Syntheses and structures of synthetic carboxylic ionophores containing 2,3-naphthylene groups

Two derivatives of omega-hydroxy carboxylic ionophore 2-[[2-[2-[2-[2-[2-[2-[2-(2-hydroxyethoxy)phenoxy]ethoxy]phenoxy]ethoxy]ethoxy]phenoxy]methyl]benzoic acid 1,2-[[3-[2-[2-[2-[2-[2-[3-(2-hydroxyethoxy)-2-naphthyloxy]-ethoxy]phenoxy]ethoxy]phenoxy]ethoxy]-2-naphthyloxy]methyl]benzoic acid 2 and 2-[[3-[2-[2-[2-[3-[2-[2-(2-hydroxyethoxy)phenoxy]ethoxy]-2-naphthyloxy]ethoxy]phenoxy]ethoxy]-2-naphthyloxy]methyl]benzoic acid 3, were prepared. Both compounds exhibited high K+ selectivity over Na+, as did 1. The structures of the Rb salt of 2 and the K salt of 3 were determined by single-crystal X-ray analyses. Both ionophores formed psuedocycles by a head-to-tail hydrogen bond between the hydroxy and carboxylato groups and enclosed each cation like the seam of a tennis ball to make lipophilic complexes. However, the three-dimensional structures of the two hydrophobic salts differed from each other in spite of the similarity of the primary structures, which might be due to the interaction of the aromatic rings.