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Stancho Stanchev Javor Mitkov Maya Georgieva Alexander Zlatkov 《International journal of quantum chemistry》2013,113(9):1384-1393
Nine biologically active theophylline derivatives were investigated using quantum chemical methods (density functional theory level). All calculations were performed at B3LYP/6‐31G** level of theory. The electrostatic potential charges, highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) gap, dipole moment, vibration frequencies, and electronic spectra were calculated. Log P was determined by Ghose‐Crippen method. All of the compounds under study are polar and negatively charged, which is necessary for their interaction with the receptors/enzymes. Majority of the compounds are lipophilic and they can easily diffuse through the cell membrane. The observed differences between the calculated and the experimental vibration frequencies in the Fourier Transform Infrared Spectroscopy (FTIR) spectra are established to be mainly in NH and OH bands, due to hydrogen bonds formation. The discrepancies between theoretical and experimental electronic spectra may be due to vibration effects and H‐bonding with the solvent molecules. The obtained results show that this type of spectrum is formed mainly by the xanthine fragment of the molecule, especially in the fingerprint region. All calculated properties could be useful for future qualitative‐structure activity relationship (QSAR) analysis. © 2012 Wiley Periodicals, Inc. 相似文献
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Tsocheva D. Zlatkov T. Terlemezyan L. 《Journal of Thermal Analysis and Calorimetry》1998,53(3):895-904
The thermal behaviour of polyaniline-‘emeraldine base’ (PANI-EB) was studied using thermogravimetric analysis (TG) and differential
scanning calorimetry (DSC). We assume that during heating over 150°C three exothermal processes proceed - reorganization and
crosslinking between PANI-EB chains followed by post-polymerization. The low temperature relaxation transition for PANI-EB
was registered for the first time by DSC. We suppose that it might be due to the motion of polymer chains non-crosslinked
during the first heating, chain fragments resulting from high-temperature decomposition over 300°C and chain ends of the already
crosslinked polymer.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Barium hexaferrite permanent magnets were produced by powder injection molding. Starting barium hexaferrite powder was prepared from a Fe2O3 and BaCO3 powder mixture by calcination followed by milling. The feedstock for powder injection molding was prepared by mixing barium hexaferrite powder with a low viscosity binder. Magnetic alignment was achieved by applying a high intensity magnetic field to the melted feedstock during the injection process. Green samples (with and without magnetic alignment) were subjected to solvent debinding and subsequent thermal debinding followed by sintering. Sintering conditions were optimized in order to achieve a maximum energy product value. Magneto-crystalline aligning in barium hexaferrite was studied on both green and sintered samples using X-ray diffraction, scanning electron microscope (SEM) and magnetic measurements (hysteresisgraphs). All measurements were made both in a parallel and perpendicular direction to the aligning magnetic field. The obtained results confirmed magneto-crystalline alignment. 相似文献
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