A PGSE diffusion and electrophoretic NMR study of Cs+ and Na+ dynamics in aqueous crown ether systems.
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 approximately 2 M-1), whereas Na+ had almost equal affinity (K approximately 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.
Price
William S
WS
Nanoscale Organisation and Dynamics Group, College of Science, Technology and Environment, University of Western Sydney, Penrith South, NSW 1797, Australia. w.price@uws.edu.au
Hallberg
Fredrik
F
Stilbs
Peter
P
D002586:Cesium / Q000737:chemistry*; D043844:Crown Ethers / Q000737:chemistry*; D004058:Diffusion; D004586:Electrophoresis; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D012964:Sodium / Q000737:chemistry*; D012996:Solutions; D014867:Water / Q000737:chemistry*
D043844:Crown Ethers; D012996:Solutions; D014867:Water; D002586:Cesium; D012964:Sodium