A new type of ionophore family utilizing the cation-olefinic pi interaction: theoretical study of [n]beltenes

The possible utilization of n]beltenes as a new family of ionophores, which exhibit a cation-olefinic pi type of interaction in contrast to the cation-aromatic pi type of interaction exhibited by n]collarenes, has been investigated using both ab initio calculations and molecular dynamic simulations. Like n]collarenes, n ethene groups are linked by -CH(2)- linkages in the n]beltenes. Our calculations indicate that these n]beltenes exhibit strong binding affinities and high selectivity for alkali metal cations (5]beltene to Li(+), 6]beltene to Na(+), 7]beltene to Na(+) and K(+), 8]beltene to K(+) and Rb(+), and 9]beltene to Cs(+) and Rb(+)). Compared to n]collarenes, n]beltenes are expected to have a finer ion selectivity because their cavity sizes can be varied with integral number n, while that of the former can be varied with an even number n. Suitable substituents could be employed to enhance both the binding and specificity of various sizes of n]beltenes to different cations, as well as to increase the solubility.