Low‐temperature Raman spectra of racemate DL‐Alanine crystals

Raman spectra of DL ‐Alanine crystals were investigated in the 50–3200 cm⁻¹ spectral region for temperatures ranging from 15 to 295 K. The crystalline structure of DL ‐Alanine represents a rare example of an amino acid racemate crystallizing in a non‐centrosymmetric space group. From this study, we have observed changes in the wavenumber of modes associated with both rocking of CO₂⁻ and skeletal vibrations. On the other hand, neither changes in the modes associated to CH or CH₃ vibrations nor substantial modifications of the lattice modes of the crystal were observed. Such result indicates slight changes of the CO₂ group orientation without observation of a solid–solid phase transition in the DL ‐Alanine crystal. Copyright © 2009 John Wiley & Sons, Ltd.     

Kinetic Parameters of Polyethylene Degradation by the Natural Zeolite Chabazite

High-density polyethylene (PE) was subjected to thermal degradation alone and in the presence of an ammonium-exchanged zeolite chabazite (CHA/PE). The processes were carried out in a reactor connected online to a gas chromatograph/mass spectrometer in order to analyse the evolved products. Polymer degradation was also evaluated by thermogravimetry, from room temperature up to 800°C, under a dynamic nitrogen atmosphere, with multiple heating rates. From the TG curves, the activation energy relating to the degradation process was calculated by using the Flynn and Wall multiple heating rate kinetic model for pure PE and for CHA/PE. The exchanged chabazite exhibited good selectivity for the catalytic degradation of PE to low molecular mass hydrocarbons. This revised version was published online in August 2006 with corrections to the Cover Date.     

Antiviral Therapeutic Potential of Curcumin: An Update

The treatment of viral disease has become a medical challenge because of the increasing incidence and prevalence of human viral pathogens, as well as the lack of viable treatment alternatives, including plant-derived strategies. This review attempts to investigate the trends of research on in vitro antiviral effects of curcumin against different classes of human viral pathogens worldwide. Various electronic databases, including PubMed, Scopus, Web of Science, and Google Scholar were searched for published English articles evaluating the anti-viral activity of curcumin. Data were then extracted and analyzed. The forty-three studies (published from 1993 to 2020) that were identified contain data for 24 different viruses. The 50% cytotoxic concentration (CC50), 50% effective/inhibitory concentration (EC50/IC50), and stimulation index (SI) parameters showed that curcumin had antiviral activity against viruses causing diseases in humans. Data presented in this review highlight the potential antiviral applications of curcumin and open new avenues for further experiments on the clinical applications of curcumin and its derivatives.     

Synthesis,structure and electrochemical performance of cobaltite‐based composite cathodes for IT‐SOFC

The development of novel and high‐performance cathodes is a critical issue to be addressed in order to reduce Solid Oxide Fuel Cells (SOFCs) operation temperature to the 600‐800 °C range or less. The performance of CeO₂‐based composite cathodes is very attractive to such operational temperatures. In this work, La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) and Ce_0.8Sm_0.2O_1.9 (SDC) powders were synthesized by different synthesis methods and mechanically mixed to prepare LSCF‐SDC composite cathodes. Screen‐printed LSCF‐SDC/CGO/LSCF‐SDC symmetrical cells were sintered at 1150 °C for 4 h and characterized by electrochemical impedance spectroscopy in static air. X‐ray diffraction and scanning electron microscopy were employed to characterize the powders. Area specific resistance values of 0.72 and 2.77 Ω cm² at 800 °C were found for composite cathodes containing SDC powder synthesized by modified Pechini and microwave‐assisted combustion methods, respectively. Furthermore, the activation energy of the composite cathode containing SDC derived from modified Pechini method is 1.18 eV, i.e., much lower than 1.73 eV, value determined for LSCF with SDC from microwave‐combustion method.     

β-Myrcene Coordination Polymerization: Experimental and Kinetic Modeling Study

The present work presents phenomenological models to describe the coordination polymerization of β-myrcene using the Ziegler–Natta catalyst system composed by neodymium versatate (NdV₃), diisobutylaluminum hydride (DIBAH), and dimethyldichlorosilane. The kinetic parameters required to simulate the reactions are estimated, and the amount of DIBAH used as a chain transfer agent (CTA) is obtained by a data reconciliation strategy since it can participate in side reactions. Several experiments are performed at different conditions to evaluate the impact of key operation variables on the control of monomer conversion and average molar masses. It is shown that the initial NdV₃, β-myrcene, and DIBAH concentrations exert strong influences on the course of the polymerization. The kinetic mechanism of Coordinative Chain Transfer Polymerization (CCTP) fits well with the data of final average molar masses and monomer conversion, while the dynamic trajectories of these variables are fitted better by kinetic mechanisms of more conventional coordination polymerizations, considering site deactivation and termination by chain transfer. In all cases, the proposed models are able to predict the experimental data well after successful parameter estimation and reconciliation of CTA concentrations, indicating that the kinetic mechanism can be characterized by different kinetic regimes.     

A study on red lead degradation in a medieval manuscript Lorvão Apocalypse (1189)

The mechanisms of red lead degradation were studied in a medieval Portuguese codex, Lorvão Apocalypse (1189), by Raman microscopy (µ‐Raman) and micro‐X‐ray diffraction (µ‐XRD). The range of pigments found for the illuminations is mainly limited to vermilion, orpiment and red lead. Micro‐Fourier transform infrared spectroscopy (µ‐FTIR) determined that the pigments were applied in a proteinaceous binding medium. In the red and orange colours, arsenic (As) was determined, by micro‐energy dispersive X‐ray fluorescence (µ‐EDXRF), to be ranging 1–4% (wt %). For those colours, lead white and calcium carbonate were found as fillers whereas orpiment was applied as a pure pigment. Raman microscopy identified, unequivocally, the degradation product of red lead as galena [lead (II) sulphide, PbS]. To determine the main factors affecting red lead degradation, a set of accelerating ageing experiments was designed to assess the influence of extenders and of the two other pigments, vermilion and orpiment. The experiments were followed by µ‐Raman, µ‐EDXRF and XRD. Raman microscopy results for the simulation of degradation of red lead, in the presence of orpiment, are in agreement to what was found in the Lorvão Apocalypse, galena being the main degradation product; also in common is a Raman band at ca. 810 cm⁻¹, which was attributed to a lead arsenate compound. It was concluded that in Lorvão Apocalypse, the degradation of red lead was a result of its reaction with orpiment. Copyright © 2009 John Wiley & Sons, Ltd.     

New blow-up criteria for local solutions of the 3D generalized MHD equations in Lei–Lin–Gevrey spaces

This paper determines the existence of a unique local solution for the 3D generalized magnetohydrodynamics equations. In order to be more precise, our solution is obtained by involving Lei–Lin–Gevrey spaces as well as Lei–Lin spaces. Furthermore, we present five new blow-up criteria for this same system when the maximal time of existence is finite. It is important to point out that one of these criteria is obtained by assuming fractional Laplacians with equal powers.