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Theoretical Ones (theoretical + ones)
Selected AbstractsCombined 13C NMR and DFT/GIAO studies of the polyketides Aurasperone A and Fonsecinone AINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 13 2008Sergio de Lazaro Abstract Structural characterization by NMR spectroscopy and DFT calculations was performed for two dimeric naphtho-,-pyrones, the polyketides Aurasperone A and Fonsecinone A. Experimental data (13C NMR chemical shifts and interatomic geometries) were found to be in reasonable agreement with theoretical ones, obtained at B3LYP level for three different basis sets (6-31G/6-31G(d)/6-31G(d,p)). Additionally, the dipolar moments calculation allowed explaining the different solubility for these molecules. The 13C NMR theoretical chemical shifts were calculated with the GIAO method and the solvent effects were taken into account by means of the PCM approximation. In this work, the DFT/GIAO methodology shows to be a reliable tool in the assignment of experimental NMR chemical shifts of similar molecules. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Polyesterification of aromatic dicarboxylic acids and bisphenols with tosyl chloride/dimethylformamide/pyridine promoted by the improvement of the difficult solubility of the activated diacids with lithium chlorideJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2004Fukuji Higashi Abstract The solution polyesterification of dicarboxylic acids in pyridine, the activated intermediates of which were difficult to dissolve in tosyl chloride/dimethylformamide/pyridine, was investigated in the presence of lithium chloride. The solubility of the activated dicarboxylic acids was largely improved by the presence of the salt, and the polycondensation with bisphenols was greatly facilitated. The salt was more effectively added to a pyridine solution of dicarboxylic acids than to the activated dicarboxylic acids in pyridine. The favorable additive effect on the improved solubility was attributed to a lowered degree of association of the activated dicarboxylic acids, which led to distributions of the resulting oligomers from bisphenols at an earlier stage closer to the theoretical ones and yielded better polycondensation results. The reaction, which proceeded through favorable distributions of the co-oligomers, produced copolymers of higher inherent viscosities and slightly block sequence distributions determined by NMR. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2725,2733, 2004 [source] Crosslinking polymerization leading to interpenetrating polymer network formation.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2003Abstract At the start of our research program concerned with the elucidation of the crosslinking polymerization mechanism leading to interpenetrating polymer network (IPN) formation, in which IPNs consist of both polymethacrylates and polyurethane (PU) networks, this article deals with the polyaddition crosslinking reaction leading to PU network formation. Therefore, 2-methacryloyloxyethyl isocyanate (MOI) was radically copolymerized with methyl methacrylate (MMA) in the presence of CBr4 as a chain-transfer agent. The resulting poly(MMA- co -MOI)s, having pendant isocyanate (NCO) groups as novel multifunctional polyisocyanates, were used for polyaddition crosslinking reactions with ethylene glycol as a typical diol. The second-order rate constants depended on both the functionality of poly(MMA- co -MOI) and the NCO group concentration. The actual gel points were compared with the theoretical ones calculated according to Macosko's equation; the deviation of the actual gel point from the theoretical value became more remarkable for a greater functionality of poly(MMA- co -MOI) and at a lower NCO group concentration or at a lower poly(MMA- co -MOI) concentration. These are discussed mechanistically, with consideration given to the significance of intramolecular cyclization and intramolecular crosslinking reactions leading to the shrinkage of the molecular size of the prepolymer, along with the data of the intrinsic viscosities of resulting prepolymers and the swelling ratios of resulting gels. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 606,615, 2003 [source] Atom-Transfer Radical Polymerization: A Strategy for the Synthesis of Halogen-Free Amino-Functionalized Poly(methyl methacrylate) in a One-Pot ReactionMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 17 2004Veera Bhadraiah Sadhu Abstract Summary: An initiator containing an alkyl bromide unit and a protected amine functional group is used with CuBr/N,N,N,,N,,N,-pentamethyldiethylenetriamine (PMDETA), in a 1:2 molar ratio with respect to initiator concentration, in order to obtain amino-group terminated as well as halogen-free poly(methyl methacrylate) (PMMA) in a one-pot atom-transfer radical polymerization (ATRP). The terminal bromines are replaced by hydrogen atoms of the PMDETA ligand, which acts as a transfer agent. However, terminating side reactions like disproportionation or dehydrobromination occur from the beginning of the polymerization. Kinetic studies by in-line Raman spectroscopy and off-line 1H NMR spectroscopy revealed that the controlled character of the ATRP is lost under these conditions. The measured molecular weights were consistently higher than the theoretical ones and the molecular weight distributions are relatively broad. Thermal analysis of the obtained poly(methyl methacrylate) shows two main degradation steps, one starting from unsaturated end groups (depolymerization), and one caused by main-chain scission, a further proof for the occurrence of terminating side reactions. Structural analysis of PMMA by matrix-assisted laser desorption-ionization mass spectrometry. [source] Theoretical and experimental study of polarization characteristics of polarization maintaining fiber based on wavelength-sweeping modulationMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 7 2010Zuo-Liang Duan Abstract We analyze theoretically the polarization characteristics of polarization maintaining fiber and study the basic measurement principles of beat length and polarization extinction ratio of this kind of optical fiber. According to the dependence of the phase difference between two orthogonally polarized modes (denoted as HE and HE) transmitted in the polarization maintaining fiber on the light wavelength, we propose the wavelength-sweeping modulation method to measure the beat length and the model birefringence. Based on this technique, the beat length and polarization extinction ratio of the PANDA polarization maintaining fibers (PMFs) (provided by Yangtze Optical Fiber and Cable Company, Wuhan, China) were investigated in detail. Experimental results show good consistent with the theoretical ones. We find that this method shows high measurement precision with the advantages of clear measurement principle and easy to operate. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1466,1469, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25244 [source] Design, Synthesis, and Biological Evaluation of Prenylated Chalcones as Vasorelaxant AgentsARCHIV DER PHARMAZIE, Issue 7 2009Xiaowu Dong Abstract Five prenylated chalcones and one allylated chalcone were prepared according to the analysis based on support vector machine (SVM) classification model. Most of the synthesized chalcones showed potent vasorelaxant activities through evaluation in aortic rings with the endothelium pre-contracted by phenylephrine (PE), indicating that the experimental activities were in good agreement with the theoretical ones. Structure-activity relationship of these compounds showed that the substituent pattern and number of hydroxyl groups were crucial for their vasorelaxant activities and that the replacement of prenyl group with allyl group retained the potent activity. [source] | |||||||||||||