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Substitution Position (substitution + position)
Selected AbstractsBisthienylethenes Containing a Benzothiadiazole Unit as a Bridge: Photochromic Performance Dependence on Substitution PositionCHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2010Weihong Zhu Prof. Abstract A conveniently synthesized photochromic compound, BTB-1, containing an unprecedented six-membered 2,1,3-benzothiadiazole unit as the center ethene bridge, possesses good photochromic performance, with a high cyclization quantum yield and moderate fatigue resistance in solution or an organogel system. The fluorescence of BTB-1 can be modulated by solvato- and photochromism. However, the analogue BTB-2, in which the dimethylthiophene substituents are relocated to the 5,6-positions of benzothiadiazole, does not show any detectable photochromism. To the best of our knowledge, this is the first example of six-membered bridge bisthienylethenes (BTEs) in which the photochromism can be controlled by the substitution position. The photochromism difference is elucidated by the analysis of resonance structure, the Woodward,Hoffmann rule, and theoretical calculations on the ground-state potential-energy surface. In a well-ordered single-crystal state, BTB-1 adopts a relatively rare parallel conformation, and forms an interesting two-dimensional structure due to the presence of multiple directional intermolecular interactions, including CH,,,N and CH,,,S hydrogen-bonding interactions, and ,,, stacking interactions. This work contributes to several aspects for developing novel photochromic BTE systems with fluorescence modulation and performances controlled by substitution position in different states (solution, organogel, and single crystal). [source] Liquid chromatography/electrospray ionization mass spectrometry for the characterization of twenty-three flavonoids in the extract of Dalbergia odoriferaRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2005Rongxia Liu A method incorporating high-performance liquid chromatography (HPLC) with electrospray ionization and tandem mass spectrometry, with parallel analysis by HPLC with UV detection using a diode-array detector, was developed for the qualitative characterization of flavonoids in D. odorifera. Twenty-three flavonoids, including six isoflavones, six neoflavones, four isoflavanones, three flavanones, two chalcones, one isoflavanonol and one pterocarpan, were unambiguously identified by comparing their retention times, UV and MS spectra with those of authentic compounds. Furthermore, the collision-induced dissociations of the [MH], ions were studied to clarify the MS behavior of the different types of flavonoids. In negative ion ESI-MS all the flavonoids yielded prominent [MH], ions in the first order mass spectra. Fragments involving losses of CH, H2O, CO, C2H2O, and CO2 were observed in the MS/MS spectra. Each of the seven types of flavonoid showed characteristic MS/MS fragmentation patterns. The isoflavanones, flavanones and chalcones were observed to undergo retro-Diels-Alder fragmentations. The spectra of almost all the neoflavonoids unexpectedly exhibited only [MHCH3],. radical anions as base peaks without any further fragmentation. Substitution positions also remarkably influenced the fragmentation behavior, which could assist in distinction among the flavonoid isomers. The fragmentation rules deduced here could aid in the characterization of other flavonoids of these types. Copyright © 2005 John Wiley & Sons, Ltd. [source] Application of the MTD-PLS method to heterocyclic dye,cellulose interactionsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 11 2007Ludovic Kurunczi Abstract The minimal topologic difference method in a projection in latent structures variant procedure was applied to a series of heterocyclic monoazo dyes of the type: RC6H4N = NY (R = benzothiazole, benzimidazole, N-containing aromatic pentacycles; Y = , acid, H acid, chromotropic acid, R acid). A statistically excellent model was obtained: RX2 = 0.625, RY2 = 0.940, Q2 = 0.822. The analysis of this model reveals the nature of dye,fiber interactions, which determine the dye affinity. Hydrophobic character in the R group and H-bond donor groups in a specific Y substitution position augment the dye affinity for cellulose. An increase of the polar nature of atoms in R depletes the affinity. Also some lateral substituents belonging to the Y coupling components suffer steric hindrance, and their presence is detrimental for the affinity. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Liquid chromatography coupled to nuclear magnetic resonance spectroscopy for the identification of isoflavone glucoside malonates in T. pratense L. leaves.JOURNAL OF SEPARATION SCIENCE, JSS, Issue 13 2004Eva de Rijke Abstract Previous studies revealed that the main isoflavones in extracts of leaves of T. pratense L. are biochanin A and formononetin, their 7- O -glucosides, and two glucoside malonate isomers of each of them. Since LC,MS(/MS) did not provide sufficient information to distinguish the glucoside malonate isomers, in the present paper LC,NMR as well as off-line two-dimensional NMR were used to obtain further structural information. Matrix solid-phase dispersion (MSPD) was applied to obtain sufficiently high analyte concentrations to perform LC,NMR. Stop-flow reversed-phase LC,NMR was performed using a gradient of deuterated water and deuterated acetonitrile. Off-line COSY and NOESY experiments were carried out to determine the positions of the glucose moiety on the flavonoid aglycone, and of the malonate moiety on the glucose. Based on the fragmentation patterns in MS/MS and the NMR spectra, the two formononetin glucoside malonate isomers were identified as 7- O -,-D-glucoside 6´´- O -malonate and 7- O -,-D-glucoside 4´´- O -malonate; i.e. they only differ in the substitution position of the malonate group on the glucoside ring. The biochanin A glucoside malonate isomers, however, have quite different structures. The main and later eluting isomer is biochanin A 7- O -,-D-glucoside 6´´- O -malonate, and the minor and earlier eluting isomer is 5-hydroxy-7-methoxyisoflavone 4´- O -,-D-glucoside 4´´- O -malonate: the positions of the methoxy group and the glucoside 6´´- O -malonate group on the flavonoid skeleton are interchanged. [source] Bisthienylethenes Containing a Benzothiadiazole Unit as a Bridge: Photochromic Performance Dependence on Substitution PositionCHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2010Weihong Zhu Prof. Abstract A conveniently synthesized photochromic compound, BTB-1, containing an unprecedented six-membered 2,1,3-benzothiadiazole unit as the center ethene bridge, possesses good photochromic performance, with a high cyclization quantum yield and moderate fatigue resistance in solution or an organogel system. The fluorescence of BTB-1 can be modulated by solvato- and photochromism. However, the analogue BTB-2, in which the dimethylthiophene substituents are relocated to the 5,6-positions of benzothiadiazole, does not show any detectable photochromism. To the best of our knowledge, this is the first example of six-membered bridge bisthienylethenes (BTEs) in which the photochromism can be controlled by the substitution position. The photochromism difference is elucidated by the analysis of resonance structure, the Woodward,Hoffmann rule, and theoretical calculations on the ground-state potential-energy surface. In a well-ordered single-crystal state, BTB-1 adopts a relatively rare parallel conformation, and forms an interesting two-dimensional structure due to the presence of multiple directional intermolecular interactions, including CH,,,N and CH,,,S hydrogen-bonding interactions, and ,,, stacking interactions. This work contributes to several aspects for developing novel photochromic BTE systems with fluorescence modulation and performances controlled by substitution position in different states (solution, organogel, and single crystal). [source] Complete NMR signal assignments of flavonol derivativesMAGNETIC RESONANCE IN CHEMISTRY, Issue 2 2006Hojung Kim Abstract Common substitution positions of flavonols are at C-5 and C-7; 6-substituted flavonol derivatives are rarely found in natural sources. Here, we report complete assignments of 1H and 13C chemical shifts of eight flavonol derivatives including four 6-substituted flavonols. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||