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  • NMR study of heterogeneity in pyridine-N-oxide...HCl crystal
    Balevičius, Vytautas ; Gaćeša, Aleksandar ; Plavec, Janez
    An origin of narrow 1H NMR signals in pyridine-N-oxide (PyO)...HCl crystal has been investigated by means of MAS, SPEDAS, NOESY and COSY techniques. Spectra of crystalline samples are compared with ... those of solid phase obtained from liquid PyO...HCl solutions (in acetonitiležH2O) after the heterogeneous phase separation. It has been concluded that partially resolved peaks in 1H NMR spectra of solids are related with heterogeneity of spin system and presence of different H-bond clusters of water molecules. NOESY spectra show no cross-peaks even at very long mixing time (500 ms). This indicates there is no exchange process between spins causing different peaks, and thus the corresponding molecular aggregates are captured in Ćislands of mobility8 without any channels sufficient for exchange. Appearance of MAS sidebands as Ćpseudo8 cross-peaks in 2D NMR spectra using MAS/COSY technique is reported. In the case of accidental coincidence of spinning frequency ( omega-MAS) with spectral distances between some diagonal signals, intensive non-diagonal peaks are observed at the corresponding cross-positions. A misleading conclusion concerning spin coupling is easy to avoid using various omega-MAS .
    Source: Central European journal of physics [Elektronski vir]. - ISSN 1644-3608 (Vol. 2, no. 1, 2004, str. 120-131)
    Type of material - e-article
    Publish date - 2004
    Language - english
    COBISS.SI-ID - 2966554

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