RSD921 in human plasma by liquid chromatography coupled with tandem mass spectrometry using tri-deuterated RSD921 (3d-RSD921) as an internal standard. A single-step liquid/liquid extraction was performed with diethyl ether/hexane (80 : 20, v/v) using 0.5 ml of plasma. The plasma calibration curves were linear from 0.1 to 20 ng ml(-1) (r > 0.999). Between-run precision, based on the percent relative deviation for replicate (n = 40) quality controls, was < or =7.27% (0.5 ng ml(-1)), < or =7.39% (5.0 ng ml(-1)), and < or =5.06% (20.0 ng ml(-1)). Between-run accuracies, based on the relative error, were +/-2.59%, +/-1.23% and +/-1.64% respectively. The method was developed to evaluate the pharmacokinetic profile after 15 min of intravenous stepwise-ascending infusion dose of RSD921 in 18 healthy volunteers. A dissociation study of protonated RSD921 and 3d-RSD921 by collision-induced dissociation using in-source fragmentation and tandem mass spectrometry is also presented.     

Spectral and Informational Analysis of Temperature and Chemical Composition of Solfatara Fumaroles (Campi Flegrei,Italy)

Temperature and composition at fumaroles are controlled by several volcanic and exogenous processes that operate on various time-space scales. Here, we analyze fluctuations of temperature and chemical composition recorded at fumarolic vents in Solfatara (Campi Flegrei caldera, Italy) from December 1997 to December 2015, in order to better understand source(s) and driving processes. Applying the singular spectral analysis, we found that the trends explain the great part of the variance of the geochemical series but not of the temperature series. On the other hand, a common source, also shared by other geo-indicators (ground deformation, seismicity, hydrogeological and meteorological data), seems to be linked with the oscillatory structure of the investigated signals. The informational characteristics of temperature and geochemical compositions, analyzed by using the Fisher–Shannon method, appear to be a sort of fingerprint of the different periodic structure. In fact, the oscillatory components were characterized by a wide range of significant periodicities nearly equally powerful that show a higher degree of entropy, indicating that changes are influenced by overlapped processes occurring at different scales with a rather similar intensity. The present study represents an advancement in the understanding of the dominant driving mechanisms of volcanic signals at fumaroles that might be also valid for other volcanic areas.     

Thermoanalytical and dynamic mechanical analysis of commercial geomembranes used for fluid retention of leaching in sanitary landfills

Journal of Thermal Analysis and Calorimetry - Studying thermal behavior is very important for monitoring the quality of polymers on an industrial scale. Commercial geomembranes are materials with...