Department of Chemistry, University of Illinois, Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, USA.
J Am Chem Soc. 2011 Jul 27;133(29):11136-46. doi: 10.1021/ja107383c. Epub 2011 Jun 30.
Crown ethers are an important family of compounds that are closely related to naturally occurring ionophores. Thus, crown ethers are useful in modeling the size-selective behavior of ionophores. Using a combination of infrared predissociation spectroscopy and density functional theory calculations, we have investigated M(+)(18-crown-6 ether)(H(2)O)(1-4) Ar complexes, where M = Li, Na, K, Rb and Cs in the gas phase. The argon-tagging technique was used to lower the internal energies (effective temperatures ~100 K), yielding well-resolved spectra in the OH stretching region for systems containing up to three waters. Spectral changes were monitored as both the size of the ion and degree of hydration were varied. While there is not a particular spectroscopic signature of gas-phase selectivity reported in this work, the unique role that K(+) plays in the systems studied, as a "bridge" between the smaller and larger alkali metal ions, is consistent with the well-known special affinity for K(+) by 18-crown-6 ether in the aqueous phase.
冠醚是一类与天然离子载体密切相关的重要化合物。因此，冠醚在模拟离子载体的尺寸选择性行为方面非常有用。我们结合红外预解离光谱和密度泛函理论计算，研究了 M(+)(18-冠-6 醚)(H(2)O)(1-4)Ar 复合物，其中 M = Li、Na、K、Rb 和 Cs 在气相中。氩标记技术用于降低内部能量（有效温度约 100 K），为含有多达三个水分子的系统在 OH 伸缩区域产生了分辨率良好的光谱。随着离子大小和水合度的变化，监测光谱变化。虽然本工作中没有报道气相选择性的特定光谱特征，但在研究的系统中，K(+) 作为较小和较大碱金属离子之间的“桥梁”所起的独特作用，与 18-冠-6 醚在水溶液中对 K(+) 的特殊亲和力是一致的。
