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  • 1
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 27 (1989), S. 1148-1154 
    ISSN: 0749-1581
    Keywords: Self-diffusion ; Pulsed gradient ; Complexation phenomena ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H and 133Cs NMR self-diffusion measurements were performed by means of the pulsed gradient spin-echo method (PGSE) to evaluate the complex formation constants of Cs and 18-crown-6 and those of Cs and some ethylene glycols in D2O. The calculated complex formation constants were checked as far as possible by using similar calculations based on relaxation data. Chemical shift measurements do not allow the evaluation of complex formation constants in these systems. A cross-check was introduced to verify the calculations based on the diffusion data. Similar investigations were performed on Na, K, Cs complexes and N-phenylaza-15-crown-5 in methanol. In this case, analysis of the diffusion data and as the relaxation rate and chemical shift data led to complex formation constants for 1:1 complexes, which is in contrast to a previous report suggesting the formation of 2:1 complexes.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. 387-392 
    ISSN: 0749-1581
    Keywords: Vasopressins ; Peptide dynamics in solution ; NMR relaxation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dynamic behaviour of [Lys8]-vasopressin derivatives, especially of N-Gly-Gly-Gly-[Lys8]-vasopressin in solution, was investigated by NMR relaxation studies. One can derive a set of dynamics data which describe the molecular tumbling in solution from 13C spin-lattice relaxation times, T1, spin-spin relaxation times, T2, and heteronuclear nuclear Overhauser enhancements (NOE). Two different approaches, the scheme proposed by Jardetzky and co-workers and the ‘model-free’ approximation of Lipari and Szabo, are used to analyse the dynamics and a comparison of the corresponding data is given. In addition to a mobility of 108-109 s-1, we observe a faster mobility of the order of 109-1010 s-1 in addition to slow dynamic contributions. The latter can be associated by means of T1, measurements with a motion involving the S—S linkage in the vasopressin. Some additional motion is described as the overall mobility of an associate. The results from 13C relaxation were corroborated by 15N T1 measurements, performed at the 15N natural abundance level by an INEPT-reverse INEPT method, and by 15N NOE investigations.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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