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Heterocyclic Structures (heterocyclic + structure)
Selected AbstractsLyotropic Liquid Crystalline Polyamides Containing Aromatic, Heterocyclic Structures: Preparation and PropertiesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 17 2006Pengtao Liu Abstract Summary: A series of novel lyotropic liquid crystalline polyamides derived from 1,2-dihydro-2-(4-aminophenyl)-4-[4-(4-(aminophenoxyl)phenyl)]-phthalazinone (DHPZ-DA), p -phenylene diamine (PPD) and terephthaloyl dichloride (TPC) have been successfully synthesized by the low temperature solution polycondensation method. The copolymers obtained with inherent viscosity of ,1.21 to 3.29 dl,·,g,1, determined in NMP (1 wt.-% LiCl) or concentrated H2SO4 at 25,°C, were confirmed to be amorphous by WAXD and differential scanning calorimetry (DSC). Their solubility was improved by the introduction of non-coplanar, twisted phthalazinone moieties and ether linkages into the main chain with the result that they can be soluble in some polar solvents containing a small amount of LiCl. Their Tgs were all above 310,°C and 10% weight loss temperatures in nitrogen above 500,°C. Most of these polyamides can form an anisotropic phase in concentrated H2SO4, NMP (1 wt.-% LiCl) and DMAc (1 wt.-% LiCl) solutions, observed on a polarizing light microscope. Optical micrograph (×40) of polyamide P-4060 at 10 wt.-% in NMP/LiCl (1% w/v) solution at room temperature. [source] Synthesis of Novel Heterocyclic Structures via Reaction of Isocyanides with s-trans-Enones.CHEMINFORM, Issue 2 2007Jeffrey D. Winkler Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Derivatization reaction of the mycotoxin moniliformin with 1,2-diamino-4,5-dichlorobenzene: structure elucidation of an unexpected reaction product by liquid chromatography/tandem mass spectrometry and liquid chromatography/nuclear magnetic resonance spectroscopyJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 7 2003Peter Zöllner Abstract The derivatization reaction of the mycotoxin moniliformin with 1,2-diamino-4,5-dichlorobenzene was previously introduced to improve distinctly the sensitivity of an assay applying high-performance liquid chromatography prior to fluorescence detection. In the course of the implementation of this derivatization approach into a liquid chromatographic/mass spectrometric method, an unexpected derivatization product has now been discovered by mass spectrometry. In order to elucidate its structure, detailed investigations with liquid chromatography/tandem mass spectrometry and liquid chromatography coupled on-line with NMR spectroscopy were performed. These studies give evidence for a heterocyclic structure that has been formed by the loss of one water and one carbon monoxide molecule. A reasonable mechanism for this derivatization reaction is proposed. Copyright © 2003 John Wiley & Sons, Ltd. [source] Influence of substituent groups at the 3-position on the mass spectral fragmentation pathways of cephalosporinsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2010Jin Li The structural fragment ions of nine cephalosporins were studied by electrospray ionization quadrapole trap mass spectrometry (Q-Trap MSn) in positive mode. The influence of substituent groups in the 3-position on fragmentation pathway B, an ,-cleavage between the C7C8 single bond, coupled with a [2,4]-trans-Diels-Alder cleavage simultaneously within the six-membered heterocyclic ring, was also investigated. It was found that when the substituent groups were methyl, chloride, vinyl, or propenyl, fragmentations belonging to pathway B were detected; however, when the substituents were heteroatoms such as O, N, or S, pathway B fragmentation was not detected. This suggested that the [M,R3]+ ion, which was produced by the bond cleavage within the substituent group at the 3-position, had a key influence on fragmentation pathway B. This could be attributed to the strong electronegativity of the heteroatoms (O, N, S) that favors the production of the [M,R3]+ ion. Moreover, having the positive charge of the [M,R3]+ ion localized on the nitrogen atom in the 1-position changed the electron density distribution of the heterocyclic structure, which prohibits a [2,4]-reverse-Diels-Alder fragmentation and as a result fragmentation pathway B could not occur. The influence of the substituent group in the 3-position was determined by the intensity ratio (e/d) of ions produced by fragmentation pathway A, a [2,2]-trans-Diels-Alder cleavage within the quaternary lactam ring, including the breaking of the amide bond and the C6C7 single bond (ion d), and fragmentation pathway B (ion e). The results indicate that the electronegativity of the substituent group was a key influencing factor of pathway B fragmentation intensity, because the intensity ratio (e/d) is higher for a chlorine atom, a vinyl, or a propenyl group than that of a methyl group. This study provided some theoretical basis for the identification of cephalosporin antibiotics and structural analysis of related substances in drugs. Copyright © 2010 John Wiley & Sons, Ltd. [source] New heterocyclic structures from unsaturated aldehyde derivatives.JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 3 2000-L-fucosidases, Inhibition of First page of article [source] | |||||||||||||||||||