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 language | English |
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Number of pages | 5 |
Journal | Magnetic Resonance in Chemistry |
DOIs | |
Publication status | Published - 2007 |
Keywords
- PGSE NMR
- binding
- crown ether
- diffusion
- electrophoretic NMR