A PGSE diffusion and electrophoretic NMR study of Cs+ and Na+ dynamics in aqueous crown ether systems

William S. Price, Frederik Hallberg, Peter Stilbs

    Research output: Contribution to journalArticle

    Abstract

    Multinuclear pulsed gradient spin-echo (PGSE) NMR diffusion and linewidth measurements were used to probe binding and transport in aqueous Na+-15-crown-5, Na+-18-crown-6, Cs+-15-crown-5 and Cs+-18-crown-6 systems. Since direct PGSE observation of many alkali cations is precluded by either low inherent sensitivity or rapid relaxation (or both), the feasibility of proton-detected electrophoretic NMR (ENMR) measurements to complement PGSE data was investigated. ENMR measurements were performed on aqueous Cs+-, Li+-, Na+-, K+-, and Rb+- 18-crown-6 systems. The data analysis is based on a two-site binding model and its corresponding association constants. Cs+ was found to bind considerably more tightly to 18-crown-6 (K = 8 M-1) than to 15-crown-5 (K 2 M-1), whereas Na+ had almost equal affinity (K 4.5 M-1) for 15-crown-5 and 18-crown-6. The difficulties encountered in analysing the NMR parameters, methodological limitations and the implied need for more complicated binding models are discussed.
    Original languageEnglish
    Number of pages5
    JournalMagnetic Resonance in Chemistry
    DOIs
    Publication statusPublished - 2007

    Keywords

    • PGSE NMR
    • binding
    • crown ether
    • diffusion
    • electrophoretic NMR

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