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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Monatshefte für Chemie 126 (1995), S. 1051-1059 
    ISSN: 1434-4475
    Schlagwort(e): Conformational analysis ; LIS method ; NMR spectroscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Zwei neue Methoden zur Bestimmung von Vorzugskonformeren leicht beweglicher Moleküle mit Hilfe lanthaniden-induzierter chemischer Verschiebungen (RANDOM-LIS und STEED-LIS mit Zufallsauswahl von bis zu 10 Diederwinkeln) werden auf unterschiedliche Substanzklassen mit nur einem potentiellen Koordinationszentrum (Alkohole, Aldehyde, Ester, Amine) angewandt. Die Ergebnisse der Konformationsanalyse stimmen mit der Literatur gut überein; Abweichungen werden unter Beachtung von Konformationsänderungen bei der Komplexierung der Substrate an das LIS-Reagens verständlich. Kraftfeldberechnungen (RANDOM-PIMM) und Berechnungen nach dem Simple Hard Sphere Model (RANDOM-SHSM und STEED-SHSM) unter ebensolcher Nutzung der Zufallsauswahl der Diederwinkel führen zu nahezu identischen Vorzugskonformeren.
    Notizen: Summary Two new methods (RANDOM-LIS and STEED-LIS) with random selection of up to ten dihedral angles were applied for the determination of preferred conformers of flexible molecules (alcohols, aldehydes, esters, and amines, respectively, with only one coordination site) by LIS studies. The results proved to be useful. The preferred complexation conformation was detected only in cases where conformational changes of the substrate took place to improve complexation to the LIS reagent. Force field calculations (RANDOM-PIMM) and Simple Hard Sphere Model calculations (RANDOM-SHSM and STEED-SHSM), using the same algorithm of randomly varying the dihedral angles, support the results obtained.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Monatshefte für Chemie 114 (1983), S. 289-302 
    ISSN: 1434-4475
    Schlagwort(e): Formylmethylenthiopyranes ; LIS-method ; Rotational barriers
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The rotational barriers ΔG ≠ toE,Z- ands-cis, s-trans-isomerisation in formylmethylenthiopyranes are determined and discussed with regard to their dependence on substituent effects. Preferential conformers are distinguished by lanthanide induced shifts. Best fits between calculated and experimental shifts are obtained forE,s-trans andZ,s-cis isomers. The results indicate a nonbonding interaction between aldehyde oxygen and ring sulphur, favourings-cis conformation in case ofZ configuration.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Structural chemistry 7 (1996), S. 139-151 
    ISSN: 1572-9001
    Schlagwort(e): Cyclicβ-casomorphins ; conformational analysis ; NMR spectroscopy ; cyclic pentapeptides ; force field calculations
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The solution conformation of two cyclicβ-casomorphin-5 analogues H-Tyr-c(-d-Orn-Phe-Pro-Gly-)1 and H-Tyr-c(-Orn-Phe-Pro-Gly-)2 in DMSO-d 6 was studied by NMR spectroscopy and accompanying force field calculations. By especially employing1H,13C, and15N chemical shifts, respectively, the temperature coefficient of the amide proton chemical shifts,3 J NH,CαH andJ CαH.CβH coupling constants, respectively, and nuclear Overhauser effects in the rotating frame (ROEs), in the case of1, only one preferred conformer could be identified. In the case of2, two or even more preferred conformers were found, readily interconverting on the NMR time scale. Empirical force field calculations using the SYBYL 6.0 software (TRIPOS) corroborate the experimental NMR results obtained. The conformational behavior of the compounds studied is discussed with respect to the receptor specificity of theβ-casomorphins studied.
    Materialart: Digitale Medien
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  • 4
    ISSN: 0749-1581
    Schlagwort(e): Rotational barriers ; 1H NMR spectra ; Partial double bond character ; Mesomerism in pyrylium and thiopyrylium salts ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The 13C NMR spectra and variable-temperature 1H NMR spectra of some NR2-substituted pyrylium and thiopyrylium salts were studied, and the rotational barriers thus obtained about the exocyclic partial C—N double bonds are discussed according to their dependence on the counter anion and other structural variations. The counter anion has a negligible influence on the barrier, but substituents on the ring can either strengthen electronically or weaken sterically the mesomerism of the NR2-heteroaromatic system. The competition between these two effects is readily estimated from the rotational barriers obtained. The pyrylium salts display higher rotational barriers than the identically substituted thiopyrylium salts.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 25 (1987), S. 688-695 
    ISSN: 0749-1581
    Schlagwort(e): 13C NMR ; Temperature dependent ; 1HNMR spectra ; Pyrylium/thiopyrylium salts ; Pyrones/thiopyrones ; Rotational barriers ; Partial double bond character ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Temperature-dependent 13C and 1H NMR spectra of three series of six-membered heteroaromatic systems with NR2 substituents attached to pyrylium/thiopyrylium salts and pyrones/thiopyrones have been recorded. The rotational barriers thus determined about the exocyclic partial double bonds are discussed in terms of dominating mesomeric structures, in order to describe the electronic state and the spatial conditions in the molecular framework. Cyanine and merocyanine substructures have been identified by NMR and express the electronic state predominantly present in the compounds.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 6
    ISSN: 0749-1581
    Schlagwort(e): Rotational barriers ; π-electron density alternation ; Mesomerism in pyrylium salts ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The 13C NMR spectra and the temperature-dependent 1H NMR spectra of a series of NR2-substituted pyridines and pyrones were studied, and the 13C chemical shifts and the rotational barriers about the exocyclic partial C,N double bonds were compared with the corresponding values for suitable pyridinium, pyrylium and thiopyrylium salts. The NMR spectroscopic results are discussed in the light of the electronic state and mesomerism in the species studied; the salts in question should be named, from the electronic point of view, more realistically as bridged pentamethine cyanines rather than pyridinium, pyrylium and thiopyrylium salts.
    Zusätzliches Material: 3 Tab.
    Materialart: Digitale Medien
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