Amine side arm effect on the ion selectivity of 12-crown-O3N derivatives with an amine arm in aqueous and acetonitrile solutions

Molecular geometries of crown ether derivatives play an important role in capturing and transporting alkali metal ions such as Li+ and Na+. As selectivity of the ions is observed in solution, it is necessary to know their molecular structures in solutions. Recently, we investigated stable conformations of 12-crown-O3N and its alkali ion complexes in aqueous and acetonitrile solutions. In the present study, we applied a procedure similar to that in previous papers to investigate the side arm effect of 12-crown-O3N with an amine arm for capturing Li+ and Na+ in the two solutions. It was confirmed that the stable structures of Li+ and Na+ complexes in solutions, especially the geometry of the amine side arm, are highly solvent-dependent. This conformational difference is the key to understanding the high Li+ selectivity of 12-crown-O3N derivatives with an amine side arm in acetonitrile.