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  • 1
    Electronic Resource
    Electronic Resource
    Studies of tautomerism and protonation in 2-aryl-1H-imidazo[1,2-a]imidazole derivatives using 1H and 13C NMR (1991)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 29 (1991), S. 1147-1151 
    Details
    ISSN: 0749-1581
    Keywords: Protonation ; Tautomerism ; NMR ; Imidazo[1,2-a]imidazole ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tautomerism and protonation of the putative inotropic 2-(2′,4′-dimethoxy)phenyl-1H-imidazo[1,2-a]imidazole (2) has been studied in several solvents by comparing its 1H and 13C chemical shifts with those of its 1- and 7-methyl derivatives 3 and 4, respectively, and acid salts. Tautomer and rotamer populations were also estimated from measurements of proton relaxation rates and NOE effects. Heterocycle 2 exists predominantly as the 1H-tautomer in CDCl3, but as the 7H-tautomer in DMSO-d6 and methanol-d4-D2O solutions. In CDCl3 solution, 2 appears to exist with the N-1-H and 2′-OMe groups adjacent, but in DMSO-d6 the conformation is the rotated form with N-7-H and H-6′ adjacent; 3 exists as a mixture of rotamers in CDCl3 and in DMSO-d6 whereas 4 is in the form with the N-7-Me and H-6′ adjacent in both solvents. The observed conformational preferences have been compared with the results of semi-empirical molecular orbital calculations and found to be in broad agreement. Protonation of 2 occurs mainly at N-1 in DMSO-d6 and at N-7 in CDCl3, as expected from observed tautomeric ratios in the free base.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260291112
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  • 2
    Electronic Resource
    Electronic Resource
    Measurement of inter-proton distances from cross-relaxation rates determined by a selective null inversion-recovery NMR method (1992)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. 173-176 
    Details
    ISSN: 0749-1581
    Keywords: NMR ; Relaxation ; Selective pulses ; Distance ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An efficient method of measuring proton spin-lattice cross-relaxation rates in small molecules is proposed. The method involves measuring the difference in relaxation rates in a non-selective experiment and in one with all resonances except one of interest inverted. This procedure yields cross-relaxation rates between this nucleus and all other nuclei. These rates are independent of the effects of non-excited heteronuclei and of non-dipolar contributions and can be used to determine relative inter-proton distances. The method was tested using 7-azaindole and compared favourably with the standard NOE method for estimating proton proximities requiring less data acquisition time.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260300215
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  • 3
    Electronic Resource
    Electronic Resource
    Sites of protonation in cardiotonic polyazaindolizines by NMR spectroscopy (1991)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 29 (1991), S. 468-475 
    Details
    ISSN: 0749-1581
    Keywords: Polyazaindolizines ; Protonation ; 13C NMR ; 1H NMR pK values ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pKa, values of six sulmazole analogues were measured spectrophotometrically. The major protonation sites for most of these bridgehead nitrogen heterocycles were determined by 1H and 13C NMR methods. The aryl-substituted imidazo[1,2-a]pyrimidine (4), 8-methoxyimidazo[1,2-a]pyrazine (6), imidazo[1,2-b]pyridazine (9) and imidazo[1,2-b][1,2,4]triazine (11) undergo protonation at the imidazo nitrogen. The imidazo[1,2-a]pyrazine (5) protonates mainly at N-7. In some cases differences in basicity properties between these aryl analogues and the bridgehead heterocycles have been observed.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260290511
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  • 4
    Electronic Resource
    Electronic Resource
    Two-dimensional 1H—1H and 13C—1H maximum-quantum correlation NMR spectroscopy with application to the assignment of the NMR spectra of the bile salt sodium taurocholate (1995)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 33 (1995), S. 212-219 
    Details
    ISSN: 0749-1581
    Keywords: multiple quantum ; NMR ; two-dimensional ; taurocholate ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Following earlier studies on the development of one- and two-dimensional NMR methods based on selection of coherences via maximum-quantum pathways and using inverse 1H detection, a pulse sequence is now described for analogous direct heteronuclear detection for use in laboratories which do not have access to inverse detection technology. The method has been applied to the assignment of all of the 1H and 13C NMR resonances of sodium taurocholate, an important component of bile. The assignment of the resonances of major bile salts is important for the assignments of NMR resonances in bile itself to yield understanding of altered biochemistry in disease states. The effect of deliberately missetting the refocusing delay in the pulse sequence is shown to be beneficial in the assignment process.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260330310
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