Price William S, Hallberg Fredrik, Stilbs Peter
Nanoscale Organisation and Dynamics Group, College of Science, Technology and Environment, University of Western Sydney, Penrith South, NSW 1797, Australia.
Magn Reson Chem. 2007 Feb;45(2):152-6. doi: 10.1002/mrc.1936.
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.
多核脉冲梯度自旋回波（PGSE）核磁共振扩散和线宽测量被用于探究Na⁺-15-冠-5、Na⁺-18-冠-6、Cs⁺-15-冠-5和Cs⁺-18-冠-6水体系中的结合与传输。由于许多碱金属阳离子的固有灵敏度低或弛豫速度快（或两者兼具），使得无法通过直接的PGSE观察，因此研究了质子检测电泳核磁共振（ENMR）测量以补充PGSE数据的可行性。对Cs⁺-、Li⁺-、Na⁺-、K⁺-和Rb⁺-18-冠-6水体系进行了ENMR测量。数据分析基于双位点结合模型及其相应的缔合常数。发现Cs⁺与18-冠-6（K = 8 M⁻¹）的结合比与15-冠-5（K约为2 M⁻¹）紧密得多，而Na⁺对15-冠-5和18-冠-6的亲和力几乎相等（K约为4.5 M⁻¹）。讨论了分析核磁共振参数时遇到的困难、方法学局限性以及对更复杂结合模型的潜在需求。
